Abstract
The Calvin–Bjerrum pH titration technique as modified by Irving and Rossotti has been applied to determine the stability constants of complexes of a series of thioligands, namely benzaldehyde thiosemicarbazone, pyridine-2-carbaldehyde thiosemicarbazone, and cyclopentanone thiosemicarbazone with divalent metal ions (Cu, Cd, Co, Ni, Pb, and Zn). The studies were carried out in 50% v/v dioxane-water at different temperatures (293 K, 303 K, and 313 K) keeping ionic strength at 0.1 mol KNO3. The thioligands undergo deprotonation of only one proton (–N2H–) of a thiosemicarbazone [R1R2C2=N3–N2(H)–C1(=S)N1H2]. Thermodynamic parameters, such as free energy, enthalpy, and entropy have also been evaluated. The investigations represent the first report of the solution phase studies in metal–thiosemicarbazone chemistry.
Acknowledgment
The authors are grateful to CSIR for financial support.