Copper(II) trans-1,4-cyclohexanedicarboxylate (Cu(trans-1,4-OOCC6H10COO)) was synthesized, and the heat capacity was measured by adiabatic calorimetry between 13 and 300 K. A heat capacity anomaly due to the first-order phase transition was found at 160.0 K, and the enthalpy and entropy of transition were determined to be 413.4 J mol(-1) and 2.66 J K-1 mol(-)1, respectively. The sample was found to absorb a large amount of toluene, which were desorbed and re-absorbed reversibly. The reversibility of the absorption/desorption was confirmed by measurements of heat capacity; no phase transition was observed in the fully absorbed sample, but it reappeared in the desorbed sample. A sample that absorbed 11% toluene showed about a half size of the anomaly at 174 K in the heat capacity curve. (C) 2002 Elsevier Science B.V. All rights reserved.