Discussion on the complexing ability of macrocyclic ligand, 12-crown-4 with Li+ cation in some binary mixed non-aqueous solvents

The complexation reaction of Li+ cation with 12-crown-4 (12C4) was studied in acetonitrile (AN)-methanol (MeOH), nitromethane (NM)-dimethylformamide (DMF) and propyl en carbonate (PC)-dimethylformamide (DMF) binary mixtures and in neat tetrahydrofuran (THF) at different temperatures using the conductometric method. The conductance data show that in all solvent systems, the stoichiometry of the complex formed between 12-crown-4 and Li+ cation is 1:1. The stability of (12C4-Li)(+) complex is sensitive to the solvent composition. The stability order of the complex in pure non-aqueous solvents was found to be: AN > MeOH > PC > THF > DMF. The values of thermodynamic parameters (Delta H-c(0), Delta S-c(0)) for formation of (12C4-Li)(+) complex were obtained from temperature dependence of the stability constants and the results show that the thermodynamics of complexation reaction is affected by the nature and composition of the mixed solvents. A non-linear behaviour is observed between the thermodynamic parameters and the composition of the mixed solvents.