Electrochemical oxidation of elemental indium in liquid ammonia media

Abstract

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 (Bu^t₂H₂C₆O₂-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 Bu^t₂H₂C₆(OH)₂-o(H₂dbc) 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 P2₁/n, a= 14.464(10), b= 19.194(5), c= 19.560(7)Å, β= 103.72(4)°, Z= 4, R= 0.055. The anion involves two InO₅N kernels, with In₂O₂ cross-linking responsible for the dimerization.