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

• Published in: Inorganic chemistry 2022-05, Vol.61 (17), p.6376-6391
• Main Authors: Joyce, Justin P, Portillo, Romeo I, Rappé, Anthony K, Shores, Matthew P
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.1c03418

We report on the geometric and electronic structures of a series of V2+/3+ tren-bridged iminopyridine complexes [tren = tris­(2-aminoethyl)­amine] that enable the observation of an unexpected doublet ground state for a nominally 3d3 species. Tren undergoes condensation reactions with picolinaldehyde or methyl-6-formylnictonate to form the respective tripodal ligand sets of (py)3tren and (5-CO2Mepy)3tren. The (py)3tren ligand is coordinated to V2+ and V3+ metal centers to form complex salts [1-H](OTf)2 and [1-H](OTf)3, respectively (OTf– = CF3SO3 –). For [1-H] 2+ , strong metal–ligand π-covalency with respect to the V2+ (3d3) and iminopyridine ligands weakens its interelectronic repulsion. For [1-H] 3+ , the bridgehead nitrogen of the tren scaffold forms a seventh coordinate covalent bond with a V3+ (3d2) metal center. The coordination of (5-CO2Mepy)3tren to a V2+ metal center results in the redox noninnocent and heptacoordinate compound [1-CO 2 Me](OTf)2 with a doublet (S = 1/2) 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.