Spectrophotometric Studies of the Thermodynamics of Molecular Complexation between Free Base Meso-Tetraarylporphyrins and Iodine(III) Chloride

Abstract

A spectrophotometric method was used for the molecular complexation of ICl3 with para-substituted meso-tetraarylporphyrins (H2t(4-X)pp; X: OCH3, CH(CH3)2, CH3, H and Cl) in methanol/chloroform (2.5% v/v) solution. The equilibrium constants and the thermodynamic parameters were measured spectrophotometrically at various temperatures for 1:1 molecular complex formation of meso-tetraarylporphyrins as electron donors with ICl3 as the electron acceptor. The formation constants for the molecular complexes change according to the following trend: [ICl3(H2t(4-OCH3)pp)]>[ICl3(H2t(4-CH(CH3)2)pp)]>[ICl3(H2t(4-CH3)pp)]>[ICl3(H2tpp)]>([ICl3(H2t(4-Cl)pp)]. Further, the thermodynamic parameters, ΔG o,ΔH o and ΔS o, for formation of the complexes were obtained.