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1Author    Takahiro Ueda, Nobuo NakamuraRequires cookie*
 Title    Sb NMR and SCF-MS-Xa Studies of Quadrupole Interaction and The Electronic Structure of Mixed-Valence Compound, Cs 2 SbCl 6  
 Abstract    Cs 2 SbCl 6 is known as a typical mixed-valence compound. It crystallizes into a tetragonal space group I4 1 /amd and contains two different complex anions, Sb(III)Cl| _ and Sb(V)Clg . The dark blue color of this compound has been considered to originate from a charge transfer between the above two anions. In order to study the electronic structure of these complex anions and the existence of charge transfer between them we measured the 121 Sb NMR spectrum and carried out molecular orbital calculations on the electronic states of these anions. The 121 Sb NMR spectrum consists of two peaks at 0 and 30 kHz which can be assigned to the central transition of l21 Sb in Sb(V)Cl<~ and Sb(III)Cl| _ , respectively. The line shape analyses of the spectra led to nuclear quadrupole coupling constants of nearly zero for Sb(V)Cl7 and 4.9 ±0.5 MHz for Sb(III)Cl| at room temperature. The quadrupole coupling constant of 1 Sb(III) decreases steadily on heating. The calculations of the electronic ground state energies of both anions were calculated by the MS-Xa molecular orbital method. The calculated charge-transfer band from the A lg state of Sb(III)Clg" to the A lg state of Sb(V)Cl6 appears at 610 nm and can account for the experimental electronic spectrum, the calculated quadrupole coupling constant in Sb(III)Clg" however is far larger than the experimental one. The contribution of the charge-transferred state to the ground state is negligible and so the temperature dependence of the quadrupole coupling constant of 121 Sb(III) is attributed to an anisotropic thermal expansion of the compound. 
  Reference    Z. Naturforsch. 51a, 672—676 (1996); received October 10 1995 
  Published    1996 
  Keywords    NMR, Quadrupole interaction, Molecular orbital, Mixed valence 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0672.pdf 
 Identifier    ZNA-1996-51a-0672 
 Volume    51 
2Author    Nobuo Nakamura, Hirotsugo Masui, Takahiro UedaRequires cookie*
 Title    Effect of Intermolecular Hydrogen Bonding on the Nuclear Quadrupole Interaction in Imidazole and its Derivatives as Studied by ab initio Molecular Orbital Calculations  
 Abstract    Ab initio Hartree-Fock molecular orbital calculations were applied to the crystalline imidazole and its derivatives in order to examine systematically the effect of possible N-H---N type hydrogen bond-ing on the nuclear quadrupole interaction parameters in these materials. The nitrogen quadrupole coupling constant (QCC) and the asymmetry parameter (r?) of the electric field gradient (EFG) were found to depend strongly on the size of the molecular clusters, from single molecule, to dimer, trimer and to the infinite molecular chain, i.e., crystalline state, implying that the intermolecular N-H -N hydrogen bond affects significantly the electronic structure of imidazole molecule. A certain correla-tion between the QCC of l4 N and the N-H bond distance R was also found and interpreted on the basis of the molecular orbital theory. However, we found that the value of the calculated EFG at the hy-drogen position of the N-H group, or the corresponding QCC value of 2 H, increases drastically as /C* when R is shorter than about 0.1 nm, due probably to the inapplicability of the Gaussian basis sets to the very short chemical bond as revealed in the actual imidazole derivatives. We suggested that the ob-served N-H distances in imidazole derivatives should be re-examined. 
  Reference    Z. Naturforsch. 55a, 315—322 (2000); received August 26 1999 
  Published    2000 
  Keywords    Hydrogen Bond, Nuclear Quadrupole Interaction, Molecular Orbital, Imidazole 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0315.pdf 
 Identifier    ZNA-2000-55a-0315 
 Volume    55 
3Author    Z. NaturforschRequires cookie*
 Title    Bonding in an Unusual Nickel Carbide  
 Abstract    The bonding in an unusual nickel carbide polymer network synthesized by Musanke and Jeitschko is analyzed using qualitative, band-structure calculations in the framework of extended Hiickel tight-binding theory. The carbide features infinite, one-dimensional, vertex-sharing chains of Ni squares. Each square is centered by a carbon and flanked by C: units. -In this electron-rich polymer, the Ni atoms act as electron acceptors through their s and p orbitals. The orbital interaction schemes reveal that there is little Ni-Ni bonding and essentially no Ni to C2 back-donation. Molecular orbital interaction diagrams of some molecular models are used to describe the bonding in ^[N i^C s]8 -. We also discuss the stability of the planar building block of the polymer, (CNi.;)4"' (which resembles planar CH4) with respect to a "tetrahedral" alternative and we do so for the extended ^ [ N i3C]4-and ^[Ni.^C?]8-chains. In each model case the tetrahedral alternative is favored, and there is no sign of stabilization of a crucial C L4 orbital. Such stabilization is partially achieved through bonding to two Ca axial to the C in the center of the Ni4 ring, but it takes the entire inter-chain calcium network to effect the observed stabilization. 
  Reference    Z. Naturforsch. 53b, 322—332 (1998); received November 4 1997 
  Published    1998 
  Keywords    Carbides, Molecular Orbitals, Electronic Structure, Metal Carbides, Square-Planar Carbon 
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 TEI-XML for    default:Reihe_B/53/ZNB-1998-53b-0322.pdf 
 Identifier    ZNB-1998-53b-0322 
 Volume    53 
4Author    J. Schmidt, H. Gottstein, Scheer, A. ScherzRequires cookie*
 Abstract    Micellar aggregates have been prepared from chloro­ phyll a. Whereas most detergents including non-ionic, zwitterionic and anionic ones, produce aggregates with long-wavelength shifted and enhanced Q Y absorption, the cationic detergents hexadecyl-trimethylammonium-bromide and hexadecyl-pyridiniumchloride produce complexes with opposite traits: The Q Y absorption is shifted to shorter wavelengths, and it is hypochromic. The optical activity is increased as in the long-wave­ length shifted complexes, but the cd bands are non-con­ servative and coincide with the absorption maxima. The complexes are most likely small aggregates o f chloro­ phyll with a changed geometry as compared to the "standard" ones. 
  Reference    Z. Naturforsch. 45c, 729—732 (1990); received January 26 1990 
  Published    1990 
  Keywords    Chlorophyll, Micelles, Detergent, Aggregation, Absorp­ tion, Circular Dichroism, Molecular Orbital 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0729_n.pdf 
 Identifier    ZNC-1990-45c-0729_n 
 Volume    45 
5Author    Christian KollmarRequires cookie*
 Title    A Simplified Approach to the Density Functional Theory of Molecules  
 Abstract    A simplified molecular orbital (MO) formalism based on density functional theory is developed. Starting from the same energy expression as Kohn-Sham theory the electronic density is expanded in terms of atomic mono-center densities. Application of the variational principle leads to a secular matrix with a particularly transparent structure which allows the definition of a resonance integral taking into account the effect of interference in a natural way. The construction of the secular matrix scales formally as N 2 instead of A'' 3 in the Kohn-Sham formalism with N being the dimension of the atomic orbital (AO) basis set. 
  Reference    Z. Naturforsch. 54a, 101—109 (1999); received December 2 1998 
  Published    1999 
  Keywords    Density Functional Theory, Molecular Orbital, Kohn-Sham Theory, Ruedenberg Approximation, Resonance Integral 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0101.pdf 
 Identifier    ZNA-1999-54a-0101 
 Volume    54