Crystalline compounds (C14H29NH3)(2)CuCl4(s) and (C15H31NH3)(2)CuCl4(s) were synthesized. X-ray crystallography was applied to characterize crystal structures of the two compounds. The crystal system is both monoclinic, the space group is both C2/c, and Z=4. The lattice potential energies of the title compounds were calculated to be U-POT [(C14H29NH3)(2)CuCl4, s]=853.12 kJ/mol and U-POT [(C15H31NH3)(2)CUCl4, s]=854.93 kJ/mol. Low-temperature heat capacities of the two compounds were measured by a precision automatic adiabatic calorimeter over the temperature range from 78 to 395 K. The temperatures, molar enthalpies, and entropies of two phase transitions for each of the two complexes were determined to be: for (C14H29NH3)(2)CuCl4(s), 342.35 +/- 0.11 K, 76.17 +/- 0.40 kJ/mol, and 222.49 +/- 1.20 J/K mol for the first peak; 352.61 +/- 0.09 K, 27.83 +/- 0.27 kJ/mol, and 78.92 +/- 0.78 J/K mol for the second peak, and for (C15H31NH3)(2)CuCl4(s), they were 345.40 +/- 0.93 K, 62.06 +/- 1.07 kJ/mol, and 179.67 +/- 2.63 J/K mol for the first peak; 360.98 +/- 0.25 K, 21.66 +/- 0.76 kJ/mol, and 60.00 +/- 2.09 J/K mol for the second peak, respectively. The smoothed heat capacities and thermodynamic functions (H-T(o)-H-298.15(o)) and (Delta S-trs(m)=Delta H-trs(m)/T-trs) of the two compounds were calculated with an interval of 5 K based on the experimental heat capacities. (C) 2011 Elsevier B.V. All rights reserved.