Crystal structure and heat capacity study of (C12H25NH3)2CoCl4(s) phase change material

Abstract

Crystal structure of a novel complex (C12H25NH3)2CoCl4(s) has been determined by X-ray crystallography. Crystal system of the compound is monoclinic, and space group is P2(1)/c. Unit cell dimensions are a = (0.73492 ± 0.00010) nm, b = (1.02115 ± 0.00013) nm, and c = (4.2486 ± 0.0003) nm; α = 90°, β = (94.061 ± 0.002)°, γ = 90°, and Z = 4. Low-temperature heat capacities of the title compound are measured by an improved precision automated adiabatic calorimeter in the temperature range from 77 to 396 K. A solid to solid phase transition process occurs in the temperature range of 330 ∼ 365 K in the heat capacity curve, and peak temperature, molar transition enthalpy and entropy from three series of heat capacity measurements of the title compound are determined. The average phase transition temperature Ttrs, phase transition enthalpy ∆trsHm and phase transition entropy ∆trsSm from three series of experiments are (363.06 ± 0.54) K, (83.119 ± 0.197) kJ•mol−1 and (228.94 ± 0.34) J•K−1•mol−1, respectively. Experimental values of molar heat capacities in the temperature regions of 77–327 K and 367–396 K are, respectively fitted to two polynomial equations. Polynomial fitted values of molar heat capacities and fundamental thermodynamic functions of the sample relative to standard reference temperature 298.15 K are calculated and tabulated at an interval of 5 K.