Proton NMR study of the stoichiometry, stability and thermodynamics of complexation of Ag+ ion with octathia-24-crown-8 in binary dimethylsulfoxide-nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Ag+ with octathia-24-crown-8 (OT24C8) in a number of binary dimethylsulfoxide (DMSO)–nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed OT24C8 was fast on the NMR time scale and only a single population average 1H signal was observed. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shiftmole ratio data. There is an inverse relationship between the complex stability and the amount of DMSO in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of formation constants. In all solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. The TDS versus DH plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reaction.