Electronic structure of cubane-likevanadium-nitrogen cationic clusters [V4N4]+ and [V6N6]+

Density Functional Theory and Complete Active Space Self-Consistent Field (CASSCF) methodologies are used to explore the electronic structure of the cationic V-N clusters, [V4N4]+ and [V6N6]+, that have been identified in recent mass spectrometric experiments. Our calculations indicate that both clusters are based on cubane-like fragments of the rock-salt lattice. In the smaller [V4N4]+ cluster, the V-V bonding is delocalized over the tetrahedron, with net bond orders of 1/3 per V-V bond. In [V6N6]+, in contrast, the V-V bonding is strongly localized in the central V2N2 unit, which has a short V=V double bond. CASSCF calculations reveal that both localized and delocalized V-V bonds are highly multi-configurational.