METAL COMPLEXES OF TRIAZINE SCHIFF BASES: SYNTHETIC, THERMODYNAMIC, SPECTROSCOPIC, AND ELECTROCHEMICAL STUDIES ON COMPLEXES OF SOME DIVALENT AND TRIVALENT METAL IONS OF 3-(α-BENZOYLBENZYLIDENHYDRAZINO)-5,6-DIPHENYL-1,2,4-TRIAZINE

Abstract

Metal complexes of some divalent and trivalent metal ions, viz. Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pr(III), Nd(III), Sm(III) and Yb(III) with a Schiff base 3-(α-benzoylbenzylidene-hydrazino)- 5,6-diphenyl-1,2,4-triazine (HBZDT) have been investigated potentiometrically, spectrophotometrically and electrochemically and found to have the metal : ligand ratios 1 : 1 and 1 : 2. The dissociation constant of the ligand and the formation constants of the metal-ligand complexes have been determined potentiometrically at different temperatures and 0.1 M ionic strength (KNO₃) in 75% (v/v) dioxan-water solution. The standard thermodynamic parameters, viz. Δ G°, ΔH°, and ΔS°, terms for dissociation and the stepwise formation of the metal-ligand complexes have been evaluated. The thermodynamic functions have been analyzed in terms of the electrostatic (el) and non-electrostatic (non) components. ΔH° _non was found to be linearly correlated with the acceptor number of the metal ion (AN_M), whereas ΔH° _el was correlated with the ionic radii of the metal ion. Van't Hoff plots show a common point of intersection (IKR) at an isokinetic temperature, T_iso, of 306.25K and 300.26K for both K₁ and K₁* K ₂. Polarographic reduction of the free ligand and its Cu(II) complexes are irreversible and diffusion controlled. UV/Vis and IR spectroscopy have been used to characterize the free ligand (HBZDT) and its complexes with Cu(II), Ni(II) and Co(II) ions. The formation constant values obtained from spectrophotometric and electrochemical studies are found to be consistent with those obtained from potentiometric studies.

Acknowledgments