BINDING IN 2ND-ROW TRANSITION-METAL DIOXIDES, TRIOXIDES, TETRAOXIDES,PEROXIDES, AND SUPEROXIDES

In a continuing systematic project investigating complexes of second-r ow transition metals, results are presented here for different types o f systems where metal-oxygen bonds are present. The entire sequence of second-row dioxides and some trioxides and the single tetraoxide of i nterest, RuO4, have been studied. An interesting result for the dioxid es is that most of these systems are bent, which is in contrast to the corresponding dichloride systems. The origin of the bent structures o f the dioxides is a more optimal mixing between metal 4d-orbitals and oxygen orbitals for bent than for linear geometries. This type of mixi ng is a general effect that also influences the structure of other tra nsition metal complexes, such as MoH6, which obtains a C3nu structure. Complexes involving molecular oxygen as a ligand have also been studi ed. Two types of structures occur, the symmetric peroxide low-spin str uctures and the superoxide high-spin structures which are bound to the metal by a single covalent bond. The superoxide structures can be eta 1- or eta2-coordinated to the metal. Comparisons are made to previous calculations on transition metal oxides, and it is shown that the pres ent higher level of accuracy is of large importance even for the quali tative chemistry of these systems.