Thermodynamic study of charge-transfer complex of iodine with HT18C6 in chloroform solution

Abstract

A spectrophotometric study concerning the interaction between HT18C6 as n-donor and I₂ as s-acceptor has been performed in chloroform solution at different temperatures. The results are indicative of the formation 1:1 complex through equilibrium reaction. The stability constant of the complex at 7, 13, 19 and 25 ^oC is obtained by the computer-fitting of absorbance-mole ratio data in MATLAB software. The ΔH^o and ΔS^o values are obtained by the Vant Hoff method. The obtained data show that the complex is enthalpy stabilized and entropy destabilized. The entropy destabilitization is attributed to the decrease of the entropy of the free donor upon complexation. Comparison of the data from this work with those of previous works done on 18C6-I₂ and HA18C6-I₂ is indicative of different stability, stoichiometry and products. The possible reasons for such differences are discussed.

KEY WORDS: Charge-transfer complex, Iodine, HT18C6, Stability constant, Thermodynamic data, Spectrophotometry, Chloroform

Bull. Chem. Soc. Ethiop. 2008, 22(2), 287-294.