Crystal structures and solid–solid phase transitions on phase change materials (1−CnH2n+1NH3)2CuCl4(s) (n=10 and 11)

Two novel crystalline complexes (C10H21NH3)2CuCl4(s) and (C11H23NH3)2CuCl4(s) (abbreviated as C10Cu(s) and C11Cu(s)), which may be used as the phase change materials, were synthesized by liquid phase reaction. Crystal structures and chemical compositions of the two complexes were determined by X-ray single crystal diffraction technique, chemical analysis and elemental analysis. Low-temperature heat capacities of the two new phase change materials were measured by a precise automatic adiabatic calorimeter in the temperature range from 78 to 395 K. The temperatures, molar enthalpies and entropies of the phase transitions for each of the two complexes were determined to be: for (C10Cu(s)), 310.64±0.05 K, 81.12±0.11 kJ/mol, and (261.24±0.06) J/K mol for the first peak, 315.17±0.04 K, 10.17±0.52 kJ/mol, and 32.28±1.66 J/K mol for the second peak; for (C11Cu(s)), they were 311.39±0.69 K, 70.17±0.25 kJ/mol, and 225.36±0.66 J/K mol for the first peak, 321.85±0.46 K, 10.58±0.26 kJ/mol, and 32.86± 0.07 J/K mol for the second peak, respectively. Two polynomial equations of the heat capacities as a function of temperature were fitted by the least-square method. Smoothed heat capacities and thermodynamic functions of the two phase change materials were calculated based on the fitted polynomial equations. In addition, the solid–solid phase transitions and melting processes of the two complexes were verified by DSC and TG techniques, and the reversibility and repeatability of the two phase transitions for each of the two complexes were discussed.

Graphical abstractTwo novel crystalline complexes (C10H21NH3)2CuCl4(s) and (C11H23NH3)2CuCl4(s) were synthesized by liquid phase reaction. The crystal structures and chemical compositions of the complexes have been determined. Low-temperature heat capacities of the two new phase change materials were measured. The temperatures, molar enthalpies and entropies of the phase transitions for each of the two complexes were determined. Two polynomial equations of the heat capacities as a function of temperature were fitted by the least-square method. In addition, solid–solid phase transitions and melting processes were verified by DSC and TG techniques.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Crystal structures of two novel crystalline complexes were determined. ► Low-temperature heat capacities of the compounds were measured. ► Solid–solid phase transitions were observed. ► Temperatures, enthalpies and entropies of the phase transitions were determined. ► DSC/TG were used to investigate solid–solid phase transitions and melting process.