OXO AND NITRIDO COMPLEXES OF MOLYBDENUM, TUNGSTEN, RHENIUM, AND OSMIUM - A THEORETICAL-STUDY

Quantum mechanical ab initio calculations at the Hartree-Fock and MP2 level of theory using relativistic effective core potentials for the m etal atoms are reported for neutral and negatively charged oxo and nit rido complexes of molybdenum, tungsten, rhenium, and osmium with the g eneral formula MXL(n) (L = F, Cl; n = 3-5). The calculated geometries and vibrational frequencies at the HF level are in good agreement with experimental data. The analysis of the electronic structure of the co mplexes shows that the M-O and M-N bonds are strongly covalent but the M-L bonds have mainly ionic character. The a and n contributions to t he M-O bonds are strongly polarized toward oxygen. The M-N bonds are m uch less polarized and should be considered as triple bonds. The metal bonding in the M-X and M-L bonds has mainly hl(d) character.