Solubility of Hexaamminenickel(II) Complexes in Aqueous Ammonia Solution and the Thermal Decomposition of Ammine Complexes of Nickel(II)

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Abstract
The solubility of hexaamminenickel(II) complexes in aqueous ammonia solution (0 to 37 g-free NH3/100g-solv.) was investigated at temperatures 0–55 °C. It rapidly decreases with increase in free ammonia concentration but increases with rise in temperature. Hexaamminenickel(II) carbonate, sulfate, and chloride are slightly soluble at ammonia concentration above 30 g-free NH3/100 g-solv., but nitrate is considerably soluble even at ammonia concentration of 35 g-free NH3/100 g solv. The thermal decomposition of ammine complexes of nickel(II) was also investigated by means of TG and DTA under a streaming nitrogen gas atmosphere. Ammine complexes of nickel(II) decompose as shown in the following, the reaction orders and activation energies for steps a, b, c, and d being 0.5, 1.5, 1.0, and 0.5, and 16.5, 38.8, 25.3, and 79.4 kcal/mol, respectively. (Remark: Graphics omitted.) X-Ray diffraction data for [Ni(NH3)6]Cl2·0.5H2O, [Ni(NH3)6](NO3)2, [Ni(NH3)5]SO4·H2O, and [Ni(NH3)2]SO4 powder are given.