ELECTROCHEMICAL OXIDATION OF ELEMENTAL INDIUM IN LIQUID-AMMONIA MEDIA

The electrochemical oxidation of indium metal in solutions of NH4X (X = Cl, Br or I) in liquid ammonia proceeds with an electrochemical efficiency which implies the formation of indium(II) species at the anode. In the case of NH4I-NH3, Raman spectroscopy confirmed the presence of In2I4 in solution; it was not possible to isolate neutral or anionic derivatives of indium(II), since disproportionation occurs on removal of solvent to give indium-(0), -(I) and -(III) derivatives. Mass-balance experiments have been made for these systems. Solutions of NH4I + substituted o-quinone (But2H2C6O2-o or Br4C6O2-o) yielded InI3.3NH3, while with substituted catechols [X4C6(OH)2; X = Cl or Br] the products were [NH4]3[In(O2C6X4)3].Et2O. In the case of a solution of But2H2C6(OH)2-o (H-2dbc) in liquid NH3-Et2O media, the final product is a derivative of the dimeric anion [In2(dbc)4(NH3)2]2-, in a lattice which also contains NH4+, Hdbc- and Et2O. The crystal parameters of [NH4]4[In2(dbc)4(NH3)2].(2Hdbc).2Et2O are monoclinic, space group P2(1)/n, a = 14.464(10), b = 19.194(5), c = 19.560(7) angstrom, beta = 103.72(4)-degrees, Z = 4, R = 0.055. The anion involves two InO5N kernels, with In2O2 cross-linking responsible for the dimerization.