Density-functional investigation of bonding in tetrahedral MO 4 anions

Abstract

The structure and bonding in main-group and transition-metal oxoanions with MO 4 stoichiometry have been investigated by density-functional methods. Nine main-group (SiO 4 4− , PO 4 3− , SO 4 2− , ClO 4 − , GeO 4 4− , AsO 4 3− , SeO 4 2− , BrO 4 − , IO 4 − ) and ten transition-metal (TiO 4 4− , VO 4 3− , CrO 4 2− , MnO 4 − , NbO 4 3− , MoO 4 2− , TcO 4 − , TaO 4 3− , WO 4 2− , ReO 4 − ) oxoanions have been studied. For most species, the optimized geometry of the isolated molecule satisfactorily reproduces the experimental structural parameters in the crystalline phase. Mulliken charges have been calculated, and have been found to be, in all cases, significantly smaller than the formal oxidation states. Mayer bond-order indexes and the composition of the Kohn–Sham orbitals have been utilized for the analysis of bonding in the oxoanions. The former reveal some MO multiple-bonding character in all MO 4 systems, and are in good agreement with values determined from classical bond-valence analysis. The molecular-orbital analysis indicates that the chemical bonds possess Msp and Osp character in the main-group species, and Md and Op character in the transition-metal systems.