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

摘要

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 Y b(III) with a Schiff base 3-(#alpha#-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 (KNO_3) in 75 percent (v/v) dioxan-water solution. The standard thermodynamic parameters, viz. #DELTA#G ~0, #DELAT#H ~0, and #DELTA#S ~0, 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. #DELTA#H ~0_(non) was found to be linearly correlated with the acceptor number of the metal ion (AN_M), whereas #DELTA#H ~0_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 K_1 and K_1 * 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.