THERMOLYSIS OF TERNARY AMMONIUM CHLORIDES OF RHENIUM AND THE NOBLE-METALS

Thermal decomposition of the ammonium hexachlorometalates (NH4)2[MCl6] (M = Pd, Re, Os, Ir, Pt), (NH4)3[RhCl6].H2O (NH4)4[Ru2Cl10O] was investigated by means of thermogravimetry, differential thermal analysis, mass spectrometry and X-ray diffraction dependent upon temperature. All ammonium compounds produce, finally, finely divided metal powders. Nitrogen and hydrogen chloride, are released as gases attesting to the internal redox reaction M4+ (M3+) + N3- --> N2+/-0 + M+/-0 which takes place in all cases at temperatures between 300 and 450-degrees-C depending upon the heating rates and the element M. For M = Rh and Pd, stable intermediates could be detected, namely (NH4)2[Rh(NH3)Cl5] and (NH4)2[PdCl4].