Complexing ability of kryptofix5 with Ag+ in some binary mixed solvents at different temperatures

Abstract

The stability constant (log Kf ) for complexation of 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix5) with Ag+ has been determined conductometrically in acetonitrile–ethyl acetate (AN–EtOAc), methanol–ethyl acetate (MeOH–EtOAc), methanol–water (MeOH–H2O) and dimethyl sulfoxide–ethyl acetate (DMSO–EtOAc) solutions at different temperatures. A 1 : 1 [ML] complex was formed between the metal cation and ligand in most solvent systems. The stability constant of the resulting 1 : 1 complex was determined from computer fitting of the conductance–mole ratio data. The stability order of the (kryptofix5.Ag)+ complex in the studied binary mixed solvent solutions at 25°C was found to be MeOH–EtOAc > AN–EtOAc > DMSO–EtOAc. The results show that in some cases the stoichiometry of the complex formed between Ag+ and the ligand changes with the nature of the solvent and that solvation numbers of the metal cation and the resulting complexes change with temperature. The values of the standard thermodynamic parameters (, ) show that in all cases the (kryptofix5.Ag)+ complex is entropy stabilized, but the enthalpy, depending on solvent system, is stabilizing or destabilizing.