Thermochemical study on the Schiff base [H2salen = N,N′-bis(salicylidene) ethylendiamine] and its binuclear copper (II) complex

• Thermochemical cycles of two synthetic reactions were designed.
• The dissolution enthalpies were measured by a solution-reaction calorimeter.
• According to the Hess's law, we obtained the standard molar enthalpies of formation.

The Schiff-base ligand [H2salen = N,N′-bis(salicylidene) ethylendiamine] and the binuclear copper (II) complex [Cu2(salen)2(μ − O)2] were synthesized and the structure of the complex was characterized by X-ray crystallography. Two thermochemical cycles were designed on basis of Hess's law. According to the two cycles, the dissolution enthalpies of relevant substance in the calorimetric solvent of DMF were determined by a solution-reaction isoperibol calorimeter. The measurement experiment was performed at a constant ambient temperature of 298.15 K. After that, the rationality of these two thermochemical cycles was demonstrated by UV spectra and refractive indexes. Base on the measurement results and relevant literature data, the standard molar enthalpies of formation of the Schiff base and the complex were reckoned to be: ΔfHmθ[H2salen(s), 298.15 K]=−(146.4 ± 1.9) kJ mol−1; ΔfHmθ[Cu2(salen)2(μ−O)2(s), 298.15 K]=−(171.8 ± 3.9) kJ mol−1.