One- and Two-Electron Reduced 1,2-Diketone Ligands in [Cr^III(L^•)₃] (<i>S</i> = 0) and Na₂(Et₂O)₂[V^IV(L^Red)₃] (<i>S</i> = ¹/₂)

Abstract

The electronic structures of chromium and vanadium centers coordinated by three reduced 1,2-diketones have been elucidated by using density functional theory (DFT) calculations and a host of physical methods: X-ray crystallography; cyclic voltammetry; ultraviolet−visible (UV−vis), nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) spectroscopy; and magnetic susceptibility measurements. The metal center in octahedral [Cr^III(L^•)₃]⁰ (<b>1</b>), a Cr^III (d³) ion is coupled antiferromagnetically to three monoanionic ligand π-radicals affording an <i>S</i> = 0 ground state. In contrast, Na₂(Et₂O)₂[V^IV(L^Red)₃] (<b>2</b>) (<i>S</i> = ¹/₂), possesses a central V^IV (d¹) ion <i>O,O′</i>-coordinated to three closed-shell, doubly reduced ligands which in turn are coordinated by two Na cations enforcing a trigonal prismatic geometry at the vanadium center. <b>2</b> can be oxidized electrochemically by one and two electrons generating a monoanion, [V(L)₃]¹⁻, and a neutral species, [V(L)₃]⁰, respectively. DFT calculations at the B3LYP level show that the one-electron oxidized product contains an octahedral V^IV ion coupled antiferromagnetically to one monoanionic ligand π-radical [V^IV(L^•)(L^Red)₂]¹⁻ (<i>S</i> = 0). In contrast, the two-electron oxidized product contains a V^III ion coupled antiferromagnetically to three ligand π-radicals in an octahedral field [V^III(L^•)₃]⁰ (<i>S</i> = ¹/₂).