Cations M₂(O₂C^tBu)₄ ⁺, where M = Mo and W, and MoW(O₂C^tBu) ₄⁺. Theoretical, spectroscopic, and structural investigations

With the aid of density function theory, the molecular and electronic structures of the molecules Mo₂(O₂CMe)₄, MoW(O₂CMe)₄, and W₂(O₂CMe) ₄ and their single-electron oxidized radical cations have been determined; this includes calculated observables such as v(MM) and the δ → δ* electronic transition energies. The calculated properties are compared with those for the corresponding pivalates, M₂(O ₂C^tBu)₄ (M = Mo or W) and MoW(O ₂C^tBu)₄ and their radical cations prepared in situ by oxidation with Cp₂FePF₆. The EPR spectra of the radical cations are also reported. The EPR spectrum of the MoW(O ₂C^tBu)₄⁺ cation reveals that the unpaired electron is in a polarized MM δ orbital having 70% Mo and 30% W character. The MM stretching frequencies show good correlation with the MM bond lengths obtained from single-crystal X-ray diffraction studies of MoW(O ₂C^tBu)₄, W₂(O₂C ^tBu)₄, and W₂(O₂C ^tBu)₄⁺PF₆^- compounds, along with previously reported structures. These data provide benchmark parameters for valence trapped dicarboxylate bridged radical cations of the type [(^tBuCO₂)₃M₂]₂(μ- O₂C-X-CO₂)⁺ (X = conjugated spacer).