Low temperature heat capacity study of Co3(BTC)2·12H2O and Ni3(BTC)2·12H2O

Abstract

Metal-organic coordination compounds have been extensively concerned in recent years due to their attracting chemical and physical properties. However, their thermodynamic properties have not been well investigated compared with the other properties, which would limit understanding their relationship between molecular structure and functional performance from a basic thermodynamic view. In the present work, two crystalline compounds of Co3(BTC)2·12H2O (1) and Ni3(BTC)2·12H2O (2) (BTC = 1,3,5- benzenetricarboxylate) have been designed and synthesized using a solvothermal method. The variable-temperature magnetic susceptibilities of these two compounds have been measured and the results revealed that compounds 1 and 2 possessed antiferromagnetic interaction between CoII/NiII ions. Low temperature heat capacities of these two compounds have been measured using a heat capacity option of Physical Property Measurement System in the temperature range from (1.9 to 300) K, and a Schottky effect has been revealed in the heat capacity curve below 10 K. The experimental heat capacity data have been fitted to a series of theoretical and empirical heat capacity models, and the corresponding thermodynamic functions such as enthalpy and entropy have been calculated in the temperature range from (0–300) K based on these models and fitting parameters. Also, the entire Schottky effect peak has been well presented in the heat capacity curve using these fitted heat capacities. The thermodynamic properties obtained in this work may provide significant thermodynamic basis for further investigating the related functional properties of these two compounds.