Low temperature heat capacity study of Zn, Cd and Mn based coordination compounds synthesized using phenanthroline and halogenated benzoic acid

Four Zn, Cd and Mn based 1,10-phenanthroline and halogenated benzoic acid coordination compounds, formulated as Zn2II(H2O)3(phen)(SO4)·H2O (1, phen = 1,10-phenanthroline), ZnII(phen)(L2)2(H2O) (2, L2 = 2-chloro-4-fluorobenzoic acid), MnIV(phen)(L1)4 (3, L1 = 2-Chloro-4,5-difluorobenzoic acid) and CdII(phen)2(NO3)2 (4), were successfully synthesized and structurally characterized. The low temperature heat capacities of these four compounds were further investigated using a Physical Property Measurement System calorimetric method. The experimental heat capacities were fitted to a series of theoretical and empirical heat capacity models, and the corresponding thermodynamic functions were calculated in the temperature range from (0 to 300) K based on these models and fitting parameters. The low temperature fits indicated that compound 1 can be modeled using only lattice heat capacity contribution, compound 3 modeled using lattice and A-2 term or Schottky heat capacity contributions, and compound 2 and 4 modeled using contributions from lattice, vacancies and one-dimensional phonons with a finite energy onset or gap.