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'Angular Overlap Model' in keywords
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1999 (1)
1990 (1)
1Author    Lars Hemmingsen, Ulf Ryde, Rogert BauerRequires cookie*
 Title    Nuclear Quadrupole Interactions in Cadmium Complexes: Semiempirical and ab initio Calculations  
 Abstract    Semiempirical calculations, based on the so-called angular overlap model, have been compared with ab initio methods (MP2) for the calculation of nuclear quadrupole interactions (NQPs) in cadmium complexes with biologically relevant ligands (H2O, OH -, cysteinate, carboxylate, and imidazole). The assumptions on which the semiempirical model is based have been tested and the comparison indicates that: 1) A change in the Cd-ligand bond length by 0.1 A may change the electric field gradient (EFG) by about 0.2 a. u.. A simple scheme to incorporate such effects in the semiempirical method is suggested. 2) The effect of ligand-ligand interactions is up to about 0.2 a. u. for the largest diagonal element of the EFG tensor for the tested complexes, and such effects can significantly influence the so-called asymmetry parameter. 3) The position of non-coordinating atoms on the ligands can in some cases (e. g. the hydrogen atoms of water) significantly influence the EFG. The combined effect of non-coordinating atoms and ligand-ligand interactions may cause deviations of up to 0.35 a.u. between ab initio and the semiempirical calculations. 4) In the semiempirical model each ligand is characterised by one parameter, the so-called partial nuclear quadrupole interaction. This parameter has been evaluated by ab initio calculations, and agreement was found within about 0.2 a. u. (« 40 Mrad/s) for all ligands except imidazole. 5) A change in the coordination number from 2 to 6 may change the partial NQI by about 0.3 a. u. 
  Reference    Z. Naturforsch. 54a, 422—430 (1999); received March 29 1999 
  Published    1999 
  Keywords    Electric Field Gradient, Angular Overlap Model, Ligand Additivity 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0422.pdf 
 Identifier    ZNA-1999-54a-0422 
 Volume    54 
2Author    Thomas Schönherr, Joachim DegenRequires cookie*
 Title    Electronic Spectra and an Angular-Overlap-Model Analysis of fra/!s-[Cr(ox) 2 (py) 2 ]~  
 Abstract    The quartet and doublet transition in frans-[Cr(ox) 2 (py) 2 ]~ show considerable band splittings due to the low-symmetry of the ligand field. The components of 2 E g (O h) and 2 T lg (O h) have been assigned by analysis of vibrational sideband structures in the low-temperature absorption and emission spectra. The energy level scheme has been rationalized in terms of the angular-overlap model. The different contributions of n bonding from the oxalate (n donor) and pyridine (n acceptor) ligands give an explanation of the uncommon quartet band splittings. The doublet energies depend strongly on the molecular geometry. In particular, a reduction of the oxalate bite angle to about 84° has been derived from the spectral band fit. 
  Reference    Z. Naturforsch. 45a, 161—168 (1990); received October 10 1989 
  Published    1990 
  Keywords    Angular-overlap model, Chromium (III) complexes, Vibronic spectra, Spectrum-struc-ture correlations 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0161.pdf 
 Identifier    ZNA-1990-45a-0161 
 Volume    45