Delocalization and Valence Tautomerism in Vanadium Tris(iminosemiquinone) Complexes.

To survey the noninnocence of bis(arylimino) acenaphthene (BIAN) ligands (L) in complexes with early metals, the homoleptic vanadium complex, [V(L)3 ] (1), and its monocation, [V(L)3 ]PF6 (2), were synthesized. These complexes were found to have a very rich electronic behavior, whereby 1 displays strong electronic delocalization and 2 can be observed in unprecedented valence tautomeric forms. The oxidation states of the metal and ligand components in these complexes were assigned by using spectroscopic, crystallographic, and magnetic analyses. Complex 1 was identified as [V(IV) (L(red) )(L(.) )2 ] (L(red) =N,N'-bis(3,5-dimethylphenylamido)acenaphthylene; L(.) =N,N'-bis(3,5-dimethylphenylimino)acenaphthenesemiquinonate). Complex 2 was determined to be [V(V) (L(red) )(L(.) )2 ](+) at T<150 K and [V(IV) (L(.) )3 ](+) at T>150 K. Cyclic voltammetry experiments reveal six quasi-reversible processes, thus indicating the potential of this metal-ligand combination in catalysis or materials applications.