Measured and Calculated Oxidation Potentials of 1-X-12-Y-CB11Me10- Anions

Cyclic voltammetry of 31 icosahedral carborane anions 1-X-12-Y-CB11Me10- at a Pt electrode in liquid SO2 revealed a completely reversible one-electron oxidation even at low scan rates, except for the anions with Y = I, which are oxidized irreversibly up to a scan rate of 5.0 V/s, and the anion with X = COOH and Y = H, whose oxidation is irreversible at scan rates below 1.0 V/s. Relative reversible oxidation potentials agree well with RI-B3LYP/TZVPP,COSMO and significantly less well with RI-BP86/TZVPP,COSMO or RI-HF/TZVPP,COSMO calculated adiabatic electron detachment energies. Correlations with HOMO energies of the anions are nearly as good, even though the oxidized forms are subject to considerable Jahn-Teller distortion. Except for the anion with X = F and Y = Me, the oxidation potentials vary linearly with substituent sigma(P) Hammett constants. The slopes (reaction constants) are similar to 0.31 and similar to 0.55 V for positions 1 and 12, respectively.