Thermodynamic studies of sitting-atop (SAT) complexation of uranyl and free base meso -tetraarylporphyrins

Abstract

The interaction of uranyl with meso-tetraphenylporphyrin and its para-substituted derivatives (H2t(4-X)pp, X : H, Br, Cl, CH(CH3)2, OCH3, CH3) in chloroform produced 1 : 1 sitting-atop (SAT) complexes ((uranyl)H2t(4-X)pp). Formation constants were calculated by computer fitting of complex absorbance versus mole ratio data to appropriate equations and found to decrease with temperature increase. Thermodynamic parameters, ΔG 0, ΔH 0 and ΔS 0 were obtained. The formation constants vary with changing of the substituent on the aryl rings of H2t(4-X)pp in the following order: (uranyl)H2t(4-OCH3)pp > (uranyl)H2t(4-CH3)pp > (uranyl)H2t(4-CH(CH3)2)pp > (uranyl)H2tpp > (uranyl)H2t(4-Br)pp > (uranyl)H2t(4-Cl)pp.