Low temperature heat capacity and magnetic property of two H2ZTO-Co(II) coordination polymers (H2ZTO = 4,4′-azo-1,2,4-triazol-5-one)

In this paper, two new H2ZTO-Co(II) coordination polymers (H2ZTO = 4,4′-azo-1,2,4-triazol-5-one), [Co(H2ZTO)2(H2O)4](NO3)2 (1) and {[Co(H2ZTO)(H2O)4](NO3)2·2H2O}n (2), have been synthesized and characterized. Polymer 2 is derived from 1 and undergoes a multistage transformation by soaking 1 in distilled water. X-ray single crystal structure analyses showed that 2 exhibit a one-dimensional (1D) chain geometry coordinated by 0D units of 1 through uncoordinated nitrogen atoms of H2ZTO ligands. The thermal decomposition behaviors and magnetic properties of 1 and 2 were discussed. In addition, the low-temperature (1.9-300 K) heat capacities of 1 and 2 were measured using the heat capacity option of a Quantum Design Physical Property Measurement System (PPMS). The thermodynamic functions of 1 in the experimental temperature range were derived by fitting the heat capacity data to a series of theoretical and empirical models. Using the fitted heat capacity results, the standard molar entropy and standard molar enthalpy have been respectively calculated to be (871.1 ± 8.7) J·mol−1·K−1 and (132.7 ± 1.3) kJ·mol−1 for 1.