Density-functional investigation of bonding in tetrahedral MO4 anions

The structure and bonding in main-group and transition-metal oxoanions with MO4 stoichiometry have been investigated by density-functional methods. Ni ne main-group (SiO44-, PO43-, SO42-, ClO4-, GeO44-, AsO43-, SeO42-, BrO4-, IO4-) and ten transition-metal (TiO44-, VO43-, CrO42-, MnO4-, NbO43-, MoO42 -, TcO4-, TaO43-, WO42-, ReO4-) oxoanions have been studied. For most speci es, the optimized geometry of the isolated molecule satisfactorily reproduc es the experimental structural parameters in the crystalline phase. Mullike n charges have been calculated, and have been found to be, in all cases, si gnificantly smaller than the formal oxidation states. Mayer bond-order inde xes and the composition of the Kohn-Sham orbitals have been utilized for th e analysis of bonding in the oxoanions. The former reveal some M-O multiple -bonding character in all MO, systems, and are in good agreement with value s determined from classical bond-valence analysis. The molecular-orbital an alysis indicates that the chemical bonds possess Msp and Osp character in t he main-group species, and Md and Op character in the transition-metal syst ems. (C) 2001 Elsevier Science Ltd. All rights reserved.