Two novel crystalline compounds (1-C10H21NH3)(2)MnCl4(s) and (1-C11H23NH3)(2)MnCl4(s), which may be used as solid-solid phase change materials, were synthesized. The compositions and mass fraction purities of the samples prepared were determined by chemical and elemental analyses. The crystal structures of the two compounds were characterised by X-ray crystallography. The lattice potential energies of the two compounds were obtained from crystallographic data. Molar enthalpies of dissolution of the compounds at various values of molality were measured in the double-distilled water at T = 298.15 K by means of an isoperibol solution-reaction calorimeter. According to Pitzer's unsymmetrical mixing electrolyte solution theory, the values of molar enthalpies of dissolution at infinite dilution and Pitzer's parameters of the compounds were obtained. Finally, using the values of molar enthalpies of dissolution at infinite dilution (Delta H-s(m)infinity) and other auxiliary thermodynamic data, the enthalpy change of the dissociation of [MnCl4](2) (g) for the reaction [MnCl4](2-) (g) -> Mn2+(g) + 4Cl(-) (g) was derived. (C) 2014 Elsevier Ltd. All rights reserved.