SPIN-CHARGE EXCHANGE IN ALLODIAL RADICAL IONS, A NOVEL INTRAMOLECULAR SINGLE ELECTRON-TRANSFER EQUILIBRIUM

The intramolecular single-electron transfer in radical anions and radical cations, constituted by two identical triphenylmethyl moieties, has been studied. The preparation of the radical ions has been effected by mixing the corresponding stable diions (tetra-n-butylammonium or hexachloroantimonate salts) and chemically inert diradicals: by partial oxidation of the dianion salts with iodine (radical anions) and by partial oxidation of the diradicals with SbCl5 (radical cations). The ESR C-13 hyperfine coupling constants and linewidths and UV-vis absorptivity spectra afford compelling evidence for a rapid spin-charge exchange equilibrium: (C6Cl5)2C-C6Cl4-Sp-C6Cl4-C(C6Cl5)2 = (C6Cl5)2C-C6Cl4-Sp-C6Cl4-C(C6Cl5)2 (Sp = none, CH2CH2, C=C. * = -, +). Relevant structural aspects, such as steric inhibition of resonance, electron paths, and counterion involvement, are discussed. The synthesis and isolation of related disalts from the corresponding diradicals are also described.