Synthesis, identification and thermal decomposition of double sulfates of Mn, Cu and Cd with benzylammonium

On evaporation of an aqueous mixture of M(II) sulfate (M(II) = Mn, Co, Ni, Cu, Zn or Cd) and benzylammonium sulfate in a molar ratio of 1:2 at room temperature in the presence of sulphuric acid, double sulfates of only Mn, Cu and Cd were obtained. The stoichiometries of the compounds were determined by means of elemental and TG analysis. It was concluded that these compounds have the same general formula: M(C₆H₅CH₂NH₃)₂(SO₄)₂·4H₂O. These compounds have the same stoichiometry as that of the corresponding double sulfates with ethanolammonium cation, but have different crystal structures. The thermal decompositions of the investigated compounds in the temperature range from ambient temperature up to 1000 °C take place in a similar way, in three well-differentiated stages, but with different pathways in the second and third stages. Metal oxides were obtained as final products.