4-COORDINATE AND 5-COORDINATE OXOVANADIUM(V) ALKOXIDES - DO STERIC EFFECTS OR ELECTRONIC-PROPERTIES DICTATE THE GEOMETRY

Sterically hindered ligands generally form metal complexes with lower coordination numbers than less hindered ligands. In contrast to dogma, the solid state vanadium(V) complexes with ethylene glycol and pinaco l contain four- and five-coordinate vanadium atoms, respectively. Ab i nitio and electrostatic potential distribution calculations were condu cted on both experimental and optimized geometries of the four- and fi ve-coordinate oxovanadium chloroalkoxides. Ab initio energy calculatio ns favor the five-coordinate species for all ligands at all levels of theory examined. No significant differences in the electrostatic prope rties of the vanadium atoms in the two types of molecules were observe d by using electrostatic potential distribution analysis. Methyl group substitutions on the ligand did not change the electronics of the van adium atoms sufficiently to be a factor. Thus, we conclude that neithe r electronics nor sterics at the metal center explains the experimenta l geometries. In the absence of a significant observable electronic ef fect at the vanadium, we note that the experimental observations can b e attributed to ligand geometric effects such as the Thorpe-Ingold and /or gem-dialkyl effects.