Thermochemical analysis on rare earth complex of gadolinium with salicylic acid and 8-hydroxyquinoline

The rare earth complex, Gd(C7H5O3)2·(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: ΔsHmΘ [2 C7H6O3(s) + C9H7NO(s), 298.15 K] = 41.95 ± 0.44 kJ mol−1, ΔsHmΘ [Gd(NO3)3·6H2O(s), 298.15 K] = −29.11 ± 0.39 kJ mol−1, ΔsHmΘ [Gd(C7H5O3)2·(C9H6NO)(s), 298.15 K] = −46.99 ± 0.39 kJ mol−1 and ΔsHmΘ [Solution D(aq), 298.15 K] = −90.33 ± 0.37 kJ mol−1. The enthalpy change of the synthesized reaction was estimated to be ΔrHmΘ=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·(C9H7NO)(s) was calculated to be ΔfHmΘ [Gd(C7H5O3)2·(C9H6NO)(s), 298.15 K] = −1890.7 ± 3.1 kJ mol−1.

► A new novel rare earth complex Gd(C7H5O3)2·(C9H6NO) was synthesized and characterized.
► The dissolution enthalpies of the relevant substances were determined.
► The enthalpy change of the reaction was determined to be (211.54 ± 0.69) kJ mol−1.
► The standard molar enthalpy of formation of complex was −(1890.7 ± 3.1) kJ mol−1.