Solvent influence upon complex formation between 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane with samarium(III) metal cation in binary mixed non-aqueous solvents

The complexation reaction of macrocyclic ligand, 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (kryptofix 22 DD) with Sm 3+ cation was studied in acetonitrile-1,2-dichloroethane (AN–1,2-DCE), acetonitrile–methylacetate (AN–MeOAc), acetonitrile–ethylacetate (AN–EtOAc) and acetonitrile–methanol (AN–MeOH) binary mixtures at different temperatures using conductometric method. The conductance data show that in most of the solvent systems, the stoichiometry of the complex formed between kryptofix 22 DD and Sm 3+ cation is 1: 1 [M: L]. But, in some cases a 2: 2 [M 2 L 2 ] complex is formed in solution. The stability constant of the resulting complex in binary mixed non-aqueous solvents decreases in the order AN–EtOAc > AN–MeOAc > AN–1,2-DCE > AN–MeOH. A non-linear behavior was observed for changes of log K f of (kryptofix 22 DD·Sm) 3+ complex vs. the composition of the binary mixed solvents. The obtained results show that the stability of the complex is quite sensitive to the composition of the mixed solvents. The values of thermodynamic quantities (ΔH° c and ΔS° c ) for formation of (kryptofix 22 DD·Sm) 3+ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots. The results show that in most cases the complex is entropy stabilized and both parameters are affected by the nature and composition of the mixed solvents.