Preparation and Thermochemical Properties of Ternary Complexes of Rare Earth Chlorides with Nicotinic Acid and 8-Hydroxylquinoline

Two solid ternary complexes were synthesized by using three raw materials: rare earth chlorides, nicotinic acid (C6H5NO2, HL), and 8-hydroxylquinoline (C9H7NO, Hhq) in a water bath (333.15 K). During the process of coordination, HL was bidentate-coordinated with rare earth ions (RE3+) through an acidic group which was formed by removing the proton; the hydroxyl oxygen atom and heterocyclic nitrogen atom of hq(-) formed a chelate ring with RE3+ for coordination. At a constant temperature of 298.15 K, the dissolution enthalpies of the reactants and the products of the designed thermochemical cycle in the calorimetric solvent (V-HCl/V-DMF/V-EtOH = 3:1:1) were determined by a solution-reaction isoperibol calorimeter, respectively. At the same time, the rational design of the thermochemical cycle was verified by UV spectra and refractive indexes. Finally, supported by the thermodynamic data from literature, the standard molar enthalpies of formation of the two complexes were estimated to be: Delta H-f(m)Theta [LaL2 center dot hq center dot 2H(2)O(s), 298.15 K] = -(2181.1 +/- 2.4) kJ.mol(-1); Delta H-f(m)Theta [CeL2 center dot hq center dot 2H(2)O(s), 298.15 K] = -(2102.7 +/- 2.4) kJ.mol(-1).