Cations M2(O2CtBu)4+, where M = Mo and W, and MoW(O2CtBu)4+.: Theoretical, spectroscopic, and structural investigations

With the aid of density function theory, the molecular and electronic structures of the molecules Mo-2(O2CMe)(4), MoW(O2CMe)(4), and W-2(O2CMe)(4) and their single-electron oxidized radical cations have been determined; this includes calculated observables such as vi(MM) and the delta-->delta(*) electronic transition energies. The calculated properties are compared with those for the corresponding pivalates, M-2((O2CBO4)-B-t (M = Mo or W) and MoW((O2CBu)-Bu-t)(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((O2CBu)-Bu-t)(4)(+) cation reveals that the unpaired electron is in a polarized MM 6 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((O2CBu)-Bu-t)(4), W-2((O2CBu)-Bu-t)(4), and W-2((O2CBu)-Bu-t)(4)+PF6- compounds, along with previously reported structures. These data provide benchmark parameters for valence trapped dicarboxylate bridged radical cations of the type [((BuCO2)-Bu-t)(3)M-2](2)(mu-O2C-X-CO2)(+) (X = conjugated spacer).