Copper(II) fumarate (Cu(OOCC2H2COO)) and copper(II) terephthalate (Cu(OOCC6H4COO)) have been synthesized, Their heat capacity has been measured by adiabatic calorimetry between 13 and 300 K and their magnetic susceptibility determined with a SQUID magnetometer between 5 and 300 K. No phase transition has been observed in the whole temperature range covered by the experiments. The thermodynamic properties of these compounds are compared with those of copper(II) trans-1.4-cyclohexane dicarboxylate, in which a structural first-order phase transition was observed at 160 K. (c) 2005 Elsevier B.V. All rights reserved.