The crystals of four complexes of rare earth perchlorate with DL-alpha-alanine and imidazole were synthesized and characterized. The components of them were determined to be [RE(C3H7NO2)(2)(C3H4N2)(H2O)](ClO4)(3) (RE: Sm, Eu, Dy, Er) by FT-IR, chemical, elemental and thermal analysis. The enthalpies of dissolution of [2C(3)H(7)NO(2)(s) + 3NaClO(4)(s)] [C3H4N2(s) + RECl3 . 6H(2)O(s)] and [3NaCl(s)], { [RE(C3H7NO2)(2)(C3H4N2)(H2O)](ClO4)(3)(s)} Were determined by a solution-reaction isoperibol calorimeter at T = 298.15 K, respectively. According to Hess's law, the standard molar enthalpies of reaction of four reactions, RECl3 . 6H(2)O(s) + 2C(3)H(7)NO(2)(s)+ C3H7N2(s)+ 3NaCl(s) = [RE(C3H7NO2)(2)(C3H4N2)(H2O)](ClO4)(3)(s) + 3NaCl(s) + 5H(2)O(1) (RE: Sm, Eu, Dy, Er) were determined to be 4.87 +/- 0.20, 7.23 +/- 0.19, 0.96 +/- 0.27and 12.88 +/- 0.32 kJ mol(-1), respectively. The standard molar enthalpies of formation of the four complexes at T = 298.15K, Delta(f)H(m)(Theta) {[Re(C3H7NO2)(2)(C3H4N2)(H2O)](ClO4)(3)(s)} (RE: Sm, Eu, Dy, Er), were determined to be -(2448.1 +/- 3.3),-(2360.3 +/- 3.3),-(2451.8 +/- 3.3) and -(2444.3 +/- 3.3) U mol(-1), respectively. (C) 2004 Elsevier B.V. All rights reserved.