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

Abstract

log K_f, ΔHº and ΔSº values are reported for the complexation   reactions of Cu²⁺, A^g+ and T^l+ metal cations with macrocyclic   ligand, 4′,4″,(5″)-ditert-butyldibenzyl-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_f 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 acetonitriledimethylformamide   binary solution, and in some cases, the   stability order is changed with the composition of the binary   solution. The values of the thermodynamic quantities (ΔH_cº,   ΔS_cº) for formation of (DTDB18C6-Cu²⁺), (DTDB18C6-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.