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  • 1
    ISSN: 1432-0630
    Keywords: 72.70 ; 73.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We report on temperature (77 to 300 K) and voltage dependent low frequency (100 Hz to 100 kHz) noise behavior of InGaAs/InP photodiodes in non-equilibrium steady state. In addition to common white, 1/f, and Lorentz noise we are able to observe for the first time minima and maxima in the photocurrent noise spectra. The recombination of a pair of free carriers through a recombination center at the heterointerface provides the correlation between the electron and hole ensembles necessary to explain the observed noise reduction.
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  • 2
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We analyze the dependence of heavy quark free energies on the baryon chemical potential μb in 2-flavor QCD by performing a 6th order Taylor expansion in the chemical potential which circumvents the sign problem. The bare quark mass at $\hat m / T = 0.4$ corresponds to a pion mass of about 770 MeV and is thus not in the range of physical quark masses but the quark mass dependence is known to be small above Tc. At Nτ = 4 the lattices are coarse, however, we are using improved (p4 staggered) fermions. The Taylor expansion coefficients of color singlet and color averaged free energies are calculated and from this the expansion coefficients for the corresponding screening masses are determined. We find that for small μb the free energies of a static quark-antiquark pair decrease in a medium with a net excess of quarks and that screening is well described by a screening mass which increases with increasing μb. The μb-dependent corrections to the screening masses are well described by perturbation theory for T ≳ 2Tc. In particular, we find for all temperatures above Tc that the expansion coefficients for singlet and color averaged screening masses differ by a factor 2.PACS. 11.15.Ha, 11.10.Wx, 12.38Gc, 12.38.Mh
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 4393-4397 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A procedure for operating an Eigler-style, low temperature scanning tunneling microscope (STM) at variable temperatures has been developed. A critical exchange gas pressure regime was found to allow for controlled variation of the STM temperature while it is encapsulated in a liquid helium Dewar. The sensitivity of various parameters to the ability to generate stable variable temperatures above 4 K is discussed. © 2001 American Institute of Physics.
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  • 4
    ISSN: 1572-8943
    Keywords: complexes ; coordination chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Das Zersetzung Verhalten der Komplexverbindungen vom Typ C0D2I2 (P = acetylaceton, Benzoylaceton;I = Imidazol oder Derivate) erfolgt stufenweise. Im Falle vonD = Acetylaceton erfolgt zuerst eine Eliminierung von Acetylaceton wärend beiD = Benzoylaceton zuerst ein Heteroligand eine Abspaltung erfährt. Bei einer unsubstituiertenΒ-Position von Nickelacyclen des Typs (bipy)Ni(CH2CH2CH2COO) erfolgt eine thermisch induzierteΒ-Hydrideliminierung unter Ringspaltung und Freisetzung von CO2. Im Gegensatz zur hohen thermischen Stabilität des Trimesityl Aluminium erfahren die Zwischenverbindungen Almes2Cl und AlmesCl2 mit abnehmenden Mesityl- bzw. zunehmenden Chlorgehalt einen wessentlich früheren thermischen Zerfall. Bei zunehmenden Kovalenzgrad ist hier ein Einfluss der veränderten Polarisation anzunehmen. Der thermische Abbau der prinzipiell wasserhaltig kristallisierenden Nickelchelate von alkylsubstituierten Chinolin-8-ol beginnt jeweils mit der Dehydratisierung. In Abhängigkeit von der Kettenlänge und der Position der Substitution am Chinolin schliesst sich der thermische Abbau der Chelatliganden ein- bzw. mehrstufig an.
    Notes: Abstract The behaviour of complexes of the type MeD2I2 (Me=Co,D = acetylacetone or benzoylacetone,I = imidazole and derivatives in the course of the stepwise thermal degradation is different. In the case ofD = acetylacetone in the first step acetylacetone is split off. At D = benzoylacetone the decomposition starts with the partial elimination of the heterocyclic ligands. InΒ-position unsubstituted nickelacyclic complexes from type (bipy)Ni(CH2CH2CH2COO) decompose by a reductive elimination and separating of CO2 forming a ‘(bipy)Ni’-intermediate. A single reductive decoupling is hindered by blocking up theΒ-position. Opposite to the high thermal stability of the trimesityl aluminium the intermediates Almes2Cl and AlmesCl2 show with decreasing amounts of mesityl groups and increasing content of halogene, respectively, a significant decreasing thermal stability. The thermal degradation of nickelchelates of alkylsubstituted chinolin-8-ol starts with the dehydration followed by a different separation of the ligands as a function of the chain-length and the position of the substituents of the ligands.
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  • 5
    ISSN: 1572-8943
    Keywords: crystal structure ; metal(II) picolinate and quinaldinate ; thermal degradation of imidazole and pyrazole complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Complexes of the type M(Pa)2(HAz)2 and M(QA)2(HAz)2 (M=cobalt(II) and nickel(II); HPa=picolinic acid, HQa=quinaldic acid; HAz=azoles like imidazole (Him), pyrazole (HPz), benzimidazole (HBzIm) etc.) show a similar thermal behaviour. In the first step of decomposition the corresponding azolinium picolinates or quinaldinates (H2AzPa, H2AzQa) are split off with formation of polymeric mixed ligand complexes M(Pa)(Az) or M(Qa)(Az). X-ray analysis of Co(Qa)2(HBzIm)2 XIIIa illustrates a proton transfer and a subsequent thermal removal of benzimidazolinium quinaldinate (H2BzImQa): Hydrogen bridges from pyrrole nitrogen of the benzimidazole to the non-coordinated oxygen of the quinaldinate predetermine the thermal initiated proton transfer. The high volatility of the heterocyclic acids and the nitrogen coordination are responsible for the formation of the mixed ligand complex Co(Qa)(BzIm) XIVa. Exceptions are the complexes M(Pa)2(HPz)2 XIa-b and M(Qa)2(HIm)2 XVIIa-b. Pyrazole is eliminated from the complexes XIa-b with formation of the solvent-free inner complex M(Pa)2 XIIa-b. From compounds XVIIIa-b quinaldic acid or their decomposition products are split off and a high temperature modification of M(Im)2 XVIIIa-b is formed at elevated temperature. XVIIIa-b are decomposed to the cyanides M(CN)2 similarly to the thermal behaviour of Cu(Im). In the first step the thermal degradation of imidazole and pyrazole adducts of copper(II) picolinates and quinaldinates is characterized by the elimination of azoles. The reason for this thermal behaviour is the weaker coordination of the azole heterocycles in copper chelate compounds.
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  • 6
    ISSN: 0044-2313
    Keywords: Nickel complex, Ni(BPSH)2 · H2O ; bis(benzoylpyridin-p-toluensulfonylhydrazido)nickel ; heterocyclic sulfonamido chelates ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Bis(benzoylpyridin-toluensulfonylhydrazido)nickel Ni(BPSH)2 · H2O  -  Relations between Structure, Redox, and Extraction Properties of Heterocyclic Sulfonamido ChelatesThe crystal structure of Ni(BPSH)2 · H2O was determined by x-ray diffraction: monoclinic, space group P21/c (Nr. 14); a = 15.077(4) Å, b = 14.901(3) Å, c = 16.335(3) Å, β = 95.74(1)°. R = 0.047 for a total of 5564 observed reflexions. Ni(BPSH)2 · H2O has a distorted tetrahedral structure with two six-membered chelate rings, one of them with a boat from. The electron system of the building blocks CNN⊖ within the chelate rings approaches that of a diazallyl group. The result is a high electron density on the sp2-hybridized donor atom N⊖ and, as a consequence, a short Ni—N⊖-distance (1.908 or 1.924 Å). The electronic properties of N⊖ also explain the high NH-acidity of the acid H(BPSH) (pks = 9,51 in 75 per cent dioxane) and the ligand field strength of BPSH⊖ which is low compared to that of other bidentate sulfonamido ligands and which is reflected in the paramagnetism of Ni(BPSH)2 · H2O.The redox behavior of metal chelates of the type, which is represented by Ni(BPSH)2 · H2O, is caused by a building block of the ligand which is also present in bipyridyl or in the 1,4-diaza-1,3-dienes. The central atoms M11 have only the function of interference factors.
    Notes: Die Kristallstruktur von Ni(BPSH)2 · H2O wurde durch Röntgenbeugung bestimmt: monoklin, Raumgruppe P21/c (Nr. 14), a = 15,077(4) Å, b = 14,901(3) Å, c = 16,335(3) Å, β = 95,74(1) ° R = 0,047 für 5564 beobachtete Reflexe. Ni(BPSH)2 ° H2O besitzt eine verzerrt tetraedrische Struktur mit zwei Chelatsechsringen, von denen einer in der Wannenform vorliegt. Die Baugruppen CNN⊖ innerhalb der Ringe weisen ein Elektronensystem auf, das sich an das einer Diazallylfunktion annähert. Die Folge davon ist eine hohe Elektronendichte auf dem sp2-hybridisierten Stickstoffhaftatom N⊖ und ein kurzer Ni—N⊖-Abstand (1,908 bzw. 1,924 Å). Die elektronischen Eigenschaften von N⊖ erklären weiterhin die hohe NH-Acidität der Säure H(BPSH) pks = 9,51 in 75% (Dioxan) und die verglichen mit anderen Sulfonamidochelatliganden geringe Ligandenfeldstärke von BPSH⊖, die sich im Paramagnetismus von Ni(BPSH)2 · H2O äußert.Das Redoxverhalten der Metallchelate des durch Ni(BPSH)2 · H2O repräsentierten Typs wird durch ein Bauelement des Liganden bestimmt, das sich im α, α′-Dipyridyl und in den 1,4-Diaza-1,3-dienen wiederfindet. Metallionen M2+ wirken über das Diazalylsystem lediglich als Störfaktoren.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 620 (1994), S. 551-560 
    ISSN: 0044-2313
    Keywords: Metal complexes ; Amidines ; Oxalic derivates ; Imidazolidines ; Diazadiene ligands ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Nitrogen Derivates of Oxalic Acid as New Complexing AgentsHeterocycles with a exocylic 1,4-diaza-1, 3-diene structure 5a-d have σ-bonding and π-backbonding properties similar to the diazadienes (DAD) 1. The investigations of the molybdenum complexes 11 and 12 of the ligands 5 show a dominant σ-interaction and only a small π-backbonding, comparable with the compound (CO)4Mo(iPYC) 14, a complex of pyridinecarbaldehyde isopropylimine (iPYC).The oxalamidine (TPOA) 4 (precursor of the heterocycles 5a-d) are present in a s-trans (E/E)-form with two stable intra-molecular hydrogen bridges. 4 reacts with ferrous and cobaltous chloride to the polymer coordination compounds 8 and 9. According to the diazadiene 1 oxalamadine 4 substitutes two carbonyls in Mo(CO)6 by formation of (CO)4Mo(TPOA) 10. The coordinated ligand 4 shows in the complex 10 a s-cis(E/E)-form with respect to the free ligand and no H-bridges were observed. The crystal structures of TPOA 4 and (CO)4Mo(TPOA) 10 were determined. Cyclisation reactions on the coordinated oxalamidine are possible.
    Notes: Heterocyclen mit einer exocyclischen 1,4-Diaza-1,3-dien-Struktur 5a-d besitzen in Analogie zu den Diazadienen (DAD) 1 α-Donor und π-Akzeptoreigenschaften. Durch vergleichende Untersuchungen an deren Molybdäncarbonylkomplexen 11 und 12 konnte festgestellt werden, daß der σ-Bindungscharakter dominant ist und nur geringe π-Rückbindungsanteile vorliegen, vergleichbar mit Verbindung (CO)4Mo(iPYC) 14, einem Komplex des Pyridin-2-carbaldehyd-isopropylimins (iPYC).Der Vorläufer dieser Heterocyclen, das Oxalamidin 4 (TPOA), liegt als Molekül in einer s-trans-(E/E)-Form mit zwei stabilen intramolekularen Wasserstoffbrücken vor. 4 bildet mit Eisen(II)- bzw. Cobalt(II)-chloriden polymere Koordinationsverbindungen 8 und 9. Mit Molybdänhexacarbonyl reagiert 4 analog den Diazadienen 1 unter Substitution zweier Carbonyl-gruppen zu (CO)4Mo(TPOA) 10. In 10 liegt der Ligand 4 in der s-cis-(E/E)-Form vor, wobei keine Wasserstoffbrücken-bindungen mehr beobachtet werden. Von 4 und 10 wurden Röntgenstrukturanalysen angefertigt. Am koordinativ fixierten Oxalamidin in 10 können Cyclisierungsreaktionen durchgeführt werden.
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  • 8
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Sulfonamides with Heterocyclic Substituents as Extractants for Copper(II)With 2-picolylbenzenesulfonamide (N2NHO2SC6H5) as a model of the technical extractant LIX 34, the influence of functional variations on the extraction of copper(II) is studied and estimated by a comparison of the pH1/2 values.The relation pH1/2∼-σp is observed for extractants with substituents in p-position of the benzene ring. Turning to 2-pyridylethylbenzenesulfonamide, which forms six-membered rings, an increase of pH1/2 is observed. But no direct comparison is possible with 2-pyridylbenzenesulfonamide as the copper(II) complexes are dimeric having a structure analogous to copper(II) acetate. The substitution of the methylene group by an SO2-(PSA—H) or an NH-residue (PTSH—H) is connected with an with an increase of pH1/2 in the first case, but a decrease of pH1/2 in the second one (7,25 and 2,70). The application of PTSH—H as an extractant for copper(II) is confined by a slow redox reaction with this ion.π-electron delocalization within the chelate rings, which are derived from sulfonylhydrazones of heterocyclic ketones, is a factor which, in general, improves the extraction properties.There is a strong differentiation of PH1/2 (APSH—H 1,4; BBSH—H 6,9). An increase of the tetrahedral distortion of the chromophore CuN4, as it is indicated by ESR, measurements, is connected with a decrease of pH1/2.The benzenesulfonyl group influences the copper(II) extraction by bidentate nitrogen containing ligands in a twofold may: The protonation of the pyridyl and also that of other heterocyclic residues is rendered more difficult, but NH-acidity is increased. Some of the new extractants (APSH—H, BPSH—H) are as active as LIX reagents.
    Notes: Am Beispiel von 2-Picolylbenzensulfonamid (N2NHO2SC6H5), einem Modell des technischen Extraktanten LIX 34, wird der Einfluß funktioneller Veränderungen auf das Extraktionsverhalten gegenüber Kupfer(II) untersucht und zur Beurteilung der pH1/2 herangezogen.Bei Einführung von p-Substituenten am Benzenring erweist sich pH1/2∼-σp. Der übergang zu 2-Pyridylethylbenzensulfonamid (N3NHO2SC6H5), einem Sechsringbildner, ist mit einer Erhöhung von pH1/2 verbunden. Dagegen ist kein unmittelbarer Vergleich mit dem potentiellen Vierringbildner 2-Pyridylbenzensulfonamid möglich, weil die gebildeten Kupfer(II)-Komplexe eine dem Kupfer(II)-acetat analoge dimere Struktur haben.Die Substitution der Methylengruppe von N2NHO2SC6H5 durch einen SO2—(PSA—H) oder NH-Rest (PTSH—H) führt im ersten Fall zu einer Erhöhung, im zweiten zu einer Erniedrigung von pH1/2 (7,25 bzw. 2,70). Gegen den Einsatz von PTSH—H als Extraktionsmittel spricht eine langsame Redoxreaktion mit Kupfer(II).Die π-Elektronendelokalisierung in den Chelatringen, die sich von Sulfonylhydrazonen heterocyclischer Ketone ableiten, ist ein Faktor, der das Extraktionsverhalten im allgemeinen verbessert. Man findet eine starke Abstufung von pH1/2 (APSH—H 1,4; BBSH—H 6,9); der Wert sinkt mit wachsender tetraedrischer Verzerrung der ZKE CuN4 (Bestimmung durch ESR-spektroskopische Untersuchungen).Die Benzensulfonylgruppierung beeinflußt die Kupfer(II)-Extraktion mit zweizähligen stickstoffhaltigen Liganden in zweierlei Weise: Die Protonierung von Pyridin- und anderen heterocyclischen Stickstoffatomen wird erschwert, die NH-Acidität erhöht. Einige der untersuchten Extraktanten (APSH—H, BPSH—H) sind in ihrer Wirksamkeit mit den LIX-Reagenzien zu vergleichen.
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  • 9
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Sulfonamide Substituted Thionocompounds as Ligands in Copper(II) Chelates and as Extractants for the Late 3d-Element IonsWith copper(II) thiono ligands containing arenesulfonamido or arenesulfonylhydrazido functions as a second donor group (STAT-, PST-, BPTS-, BMTH-, and TPTH-, meaning of the abbreviations see text) react in a different way. Normal 1,2-chelates are formed by PST-, BMTH-, and TPTH-. But the reactions with STAT- and BPTS- are connected with a redox process and copper(I) complexes are obtained. PST- is an flexidentate ligand, forming both five- and four-membered chelate rings. Probably the formation of the two Cu(PST)2 isomeres depends on this property. The new chelates are characterized by ESR and ESCA spectra.As extractants for copper(II), the compounds STAT-H, BPTS-H, and BPTH-H, forming five- or six-membered rings, are comparable to the arenesulfonylthioureas which form only four-membered ones. But PST-H is an attractive extractant for copper(II), nickel(II), cobalt(II), and zinc(II). As to the pH1/2 values PST-H reaches the widely used extractant dithizone.
    Notes: Thionoliganden, die Arensulfonylamido- bzw. Arensulfonylhydrazido-funktionen als zweite Donatorgruppen enthalten (STAT-, PST-, BPTS-, BMTH- und TPTH-, zur Bedeutung der Abkürzungen vergleiche Text), reagieren in unterschiedlicher Weise mit Kupfer(II). Normale 1,2-Komplexe werden mit PST-, BMTH- und TPTH- gebildet. Dagegen ist die Umsetzung mit STAT- und BPTS- mit einem Redoxprozeß verbunden, der zur Bildung von Kupfer(I)-Komplexen führt. PST- ist ein ambidenter Ligand, der sowohl fünf-als auch viergliedrige Chelatringe bilden kann. Wahrscheinlich beruht die Bildung der beiden Isomeren von Cu(PST)2 auf diesem Effekt. Die Charakterisierung der neuen Chelate erfolgt anhand von ESR-Spektren und ESCA-Daten.Als Extraktionsmittel für Kupfer(II) bringen die Verbindungen STAT-H, BPTS-H und TPTH-H als Fünf- bzw. Sechsringbildner keine Vorteile gegenüber den früher beschriebenen Arensulfonylthioharnstoffen, die nur viergliedrige Chelatringe bilden. Dagegen ist PST-H ein attraktives Extraktionsmittel für Cu(II), Co(II) und Zn(II). In bezug auf die pH1/2-Werte kann es mit Dithizon verglichen werden.
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  • 10
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Control of the Dimerization of the Cobalt(II) Chelates (N-Ligand)Co(acac)2 by the Amine LigandBesides the trans-octahedral cis-adduct (Ampy)2Co(acac)2, bis(acetylacetonato)cobalt(II) forms the mono-adduct (Ampy)Co(acac)2 (II). In the solid state tetragonal-pyramidal molecules of II are dimerized by intermolecular hydrogen-bonds. 2-Pyridinamine is coordinated by the endo-nitrogen in an apical position. By the short Co—Nendo-bond (2.104 Å) 2-pyridinamine proves as an n- and a π-donor. Therefore the coordination center of II is extensively saturated and a dimerization, comparable to that of (CyNH2)Co(acac)2 (Cy = cyclohexyl) and (py)Co(acac)2, which is connected with an increase of the coordination number (5 → 6), is not observed.
    Notes: 2-Pyridinamin (Ampy) bildet mit Bisacetylacetonato-cobalt(II) neben dem trans-oktaedrischen Bis-Addukt (Ampy)2Co(acac)2 auch ein Mono-Addukt (Ampy)Co(acac)2 (II). Im Kristallgitter von II liegen tetragonal-pyramidale Moleküle vor, die über intermolekulare Wasserstoffbrücken zu Dimeren zusammentreten. 2-Pyridinamin koordiniert mit dem endo-Stickstoff in apicaler Position. Der kurze Co—Nendo-Abstand (2,104 Å) weist 2-Pyridinamin als n- und π-Donator aus. Dadurch wird eine weitgehende Absättigung des Koordinationszentrums von II erreicht. Eine Dimerisierung unter Erhöhung der Koordinationszahl auf 6, wie sie bei (CyNH2)Co(acac)2 und (py)Co(acac)2 eintritt, bleibt daher aus. Nur als n-Donator fungiert 2-Pyridinamin im Komplex (Ampy)2Co(acac)2 (Co—Nendo) = 2,203 Å).
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