Solvent influence upon complex formation between kryptofix5 and Cd~(2+) in some pure and binary mixed non-aqueous solvents using conductometry

摘要

The complexation reaction of Cd~(2+) with l,13-bis(8-quinolyl)-l,4,7,10,13-pentaoxatridecane (kryptofix5) was studied in pure acetonitrile (AN), ethylacetate (EtOAc), methanol (MeOH), dimethylformamide (DMF), and in acetonitrile-ethylacetate (AN-EtOAc), acetonitrile-dimethylform-amide (AN-DMF), methanol-acetonitrile (MeOH-AN), and dimethylformamide-ethylacetate (DMF-EtOAc) binary mixed solvent solutions at different temperatures using conductometric method. The conductance data show that the stoichiometry of the complex in all solvent systems, is 1 :1 [ML]. The fitting and experimental curves were obtained from Sigma plot computer program to make it more clear of the 1:1 [ML] complexation model. The stability constant of (kryptofix5-Cd)~(2+) complex was obtained using a GENPLOT computer program. The results show that the stability of (kryptofix5-Cd)~(2+) complex at all studied temperatures in the binary solvent solutions decreases in order: AN-EtOAc>AN-MeOH> AN-DMF ~ EtOAc-DMF and in pure non-aqueous solvents, the stability order of the complex was found to be: AN>EtOAc> MeOH > DMF. The values of standard thermodynamic parameters ( ΔH_c°, ΔS_c°) for formation of the complex were obtained from temperature dependence of the stability constant using the van't Hoff plot. The results show that in most cases, the complex formation reaction between kryptofix5 and Cd~(2+) is entropy stabilized.