The thermal decompositions of [Mg(NH3)(6)](NO3)(2), [Ni(NH3)(6)](NO3)(2) and [Ni(ND3)(6)](NO3)(2) were studied by thermal gravimetry analysis (TGA) and simultaneous differential thermal analysis (SDTA) at a constant heating rate. The gaseous products of the decomposition were on-line identified by a quadruple mass spectrometer (QMS). The solid products were identified on the basis of Fourier transform mid infrared spectra (FT-MIR) and X-ray powder diffraction (XRPD) patterns. Deamination of hexaaminemagnesium nitrate(V) to diaminemagnesium nitrate(V) undergoes in two steps and two-third of the all NH3 molecules are liberated. Deamination of both hexaaminenickel(II) nitrates(V) (non-deuterated and deuterated) to the diamines undergoes in three steps, and at two first steps one half of the NH3 molecules are liberated. The thermal decomposition of [Ni(NH3)(2)](NO3)(2) and [Ni(ND3)(2)](NO3)(2) is also different than that of [Mg(NH3)(2)](NO3)(2), In both cases the decomposition is connected with the redox processes, but in the case of magnesium compound, contrary to the nickel compounds, in the second stage, besides of liberation of nitrogen, nitrogen oxides and H2O, undergoes the liberation of NH3 and the formation of Mg(NO3)(2), which in turn decomposes next, in the third stage, to the oxygen, nitrogen oxides and MgO. This third stage is not present in the case of both nickel compounds, and the decomposition of diaminenickel(II) nitrates(V) undergoes directly to the final products (NiO1+x, nitrogen, nitrogen oxides and H2O) without the formation of Ni(NO3)(2), because of the autocatalytic effect of the formed NiO. (C) 2004 Elsevier B.V. All rights reserved.