Spectrophotometric evaluation of solvent effect on the stability constant of charge transfer complexes of FeIII with 5-sulphosalicylic acid and 5-chlorosalicylic acid

The charge transfer complex (CTC) formed by Fe-III with 5-sulphosalicylic acid 5-chlorosalicylic acid were studied using spectrophotometric method in mixed solvent system. Four solvent mixtures were taken having variation in amount of 1,4-dioxane as 5, 10, 15 and 20%. In acid range of pH 1-3, both the ligands formed 1 : 1 complex. A graphical method with computer software program was developed for determination of stability constant and molar absorptivity of 1 : 1 complex at pH 2.35 +/- 0.05 and ionic strength 0.1 M, maintained by NaClO4. This approach gave better value than obtained from graphical method neglecting certain terms to make a linear plot. It was observed that both the value of stability constant as well as molar absorptivity increases with increase in the percentage of 1,4-dioxane in the mixed Solvent.