Tetrachlorocuprate (II) ethylenediammonium (C2H10N2)CuCl4(s) and tetrachlorocadmate (II) ethylenediammonium (C2H10N2)CdCl4(s) were synthesized. Chemical analysis, elemental analysis, and X-ray crystallography were applied to characterize the compositions and crystal structures of the two complexes. In accordance with Hess law, two thermochemical cycles were designed, and the enthalpy changes of the reactions of ethylenediamine dihydrochloride with CuCl2 center dot 2H(2)O(s) and CdCl2 center dot 2.5H(2)O(s) were determined as Delta H-r(m.1)0 = (5.89 +/- 0.22) kJ . mol(-1) and Delta H-r(m.2)0 = -(2.88 +/- 0.26) kJ . mol(-1) by use of an isoperibol solution-reaction calorimeter, respectively. The standard molar enthalpies of formation of the title complexes (C2H10N2)CuCl4(s) and (C2H10N2)CdCl4(s) were derived to be Delta H-r(m)0 [(C2H10N2)CuCl4. s] = -(784.51 +/- 1.35) kJ . mol(-1) and Delta H-r(m)0 [(C2H10N2)CdCl4. s]= -(960.99 +/- 1.36) kJ . mol(-1), respectively. (C) 2010 Elsevier Ltd. All rights reserved.