The title complex [Pr(H(2)vanen)(NO3)(2)(H2O)(2)-NO3] was synthesized reacting of Valen Schiff-base ligand [H2vanen N,N' -ethylene-bis(3-methoxysalicylideneimine)] and Pr(NO3)(3).6H(2)O in ethanol at 60 degrees C. The complex was crystallized in the monoclinic crystal system with space group P21/c. The coordination polyhedron of Pr(III) ion was consisted of two bidentate nitrate ions, two molecules of water and one ligand which coordinated through oxygen atoms of the two phenolic and methoxy groups. After designing two reasonable thermochemical cycles according to Hess's law, the calorimetric experiments were conducted using isoperibol solution-reaction calorimeter at a constant temperature of 298.15 K. The standard molar enthalpy changes of two reactions were determined to be Arfig,(1a) = -(51.94 1.26) kJ mo1-1 and Artegib) = -(8.62 1.34) kJ mo1-1. Then the standard molar enthalpies of formation of the ligand and the title complex were calculated to be At- Ng, [H2vanen(s), 298.15K] = -(517.75 2.36) kJ mo1-1 and Affig, [Pr(H2vanen)(NO3)2(F120)2.NO3 (s), 298.15 Kl= -(2454.8 2.7) kJ mol-1, respectively. The rationality of two thermochemical cycles was verified by UV spectra and refractive indexes. (C) 2014 Elsevier B.V. All rights reserved.