DENSITY-FUNCTIONAL STUDY OF THE TETRAOXOMETALLATES OF CRVI, MNVI AND FEVI

Local density approximation (LDA) density functional theory (DFT) calc ulations are reported for the tetrahedral anions [CrO4]2-, [MnO4]2- an d [FeO4]2- . A range of STO basis sets is considered to determine the sensitivity of the optimised M=O bond lengths and charge-density distr ibutions. For a given complex, the computed bond lengths decrease smoo thly as the basis set increases. The overall spread of predicted value s is 0.04 angstrom, with experiment reproduced to within 0.02 angstrom for bases which include polarisation functions. The charge-density an alysis across the series describes increasing covalence from [CrO4]2- to [FeO4]2-, while the computed relative bond strengths decrease. The latter correlate well with the observed increase in reactivity along t his series. The computed values for the ligand-field parameter, DELTA( tet), are about 2000 cm-1 too high for do [CrO4]2-and d1 [MnO4]2-, and 600 cm-1 too low for [FeO4]2-. In conjunction with theoretical estima tes of the Racah parameters from spin-unrestricted LDA calculations, t he computed d-d spectrum of [FeO4]2- is in reasonable agreement with e xperiment.