Complexes of Zn(II) and Cd(II) with 4-(2-pyridylazo)resorcinol sorbed on sephadex QAE: characterization and theoretical study

The nature of the complexes produced in the reaction between Zn(II) or Cd(II) and 4-(2-pyridylazo)resorcinol (PAR), sorbed on a Sephadex QAE anion exchanger have been studied. The visible and IR absorption spectra of the species fixed on the exchanger have been established; the stoichiometry of the complexes is 1:2 (metal:ligand).To propose a structure for the metal complexes, semi-empirical molecular orbital calculations have been performed for the dianionic form of PAR (L2-) and for its complexes ZnL2-2 and CdL2-2 by means of the SPARTAN program. The role of MOs for the ligand in possible coordination to metal ions is discussed and a distorted octahedral structure is proposed for both complexes. For comparison, Zn(HL)2·H2O and Cd(HL)2·H2O have been synthesized and characterized by the normal instrumental techniques. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)