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)

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 [CrIII(L•)3]0 (1), a CrIII (d3) ion is coupled antiferromagnetically to three monoanionic ligand π-radicals affording an S = 0 ground state. In contrast, Na2(Et2O)2[VIV(LRed)3] (2) (S = 1/2), possesses a central VIV (d1) ion O,O′-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. 2 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 VIV ion coupled antiferromagnetically to one monoanionic ligand π-radical [VIV(L•)(LRed)2]1− (S = 0). In contrast, the two-electron oxidized product contains a VIII ion coupled antiferromagnetically to three ligand π-radicals in an octahedral field [VIII(L•)3]0 (S = 1/2).