Geometrical structure, potentiometric and thermodynamic studies of rhodanine azodye and its metal complexes

5-(2,3-Dimethyl-1-phenylpyrazol-5-one azo)-2-thioxo-4-thiazolidinone (HL) was synthesized and characterized using different spectroscopic techniques. The molecular structures of the ligand are optimized theoretically and the quantum chemical parameters are calculated. The proton-ligand dissociation constants of HL and its metal stability constants with Mn2 +, Co2 +, Ni2 + and Cu2 + have been determined potentiometrically. The potentiometric studies were carried out in 0.1 M KCl and 10% (by volume) DMF-water mixture. At constant temperature the stability constants of the formed complexes decreases in the order Cu2 +, Ni2 +, Co2 + and Mn2 +. The effect of temperature was studied at (298, 308 and 318 K) and the corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were derived and discussed. The dissociation process is non-spontaneous, endothermic and entropically unfavorable. The formation of the metal complexes has been found to be spontaneous, endothermic and entropically favorable