Stepwise Stability Constants and Thermodynamic Functions of Di-p-tolylthiovioluric Acid Complexes with Transition Metals

Department of Chemistry, University of Delhi, Delhi-110 007, (India) Manuscript received 14 May 1976, revised 20 September 1977, accepted 7 July 1978 The complexes of transition metal ions with di-p-tolylthiovioluric acid have been investigated by the potentiometric technique in 75% aqueous dioxan media in the presence of 0.1M sodium perchlorate. The proton-ligand stability constants and the stepwise formation constants of the complexes have been determined by Calvin-Bjerrum's pH-titration technique modified by Irving and Rossotti. The log K values have been computed by the weighted least Square's method. The values of stepwise and overall changes in ∆G°, ∆H° and ∆S° accompanying the complex formation reactions have been evaluated by carrying out the experiments at 30°, 40°, 45° and 50°. It is found that as the temperature increases the stability of complexes decreases