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  • crystal structure  (3)
  • Computational Chemistry and Molecular Modeling  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Cooperative effects in extended hydrogen bonded systems involving O—H groups. Ab initio studies of the cyclic S4 water tetramer (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 8 (1987), S. 1090-1098 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The additional energy stabilization due to cooperative effects was calculated in extended hydrogen bonded systems O—H⃛O—H⃛O—H with unidirectional (homodromic) orientation of the O—H groups. Ab initio restricted Hartree Fock, MP2 and MP3 calculations with geometry optimization and BSSE correction have been performed using the GAUSSIAN 83 program package for the ground states of the linear water dimer with Cs symmetry and the cyclic water tetramer with S4 symmetry. The latter represents the smallest possible, experimentally observed cooperative structure. A new definition for a cooperativity parameter is proposed. The definition is based on the two-body, non-neighbour interaction energy, plus three- and four-body contributions, including one-body deformation terms in relation to the total interaction energy of the water tetramer. The advantage of this definition is its independence of the reference system, which is necessary in complicated molecular systems with an undefined number of hydrogen bonds, such as disordered or flip-flop systems. According to this definition the energy gain based on cooperativity in the S4 water tetramer is 29% with the MP3/6-31G** approximation, (30% with HF/4-31G* and 46% with HF/3-21G). The largest contribution of 18% is due to the three-body term on the MP3/6-31G** level, followed by the two-body, non-neighbour term with 11%. The four-body term and the deformation term are in the order of 1% and cancel each other because they have opposite sign.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540080804
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  • 2
    Electronic Resource
    Electronic Resource
    Charge distributions of phosphorylcholine and its derivatives (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 318-328 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Hartree-Fock self-consistent field calculations on the 3-21G(*) level of approximation have been performed to phosphorylcholine and its derivatives in a geometry close to an X-ray structure of an antibody/antigen complex. Wave functions have been analyzed using different methods for derivation of atomic charges used as Coulomb charges in empirical force fields for molecular dynamics simulations. Among the three applied methods - Mulliken population analysis, natural population analysis, and electrostatical fit - the natural population analysis seems to give best results for these molecules.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540130306
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  • 3
    Electronic Resource
    Electronic Resource
    LiSmAlF6  -  das erste Fluoroaluminat mit zweiwertigem Samarium (1991)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 606 (1991), S. 169-176 
    Details
    ISSN: 0044-2313
    Keywords: Lithium samarium hexafluoroaluminate ; preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: LiSmAlF6  -  the First Fluoroaluminate with Divalent SamariumLiSmAlF6, the first quaternary fluoride with Sm2+ that has been obtained as red transparent single crystals, is formed while heating corresponding mixtures of the starting materials in niobium or tantalum crucibles under argon after 7-10 d at about 800°C. Orange-red, microcrystalline powder samples of LiSmAlF6 could be prepared at T ≤ 700°C after 1-2 d under the same conditions.LiSmAlF6, crystallizes as a new structure type in P6322 (Nr. 182) with a = 507.9(1), c = 1 040.5(1) pm and Z = 2 (CAD4, 2 512 Io, Rw = 2,3%). The crystal structure of LiSmAlF6 is related to the LiCaAlF6 structure type whereby the essential difference lies in the coordination of the M2+ ions. Ca2+, as well as Sr2+ in LiSrAlF6, exhibit octahedral coordination, whereas Sm2+ has, surprisingly, trigonal prismatic coordination to F-. The two triangles of the SmF6 prism are twisted by 8.3° with respect to each other.Measurements of the magnetic susceptibility show the temperature dependence typically found for Sm2+. The Madelung part of the lattice energy has been calculated and is discussed.
    Notes: LiSmAlF6, das erste in Form roter, transparenter Einkristalle erhaltene quaternäre Fluorid mit Sm2+, bildet sich beim Erhitzen geeigneter Ausgangsmenge in Niob- oder Tantaltiegln unter Ar nach 7-10 d bei ca. 800°C. Orangerote, mikrokristalline Pulverproben von LiSmAlF6 können bei T ≤ 700°C bereits nach 1-2 Tagen unter sonst gleichen Bedingungen dargestellt werden.LiSmAlF6 kristallisiert in einem neuen Strukturtyp in P6322 (Nr. 182) mit a = 507,9(1), c = 1 040,5(1) pm und Z = 2(CAD4, 2 512 Io, Rw = 2,3%). Die Kristallstruktur von LiSmAlF6 ist dem LiCaAlF6-Typ verwandt, zeigt aber den wesentlichen Unterschied in der Umgebung für M2+ : Ca2+, wie auch Sr2+ in LiSrAlF6, werden oktaedrisch, Sm2+ jedoch überraschenderweise trigonal-prismatisch von F- koordiniert. Die beiden Dreiecke des SmF6-Prismas sind um 8,3° gegeneinander verdreht.Messungen der magnetischen Suszeptibilität zeigen die für Sm2+ typische Temperaturabhängigkeit. Der Madelunganteil der Gitterenergie wurde berechnet und diskutiert.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19916060117
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  • 4
    Electronic Resource
    Electronic Resource
    SmAlF5  -  ein neues SmII-fluoroaluminat mit Al2F10-Oktaederdoppeln und [AlF2/2F4/1]-Ketten (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 619 (1993), S. 181-188 
    Details
    ISSN: 0044-2313
    Keywords: Samarium(II) fluoroaluminate ; preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: SmAlF5  -  a New Samarium(II) Fluoroaluminate with Al2F10 Bioctahedra and [AlF2/2F4/1] Chains.SmAlF5 has been obtained as orange-red transparent single crystals while heating mixtures of SmF3, Sm-powder and AlF3 (2:1:3) in a niobium crucible under Ar after 7-10 d at about 750°C. SmAlF5 crystallises in I 4/m (Nr. 87) with a=1 414.4(4), c=722.2(3) pm and Z=8 (CAD4, 4 340 IO, Rw=1.7%).The crystal structure of SmAlF5 is isotypic to BaTiF5. Characteristic building units are linear chains of trans-corner sharing AlF6 octahedra, which are connected via corners to two further AlF6 octahedra. Isolated Al2F10 octahedra lie disordered between such chains. The Sm atoms connect the AlF6 octahedra to a three-dimensional network. Measurements of the magnetic susceptibility show the temperature dependence typically found for Sm2+. The Madelung part of the lattice energy has been calculated and is discussed.
    Notes: SmAlF5 wurde in Form orangeroter transparenter Einkristalle beim Erhitzen von SmF3, Sm-Pulver und AlF3 (2:1:3) im Niobtiegel unter Ar nach 7-10 d bei ca. 750°C erhalten. SmAlF5 kristallisiert in I4/m (Nr. 87) mit a=1 414,4(4), c=722,2(3) pm und Z=8 (CAD4, 4 340 IO, Rw=1,7%).Die Kristallstruktur von SmAlF5 ist isotyp zu BaTiF5. Charakteristische Baugruppen sind lineare Ketten trans-Spitzen verknüpfter AlF6-Oktaeder, die über Spitzen mit zwei weiteren AlF6-Oktaedern verknüpft sind. Isolierte Al2F10-Oktaederdoppel liegen fehlgeordnet zwischen solchen Ketten. Die Sm-Atome verknüpfen die AlF6-Oktaeder zum dreidimensionalen Gerüst. Messungen der magnetischen Suszeptibität zeigen die für Sm2+ typische Temperaturabhängigkeit. Der Madelunganteil der Gitterenergie wurde berechnet und diskutiert.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19936190130
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  • 5
    Electronic Resource
    Electronic Resource
    Über das neue gemischtvalente Ge7F16: [GeF6]2--Oktaeder zwischen [Ge6F10]2+-Schichten - zur stereochemischen Aktivität freier Elektronenpaare (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 596-602 
    Details
    ISSN: 0044-2313
    Keywords: Germanium fluoride ; stereochemical activity ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: About the New Mixed Valent Ge7F16: [GeF6]2- Octahedra between [Ge6F10]2+ Sheets - a Contribution to the Stereochemical Activity of Lone PairsFor the first time Ge7F16 colourless transparent single crystals have been prepared by the reduction of GeF4 with Ge at 300°C. The extremely hygroscopic fluoride crystallizes in a new structure type in Cc with a = 1818.0(6) pm, b = 754.3(2) pm, c = 1030.4(3) pm, β = 90.33(3)° und Z = 4.Ge7F16 is a mixed valent fluoride according to 6GeF2 × GeF4. Characteristical building units of the new structure type are [Ge6F10]2+ sheets, which are connected via [GeF6]2- octahedra. The Ge2+ within the sheets are coordinated by three nearest F- with distances of 183-218 pm and together with these form distorted trigonal pyramids. The structure of Ge7F16 can be considered as a member of the homologues series Gem4+Gen2+F4m+2n with m = 1 and n = 6. Bond order summations, band structure calculations and calculations of the Madelung part of the lattice energy. MAPLE, have been used for the discussion of the bonding situation.
    Notes: Neu dargestellt wurden farblose transparente Einkristalle von Ge7F16 durch Reduktion von GeF4 mit Ge bei 300°C. Das äußerst hygroskopische Fluorid kristallisiert in einem neuen Strukturtyp in der Raumgruppe Cc (Nr. 9) mit a = 1818.0(6) pm, b = 754.3(2) pm, c = 1030.4(3) pm, β = 90.33(3)° und Z = 4.Ge7F16 ist gemäß 6GeF2 × GeF4 ein gemischtvalentes Fluorid. Charakteristische Baugruppen des neuen Strukturtyps sind [Ge6F10]2+-Schichten, die über [GeF6]2--Oktaeder verbrückt sind. Die Ge2+ innerhalb der Schichten sind von je drei nächsten F- im Abstand von 183-218 pm koordiniert und bilden mit diesen verzerrte trigonale Pyramiden. Die Struktur von Ge7F16 läßt sich als Glied der homologen Reihe Gem4+Gen2+F4m+2n mit m = 1 und n = 6 beschreiben. Die Bindungsverhältnisse werden anhand von Bindungsordnungssummationen, Bandstrukturrechnungen und Berechnungen des Madelunganteils der Gitterenergie, MAPLE. diskutiert.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19976230193
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