Complexation of Zn(II) by catechol in hydroxylic solvents

the stability of the complex formed by one molecule of 1,2-dihydroxybenzene and one molecule of zinc acetate in solutions with different permittivity and temperature was investigated by means of spectroscopic and chromatographic methods. the becke hybrid three-parameter nonlocal exchange functional combined with the lee-yang-parr dynamic correlation functional method (b3lyp/6-31g(d)) and the isodensity polarized continuum model (ipcm) were used in the calculations. it was assumed that the formation of the complex takes place by a reaction between ions of opposite charges. it was also proposed an equation to explain the changes of the constant of the complexation equilibrium with the permittivity of the reaction medium. the calculations allowed us to prove that the increase of the hydrogen-bond donor ability of the solvents favours a higher thermodynamic stability of the reactants with respect to the complex and, as a result, a decrease of the corresponding equilibrium constants. the non-planar structure proposed for the complex is consistent with the experimentally observed hyperchromic shift. the plane, in the complex molecule, containing the aromatic ring is tilted by approximately 18o with respect to that of the zinc and oxygen atoms. it was concluded that the formation of the complex is an endothermic process.