STUDY ON COORDINATION NUMBER-6 AND NUMBER7 IN V(III)-COMPLEXES WITH AQUO, CYANIDE AND AMINOPOLYCARBOXYLIC LIGANDS BY MEANS OF THE ANGULAR OVERLAP MODEL

Peculiarities due to six- and seven-coordination in V(III) complexes a re investigated within the framework of the angular overlap model (AOM ). Calculations of orbital schemes and d-d transitions are performed f or complexes with aquo, cyanide and aminopolycarboxylic ligands. The c ompeting influence of electronic and geometric effects on the energy l evel pattern is discussed in view of the derived AOM parameters. A cha racteristic feature of seven-coordination is the large splitting of th e T-3(1g) ground state (in O-h notation) that leads to typical absorpt ions in the near-infrared ([V(edta)H2O)](-)), (edta, ethylenediaminete traacetate) or visible ([V(CN)(7)](4-)) spectral region which can be u sed in particular to distinguish between both coordination numbers in solution spectra. In the pent agonal-bipyramidal [V(CN)(7)](4-) comple x there is an unexpectedly high covalency in the sigma-interactions wi th the axial ligands that conflicts a meaningful parametrization withi n the ligand held approach. (C) 1998 Elsevier Science B.V. All rights reserved.