Molecular orbital calculations on transition-metal complexes. Part III. Hexafluorometallate-(III) and -(IV) ions

Abstract

MO calculations using the complete neglect of differential overlap approximation are made for the octahedral hexafluorometallate(III) and the relatively high-oxidation-state hexafluorometallate(IV) complex ions of the firsttransition series. For these latter complex ions the ordering of the ‘metal’ orbitals is consistent with ligand-field theory when the calculations are performed using internuclear distances which are close to those observed experimentally. A variation in this parameter produces a movement of the ‘d’ occupied orbitals into the bonding set of molecular orbitals. Comparison with experimental data and with previous calculations shows that the changes in internuclear separation and derived quantities such as covalency incurred from MF₆^4– through MF₆^3– to MF₆^2– are always calculated to be in the right direction (increase in covalency and decrease in internuclear separation) and in general to be of the right magnitude. Distorted configurations are found for those ions which have orbitally degenerate electronic ground-states in accordance with Jahn–Teller predictions. However, the successive removal of electrons (for the process M^II→ M^III→ M^IV) from orbitals which are essentially ‘metal d’ in character places some restrictions on the method when it is used for calculations on octahedral complexes containing metals in high oxidation states.