Doublet Ground State in a Vanadium(II) Complex: Redox and Coordinative Noninnocence of Tripodal Ligand Architecture.

We report on the geometric and electronic structures of a series of V tren-bridged iminopyridine complexes [tren = tris(2-aminoethyl)amine] that enable the observation of an unexpected doublet ground state for a nominally 3d species. Tren undergoes condensation reactions with picolinaldehyde or methyl-6-formylnictonate to form the respective tripodal ligand sets of (py)tren and (5-COMepy)tren. The (py)tren ligand is coordinated to V and V metal centers to form complex salts (OTf) and (OTf), respectively (OTf = CFSO). For , strong metal-ligand π-covalency with respect to the V (3d) and iminopyridine ligands weakens its interelectronic repulsion. For , the bridgehead nitrogen of the tren scaffold forms a seventh coordinate covalent bond with a V (3d) metal center. The coordination of (5-COMepy)tren to a V metal center results in the redox noninnocent and heptacoordinate compound (OTf) with a doublet ( = /) ground state that we support with magnetic susceptibility and spectroscopy measurements. The complexes are uniformly characterized experimentally with single-crystal X-ray diffraction, electronic absorbance, and electrochemistry, and electronic structures are corroborated by computational techniques. We present a new computational procedure that we term the spin-optimized approximate pair (SOAP) method that enables the visualization and quantification of electron-electron interactions.