 1  Author
 Lars Hemmingsen, Ulf Ryde, Rogert Bauer  Requires cookie*   Title
 Nuclear Quadrupole Interactions in Cadmium Complexes: Semiempirical and ab initio Calculations    Abstract
 Semiempirical calculations, based on the socalled 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 Cdligand 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 ligandligand 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 socalled asymmetry parameter. 3) The position of noncoordinating atoms on the ligands can in some cases (e. g. the hydrogen atoms of water) significantly influence the EFG. The combined effect of noncoordinating atoms and ligandligand 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 socalled 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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 ZNA199954a0422    Volume
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