Thermal stability and decomposition behaviors of some hydrous transition metal chlorides

In this work, the thermal stability of CuCl2, CoCl2, MnCl2, and their corresponding hydrates was studied by combining with calorimetry and lattice energy calculation. The dissolution enthalpies of both anhydrates and hydrates in water with different molalities at 298.15 K were measured to calculate the standard molar enthalpies of formation. The hydration enthalpies and the lattice energies were calculated to disclose the stabilities of the compounds, indicating that the MnCl2 center dot 4H(2)O has the highest stability among the three hydrates. Meanwhile, the detailed thermal decomposition behaviors were evaluated with differential scanning calorimetry and thermogravimetric analysis. For CuCl2 center dot 2H(2)O, the crystal water is lost by one step directly with the temperature ranges from 350 to 410 K. The decomposition process contains four steps for CoCl2 center dot 6H(2)O and obtains its monohydrate in the temperature range from 320 to 479 K. For MnCl2 center dot 4H(2)O, two thermal decomposition steps occur from 325 to 500 K, while two consecutive peaks with no clear boundary indicate that the complex reactions appear.