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  • 1
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Interactions in Crystals: The Dimorphism of (2-Pyridyl)(2-pyrimidyl)aminePreceding structural studies of 2-aminopyridine derivatives prove that they form polymorphic H-pair-bonded dimmers, and, therefore, (2-pyrimidyl)amine has been crystallized under different conditions. Two different monoclinic modifications are characterized by their crystal structures of the same space group P21/c: form I exhibits the well known herringbone motif and form II the sandwich-herringbone one. Both modifications contain almost identical planar, H-pair-bridged molecular dimmers. Crystals of form I are readily obtained from any solvent, whereas those of form II result either on fast evaporation of a Et2O solution or by resolidification of the melt. Differential thermal analysis (DTA) and crystallization experiments at different temperatures prove, for both modifications, no transitions in the temperature range between -25° and the melting point at 152° and, therefore the system should be monotropic. The structural and thermodynamic aspects of the (2-pyridyl)(2-pyrimidyl)amine dimorphism are discussed in comparison to those of the trimorphism observed for di(2-pyridyl)amine.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 339 (1997), S. 26-37 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Interactions in Crystals. 96. Preparation and Structures of Salts [RnN⊕H…NRn][B⊖(C6H5)4] with Prototype Hydrogen Bridges N⊕H…NStraightforward crystallization of ammonium salts [RnN⊕H] X⊖ added lithium tetraphenylborate, and amine RnN from acetone solution yields salts [RnN⊕H…NRn][B⊖(C6H5)4] with the (under the conditions) unprotonated anions and the cations with prototype hydrogen bridges N⊕H…N. The structures of both identically substituted RnN (methylamine, trimethylamine, quinuclidine, diazabicyclooctane, and pyridine) as well as two-component cation species (quinuclidine…pyridine and diazabicyclooctane…pyridine) are reported and discussed. A Cambridge Structural Database search defines the area of charged N⊕H…N interactions which can be correlated with both pKBH+ values and PM3 formation enthalpies. Additional information is provided by PM3 calculations based on the experimental structure coordinates. The charge distribution within the hydrogen bridges N⊕H…N varies considerably with the individual proton donors N+H and proton acceptors N: Positive charges are highest at protonated quinuclidine and diazabicyclooctane centers and lowest at pyridine N acceptor centers.
    Additional Material: 2 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2075-2077 
    ISSN: 1434-1948
    Keywords: Polyion aggregates ; Crystal structure ; Density functional theory calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure determination of the lipophilically wrapped cluster {[Al2Li4O18](C36H44)}∞, a novel material crystallized from a mixture of [(C2H5)3Al]2, nBuLi, and catechol in DME solution, reveals five-coordinate Al++ and Li+ centers. According to density functional theory calculations, the eight negative charges are well-delocalized over the oxygen-rich framework.
    Additional Material: 1 Ill.
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  • 4
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Interactions in Crystals. 136. Protonated Dipyridylamine Salts with Different Anions: Monomeric Tetraphenylborate as well as Bis(trifluormethylsulfonate), Dimeric Squarate and Polymeric Chloride DihydrateDi(pyrid-2-yl)amine is monoprotonated by acetic, squaric as well as hydrochloric acid and diprotonated by trifluoromethylsulfonic acid. To explore the anion and hydrogen-bridge dependency of its salts, crystals of the monomeric tetraphenylborate, the dimeric squarate as well as the bis(trifluoromethylsulfonate) and the polymeric chloride hydrate have been grown and their structures determined: Separated by bulky tetraphenylborate anions, pyrid-2-yl(2′-pyridinium) amine cation contains an intramolecular hydrogen bridge N⊕H…N and is slightly folded. The squarate salt dimer exhibits additional bridges, N—H…O⊖ and O—H…O. The severely twisted di(2-pyridinium)amine dication is connected to its trifluormethylsulfonate counter anions by altogether three H-bridges, two N⊕H…O and one N—H…O. The chloride dihydrate crystallizes in layers of 16-membered rings, formed from three Cl anions and five water molecules. The diversity of the hydrogen-bridge dominated salt structures is discussed based on comparison with selected literature examples and on PM3 calculations.
    Additional Material: 4 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 585-592 
    ISSN: 1434-193X
    Keywords: Di(2-pyridyl) ketone ; Single and twofold protonation ; Crystal structures of tetraphenylborate and chloride salts ; Tetraphenylborates ; Chlorides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Di(2-pyridyl) ketone, intricately twisted due to its two nNσ and one nOσ lone pairs, exhibits tremendous structural differences on single and double protonation to salts containing either the anion [B(C6H5)4]-, which cannot be protonated, or Cl-, which accepts two hydrogen bonds. In the monocation, generated in acetic acid with added sodium tetraphenylborate, the pyridine rings of di(2-pyridyl) ketone are planarized due to the formation of an intermolecular hydrogen bond. Aqueous hydrogen chloride produces a dication with both nitrogen centers protonated and the resulting di(2-pyridyl) ketone hydrate embedded in a complex hydrogen-bond network. Extensive quantum-chemical calculations based on the experimental structural data allow to rationalize the unexpected results.
    Type of Medium: Electronic Resource
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