Termoquimica dos adutos de haletos da familia do zinco com bases de Lewis : estimativa de algumas entalpias de dissociação metal-ligante

AUTOR(ES)
DATA DE PUBLICAÇÃO

1992

RESUMO

The mean enthalpies of metal-ligand bond dissociation in MX2.nL adducts (M = Zn; X = Cl, Br; n = 1, 2; L = Lewis bases with CO, PO, N(aromatic), NO groups) was determined by using of extra-thermodynamic hypothesis that the molar enthalpy of adduct sublimation has the same value as the molar enthalpy of vaporization or sublimation of the ligand (hypothesis A). In order to find more arguments in favour of this hypothesis, other alternatives were studied for evaluating the D(M-Y) and the DsubH in some adducts: 1st. alternative: The molar enthalpy of ZnCl2 dissolution in liquid ligand (experimentally determined) can be partitiened in to several terms, in a thermochemical cycle. These terms are the enthalpy of halide sublimation, the enthalpy of halide reorganization, the enthalpy of cavity formation in solvent with the same size of solute molecules, and the enthalpy of solute solvent (ligand). The last term, the only unknown, was calculated. Considering the same structure in solvated ZnCl2 as in the solid adduct, when the interaction term is 2D(M-Y). The results agree well with hypothesis A. 2nd. alternative: The molar enthalpy of vaporization or sublimation for any substance was related, by a thermochemical cycle, to the enthalpy of dissolution of the same substance in a poor solvatant solvent (experimentally determined) and the enthalpy of solvation. This can be calculated using the enthalpy of molecular cavity formation and another extra-thermodynamic hypothesis where the enthalpy of solute-solvent is the same for adduct and ligand. The results agree with hypothesis A. 3rd. alternative. By Sanderson s theory on bond energy and bond order - bond length empirical correlation, it was possible to calculate D(M-Y) for some adducts. The results agree well with those of hypothesis A.

ASSUNTO(S)

termoquimica entalpia

ACESSO AO ARTIGO

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