Therodynamic studies on complexation of Cu2+, Ag+ and Tl+ metal cations with 4′,4",(5")-ditert-butyldibenzyl-18-crown-6 in acetonitrile-dimethylformamide binary solutions

log K-f Delta H degrees and Delta S degrees values are reported for the complexation reactions o fCu(2+), Ag+ and Tl+ metal cations with macrocyclic ligand, 4',4 '',(5 '')-ditet-t-butyidibehzyl-18-crown-6 (DTDB18C6) in acetonitrile-dimethylformamide binary solutions (AN-DMF) at different temperatures, using conductometric method. The conductance data show that in most cases, the stoichiometry of the complexes formed between DTDB18C6 and these metal cations is 1:1 (M:L). The values of log K, of the complexes are sensitive to the solvent composition and it was found that the stability sequences of the complexes are changed with the composition of acetonitrile-dimethylformamide binary solution, and in some cases, the stability order is changed with the composition of the binary solution. The values of the thermodynamic quantities (Delta H-c degrees, Delta S-c degrees) for formation of (DTDB 18C6-Cu2+), (DTDB 18C6-Ag+) and (DTDB18C6-Tl+) complexes were obtained from the temperature dependence of the stability constants and the results show that in most solution systems, the complexes are enthalpy stabilized but entropy destabilized.