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  • Wiley-Blackwell  (53,454)
  • 2000-2004  (495)
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  • 1
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    Wiley-Blackwell
    In:  Journal of Fish Biology, 59 . pp. 332-338.
    Publication Date: 2017-07-06
    Description: The living coelacanth Latimeria chalumnae has a unique position in world biodiversity which raises important questions about conservation and ethics. Some relevant details of coelacanth biology are summarized, including those obtained by direct observation from submersibles. The importance of the coelacanth for evolutionary theory and palaeontology is shown to be paralleled in cultural, literary and artistic areas of human heritage. Threats to the Comoran coelacanths from artisanal fishing are described and conservation measures discussed in relation to local customs and economies as well as the promotion of tourism to spread a new awareness and concern for coelacanths worldwide.
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  • 2
    Publication Date: 2017-01-31
    Description: Destructive macroalgal mass blooms threaten estuarine and coastal ecosystems worldwide. We asked which factors regulate macroalgal bloom intensity, distribution and species composition. In field experiments in the Baltic Sea, we analyzed the relative effects of nutrients, herbivores and algal propagule banks on population development and dominance patterns in two co-occurring bloom-forming macroalgae, Enteromorpha intestinalis and Pilayella littoralis. Both species were highly affected by the combined effects of a propagule bank, herbivory and nutrients. The magnitude of effects varied with season. The propagule bank was an important overwintering mechanism for both algae, and allowed for recruitment two months earlier than recruitment via freshly dispersed propagules. This provided a seasonal escape from intense herbivory and nutrient limitation later in the year. Favored by massive recruitment from the propagule bank, Enteromorpha was the superior space occupier in early spring, thereby reducing recruitment of Pilayella. Elimination of the propagule bank and recruitment via freshly dispersed propagules favored Pilayella. Strong and selective herbivory on Enteromorpha supported Pilayella in the presence, but not in the absence of the propagule bank. Nutrient enrichment in summer counteracted herbivore pressure on Enteromorpha, thereby negatively affecting Pilayella. Herbivore and nutrient effects were more pronounced for early life stages than adult algae. These results show that recruitment processes and forces affecting early life stages at the beginning of the vegetation period determine development and dominance patterns of macroalgal blooms. Herbivores naturally suppress blooms but increasing nutrient enrichment can override this important control mechanism. The propagule bank plays a previously unrecognized role for population and community dynamics.
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  • 3
    Publication Date: 2015-10-06
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  • 4
    Publication Date: 2020-04-28
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  • 5
    Publication Date: 2020-04-28
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  • 6
    Publication Date: 2020-04-28
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  • 7
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    Wiley-Blackwell
    In:  Oikos (100). pp. 592-600.
    Publication Date: 2017-01-31
    Description: Conceptual models predict counteractive effects of herbivores and nutrient enrichment on plant diversity and reversed effects of grazers under different nutrient regimes. I tested these hypotheses in 11 field experiments with periphyton communities in three different aquatic habitats (a highly eutrophic lake, an meso-eutrophic lake, and an meso-eutrophic part of the Baltic Sea coast) and in different seasons. Grazer access and nutrient supply were manipulated in a factorial design. Species richness and evenness were chosen as response variables. Both manipulated factors had significant and contrasting effects on diversity, with variable effect strength between sites and seasons. From the two aspects of diversity, evenness well reflected the changes in community composition. Fertilization tended to increase the dominance of few species and thus to decrease evenness, whereas grazers counteracted these effects by removing dominant life forms. The response of species richness was not as expected, since grazers decreased richness throughout, whereas nutrients had weaker effects but tended to increase richness. Species richness rather reflected changes in periphyton architecture. Grazers reduced algal richness presumably by co-consumption of rare species in the tightly connected periphyton assemblages, whereas enrichment may increase richness by providing more structure via increased dominance of filamentous species. Although grazer and nutrient effects on richness and evenness were opposing, there was no change in the effect of one factor by manipulation of the other.
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  • 8
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    Wiley-Blackwell
    In:  Journal of Fish Biology, 59 . pp. 1638-1652.
    Publication Date: 2017-09-08
    Description: Phylogenetic analyses, using 482 bp of the mitochondrial 16S rDNA and 461 bp of the control region of 16 Diplodus species and Oblada melanura, Pagellus bogaraveo and Pagellus acarne, all close relatives of Diplodus, identified the two representatives of Pagellus as the sister group of Diplodus. Oblada melanura was confirmed as the sister taxon of D. puntazzo, despite its different dental morphology and ecology. Within the genus Diplodus, three clades were identified, the first containing D. annularis and D. bellottii, the second D. vulgaris and D. prayensis, and the third comprising three subclades. These were formed by O. melanura clustering with D. puntazzo, D. fasciatus with D. cervinus, and by the Diplodus sargus sub-species assemblage which also included the West Atlantic taxa D. argenteus, D. bermudensis, D. holbrooki, and the Red Sea endemic D. noct. All members of the D. sargus assemblage were genetically closely related. Among them, D. sargus lineatus from the Cape Verde islands was resolved as most ancestral branch, pointing to the possibility that the diversification and spread of the D. sargus assemblage originated in this region. The hypothesis of stepwise speciation following colonization events within the D. sargus complex is fully supported by phylogenetic reconstruction.
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  • 9
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    Wiley-Blackwell
    In:  Journal of Fish Biology, 62 . pp. 253-276.
    Publication Date: 2017-09-08
    Description: A set of histological characteristics to judge ovarian development was established and used to elaborate morphological criteria of 10 maturity stages of Baltic cod Gadus morhua sampled throughout the annual cycle to represent different macroscopic maturity stages. The applied characteristics confirmed most stages of the macroscopic scale, but the separation of late immature and resting mature females remained imprecise. Atretic vitellogenic oocytes or encapsulated residual eggs identified the resting condition morphologically, but not all ovaries with visible signs of previous spawning showed such features. One ovarian stage that was previously classified as ‘ripening’ was changed to ‘spawning’, owing to the prevalence of hydrated eggs and empty follicles. Ovaries with malfunctions were defined by a separate stage. Macroscopic criteria were revised by comparing the gross anatomy of ovaries with their histology. Female length and gonado-somatic index supported stage definitions, but substantial variation in Fulton's condition factor and the hepato-somatic index rendered these of little use for this purpose. The time of sampling influenced staging accuracy. A female spawner probability function based on the proportion of ripening and ripe specimens in early spring seems to be the most appropriate method to estimate spawner biomass and reproductive potential.
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  • 10
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    Wiley-Blackwell
    In:  Journal of Fish Biology, 63 . pp. 280-299.
    Publication Date: 2017-09-13
    Description: During peak spawning of sprat Sprattus sprattus in the Baltic Sea in May–June egg specific gravity averaged ±s.d. 1·00858 ± 0·00116 g cm−3 but was significantly higher in the beginning and significantly lower towards the end of the spawning season. A close relationship was found between egg diameter and egg specific gravity (r2 = 0·71). This relationship, however, changed during the spawning season indicating that some other factor was involved causing the decrease in specific gravity during the spawning period. The vertical egg distribution changed during the spawning season: eggs were distributed mainly in the deep layers early in the season, occurred in and above the permanent halocline during peak spawning, and above the halocline towards the end of the spawning season. Consequently, poor oxygen conditions in the deep layers and low temperatures in layers between the halocline and the developing thermocline may affect egg development. Thus, opportunities for egg development vary over the spawning season and among spawning areas, and depending on frequency of saline water inflows into the Baltic Sea and severity of winters, between years
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  • 11
    Publication Date: 2019-01-22
    Description: This contribution aims to report the reflections we had with the scientific community during two international workshops on reference materials for stable isotopes in Davos (2002) and Nice (2003). After evaluating the isotopic homogeneity of some existing reference materials, based on either certificates, literature data or specific inter-laboratory rounds, we confirm these as primary reference materials or propose new ones relative to which stable isotope compositions should be reported. We propose DSM-3 for Mg, NIST SRM 915a for Ca, L-SVEC for Li and NBS28 for Si. Cadmium does not yet have a well identified delta zero material, although three commercial mono-elemental Cd solutions have yielded the same isotopic composition relative to one another. In order to scale the linearity of any mass spectrometer, some secondary reference materials are also proposed: Cambridge-1 solution for Mg, the “Münster-Cd” and JEPPIM Cd solutions for Cd and the “Big Batch” silicate for Si. The team from Nancy propose to prepare a mixed spike solution for Li isotopes. Well-characterised natural samples such as ocean or continental waters, diatoms, sponges, rocks and minerals are needed to validate the entire analytical procedure, particularly to take into account the effect of sample mineralisation and of chemical manipulations for elemental separation prior to analysis.
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  • 12
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    Wiley-Blackwell
    In:  Oikos, 106 . pp. 93-104.
    Publication Date: 2016-05-26
    Description: Ecological stoichiometry describes the biochemical constraints of trophic interactions emerging from the different nutrient content and nutrient demand of producers and consumers, respectively. Most research on this topic originates from well-mixed pelagic food webs, whereas the idea has received far less attention in spatially structured habitats. Here, we test how light as well as grazing and nutrient regeneration by consumers affects growth and biomass of benthic primary producers. In the first laboratory experiment, we manipulated grazer presence (two different snail species plus ungrazed control), in the second experiment we factorially combined manipulation of grazer presence and light intensity. We monitored snail and periphyton biomass as well as dissolved and particulate nutrients (nitrogen and phosphorus) over time. Grazers significantly reduced algal biomass in both experiments. Grazers affected periphyton nutrient content depending on the prevailing nutrient limitation and their own body stoichiometry. In the nitrogen (N-) limited first experiment, grazers increased N both in the periphyton and in the water column. The effect was stronger for grazers with lower N-content. In the phosphorus (P-) limited second experiment, grazers increased the P-content of the periphyton, but the grazer with lower N-content had additionally positive effects on algal N. Light reduction did not affect periphyton biomass, but increased chlorophyll-, N- and P-content of the periphyton. These experiments revealed that the indirect effects of grazers on periphyton were bound by stoichiometric constraints of nutrient incorporation and excretion.
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  • 13
    Publication Date: 2019-01-22
    Description: A compilation of δ44/40Ca (δ44/40Ca) data sets of different calcium reference materials is presented, based on measurements in three different laboratories (Institute of Geological Sciences, Bern; Centre de Géochimie de la Surface, Strasbourg; GEOMAR, Kiel) to support the establishment of a calcium isotope reference standard. Samples include a series of international and internal Ca reference materials, including NIST SRM 915a, seawater, two calcium carbonates and a CaF2 reference sample. The deviations in δ44/40Ca for selected pairs of reference samples have been defined and are consistent within statistical uncertainties in all three laboratories. Emphasis has been placed on characterising both NIST SRM 915a as an internationally available high purity Ca reference sample and seawater as representative of an important and widely available geological reservoir. The difference between δ44/40Ca of NIST SRM 915a and seawater is defined as -1.88 O.O4%o (δ44/42CaNISTSRM915a/Sw= -0.94 0.07%o). The conversion of values referenced to NIST SRM 915a to seawater can be described by the simplified equation δ44/40CaSa/Sw=δ44/40CaSa/NIST SRM 915a - 1.88 (δ44/42CaSa/Sw=δ44/42CaSa/NIST SRM 915a - 0.94). We propose the use of NIST SRM 915a as general Ca isotope reference standard, with seawater being defined as the major reservoir with respect to oceanographic studies.
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  • 14
    Publication Date: 2019-09-23
    Description: Ecosystem resistance to a single stressor relies on tolerant species that can compensate for sensitive competitors and maintain ecosystem processes, such as primary production. We hypothesize that resistance to additional stressors depends increasingly on species tolerances being positively correlated (i.e. positive species co-tolerance). Initial exposure to a stressor combined with positive species co-tolerance should reduce the impacts of other stressors, which we term stress-induced community tolerance. In contrast, negative species co-tolerance is expected to result in additional stressors having pronounced additive or synergistic impacts on biologically impoverished functional groups, which we term stress-induced community sensitivity. Therefore, the sign and strength of the correlation between species sensitivities to multiple stressors must be considered when predicting the impacts of global change on ecosystem functioning as mediated by changes in biodiversity.
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  • 15
    Publication Date: 2017-01-31
    Description: Recent experiments, mainly in terrestrial environments, have provided evidence of the functional importance of biodiversity to ecosystem processes and properties. Compared to terrestrial systems, aquatic ecosystems are characterised by greater propagule and material exchange, often steeper physical and chemical gradients, more rapid biological processes and, in marine systems, higher metazoan phylogenetic diversity. These characteristics limit the potential to transfer conclusions derived from terrestrial experiments to aquatic ecosystems whilst at the same time provide opportunities for testing the general validity of hypotheses about effects of biodiversity on ecosystem functioning. Here, we focus on a number of unique features of aquatic experimental systems, propose an expansion to the scope of diversity facets to be considered when assessing the functional consequences of changes in biodiversity and outline a hierarchical classification scheme of ecosystem functions and their corresponding response variables. We then briefly highlight some recent controversial and newly emerging issues relating to biodiversity-ecosystem functioning relationships. Based on lessons learnt from previous experimental and theoretical work, we finally present four novel experimental designs to address largely unresolved questions about biodiversity-ecosystem functioning relationships. These include (1) investigating the effects of non-random species loss through the manipulation of the order and magnitude of such loss using dilution experiments; (2) combining factorial manipulation of diversity in interconnected habitat patches to test the additivity of ecosystem functioning between habitats; (3) disentangling the impact of local processes from the effect of ecosystem openness via factorial manipulation of the rate of recruitment and biodiversity within patches and within an available propagule pool; and (4) addressing how non-random species extinction following sequential exposure to different stressors may affect ecosystem functioning. Implementing these kinds of experimental designs in a variety of systems will, we believe, shift the focus of investigations from a species richness-centred approach to a broader consideration of the multifarious aspects of biodiversity that may well be critical to understanding effects of biodiversity changes on overall ecosystem functioning and to identifying some of the potential underlying mechanisms involved.
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  • 16
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    Wiley-Blackwell
    In:  Fish and Fisheries, 5 (2). pp. 131-140.
    Publication Date: 2016-11-25
    Description: Marine and fisheries scientists are increasingly using metapopulation concepts to better understand and model their focal systems. Consequently, they are considering what defines a metapopulation. One perspective on this question emphasizes the importance of extinction probability in local populations. This view probably stems from the focus on extinction in Levins' original metapopulation model, but places unnecessary emphasis on extinction–recolonization dynamics. Metapopulation models with more complex structure than Levins' patch-occupancy model and its variants allow a broader range of population phenomena to be examined, such as changes in population size, age structure and genetic structure. Analyses along these lines are critical in fisheries science, where presence–absence resolution is far too coarse to understand stock dynamics in a meaningful way. These more detailed investigations can, but need not, aim to assess extinction risk or deal with extinction-prone local populations. Therefore, we emphasize the coupling of spatial scales as the defining feature of metapopulations. It is the degree of demographic connectivity that characterizes metapopulations, with the dynamics of local populations strongly dependent upon local demographic processes, but also influenced by a nontrivial element of external replenishment. Therefore, estimating rates of interpopulation exchange must be a research priority. We contrast metapopulations with other spatially structured populations that differ in the degree of local closure of their component populations. We conclude with consideration of the implications of metapopulation structure for spatially explicit management, particularly the design of marine protected area networks.
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  • 17
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    Wiley-Blackwell
    In:  Fish and Fisheries, 5 (1). pp. 86-91.
    Publication Date: 2017-02-02
    Description: Three simple fisheries indicators are presented: (i) percentage of mature fish in catch, with 100% as target; (ii) percent of specimens with optimum length in catch, with 100% as target; and (iii) percentage of ‘mega-spawners‘ in catch, with 0% as target, and 30–40% as representative of reasonable stock structure if no upper size limit exists. Application of these indicators to stocks of Gadus morhua, Sardinella aurita and Epinephelus aeneus demonstrate their usefulness. It is argued that such simple indicators have the potential to allow more stakeholders such as fishers, fish dealers, supermarket managers, consumers and politicians to participate in fisheries management and eventually hold and reverse the global pattern of convenience overfishing, which is defined here as deliberate overfishing sanctioned by official bodies who find it more convenient to risk eventual collapse of fish stocks than to risk social and political conflicts.
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  • 18
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 801-818 
    ISSN: 1434-1948
    Keywords: Zeolites ; Microporous zeolites ; Titanosilicates ; Transition metal ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stable microporous materials, such as zeolites, are extremely important for applications in catalysis, adsorption, ion-exchange, and separation. In this review we describe a new class of stable microporous materials that involves novel mixed octhaedral-tetrahedral framework oxides. The archetypal material is based on titanosilicates, although there is tremendous scope for introducing many other transition metals. These materials not only have potential novel applications in the fields normally associated with zeolites but also possible applications in the areas of optoelectronics, nonlinear optics, batteries, magnetic materials and sensors.
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  • 19
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 827-830 
    ISSN: 1434-1948
    Keywords: Ammonolysis ; Chlorine ; Nitrogen ; Silicon ; Silsesquiazane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ammonolysis of trichlorosilanes RSiCl3 [R = CH(SiMe3)2 (1a), Ph (1b), Et (1c)] leads to a series of condensed products such as six-membered rings [(Me3Si)2CHSi(OH)NH]3 (2a) and [PhSi(NH2)NH]3 (2b), disilazane [(Me3Si)2CHSi(NH2)2]2NH (3) and the cage compound (EtSi)6(NH)9 (4). The mixed Si-N-O compound 2a was obtained when liquid ammonia was not dried over sodium prior to use. The reaction with sodium gives NaCl instead of NH4Cl as a by-product which is easily removed by filtration.
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  • 20
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 835-837 
    ISSN: 1434-1948
    Keywords: Gold ; Clusters ; Quantum dots ; Monolayers ; Amphiphiles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Extended ordered monolayers of ligand stabilized Au55 clusters are formed at the phase boundary between water and dichloromethane. The water phase, containing amphiphilic molecules like per-6-deoxy-6-thio-α-cyclodextrin (1) or poly(vinylpyrrolidone) (2), is covered by a thin film of a solution of [Au55(PPh3)12Cl6] in dichloromethane. The interaction of the cluster molecules with the thiol functions of 1 or the polymer chains of 2 form perfect cluster orders of hexagonal and cubic structure. The monolayers can be transferred onto solid substrates by a simple dipping process. The use of carbon coated copper grids allows the investigation of the monolayers by transmission electron microscopy (TEM). Electron diffraction experiments under a microscope prove the hexagonal and cubic arrangements. The reason for the formation of the one or the other modification is still unknown.
    Additional Material: 4 Ill.
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  • 21
    ISSN: 1434-1948
    Keywords: Triosmium cluster ; Biphosphinine ; Crystal structure ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of the novel cluster [Os3(CO)10(4,4′,5,5′-tetramethyl-2,2′-biphosphinine)] reveals an unprecedented coordination mode of the biphosphinine ligand that occupies a doubly-bridging position spanning the open osmium triangle. The cluster is photostable, pointing to a localization of the lowest-energy electronic transition largely on the negatively charged biphosphinine ligand.
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  • 22
    ISSN: 1434-1948
    Keywords: Photochemistry ; Electrochemistry ; Ruthenium compounds ; α-Diimine complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photophysical, photochemical and redox properties of the title complexes were investigated. Resonance Raman measurements revealed the lowest-energy electronic transition to possess σ→π* character. At low temperatures, long-lived near-IR emission was observed. Irradiation in solution results in homolytic splitting of a Ru-Ru bond as the primary step, followed by secondary reactions of the radical fragments depending on the experimental conditions. (Spectro)electrochemical investigations of the title species proved that the axial [RuCp(CO)2] groups exert a stabilising influence on the corresponding radical cations, while destabilising the corresponding radical anions, compared to the redox behaviour of other ruthenium complexes of this type.
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  • 23
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 889-894 
    ISSN: 1434-1948
    Keywords: Rhodium hydride complexes ; Parahydrogen ; Tin ligands ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidative addition of dihydrogen to the [RhH(SnCl3)5]3-/PR3 system (PR3 = PPh3, PEtPh2, PEt3) leads to the formation of previously unknown dihydride complexes, the 1H-NMR spectra of which have been studied by means of the ParaHydrogen Induced Polarization (PHIP) method. The composition of the resulting complexes crucially depends on the type of the added phosphane. With PEt3 as the phosphane and acetonitrile as the solvent, a complex with a SnCl2L ligand (L = CD3CN) can be detected. All systems examined catalyze the hydrogenation of phenylacetylene. During these reactions, both the 1H-NMR resonances of the dihydride complexes and those of styrene, the hydrogenation product of phenylacetylene, can be detected simultaneously. In the case of SnBr3 ligands, hydrogen addition in the presence of phosphanes leads to similar dihydride complexes, which were also identified via 1H-NMR spectroscopy. Furthermore, a mixed complex of the structure [Rh(SnBr3)nBr6-n]3- has been isolated.
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  • 24
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 857-877 
    ISSN: 1434-1948
    Keywords: Crystal packing ; Neural networks ; Pattern recognition ; Organometallic compounds ; Close packing ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of hundreds of thousands of molecular compounds have now been determined with the quantitative information being stored in large databases. Chemists are generally interested in that specific part of this information which refers to individual molecules. The packing of molecules and their spatial relation to each other is not the focus of interest, even though the material properties of a molecular crystal are determined by both the packing arrangement of the molecules and their specific properties. The lack of interest in packing has at least one obvious reason. It is difficult for the non-expert to find the appropriate packing categories when looking at a principally infinite lattice. A tool performing this search for individual categories of packing in an automatic manner would therefore be of general importance. The development and application of such a tool is described in this paper. Novel strategies to extract a set of n points forming a specific n-point polyhedron from a set of p points (p 〉 n) is at its basis. Neural networks and second moment analysis are used as the methods of pattern recognition. In order to correlate packing and shape, second moment analysis of molecular shape is also used. This novel method is applied to three classes of organometallic compounds to determine whether the crystals formed by these compounds belong to any of the three classes fcc, bcc, or hcp in an idealized sense. A strong correlation is found between molecular shape and the membership or nonmembership of these classes. The corresponding program, including appropriate tools for visual representation, is available from the authors.
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  • 25
    ISSN: 1434-1948
    Keywords: Arenetricarbonyl chromium complexes ; Palladium ; Cross coupling reaction ; Thiophenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cross coupling reaction of (p-chloroanisole)tricarbonylchromium complex (1) with thiophene derivatives under palladium-catalyzed conditions leads to the selective formation of tricarbonyl-η6-[(2-thiophenyl)arene]- or -η6-[(2-thiophenyl)carbonylarene]chromium complexes (2 or 3) depending on reaction conditions. The conformation of complexes 2 and 3 in the solid state as well as in solution are reported.
    Additional Material: 4 Ill.
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  • 26
    ISSN: 1434-1948
    Keywords: Ruthenium ; Phenanthroline ; Luminescence ; Sterically hindered ligands ; Terpyridine ; Cyclometallation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two series of cyclometallated and noncyclometallated ruthenium(II) complexes incorporating mono- or disubstituted 1,10-phenanthroline- and 2,2′:6′,2′′-terpyridine-type ligands have been synthesized and characterized. An X-ray crystal structure for one of the complexes, Ru(ttpy)(mapH)-(Cl)(PF6), has been obtained (mapH = 2-p-anisyl-1,10-phenanthroline; ttpy = 4′-tolyl-2,2′:6′,2′′-terpyridine). Distinct electrochemical and photophysical properties have been observed for the two series: a remarkable feature is the observation of relatively long-lived MLCT excited states (from 70 to 106 ns at room temperature in CH3CN) for three of the cyclometallated complexes. A discussion is given on the role of factors like sigma donation by the cyclometallating ligands, interligand steric hindrance and interligand π-π interactions that affect the electrochemical and spectroscopic properties.
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  • 27
    ISSN: 1434-1948
    Keywords: Polymeric copper complexes ; Group-subgroup relationships ; 2D-sheets ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterisation of two new polymeric CuII complexes is described, i.e. {[Cu(btp)2(CH3CN)(H2O)](CF3SO3)2}n (1) and {[Cu(btp)2(CH3CN)2](ClO4)2}n (2), in which btp = [1,3-bis(1,2,4-triazol-1-yl)propane]. Compound 1 crystallizes in space group P21/c with a = 11.9337(15) Å, b = 20.108(6) Å, c = 12.748(6) Å, β = 92.247(14)°, and Z = 4. Compound 2 crystallizes in space group Pna21 with a = 18.770(8) Å, b = 12.648(8) Å, and c = 12.019(8) Å. The structures refined to R1 values of 0.0683 for 1 and 0.0846 for 2. In both structures the CuII ions are linked by the bridging ligands, resulting in two-dimensional networks. Two such curved layers are arranged on top of each other with center-to-center of layer distances of 2.12 Å in 1 and 1.98 Å in 2. Such double layers are separated from each other by 10.05 Å in 1 and 9.385 Å in 2. The space between the double layers is occupied with interstitial anions. No significant interaction between CuII ions is observed by EPR and magnetic susceptibility measurements. The compounds form a new class of a lattice engineered system held together by the CuII ions. - The coordination geometry of the copper ions is distorted octahedral, with the equatorial plane formed by the N4 nitrogens of the four triazole groups and the axial sites occupied by solvent molecules; acetonitrile and water in structure 1 and two acetonitrile molecules in structure 2. The two structures are related by a group-subgroup relationship, which appears to be the first such case in supramolecular chemistry. - The Cu-N vibrations in the FIR region are found at 274 cm-1 for 1, and at 276 cm-1 for 2. The ligand-field maxima are observed at about 16·103 cm-1, with a shoulder at about 12·103 cm-1. The νCN stretching vibrations of the acetonitrile molecules are found at 2303 and 2261 cm-1 for 1, and at 2313, 2294, 2278, and 2260 cm-1 for 2.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99211_s.pdf or from the author.
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  • 28
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 217-224 
    ISSN: 1434-1948
    Keywords: Reaction mechanisms ; Cyclopalladation ; Acetic acid ; Pd-C bond stability ; Polynuclear species ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The processes operating during the synthetic cyclopalladation reactions of imines in acetic acid have been studied from a kinetico-mechanistic point of view. These reactions include a fast initial coordination to the palladium through the N-donor atom of the imine, followed by the proper C-H bond activation to produce the acetato bridged dimeric species. At this point, the lability of the bridging acetato groups, the hydrolysis of the C-Pd bonds, and/or the hydrolysis of C=N exo bonds contribute to the generation of dark red polynuclear compounds. The processes occurring after the C-H activation have been followed kinetically, both from palladium acetate plus imine, and the synthetically pure isolated acetato dimers as starting materials. The kinetic and activation parameters have been found identical within experimental error whatever the starting material was (k323 = 1.5 × 10-4 s-1; ΔH# = 51 kJ mol-1; ΔS# = -163 JK-1 mol-1 ΔV# = +19 cm3 mol-1 for the 4-ClC6H4-CH=N-CH2-C6H5 imine derivative 1a). Acidolysis of C-Pd bonds has been found to occur in these polynuclear species. When alternative monomeric Cbenzylic-Pd bond-containing complexes are possible follow ups of the reactions produce them as final dead-end complexes (k323 = 2.2 × 10-5 s-1; ΔH# = 61 kJ mol-1; ΔS# = JK-1 mol-1 ΔV# ≈ 0 cm3 cm-1 for the [2,4,6-(CH3)3]C6H2-CH=N-CH2-[2-(CH3]C6[H4] imine derivative 3d). The same study has been carried out with primary amines in order to check the validity of the data if C=N bond hydrolysis is taking place in the imine derivatives with exo C=N bonds. For complexes with similar type of metallacycles, the results agree reasonably well with the proposed mechanism [k323 = 1.2·10-4 s-1, ΔH# = 46 kJ·mol-1, ΔS# = -180 J·K-1mol-1, ΔV# = -16 cm3·mol-1 for the polynuclear formation of the C6H5-CH2-NH2 derivative 4e; k323 = 3.0·10-4 s-1, ΔH# = 55 kJ·mol-1, ΔS
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  • 29
    ISSN: 1434-1948
    Keywords: Phosphanylphenolate ; Cyclopentadienylnickel complexes ; Chelates ; Ethylene polymerization ; Crystal structure ; Polymerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Diphenylphosphanyl- and 2-alkylphenylphosphanyl-4-methylphenols 1 or their silyl ethers 2 and equimolar amounts of nickelocene react in benzene preferably to give orange-brown diamagnetic cyclopentadienylnickel chelate complexes [η-CpNi(P∩O)] (3). Addition of a second equivalent of 1 or 2 affords (RR) and (SS) diastereoisomers of cis-bis(P∩O-chelates) 4a-c (R = Ph, Me, iPr) or the unsymmetrical cis-bis(P∩O-chelate) 5, whereas with bulkier substituted derivatives 1d or 2d (R = tBu) the second step is hindered or retarded. The reactivity of 1d remains high towards nickel salts in polar solvents, but in contrast to 1a-c, yielding 4, a sparingly soluble green trans-bis(P-O-chelate) nickel complex 6d is formed. Complexes formed in situ from 1 or 2 and Ni(COD)2 in toluene catalyze the polymerization of ethylene. The cyclopentadienyl (P∩O) complexes 3, however, are too stable to be active in this process. The crystal and molecular structure of 3c and 4c are described.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99035_s.pdf or from the author.
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  • 30
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 287-297 
    ISSN: 1434-1948
    Keywords: Enolates ; Nucleophilic additions ; Ruthenium ; S ligands ; Sulfenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of the chiral racemic complex [CpRu(mppe)(SO2)]PF6 (1, mppe = Me2PC2H4PPh2) with diazomethane or -ethane gave the sulfene complexes [CpRu(mppe)(RHC/SO2)]PF6 (R = H, 2a; R = Me, 2b). Treatment of 2a with prochiral enamines or deprotonated β-oxo esters yielded C-C coupling products with 32-60% de. An analog of 2a, [NmcpRu(mppe)(H2C/SO2)]PF6 (8, Nmcp = neomenthylcyclopentadienyl) was prepared in a four-step synthesis starting from LiNmcp and [RuCl2(PPh3)3]. Repeated crystallization of the intermediate [NmcpRu(mppe)Cl] (6) provided diastereomerically pure 6′ which added methylene stereospecifically to give diastereomerically pure 8′. Compound 8 turned out to be much less reactive towards nucleophiles than 2a, but still added deprotonated ethyl 2-methyl-3-oxobutanoate with 44% de. The chiral, enantiomerically pure sulfur dioxide complex [CpRu(chir)(SO2)]PF6 [10, chir = (S,S)-Ph2PCHMeCHMePPh2] was synthesized from [CpRu(chir)Cl] and SO2 and was characterized by X-ray crystallography. Reaction of 10 with diazomethane gave the enantiomerically pure sulfene complex [CpRu(chir)(H2C/SO2)]PF6 (11). Addition reactions of 11 with N-(1-cyclopentenyl)morpholine, as well as with various enolates derived from β-oxo esters or 1,3-diesters proceeded with high yields and 20-90% de. The structure of a diastereomerically pure addition product, [CpRu(chir)(SO2CH2C(Me){C(O)Me}{C(O)OtBu}] (13d′), was determined crystallographically and was shown to have (R) configuration at the quaternary carbon atom. After alkylation of one of the S/O functions, the sulfinate ligand was cleaved from the metal center by ligand substitution with acetonitrile, and the resulting acetonitrile complex 15 was converted back into 10 by treatment with SO2.
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  • 31
    ISSN: 1434-1948
    Keywords: Metal-rich antimonides ; Magnetism ; Structure and bonding ; Conductivity ; LMTO ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compounds can be synthesized in quantitative yields by arc-melting of stoichiometric amounts of HfSb2, Hf and one of the 3d metals V, Cr, Mn, Fe, Co, Ni, and Cu. These antimonides crystallize in a substitution variant of the W5Si3 type, in which one position is statistically mixed, occupied by the 3d metal atom M or the Sb2 atom in different ratios. Within the linear (M,Sb) chain, the M:Sb ratio may vary between 3:1 and 2:3. According to calculations of the electronic structures of Hf10MδSb6-δ with δ = 1, these phases are metallic compounds stabilized by strong Hf-Hf, Hf-M, and Hf-Sb bonds, and to a smaller extent by bonding interactions within the linear (M,Sb) chain. The metallic character was confirmed by measurements of the electrical resistivity and the magnetism of selected samples. Whereas Pauli paramagnetism was observed experimentally for M = V, Co, and Ni, Hf10FeSb5 is apparently the only phase with localized magnetic moments and magnetic coupling. This is in agreement with the magnetic ground state obtained solely for the ordered structure model of Hf10FeSb5 with spin-polarized calculation within the local spin density approximation.
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  • 32
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 323-330 
    ISSN: 1434-1948
    Keywords: Amino acids ; Alkynes ; Ferrocene ; Palladium ; Catalysis ; Bioorganometallic chemistry ; Biosensors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes a Pd-catalyzed coupling of ferrocene alkyne derivatives to iodo amino acids. Ferrocene carboxylic acid propargyl amides were easily obtained in high yield. The crystal structures of the propargyl amine derivative 3 and the 1,1-diethylpropargylamine derivative 4 have been determined by X-ray diffraction. Pd-catalyzed coupling to p-iodoanilide amino acids gave the corresponding ferrocene-labeled amino acid derivatives, which were easily purified by diethyl ether extraction in the case of the 1,1-diethyl derivatives 8. The coupling reaction did not require anhydrous solvents and tolerated a variety of functional groups present in peptides such as alcohols (8a, Ser), thioethers (8d, Met), disulfide bonds (cystine, 12) esters (as in the N-labeled Leu derivative 10) and of course amides. A minor by-product of the coupling reaction, namely the homo-dimer bis(ferrocene carboxylic acid propargylamide) 9, was identified in the crude reaction mixtures by mass spectrometry and independently synthesized by oxidative coupling (Glaser and Eglington) of 3. All new compounds were completely characterized spectroscopically, including 15N- and 2D NMR spectroscopy, Mössbauer spectroscopy and electrochemistry. This work introduces a versatile procedure for a selective functionalization of amino acids with organometallics at the C-terminus which is expected to be of general applicability to peptide chemistry.
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  • 33
    ISSN: 1434-1948
    Keywords: Palladium ; Insertion reactions ; Tridentate ligands ; Hydrazones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potentially tridentate hydrazonic ligands of the type HNNO have been used in the synthesis of some methyl palladium(II) complexes. Depending on the applied experimental conditions two different kinds of complexes are obtained. Thus, the reactions between HL1-HL5 and (COD)PdMeCl in diethyl ether led to the formation of bidentate methyl complexes of the type Pd(HNN)MeCl (1-5), where the ligands maintain a neutral character. However, in the presence of a base such as Et3N or NaOMe, the ligands are deprotonated with the consequent formation of tridentate methyl complexes of the type Pd(NNO)Me (7-10). In solution, complexes 1-5 tend to lose the hydrazonic proton with elimination of methane and formation of a tridentate chloride complex Pd(NNO)Cl (6); this tendency can be correlated with the acidity of the free ligands, which has been determined. On bubbling carbon monoxide through solutions of 1-5, the corresponding acetyl complexes Pd(HNN)[C(O)Me]Cl (11-15) are formed, in which both the cis and trans isomers are present. Their molar ratio is rationalised from the results of a molecular modelling study on the basis of electronic considerations. A remarkably different reactivity has been found in the carbonylation of the tridentate complexes 7-10: they decompose rapidly and quantitatively to palladium black and an organic product corresponding to the ligand with an acetyl group bonded to the hydrazonic nitrogen. The X-ray structures of a methyl complex (3) and its corresponding acetyl (13) derivative have been determined.
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  • 34
    ISSN: 1434-1948
    Keywords: Vanadyl arsenate ; Hydrates ; Layered compounds ; Vibrational spectroscopy ; X-ray scattering ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The course of the intercalation and deintercalation of water molecules in vanadyl arsenate has been studied by X-ray diffraction analysis and by infrared and Raman spectroscopies. The formation of VOAsO4 hydrates at ambient temperature has been found to depend on relative humidity (r.h.): VOAsO4 · 5 H2O (basal spacing c = 10.48 Å) is formed at r.h. above 76%, VOAsO4 · 3 H2O (c = 8.03 Å) at 43-76% r.h., VOAsO4 · 2 H2O (c = 7.33 Å) at 11-43% r.h.; dehydrated VOAsO4 (c = 4.18 Å) exists near 0% r.h. Like the thermal dehydration of VOPO4 · 2 H2O, the thermal dehydration of VOAsO4 · 3 H2O proceeds in a stepwise manner so that the dihydrate and monohydrate are formed en route to the anhydrous compound. The arsenate monohydrate is gradually dehydrated over a broad temperature range. The broad diffraction lines observed can be explained in terms of the existence of a disordered phase containing monohydrated and anhydrous forms of vanadyl arsenate. A similar phenomenon has been observed during the dehydration of VOAsO4 · 3 H2O over phosphorus pentoxide at ambient temperature. The hydration of VOAsO4 is different from that of VOPO4. The first step, i.e. the insertion of water that coordinates to the vanadium atoms, is very slow. On the contrary, the uptake of further water molecules with the formation of higher hydrates is fast. It thus seems likely that the filling of one interlayer space with water facilitates the intercalation of further water into neighboring interlayer spaces. Therefore, only higher hydrates together with the original anhydrous phase are observed. Impedance spectral measurements indicate that the conductivity of the trihydrate has a mixed ionic/electronic character.
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  • 35
    ISSN: 1434-1948
    Keywords: Coordination chemistry ; α-Imino ketones ; CO complexes ; Iron complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Fe2(CO)9 at room temperature in THF or toluene with the α-imino ketones R1N=C(R2)-C(R3)=O (L) (R1 = alkyl, R2 = H, Me, Ph, R3 = Me, Ph) (a-k), initially results in the formation of the mononuclear chelate Fe(CO)3(α-imino ketone) complexes 6 which can be isolated in moderate (6h) to high (6e-g) yield. Under these reaction conditions, complexes 6 subsequently react with [Fe(CO)4] fragments or dimerise, to form the dinuclear complexes Fe2(CO)6(α-imino ketone) (7a-j) or Fe2(CO)4(L-L) (8a,b,k), respectively. The complexes 8 contain two α-imino ketone ligands C-C coupled at the ketone carbon atoms. Complexes 8a,b react with CO at elevated temperatures to quantitatively yield Fe(CO)3(α-imino ketone) (6a,b). This reaction can be reversed photochemically. Irradiation of a solution of 6a,b in the low-energy band results in the reformation of 8a,b in almost quantitative yield. The extremely air-sensitive complexes 6 and the dinuclear complexes 7 and 8 have been characterised spectroscopically (IR, UV/Vis, 1H and 13C NMR) and by elemental analysis. The solid state structures of complexes 6g and 8a have been determined by single-crystal X-ray diffraction. The molecular structure of 6g confirms the flat σ-O,σ-N chelate coordination of the α-imino ketone. The structure of 8a consists of two metal-metal-bonded Fe(CO)2 units, bridged by a formally 10e-donating dianionic C-C coupled (tBu-ADO) ligand. A mechanism for the formation of complexes 8 is discussed.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99351_s.pdf or from the author.
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  • 36
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 929-932 
    ISSN: 1434-1948
    Keywords: Titanium ; Cyclopentadienes ; Arene complexes ; Cations ; Bridging ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The half-sandwich titanium trimethyl complex (η5-C5H4CMe2Ar)TiMe3 (Ar = 3,5-Me2C6H3) reacts with the Lewis acid B(C6F5)3 to give the ionic TiIV ansa-cyclopentadienyl-arene complex [(η5,η6-C5H4CMe2Ar)TiMe2][MeB(C6F5)3]. In bromobenzene solvent, addition of more B(C6F5)3 leads to C6F5/Me exchange and, subsequently, to formation of an unusual dimeric TiIII dicationic species, {[(η5,η6-C5H4CMe2Ar)Ti(μ-Br)]2}[B(C6F5)4]2, which was structurally characterized. Its formation involves reduction of the transition-metal center, solvent C-Br cleavage and perfluoroaryl-group scrambling.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99383_s.pdf or from the author.
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  • 37
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 939-941 
    ISSN: 1434-1948
    Keywords: Germanium ; Germanol ; Hydrogen bonds ; X-ray structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrolysis of tBu2Ge(OEt)2 is described. Depending on the amount of water used either tBu2Ge(OH)2 (1) or a mixture of the latter and (tBu2GeOH)2O (2) were obtained. A cocrystallate consisting of 2tBu2Ge(OH)2, (tBu2GeOH)2O and water was the subject of a single crystal X-ray diffraction study. In the solid state the individual molecules are connected by hydrogen bonds giving rise to the formation of a polymeric double chain ribbon.
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  • 38
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 959-969 
    ISSN: 1434-1948
    Keywords: Bipyridyldiphosphane ligands ; Macrocycles ; Metallacyclophanes ; Platinum ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5,5′-bis(hydroxyalkyl)-2,2′-bipyridines 4a-c (Scheme 1) were prepared either in one step (4b, 4c) or in four steps (4a) starting with 5,5′-dimethyl-2,2′-bipyridine in each case. Reaction of 4a-c with mesyl chloride afforded the bis(mesylates) [-C5H3N-(CH2)n-CH2-OSO2Me]2 5a-c [n = 1 (a), 2 (b), 3 (c)], which could easily be transformed into the diphosphanes 6a-c by reaction with LiPPh2. Treatment of 6c, 6b with Cl2Pt(NCPh)2 and (RC6H4)2Pt(COD) according to the high-dilution method resulted in the formation of the tetraphosphadiplatinacyclophanes [-C5H3N-(CH2)4-PPh2PtCl2PPh2-(CH2)4-C5H3N-]2 (7c) and [-C5H3N-(CH2)3-PPh2Pt(C6H4R)2PPh2-(CH2)3-C5H3N-]2 (8b, 9b) (8b: R = H, 9b: R = tBu), respectively (Scheme 2). The molecular structures of 8b and 9b were elucidated by X-ray structural analyses. The noncoordinated bipyridine moieties in 8b were employed to encapsulate copper(I) to give the host/guest complex 10b (Scheme 3), which was investigated by FAB-MS, NMR spectroscopy, and cyclovoltammetry. 10b exhibited a quasi-reversible oxidation at E1/2 = -0.31 V and an electrodeposition-redissolution redox system at E1/2 = -0.79 V, owing to the formation of copper at the surface of the working electrode.
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  • 39
    ISSN: 1434-1948
    Keywords: Lanthanides ; Ytterbium ; MRI contrast agents ; Solid-state structures ; Hydration ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The low temperature (-100 °C) X-ray structure of the complex K2[Yb(DTPA)(H2O)] has been determined. The metal ion is at the center of a tricapped trigonal prism and is nine-coordinate, binding to the three nitrogens and five oxygens of the ligand and one water molecule. From the structure obtained, three well-defined hydration shells can be observed consisting of: i) one coordinated water molecule; ii) several water molecules in the outer coordination sphere of the YbIII ion and iii) one water molecule surprisingly close to the metal center and hydrogen-bonded to proximate carboxylate groups. A variable-field and temperature NMRD study of the corresponding Gd complex has been performed and the data interpreted by taking into account the presence of second-sphere water molecule(s). The results of the analysis are in excellent agreement with the X-ray structural data.
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  • 40
    ISSN: 1434-1948
    Keywords: Catalysis ; Densitiy functional theory ; Epoxidation ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Seven-coordinated molybdenum oxobisperoxo complexes with chelate nitrogen donors like pyrazolylpyridines are catalysts for the epoxidation of olefins. An NMR spectroscopic and quantumchemical study on the fluxionality of the chelate ligand proves that during this process partial ligand dissociation takes place. This gave rise to a detailed theoretical study on the activation of CH3OOH at the model complex (NH3)2MoO(O2)2 including dissociation of one of the ammonia ligands and proton transfer from the hydroperoxide to one of the peroxo ligands.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99429_s.pdf or from the author.
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  • 41
    ISSN: 1434-1948
    Keywords: Palladium ; Tripodal ligands ; O ligands ; Fluxionality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [PdCl2(CH3CN)2] with the silver salt of the tripodal oxygen ligand L- = [(C5H5)Co{P(O)(OMe)2)}3]- yields the homoleptic oxygen ligand complex [PdL2] (1). The molecular structure of 1 was determined by single-crystal X-ray diffraction: monoclinic space group P21/n; a = 8.515(1), b = 13.627(2), c = 15.828(2) Å; β = 92.44(1)°; V = 1834.9(7) Å3; Z = 2. The complexes [Pd(PPh3)XL] [X = Cl (2a), Br (2b), I (2c)] have been prepared starting from 1. Complex 2a reacts with PPh3 to form [Pd(PPh3)2L]Cl (3a) and [Pd(PPh3)2L]L (3b). Treatment of 2a with CO in MeOH yields the carboxymethyl complex [{(PPh3)(COOMe)Pd(μ-Cl)}2] (4) and the protonated ligand HL. The carboxymethyl complex 4 shows some catalytic activity for the copolymerization of CO and ethene. Complex 4 reacts with AgL to yield [Pd(PPh3)(COOMe)L] (6). Alkylation of 2a with Me4Sn leads to the methyl complexes [Pd(PPh3)MeL] (7) and [Me2ClSnL] (8). CO insertion in the palladium-carbon bond of 7 gives the stable acetyl complex [Pd(PPh3){C(O)Me}L] (10). The palladium(II) complexes 1, 2, 3, 6, 7, and 10 of the tripodal oxygen ligand L are all fluxional molecules that have been studied by temperature-dependent 1H- and 31P-NMR spectroscopy.
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  • 42
    ISSN: 1434-1948
    Keywords: Tripod ligands ; Hindered rotation of vinylidene ligands ; CpML2 chelate ligands ; Ruthenium ; Carbenes ; Carbene-type ligands ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tripodal ligand [CH3C(CH2C5H4)(CH2PPh2)2]- reacts with RuCl2(PPh3)3 to produce CH3C(CH2-η5-C5H4)(CH2-η1-PPh2)2RuCl, [tripodCpL2RuCl], 1. Complex 1 undergoes substitution of the chlorine function with various nucleophiles L′ to produce [tripodCpL2RuL′]+. The carbonyl derivative (L′ = CO) 2, isonitrile (L′ = RNC) 3, nitrile compounds (L′ = RCN) 4, and a tolane adduct (L′ = η2-PhC≡CPh) 5 are obtained when 1 is treated with the appropriate ligands in polar solvents. Halide acceptors (e.g. TlPF6) are generally needed to promote these reactions. The cyanide derivative tripodCpL2RuCN (3a) is alkylated by F3CSO3CH3 to give the isonitrile derivative [tripodCpL2RuCNMe]+3b. Terminal alkynes HC≡CR produce vinylidene compounds [tripodCpL2RuL′]+, where L′ = C=CHR (R = tBu, 7b; R = Ph, 7c), or allenylidene derivatives, L′ = C=C=CPh2 (6), depending on the nature of R (R = CPh2OH for synthesis of 6). Trimethylsilylacetylene gives the parent vinylidene species, L′ = C=CH2 (7a), which is transformed to the Fischer-type carbene compound, L′ = C(OMe)Me (8), upon treatment with methanol. The vinylidene species 7 are deprotonated by NaOMe to produce the alkynyl compounds tripodCpL2RuC≡CR (9). Methylation of 9 with F3CSO3CH3 results in the vinylidene derivatives L′ = C=C(Me)R (R = tBu, 7d; R = Ph, 7e), having two organic substituents at the terminal carbon centre. For all vinylidene compounds with two different substituents at their terminal carbon atom, hindered rotation of the single-faced vinylidene π-ligand about its Ru-C bond is observed. Analysis by 31P-NMR spectroscopic coalescence measurements as well as line-shape analyses reveals activation enthalpies of around 40 kJmol-1 for this rotation, with small activation entropies of around ±10 Jmol-1K-1. Solid-state structures of nine compounds of the type [tripodCpL2RuL′]+n (n = 0, 1) demonstrate the remarkable conformational rigidity of the tripodCpL2Ru template. They also show that the possible strain imposed by linking the Cp ligand and the two donor groups L in one and the same chelate scaffolding does not appear to impose a serious steric strain on these templates.
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  • 43
    ISSN: 1434-1948
    Keywords: (R)-(+)-2,3-Epoxy-1-propanol ; 2,3-Dihydroxyalkyl phosphanes ; 1,3,2-Dioxaborolane ; 1,3-Dioxolane ring ; Enantiopure phosphanes ; Complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of (R)-(+)-2,3-epoxy-1-propanol with Ph2PH, Ph(Me)PH, or PhPH2 in the superbasic medium KOH/DMSO affords the novel chiral phosphanes 1a-1c. While 1a is obtained enantiomerically pure, 1b and the secondary phosphane 1c are formed as mixtures of diastereoisomers (RPRC, SPRC) with homochiral β carbon atoms. Derivatization of 1a with phenylboronic acid or 2,2-dimethoxypropane yields 2a and 3a with 1,3,2-dioxaborolane and 1,3-dioxolane ring systems, respectively. The X-ray structure of 2a (space group P21) reveals the presence of four molecules of R configuration in the unit cell. Nucleophilic phosphanylation of (R)-(-)-2,3-O-isopropylideneglycerol tosylate with Ph2PH, Ph(Me)PH, or PhPH2 yields chiral 3a-3d. Compound 3b was obtained enantiomerically pure. The secondary phosphane 3c has been employed in syntheses of the hydrophilic tertiary phosphanes 3e, 3f and of the novel bidentate phosphane ligands 3g, 3h, all of which have homochiral β carbon atoms. PdII complexes PdL2Cl2 of 1a, 2a, 3a (L) are formed as mixtures of cis/trans isomers. RhI complexes of 1a, 3a, and bidentate 3h have also been synthesized.
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  • 44
    ISSN: 1434-1948
    Keywords: Macrocycles ; Nickel ; Redox chemistry ; Schiff bases ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A single crystal X-ray analysis of [Ni2L1](ClO4)2· MeCN · 1/4 H2O, 1a [formed directly from a mixture of nickel(II) template ions, 2,6-diformyl-4-methyl-thiophenolate, and 1,4-diaminobutane] reveals that the nickel(II) ions are in square-planar N2S2 environments and that the four “bowed” dinickel macrocycles in the asymmetric unit pack around a single central perchlorate template ion encapsulating it to form “star” clusters of stoichiometry {[Ni2L1]4(ClO4)}7+. These “stars” stack together, via π-π-stacking interactions, to form two-dimensional sheets, which are separated from one another by layers of the remaining perchlorate anions and solvent molecules. Reduction, by NaBH4, of the four imine bonds in [Ni2L2](ClO4)22a (analogous to 1a but formed from 1,3-diaminopropane not 1,4-diaminobutane) or [Ni2L2](CF3SO3)22b to amine bonds produces the corresponding tetra-amine complex, [Ni2L3](ClO4)23. These complexes are shown to contain diamagnetic nickel(II) ions by a combination of magnetic, NMR and UV/Vis spectroscopic results. The 1H NMR spectra of 1-3 run in [D3]MeNO2 and in [D3]MeCN are consistent with increasing axial binding ability in the order: 3 〈 2 〈 1. Thiocyanate ion binding studies reveal that 1 and 2 are able to coordinate two thiocyanate ions, forming [Ni2L1(NCS)2] 4 and [Ni2L2(NCS)2] 5 respectively, whereas 3 does not. Single crystal X-ray analyses of complexes 4· 2 MeCN and 5· MeCN show that adjacent square-planar and octahedral nickel(II) ions result. Two one-electron oxidations and two one-electron reductions are a feature of the electrochemistry of 1-3 in MeCN: curiously, the potentials for the oxidation processes are almost invariant whereas those for the reduction processes vary as anticipated. EPR spectroscopy shows that the first one-electron reduction process and the first one-electron oxidation process are metal centred. Spectroelectrochemical studies and redox titrations indicate that a purplish-coloured complex is produced by one-electron oxidation of 2 (λ = 870 nm, ε = 1320 L mol cm-1). The synthesis of a phenolate analogue, [Ni2L′(MeCN)4](ClO4)2 (6), of the thiophenolate complex 2a is also detailed. Complex 6 undergoes two one-electron oxidations in MeCN, but, in contrast to the thiophenolate complexes 1-3, these occur at much higher potentials. Only a single one-electron reduction process is observed and this occurs at a more negative potential than for any of 1-3.
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  • 45
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 195-203 
    ISSN: 1434-1948
    Keywords: Acid derivatives ; Cyclen and cyclam derivatives ; Phosphinic acid ; Potentiometry ; Protonation and stability constants ; 31P-NMR titration ; Hydrogen bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two phenylphosphinic acid derivatives of tetraaza macrocycles, (1,4,7,10-tetraazacyclododecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid) [(H4L1) and (1,4,8,11-tetraazacyclotetradecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid)] (H4L2), were synthesised and the crystal structures of H4L2 and its bis(1-adamantylammonium) salt were determined. In both the structures, the ring conformation is virtually the same and is stabilised by hydrogen bonds. Protonation constants of the acids and stability constants of their Zn2+ and Cd2+ complexes were determined pH-metrically at 25 °C and at an ionic strength of 0.1 mol dm-3 (KNO3). The pKA values found for both the compounds are lower than those for their carboxylic analogues and correspond to the expected electron-withdrawing ability of the -P(Ph)O2H moiety. The value pK1 of the last dissociation constant of H4L1 is surprisingly high. The complexes of Zn2+ and Cd2+ with (L1)4- and (L2)4- are less stable than those with other similar ligands, which is in accordance with lower overall basicity of H4L1 and H4L2. A pronounced drop in the stability of the complexes of H4L2 can be explained by partial coordination of the ligand to the metal ions. The solution properties of the ligands were also investigated by 31P-NMR spectroscopy. The spectra observed suggest stable (on the NMR time scale) conformations of the protonated ligands in solution. A comparison of NMR spectra in solution and CP/MAS-NMR spectra indicates that the structures of the conformers roughly correspond to the structures observed in the solid state. The conformations are stabilised by intramolecular hydrogen bonds and by hydrophobic interactions of phenylphosphinic moieties. The conformers are stable even at 90 °C, but not in the presence of complexing metal ions.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99149_s.pdf or from the author.
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  • 46
    ISSN: 1434-1948
    Keywords: Rare earth complexes ; Naphthalocyaninato ligand ; Double-decker complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of rare earth(III) double-deckers RE[Nc(tBu)4]2 [RE = La, Ce, Pr, Nd, Eu, Gd, Tb, Y, Er; Nc(tBu)4 = dianion of tetra(tert-butyl)-2,3-naphthalocyanine] (1-9) have been prepared by treating RE(acac)3·n H2O (acac = acetylacetonate) with 6-tert-butylnaphthalonitrile in refluxing n-octanol in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). These novel sandwich-type complexes have been spectroscopically characterized. The electrochemical studies show that the first oxidation and the first reduction potentials increase with the size of the central metal ions with a relatively small separation (0.28-0.33 V), reflecting the narrow HOMO-LUMO gap.
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  • 47
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 229-239 
    ISSN: 1434-1948
    Keywords: Pyridine derivatives ; Bipyridine derivatives/Metal complexes ; Chromophores ; Nonlinear optics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metal complexes of pyridine and bipyridine-type ligands represent an important class of nonlinear optical (NLO) materials: (i) They can incorporate a variety of functionalised ligands with a wide range of metals which can give rise to tuneable NLO properties; (ii) they are generally associated with intense low-lying charge-transfer excitations such as metal to ligand charge-transfer (MLCT) or intraligand charge-transfer (ILCT); (iii) bipyridyl ligands are also good building blocks that allow the construction of octupolar complexes with a defined geometry and symmetry. This review describes the recent developments in the design of such dipolar and octupolar chromophores for second-order nonlinear optics.
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  • 48
    ISSN: 1434-1948
    Keywords: Heterobimetallics ; Hydride complexes ; Alkenyl complexes ; μ-Isonitrile complexes ; Silicon ; Iron ; Platinum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The heterobimetallic hydride complexes [(OC)3Fe{Si(OMe)3}(μ-Ph2PXPPh2)Pt(H)(PR3)] (1a: X = CH2, PR3 = PPh3; 1b: X = NH, PR3 = PPh3; 1c: X = CH2, PR3 = PMePh2) have been prepared by the oxidative addition of [(OC)3Fe(H){Si(OMe)3}(η1-Ph2PXPPh2)] to [Pt(H2C=CH2)(PPh3)2] or by reaction of K[(OC)3Fe{Si(OMe)3}(η1-dppm)] with trans-[Pt(Cl)(H)(PPh3)2]. The solid-state structure of compound 1b has been determined by single-crystal X-ray diffraction. 1-Alkynes such as methylpropiolate or phenylacetylene insert in a regiospecific manner into the Pt-H bond of 1 to yield the σ-alkenyl complexes [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-Ph2PXPPh2)Pt{C(R)=CH2}] (2a: X = CH2, R = CO2Me; 2b: X = NH, R = CO2Me; 3a: X = CH2, R = Ph). Addition of the Pt-H bond of 3a across the triple bond of [D1]phenylacetylene affords [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-dppm)Pt{C(Ph)=C(D)H}] (3a*) having the deuteron trans to platinum (cis addition). This insertion reaction is accompanied by dissociation of the platinum-bonded PR3 ligand and saturation of the vacant coordination site by a dative μ-η2-Si-O→Pt interaction. When 3 is treated with PR3 again, a subsequent phosphane-induced rearrangement leading to vinylidene-bridged complexes [(OC)3Fe{μ-C=C(H)R′}(μ-Ph2PXPPh2)Pt(PR3)] (4a: X = CH2, R′ = Ph, PR3 = PPh3; 4b: X = NH, R′ = Ph, PR3 = PPh3; 4c: X = CH2, R′ = Ph, PR3 = PMePh2; 4d: X = CH2, R′ = p-tolyl, PR3 = PPh3) occurs. Upon purging a solution of 3a with carbon monoxide, the labile CO adduct [(OC)3Fe{Si(OMe)3}(μ-dppm)-Pt(CO){C(Ph)=CH2}] 5a is formed, addition of 2,6-xylyl isocyanide to 2a and 3a affords the isonitrile adducts [(OC)3Fe{Si(OMe)3}(μ-dppm)Pt(CNxylyl){C(R)=CH2}] (5b: R = CO2Me; 5c: R = Ph), respectively. When hydride complex 1a is allowed to react with stoichiometric amounts of aromatic isonitriles, formal elimination of HSi(OMe)3 occurs, yielding the heterodinuclear isonitrile-bridged complexes [(OC)3Fe(μ-C=N-R)(μ-dppm)Pt(PPh3)] (6a: R = 2,6-xylyl; 6b: R = o-anisyl; 6c: R = p-anisyl; 6d: R = p-C6H4NH2) and the bis(isonitrile) complexes [(OC)2(RN≡C)Fe(μ-C=N-R)(μ-dppm)Pt(PPh3)] (7a: R = 2,6-xylyl; 7b: R = p-anisyl). Single-crystal X-ray diffraction studies perfomed on 6a and 6b reveal that the molecular structures of these μ-isonitrile complexes closely resemble the μ-vinylidene complexes 4. The two metal centers are bridged in a symmetric manner by strongly bent CNR ligands, the aromatic groups R being oriented towards the Fe(CO)3 moiety. Electrophilic addition of HBF4 to the basic nitrogen atom of the μ-CNR ligand transforms 6 to the cationic μ-aminocarbyne complexes [(OC)3Fe{μ-CN(H)R}(μ-dppm)Pt(PPh3)][BF4] (8a: R = 2,6-xylyl; 8b: R = p-anisyl; 8c: R = p-C6H4NH2).
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  • 49
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 253-264 
    ISSN: 1434-1948
    Keywords: Iron-sulfur clusters ; Crown ethers ; Electrochemical devices ; Host-guest chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of Fe4S4 cluster compounds, I, III, and V, in which the cuboidal cluster core is appended with four crown ether thiolate ligands, and II and IV, bearing thiolate ligands without crown ether parts, has been synthesized and characterized. The spectroscopic and electrochemical properties of these compounds are determined by the electronic nature of the thiolate ligands. Only in the case of III, where a very short α-thioacetyl linker was used to connect the crown ether ligands to the cluster core, was a restricted conformational freedom of the ligand observed. A detailed electrochemical study of the influence of alkali and earth alkali metal ions (Li+, Na+, K+, Mg2+, and Ba2+) on the reversible 2-/3- reduction of the cluster compounds was performed. In the case of the crown ether appended clusters I, III, and V, the addition of these metal ions resulted in an anodic shift, i.e. in positive direction, of the reduction potential (modulation effect) and to larger current responses (promotion effect). The magnitude of the modulation effects is determined by the binding affinity of the metal ions in the crown ether ligands, and by the distance between bound metal ions and the redox active cluster core. Variation of the linker between the cluster core and the metal ion binding site resulted in cluster compounds with almost inverse selectivities for e.g. K+ and Ba2+ in the case of I and III. For the large effects found for compound I a lariat binding mode is proposed.
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  • 50
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 281-285 
    ISSN: 1434-1948
    Keywords: NMR spectroscopy ; Zeolites ; Al-coordination ; Mordenite ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 27Al 3Q MAS NMR spectroscopy has been applied to study the coordination state of the species giving the 30 ppm Al NMR signal in the 27Al MAS NMR spectrum of activated mordenite materials. From the 27Al 3Q MAS NMR measurements it is evident that the broad peak at 30 ppm in the 27Al NMR spectrum of the mordenite calcined at temperatures up to 600 °C comes mainly from the distorted four-coordinated Al. By simulation a quadrupolar coupling constant of 5.8 MHz was estimated for the distorted tetrahedral Al. For samples calcined at 650 and 700 °C, a small amount of pentacoordinated Al emerges. The majority of the signal, however, arises from distorted tetrahedral Al. A two-step calcination results in a significant contribution of the pentacoordinated Al to the signal at 30 ppm. From the simulated line-shape, a quadrupole coupling constant of 6.2 MHz is obtained for the latter signal. These data show that during the calcination of the mordenite, the coordination environment at the Al centre gradually becomes distorted to give rise to the shoulder at 30 ppm. With the increase of the calcination temperature, pentacoordinated Al species form
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  • 51
    ISSN: 1434-1948
    Keywords: Copper ; Magnetic properties ; Supramolecular chemistry ; Three-dimensional architecture ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel three-dimensional copper(II) compound of the formula [Cu3(btre)5(H2O)2](ClO4)6·H2O (btre = 1,2-bis(1,2,4-triazol-4-yl)ethane) has been synthesized. The structure has been solved at 150 K by single-crystal X-ray analysis. The compound [C30H44Cu3N30O2·6(ClO4)·H2O] crystallizes in the triclinic space group P1bar with a = 12.488(1), b = 13.195(1), c = 19.756(2) Å, α = 78.959(8), β = 84.553(8), γ = 63.869(7)°, V = 2868.4(5) Å3, Z = 2 (trinuclear CuII units), 6484 reflections [I 〉 4σ(Ι)], RF = 0.0581, wR2 = 0.1214. The structure of this coordination polymer consists of a three-dimensional network built up from linear trinuclear CuII cations of formula [Cu3(btre)5(H2O)2]6+. This crystallographically independent unit comprises a linear array of three CuII ions linked by triple N1,N2-1,2,4-triazole bridges, yielding Cu1-Cu2 = 3.893(1) Å and Cu2-Cu3 = 3.889(1) Å. These linear trinuclear CuII units are linked by various pathways involving tridentate and tetradentate bridging btre ligands, which yields an unprecedented three-dimensional network. The CuII ions are weakly antiferromagnetically coupled with J = -1.01(2) cm-1 (based on the Hamiltonian: H = -J[SCu1·SCu2 + SCu2·SCu3] using the expression for the molar magnetic susceptibility S = 1/2 of a linear trinuclear system). The nature and the magnitude of the antiferromagnetic exchange have been discussed on the basis of the structural features.
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  • 52
    ISSN: 1434-1948
    Keywords: Alkenylcarbynes ; Dinuclear tungsten complexes ; Electrochemistry ; Tungsten NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Neutral trans-cyanide alkenylcarbyne complexes 2a and 2b have been prepared by reaction of the complex 1a and 1b with NaCN or [Bu4N]CN. The reaction of complexes 2a and 2b with an equimolar amount of the acetonitrile complexes 1a and 1b in CH2Cl2 leads to the cationic cyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 3a-d. Diisocyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 4a and 4b have been synthesized by the reaction of complexes 1a and 1b with 0.5 equivalents of the diisocyanide 1,4-(CN)2C6H4. IR as well as 1H-, 31P{1H}-, 13C{1H}-, and 183W-NMR data are reported. The spectroscopic data show that in the dinuclear complexes 3a-d, the bridging CN group and the alkenylcarbyne units are located in trans positions, while in the dinuclear complexes 4a and b, the isocyanide groups of the bridging ligand 1,4-(CN)2C6H4 and the two alkenylcarbyne moieties are cis. The 183W chemical shifts of complexes 2a, 2b, 3a-d, 4a, and 4b were obtained through two-dimensional indirect 31P, 183W NMR recording techniques. A downfield shifting of 183W resonances of the cyanide-bridged dinuclear complexes 3a-d with respect to the mononuclear ones, 2a and 2b, was observed. The δ183W of isocyanide bridging dinuclear complexes 4a and 4b appear at higher field than those of the corresponding mononuclear cyanide 2a and 2b in accordance with the higher π-acceptor electron properties of the isocyanide ligand. The electrochemical behaviour of all the complexes has been investigated by cyclic voltammetry and controlled potential electrolysis in aprotic media and at a Pt (or vitreous C) electrode. Complexes 1, 2, or 3 undergo multi-electron irreversible oxidation processes involving anodically induced proton dissociation from the alkenylcarbyne ligands, and irreversible cathodic processes are also observed for all the complexes. The order of the redox potentials reflects that of the net electron π-acceptor/σ-donor character of the ligands and the ligating alkenylcarbynes are shown to behave as remarkably strong π-electron acceptors (even stronger than CO).
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  • 53
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    AIChE Journal 26 (1980), S. 152-154 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 54
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 55
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    AIChE Journal 26 (1980), S. 148-150 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 56
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    AIChE Journal 26 (1980), S. 174-174 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 57
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    AIChE Journal 26 (1980), S. 175-176 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 58
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    AIChE Journal 26 (1980), S. 177-201 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This article reviews the major developments in the engineering and design of three-phase slurry catalytic reactors. A general theoretical analysis for predicting the overall rate of reaction in a slurry reactor for various kinetics is presented, incorporating all the transport effects. Modeling of semi-batch reactors is discussed and design procedures are indicated. Some major correlations and methods for determining gas-liquid and liquid-solid mass transfer coefficients and effective diffusivity in liquid filled pores are reviewed. Slurry reactors are compared with other three-phase reactors, such as trickle bed or packed bed reactors, and relative merits are pointed out.
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  • 59
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    AIChE Journal 26 (1980), S. 201-212 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Intraparticle mass transfer in coal pyrolysis is described by ternary diffusion and viscous flow, in conjunction with a simple pore model to predict concentration profiles for gases and tar. At low pressures, product yields depend on particle size only, while at high pressures they depend on pressure and particle size. Limited experimental data from a subbituminous coal confirm these trends. Data from a bituminous coal show different trends, as expected from the drastic changes the pore structure undergoes during pyrolysis.
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  • 60
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When primary control objectives cannot be measured directly, secondary measurements have to be selected and used in conjunction with estimators to infer the value of the unmeasurable variables. Unmeasured process disturbances (state excitation noise) are assumed to be of major importance, dominating the errors caused by measurement noise. Since the white noise assumption is generally insufficient for the persistent disturbances commonly occuring in the Chemical Engineering, environment, a nonstationary noise model has been employed, and is shown to yield superior estimations under these circumstances. New necessary and sufficient conditions have been developed for the observability of the dynamic system augmented to include the noise model.A variety of new measurement selection criteria is presented here, with the goal of minimizing estimation error. One class of criteria aims at minimizing the transient estimation error when a static estimator is used. The other class minimizes the measurement error caused by the unobservable subspace. The design of state reconstruction procedures (which are able to handle persistent unmeasured process disturbances) is explained in a stochastic and a deterministic framework. Finally, the synthesis of reduced order control schemes is discussed. The power of the selection criteria and the superiority of a Kalman filter design employing a nonstationary noise model is demonstrated in many examples.
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  • 61
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    AIChE Journal 26 (1980), S. 274-281 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A three-parameter model of axial and radial dispersion in a packed tubular reactor is proposed as an alternative to the Fickian dispersion model. Though it is formulated in terms of differential equations, it requires no exit boundary condition, so it is mathematically more convenient than the Fickian model. Examples of its application to chemical reactors are given.
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    AIChE Journal 26 (1980), S. 287-288 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 26 (1980), S. 308-310 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 26 (1980), S. 314-317 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 26 (1980), S. 317-319 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 26 (1980), S. 325-327 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 26 (1980), S. 1-9 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This article describes a novel approach to the systematic synthesis of heat exchanger networks. For a given synthesis problem, this approach leads to a complete listing of all solutions which exist, using a prescribed degree of energy recovery, the minimum number of exchangers, heaters and coolers, and no split streams. The approach is combinatorial, with a variety of thermodynamic criteria used to minimize the problem size by preventing infeasible solutions being generated. Two examples (5SPI and 6SPI) are discussed to illustrate complete solution by hand.
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    AIChE Journal 26 (1980), S. 24-30 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: For moving-bed solids flow in an inclined pipe leading into a fluidized bed, the pressure drop across the pipe is a retarding force while the gas leakage rate alters the flow properties of the solids. The pressure drop has been related to the pipe exit pressure, which, in turn, can be calculated by integrating the solids bulk density over the bed depth. A correlation for the rate of gas leakage in terms of the geometric features and operating conditions of the system is developed. The correlation agrees with experimental data to within ± 25%. Part II of this paper will deal with solids flow.
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    AIChE Journal 26 (1980), S. 43-51 
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    Notes: Diffusion in concentrated, non-ideal liquid solutions may take place not only through motion of single molecules but also through movement of groups of molecules, or “clusters.” Analyzing this cluster diffusion leads to predictions that the diffusion coefficient can vary with the square root of the usual activity corrections to diffusion. These predictions seem consistent with experiments, particularly in highly non-ideal solutions.
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    AIChE Journal 26 (1980), S. 60-67 
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    Keywords: Chemistry ; Chemical Engineering
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    Notes: A reactor of fiour crossflow nomolithic blocks is used to approximate a cocurrent and a countercurrent reactor-heat excanger. Essentailly isothermal reaction pass profiles are produced by flowing the coolant and reactant streams cocurrent to each other according to the criteria set down in Part I of this paper. A multiplicy of steady states is shown to exist for the autothermal countercurrent mode, but not for the autothermal cocurrent mode, under identical conditions.
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    Notes: There are several ways to remove minral matter from coal-derived liquids: antisolvent agglomeration and subsequent sedimentation is one. Adding antisolvent to coal liquids causes asphaltenes and/or preasphaltenes in the oil to precipitate. The precipitated asphaltenes then agglomerate the paraticles, increasing the sedimentation rate. The magnitude of this increase depend no the mixing conditions used to dispers the antisolvent in the oil.This article discuss the results of sedimentation experiments performed onthe antisolvent addition to coal liquids, using an x-ray detection system. The system has the capacity of high temperature (up to 315°C) and high pressure (up to 2.75 7 × 106 Pa). The important parameters are the mixing time, the impeller speed, and the antisolvent addition rate. These are studied in detail for the antisolvent Soltrol.
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    AIChE Journal 26 (1980), S. 132-134 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 26 (1980), S. 136-139 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: NO Abstract.
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    AIChE Journal 26 (1980), S. 144-148 
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    Notes: Slugging experiments were performed in a semicircular Plexiglas column 5.6 m in height to study the effect of an expanded section on slugging. The bottom section of the column (3.05 m long) is 28.6 cm in inside diameter and the expanded section 40.6 cm. Both the bed height and the fluidizing velocity were varied during the study, and the results were successfully correlated with a theoretically derived equation. The implications in designing a bed with an expanded section to reduce the slugging effectively are also discussed.
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    AIChE Journal 26 (1980), S. 154-157 
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  • 76
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    AIChE Journal 26 (1980), S. 507-510 
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    AIChE Journal 26 (1980), S. 510-513 
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    Notes: Ruthven (1976) published thermodynamic and kinetic data on the adsorption of five gases in zeolites over a wide range of temperatures and concentrations. We have described zeolite diffusivities with a model based on the discrete structure of zeolite crystals and a statistic-thermodynamic evaluation of equilibrium measurements (Fiedler and Celbin 1978). Prof. Ruthven has kindly sent us tables of results for all systems in his paper, which we analyze below.
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    AIChE Journal 26 (1980), S. 526-526 
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    AIChE Journal 26 (1980) 
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    AIChE Journal 26 (1980), S. 517-521 
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    AIChE Journal 26 (1980), S. 526-526 
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    AIChE Journal 26 (1980), S. 527-528 
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    AIChE Journal 26 (1980), S. 529-536 
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    Notes: Models of the role of the interstitial fluid for dispersion in a fixed bed for very high Reynolds numbers are examined in detail to determine how well they fit the physical requirements of finite speed of signal propagation, no backmixing, conservation and correct asymptotic form. It is concluded that no linear continuous partial differential equation of finite order can satisfy all of these requirements as well as the cell model, although all models for sufficiently large axial space and time variables are very good approximations to the cell model. Some new hyperbolic models are presented and their solutions obtained and compared with the standard solutions. In present day design it appears that no model has an outstanding advantage over any other.
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    Notes: The simultaneous solution of all the equations for a general system of interlinked, multistaged separators is considered. The interlinks may be simple streams or reciprocal streams, and a particular separator may have bypassing streams (for example, pumparounds). Algorithms are developed that automatically arrange the linearized equations so that for a Newton-Raphson type of solution procedure using, for example, the Naphtali-Sandholm technique, a minimum or nearly minimum number of nonzero blocks occur outside the tridiagonal band so that computational memory and time requirements are minimized. The nonzero and nonidentity blocks are stored in a single vector of variable dimension.
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    AIChE Journal 26 (1980), S. 602-610 
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    Notes: Measurements were made of the steady state flux of sulfur dioxide through films of water and solutions of neutral and alkaline sodium salts (0.1 to 2.0 M sodium chloride, 10-3 to 3.0M sodium hydroxide, NaHSO3 or sodium sulfite) with sulfur dioxide partial pressures between 10 and 100Pa. In agreement with equilibrium theory (Part I), data from water and sodium chloride solutions show that HSO3- is responsible for 83 to 95% of the flux (facilitation factor F between 5 and 19). In alkaline solutions, HSO3- and other sulfur containing species cause F to be as large as 1 370. Equilibrium theory, however, overpredicts F by up to a factor of 7. The NEBLA (Part I) accounts for this deviation.
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    AIChE Journal 26 (1980), S. 635-641 
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    Notes: There are many industrially important reactions in which the chemical kinetics and external diffusion govern the observed reaction rate, and the observed kinetics differ drastically from the true kinetics. This study shows that the forward stagnation flow region of a circular cylinder can be a convenient system for studying the true kinetics of a solid catalyzed reaction owing to its unique property of uniform accessibility.
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    AIChE Journal 26 (1980), S. 663-669 
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    Notes: A five plate distillation column, 100 mm in diameter, has been used to study both fluid mixing and the mass transfer separations of mixtures of methylcyclohexane and n-heptane under periodically cycled conditions. Both the fluid mixing and mass transfer could be successfully analyzed using the (2S) model to describe the liquid movement in the column. Previously reported results by McWhirter and Lloyd could not be reproduced. Only moderate improvements in separating ability can be obtained with sieve plates and packed sieve plate columns operated in the cycled mode.
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    Notes: In an earlier article, a Corresponding States Method was presented for predicting the saturated liquid densities of both pure components and mixtures. The method is based on the known saturated liquid densities of two reference fluids and requires the critical properties and acentric factors of the pure components as input parameters. We use the method here to calculate the swelling factors of CO2-crude oil mixtures using CO2 and n-dodecane as the reference fluids. The critical properties and acentric factors of the crude oils were estimated from their API gravities and Watson K-factors. Using only one adjustable coefficient to characterize each CO2-crude oil system, swelling factors were calculated to within 0.5% of their experimental values. The single, adjustable coefficient is linearly related to the boiling point of the crude.
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    AIChE Journal 26 (1980), S. 372-378 
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    Notes: A cubic perturbed, hard sphere equation of state which combines the hard sphere expression of Scott and the empirical attractive term of Redlich and Kwong with two temperature dependent parameters has been successfully applied to the calculation of pure component properties and vapor-liquid equilibrium values.
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    AIChE Journal 26 (1980), S. 390-398 
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    Notes: Trajectories of bubbles and entrained particles in the rotating fluidized bed were obtained from equations expressing a balance among inertial, centrifugal, Coriolis, gravity and drag forces. The solutions led to information on the behavior of isolated bubbles, bubbles swarms and the elutriation characteristics of the rotating fluidized bed.
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    AIChE Journal 26 (1980), S. 411-419 
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    Notes: We identify dispersion approximations to the transverse average of the solution of the convective diffusion equation on exacting equality of a finite number of axial Hermite moments. The method unifies the dispersion of chemically active and passive solutes and generalizes dispersion theory to arbitrary transverse averages. We emphasize the importance of the scalar results via their application to the dispersion of a system of chemical isomers.
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    AIChE Journal 26 (1980), S. 443-454 
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    Notes: When an aerocolloidal suspension flows through a fibrous filter, particles deposit on the fibers and form dendrites. Similar phenomena are observed with collectors other than fibers, provided that the characteristic dimension of the collector does not exceed that of the particles by more than one to two orders of magnitude. This deposition pattern leads to marked increases in capture efficiency and pressure drop, as particles accumulate within the filter. In previous publications, theoretical models of this process were developed for the cases of deposition by interception alone and of deposition by combined inertial impaction and interception. Consequently, those works apply to aerosol particles with diameters of 1 μm or larger. Here we extend the model to the case of submicron particles, where the main transport mechanism is Brownian diffusion. To keep things specific, we consider fine fibers as collectors, but the model can be easily converted to other geometries. We present solutions for the cases of nonslip flow around the fiber and nonslip, slip and free molecular flow around particles. Unlike deposition by inertial impaction and/or interception, convective Brownian diffusion forms dendrites over the entire fiber surface.
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    AIChE Journal 26 (1980), S. 471-477 
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    Notes: The performances of cylindrical and conical thickeners are compared by means of calculations, using published data on the properties of a suspension. Experimental data on the operation of cylindrical thickeners indicate that sludge funneling at the bottom of such thickeners has a large effect and is a possible cause of observed discrepancies between theory and experiment.
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    AIChE Journal 26 (1980), S. 487-496 
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model is developed for the gasification of a single-char particle in an environment of water, hydrogen, carbon dioxide, carbon monoxide and methane, existing in the gasification zone of a reactor. The model, consisting of the mass and energy conservation equations, together with the Stefan-Maxwell relations includes the intraparticle effects and the change in internal surface area. It is found that the intraparticle effects and the surface area effects are significant and hence cannot be neglected, and the situation becomes more acute with increasing particle size and high temperatures. Comparisons with other models and existing empirical relations show that the model agrees well when diffusional effects are minimal, but at higher temperature and large pariticle size there is a significant difference. The model may be used to discriminate among various idealized models such as the homogeneous and the shrinking core model. The conyective terms in the Stefan-Maxwell relations have negligible influence. The analysis can be directly used in the modeling studies of gasification reactors and will be so applied in a later paper.
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    AIChE Journal 26 (1980), S. 496-504 
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    Notes: A study of the identification of the dynamics of a pilot scale absorption-desorption system and the subsequent design of a multivariable control scheme are reported. A multivariable transfer function model was obtained from experimental input-output data in which the inputs (steam supply and liquid circulation rate) were perturbed simultaneously using uncorrelated pseudo random sequences. A two-step, least-squares estimator was employed for the identification of the model.A multivariable controller was then designed on the basis of the direct Nyquist array method. The implementation of the controller design indicated the utility of the design procedure as compared to independent single input, single output control loops; there is, however, some scope for additional tuning.
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    AIChE Journal 26 (1980), S. 513-517 
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    AIChE Journal 26 (1980), S. 828-832 
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    Notes: A new numerical method is proposed for the one-dimensional melting problem. Unlike many of the existing numerical techniques which either immobilize the moving interface by a suitable coordinate transformation or search for the moving interface under a fixed grid, fixed-time-step finite-difference formulation, the present method was a fixed grid, variable time-step approach. Each time step in the computation is determined iteratively by requiring that the interface be located at a mesh point, one grid space from the previous interface location.Results of two sample calculations show that the present method is superior to the conventional finite-difference method both in its accuracy and computational efficiency. The formulation is mathematically simple and can be applied with no difficulty to problems with nonplanar geometry and initial subcooling. The present method is applied to the analysis of the melting of a finite slab subjected to a constant heat flux boundary condition. Some interesting effects of initial subcooling on the physics of melting are illustrated and discussed.
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    AIChE Journal 26 (1980), S. 850-852 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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