Electron-transfer processes in indium(II) iodide-o-quinone systems

Indium(II) iodide reacts with various substituted o-quinones in nonaqueous solution by successive one-electron-transfer reactions to give (SQ)InI2 products (SQ = semiquinonate radical anion). Electron spin resonance spectroscopy demonstrates the presence of both mono- and diradical species in the reaction mixture. Addition of 4-picoline to a mixture of In2I4 and TBQ (=3,5-di-tert-butyl-o-quinone) in toluene causes the precipitation of the indium(III)-semiquinonate complex (TBSQ)InI2(pic)(2) whose structure has been established by X-ray crystallography: space group <P(1)over bar>, with a = 13.013(3) Angstrom, b = 13.317(3) Angstrom, c = 10.828(5) Angstrom, alpha = 97.71(3)degrees, beta = 107.98(3)degrees, gamma = 103.92(3)degrees, V = 1684.8(1.2) Angstrom(3), Z = 2. Refinement converged at R = 0.051 and R(w) = 0.064 for 5918 reflections at 23 degrees C. The InO2N2I2 kernel is pseudooctahedral, and the structure confirms the presence of the semiquinonate ligand. A reaction scheme which incorporates these results is proposed.