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|Type:||Artigo de periódico|
|Title:||Thermogravimetric and calorimetric study of cadmium iodide adducts with cyclic ureas|
|Author:||de Farias, RF|
|Abstract:||Adducts of general formula CdI2.nL [n = 1 and 2; L: ethyleneurea (eu) and propyleneurea (pu)] were synthesized by a solid state route and characterized by elemental analysis, infrared spectroscopy, thermogravimetry and reaction solution calorimetry. The infrared results shown that eu and pu coordinate through oxygen atom. All adducts release the ligand molecules in a single mass loss step, suggesting that, in the bisadducts, both ligand molecules are in equivalent coordination sites, exhibiting similar bond enthalpies. For all thermogravimetric curves, the first mass loss step is associated with the release of ligand molecules and the second one with the sublimation of cadmium iodide: CdI2.nL(s) --> CdI2(s)+nL(g);CdI2(s) --> CdI2(g). The observed thermal stability trend is: CdI2.eu (228 degreesC) > CdI2.pu (213 degreesC) > CdI2.2pu (200) > CdI2.,2eu (186 degreesC). The standard molar reaction enthalpy in condensed phase: CdI2(cr) +nL(cr) = CdI2.nL(cr); Delta(r)H(m)(theta), were obtained from reaction- solution calorimetry, to give the following values for mono and bisadducts: -7.16 and -27.61, -4.99 and -9.07 kJ mol(-1) for eu and pu adducts, respectively. Decomposition (Delta(D)H(m)(theta)) and lattice (Delta(M)H(m)(theta)) enthalpies, as well as the mean cadmium-oxygen bond dissociation enthalpy, D(Cd-O), were calculated for all adducts. (C) 2003 Elsevier B.V. All rights reserved.|
|Editor:||Elsevier Science Bv|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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