Sintese, caracterização e termoquimicade adutos entre metil, N, N -dimetil e tetrametilureia com haletos de zinco, cadmio e mercurio-II

AUTOR(ES)
DATA DE PUBLICAÇÃO

1980

RESUMO

The reactions of zinc, cadmium and mercury halides with the ligands methylurea (MU), N,N´-dimethylurea (DMU) and tetramethylurea (TMU) yielded the following adducts: ZnL2X2, MLX2 (M = Cd, Hg) (X = Cl, Br and L = MU, DMU and TMU), M(TMU)2I2 (M = Zn, Cd), Cd(DMU)3Br3 and Hg(DMU)2Cl2. These adducts were characterized by elemental analyses, melting points, conductance measurements, thermogravimetric, infra red spectra and mass spectra. From the values of standard enthalpies of dissolution of the halides, ligands and adducts in suitable calorimetric solvents, the standard enthalpy of the reaction was calculated: MX2(s) + nL(s, l) = l MLnX2 l (s); DHR For the obtention of the standard enthalpies of formation (DHf) of the adducts DHR values were used. It was also necessary to determine the standard enthalpies of formation of DMU and MU, which were obtained by means of combustion calorimetry. The standard enthalpies, DHD and DHM, for the equations below were also calculated, however, it was necessary to determine MLnX2(s) = MX2(s) + nL(g); DHD MLnX2(s) = MX2(g) + nL(g); -DHM the standard enthalpy of vaporization of TMU and the standard enthalpies of sublimation of DMU and MU. The thermal data in conjuntion with the mass spectra of the adducts suggest that possibly these compounds do not exist, at least in appreciable amounts in the gaseous phase. However, the enthalpy of the metal-oxygen bond was estimated, based on the fact that this mode of coordination has occured with these three ligands, in agreement with the infra red results. The DHR parameter establishes the order of basicity, TMU >DMU >MU, and the acidity order of the metals, Zn >Cd >Hg.

ASSUNTO(S)

termoquimica

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