Complexation of Zn(II) by Catechol in Hydroxylic Solvents

M. I. SANCHO; A.H.JUBERT; S. E. BLANCO; F.H.FERRETTI; E.A.CASTRO

J. Arg. Chem. Soc

AQA

Lugar: Buenos Aires; Año: 2006 vol. 94 p. 143 - 155

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 the Becke hybrid three-parameter nonlocal exchange functional combined with the Lee-Yang-Parr dynamic correlation functional method (B3LYP/6-31G(d)) and using the isodensity polarized continuum model (IPCM). 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 that explains the changes of the complexation equilibrium constant with the permittivity of the reaction medium. The performed calculations allowed us to prove that the increase of the hydrogen-bond donor ability of the solvents favour a higher thermodynamic stability of the reactants with respect to the complex and, therefore a decrease of the corresponding equilibrium constants. The non-planar structure proposed for the complex is coherent with the experimentally observed hyperchromic shift. In the complex molecule the plane containing the aromatic ring is tilted by 18º approximately with respect to the plane that includes the zinc and oxygen atoms. It was concluded that the formation of the complex is an endothermic process.