Crystal Structure, Low-Temperature Heat Capacities, and Thermodynamic Properties of Bis(dodecylammonium) Tetrachlorocuprate (C₁₂H₂₈N)₂CuCl₄(s)

Abstract

Crystalline bis(dodecylammonium) tetrachlorocuprate (C12H28N)2CuCl4(s) was synthesized. Chemical analysis, elemental analysis, and X-ray crystallography were applied to characterize the composition and crystal structure of the compound. The lattice potential energy (UPOT) of the title compound was calculated to be 862.56 kJ·mol−1. Low-temperature heat capacities of the compound were measured by a precision automatic adiabatic calorimeter over the temperature range from (78 to 390) K. Two continuous solid−solid phase transitions were observed. The temperatures, molar enthalpies, and entropies of the two phase transitions were determined to be: Ttrs,1 = (329.03 ± 0.24) K, ΔtrsHm,1 = (64.24 ± 0.35) kJ·mol−1, ΔtrsSm,1 = (194.57 ± 1.09) J·K−1·mol−1, Ttrs,2 = (336.98 ± 0.18) K, ΔtrsHm,2 = (20.81 ± 0.30) kJ·mol−1, and ΔtrsSm,2 = (61.75 ± 0.87) J·K−1·mol−1, respectively. Two polynomial equations of heat capacity against the reduced temperature in the region of (78 to 311) K and (340 to 390) K were fitted by a least-squares method. On the basis of the two polynomials, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature of 298.15 K were calculated and tabulated with an interval of 5 K. In addition, two solid−solid phase transitions and a melting process of the title compound were verified by the differential scanning calorimetry (DSC) technique.