Ab initio RHF and CI calculations have been carried out on the [H-3(NH3)(2)VN2V(NH3)(2)H-3], [H-3(NH3)(2)-VN2V(NH3)(2)H-3](-) and [H-3(Nh(3))(2)VN2V(NH3)(2)H-3](2-) complexes and related fragments in order to study the energetics and the mechanism of dinitrogen activation in dinuclear hexacoordinated complexes of vanadium(ll) and vanadium(III). Various energy gradient optimizations have been performed on the complexes and the various fragments, followed by MRCI calculations on the stationary structures. The results indicate that in such complexes there is a near degeneracy between the states of high and low spin multiplicity and that dinitrogen is essentially from poorly to fairly activated depending on the oxidation state of the vanadium atoms and the spin multiplicity itself. The influence of vanadium coordination (tetrahedral versus octahedral) on dinitrogen activation has been discussed.