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  • Know Res., 2015, 2(3),  pp 138-145  

    DOI:10.7598/kor2015.131

    Research Article

    Studies on Stability Constants of the Complexes of 2,3 - Dihydroxybenzal-dehyde and its Schiff Bases with Cu(II), Zn(II), Ni(II), Co(II), Cd(II) and Mg(II) Metal Ions in 50% (v/v) Water ? Ethanol Mixture at 0.1M Ionic Strength

  • CHINNAPPA C.HADIMANI*, SANDEEP R. KURUNDAWADE and BASAVAKUMAR S.SHETTAR
  • Department of Chemistry, B.V.B. College of Engineering and Technology, Vidyanagar, Hubli-580 031, Karnataka, India
  • Abstract

    The proton-ligand stability constants of 2,3 dihydroxy benzaldehyde (2,3DHB), N-[2,3 dihydroxy benzaldehyde]aniline (2,3DHBA), N-[2,3 dihydroxy benzaldehyde]o-chloroaniline (2,3DHBOCA), N-[2,3 dihydroxy benzaldehyde]m-chloroaniline (2,3DHBMCA) and N-[2,3 dihydroxy benzaldehyde]p-chloroaniline (2,3DHBPCA) and the stability constants of their complexes with bivalent Cu, Zn, Ni, Co, Cd and Mg have been determined employing Calvin-Bjerrum titration techniqueas adopted by Irving and Rossotti in 50% (v/v) water-ethanol medium at 15, 25, 35 and 45 0C and at an ionic strength of 0.1 M NaClO4. The order of stability constants was found to be Cu(II)>Ni(II)>Co(II)>Zn(II)>Cd(II)>Mg(II) which is in agreement with the Irving-Williams order of stability of the bivalent metal complexes. The logK values of the complexes were plotted against the atomic number, ionic radii, electronegativity and ionization potentials of the metal ions. The formation constants were found to increase with the increase in the above periodic properties, but decreases with increase in temperature. The values of ∆G, ∆H and ∆S have also been calculated for the various complex equilibria. The Cu-chelate is found to be relatively more stable than that of the Ni-chelate and Zn-chelate due to difference in their configurations. The former forms square planar complex while the latter gives a tetrahedral or octahedral complex. The logK values for Zn-chelate are found to be higher as compared to that of Nickel.

    Keywords

    Stability constant, Protonation constant, Schiff base, Chelate

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