An Iminosemiquinone-Coordinated Oxidovanadium(V) Complex: A Combined Experimental and Computational Study

Ligand H4Sar(AP/AP) contained two terminal amidophenolate units that were connected by a disulfane bridge. The ligand reacted with VOSO4·5H2O in the presence of Et3N under air and provided a mononuclear octahedral oxidovanadium complex (1). X-ray crystal structure analysis of complex 1 revealed that the oxidation state of the V ion was V and the VO3+ unit was coordinated to an iminosemiquinone radical anion. An isotopic signal at g = 1.998 in the X-band electron paramagnetic resonance (EPR) spectrum and the solution magnetic moment μeff = 1.98 μB at 298 K also supported the composition. The formation of complex 1 preceded through the initial generation of a diamagnetic VO2+–iminoisemiquinone species, as established by time-dependent UV–vis–near-IR (NIR), X-band EPR, and density functional theory studies. The UV–vis–NIR spectrum of complex 1 consisted of four ligand-to-metal charge-transfer transitions in the visible region, while an intervalence ligand-to-ligand charge transfer appeared at 1162 nm. The cy...