Spectrophotometric Study of Complex Formation Between Iodine and Some Thiacrown Ethers in Chloroform Solution

Abstract

Formation of the charge-transfer complexes betweenhexathia-18-crown-6, pentathia-15-crown-5,tetrathia-12-crown-4 and iodine in chloroform solution wasinvestigated spectrophotometrically. The molar absorptivities and formation constants of the resulting 1 : 1 molecularcomplexes were determined. The stability of the iodine complexes increased with the increasing number of donating sulfur atoms in thecrown ether ring. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. All molecular complexes formed were enthalpy stabilized, but entropy destabilized. From the thermodynamic data obtained, theTΔ S° - Δ H° plot shows a fairly good linear correlation, which indicates enthalpy-entropycompensation in the reactions.