Solubility measurements and thermodynamic fitting of two organoaluminium complexes supported by pyridinyl Schiff base ligands in mono-solvents

Pyridinyl Schiff base ligands and their supporting organoaluminium compounds have diverse applications in catalysis, medicine, and electrochemistry. In this study, solubility data for two ligands (L1 = 2-(OH)C₆H₄CH = N(C₅H₄N), L2 = 2-(OH)-5-ClC₆H₃CH = N(C₅H₄N)) and two organoaluminium compounds (C1 = [2-O-C₆H₄CH = NC₅H₄N)]AlMe₂, C2 = [2-O, 4-ClC₆H₃CHMeN(C₅H₄N)]₂Al₂Me₂) with differing configurations were obtained through static analysis. The data showed that at 298.15 K, for L1, the solubility (10²x) order was: toluene (42.339) > ether (23.085) > ethanol (5.025) ≥ methanol (4.888); for L2, it was: tetrahydrofuran (7.348) > dichloromethane (4.289) > toluene (3.387) > ether (1.210); and for C1 and C2, the order remained consistent as tetrahydrofuran (C1:9.192, C2:13.911) > toluene(C1:2.904, C2:6.036) > ether(C1:2.254, C2:4.358) > n-hexane(C1:0.783, C2:0.975). Subsequently, the solubility data were subjected to fitting using various thermodynamic models. The experimental findings revealed that the majority of the models exhibited good fits, with an average absolute relative deviation (ARD) of < 4 % and an average root mean square deviation (RMSD) of < 0.2 %. Notably, the Wilson model emerged as the most suitable for predicting the solubility of L1, while the Polynomial model demonstrated superior efficacy in predicting the solubility of L2, C1, and C2. In the case of the organic aluminium compound C2 with a distinct configuration, the formation of a dimerized dinuclear metal structure resulted in altered polarity, consequently influencing solubility in various solvents. Molecular electrostatic potential analysis revealed electron densities at the O atom, the NH moiety of the pyridine ring, and proximal regions of the metal atoms, indicative of electronegativity and facilitation of hydrogen bonding. Hirshfeld surface analysis underscored H···H contact as the predominant interaction among the four compounds. Additionally, calculations regarding the apparent thermodynamic functions of L1 and L2 revealed an endothermic dissolution process characterized by increased entropy and driven by enthalpy. These experimental findings provide valuable insights into the properties of pyridinyl Schiff base ligands and their associated organic aluminum compounds, revealing complex relationships among molecular structure, solubility, and thermodynamic properties. They offer valuable clues for further research and application in this field.