The rare earth complex, Gd(C7H5O3)(2)center dot(C9H6NO), was synthesized by the reaction of Gadolinium nitrate hexahydrate with salicylic acid (C7H6O3) and 8-hydroxyquinoline (C9H7NO). And it was characterized by elemental analysis, UV spectra, IR spectra, molar conductance and thermogravimetric analysis. In a optimalizing calorimetric solvent, the dissolution enthalpies were determined by an advanced solution-reaction isoperibol microcalorimeter, respectively: Delta H-s(m)(-) [2C(7)H(6)O(3)(s) + C9H7NO(s), 298.15 K] = 41.95 +/- 0.44 kJ mol(-1), Delta H-s(m)(-) [Gd(NO3)(3)center dot 6H(2)O(s), 298.15 K] = -29.11 +/- 0.39 kJ mol(-1), Delta H-s(m)(-) [Gd(C7H5O3)(2)center dot(C9H6NO)(s), 298.15 K] = -46.99 +/- 0.39 kJ mol(-1) and Delta H-s(m)(-) [Solution D(aq), 298.15 K] = -90.33 +/- 0.37 kJ mol(-1). The enthalpy change of the synthesized reaction was estimated to be Delta H-r(m)(-) = 211.54 +/- 0.69 kJ mol(-1). From data in the literature, through Hess' law, the standard molar enthalpy of formation of Gd(C7H5O3)(2)center dot(C9H7NO)(s) was calculated to be Delta H-f(m)(-) [Gd(C7H5O3)(2)center dot(C9H6NO)(s), 298.15 K] = -1890.7 +/- 3.1 kJ mol(-1). (C) 2012 Elsevier B.V. All rights reserved.