Solubility measurements and thermodynamic correlation of bis(imino)pyridine-based Cu and Ni complexes in pure solvents

In this work, the solubility of a bis(imino)pyridine-based ligand L = 2,6-Bis[1-(cyclohexylimino)ethyl]pyridine and its two metal complexes LCuCl₂ and LNiCl₂ is measured by static equilibrium method in four selected solvents. These complexes are widely used in catalysis, polymerization, cycloaddition reactions, anticancer drugs, and in optoelectronic materials where the solvation process has a critical impact on their properties. The solubility data is vital for improving the crystallization process and the efficiency of homogeneous catalysis. Six thermodynamic models (Apelblat, Polynomial, Yaws, Vant's Hoff, λh, and NRTL) are applied to analyze the solubility values of LH and four models (Apelblat, Polynomial, Yaws, Vant's Hoff) are applied for both metal complexes LCuCl₂ and LNiCl₂. To ensure the precision of experimental data, the ARD and RMSD values are calculated for accuracy evaluation. The solubility data of L indicates that dichloromethane is the best reaction solvent having its highest solubility value 7.515 × 10² x at 298.15 K and absolute ethanol is the best solvent for its crystallization. Similarly, the solubility data collected for LCuCl₂ and LNiCl₂ reveals that trichloromethane is the best reaction solvent having highest solubility values 4.188 × 10³ x and 4.279 × 10³ x respectively at 298.15 K and acetone is the crystallization solvent for both of these metal complexes. The polynomial model represents the optimal choice for accurately fitting the solubility data related to all three examined compounds having average ARD values less than 1 %. Hirshfeld surface analysis show that H⋯H contacts are the most significant interactions, about 68.2 % in the compound LCuCl₂. Moreover, molecular electrostatic potential indicates that the N atom and the metal centers of the two compounds exhibit distinct electronegativity. In addition, functions related to apparent thermodynamics were obtained. The dissolution process proved endothermic and entropy rose in the experimental settings, with spontaneous energy accounting for the variation in solubility.