Investigations in semi-empirical molecular orbital methods. IV. A modified wolfsberg-helmholz method for inorganic systems

Abstract

Semiempirical molecular orbital calculations were performed for MF 6 3− where M = Ti 3+, V 3+, Cr 3+, Fe 3+ and Co 3+, MnF 6 4−, MnF 6 2−, MnCl 4 2−,MnCl 2, VCl 6 2− and VCl 4, using a modified semi-empirical MHW method. The method of calculation is derived from the HF-SCF equations using approximations appropriate to the highly polar bonds in transition metal halides. The final equations used also take account of the site potential present for the charged molecular ion. This method is compared to other recent semi-empirical computational methods including the conventional MWH method. The computed atom charges are in better agreement with experimentally estimated atom charges than those of previous semiempirical calculations. The ligand field molecular orbital coefficients are also in good agreement with coefficients estimated from NMR and EPR spectroscopy. This method of calculations also gives results that agree with the trends shown by experimentally determined 10 Dq values and charge transfer transition energies and are in good numerical agreement with the experimental 10 Dq values.