Compostos de adição entre percloratos e nitratos de alguns lantanideos(III) e a N-(2-piridil) acetamida (AAPH)

AUTOR(ES)

Francisco Santos Dias

DATA DE PUBLICAÇÃO

1977

RESUMO

The reaction of N-(2-pyridil) acetamide (AAPH) with some lanthanide (III) salts, in acetonitrile solution, under careful experimental conditions, produces solid compounds which show the following general formulae: Ln(ClO4)3.4AAPH (Ln = Nd, Eu, Gd, Ho, Yb e Lu) and Ln(NO3}3.2AAPH (Ln =: La, Nd, Eu, Gd, Ho and Yb). The compounds are not apparently hygroscopic, however, the nitrate adducts, when powdered under atmospheric conditions display a tendency to hygroscopicity. They show a small melting range and/ or decomposition (222.6-237.7)°C for the perchlorates and (173,0-193,1)°C for the nitrates, respectively. Crystals of the nitrates are more difficult to obtain than the perchlorates, problably because, among other factors, the perchlorate anion coordinates poorly, thus minimizing the interfering (competition) reactions between the lanthanides (III) and the organic ligands. AlI addition compounds are aoluble in ethanol and acetone; they are slightly soluble in ethyl acetate, acetonitrile and nitromethane; practically insoluble in chloroform, ether and carbon tetrachoride. The compounds were characterized through elemental analysis, infrared and Raman spectra, thermogravimetry, molar conductance, and proton magnetic resonance for the lanthanum and lutetium compounds. The interpretation of the vibrational spectra together with the PMR data suggests that the N-(2-pyridil) acetamide is bound through the amide oxygen as well as through nitrogen of pyridine. The infrared results also were used to establish the anion coordination in the complexes. The analysis of the spectra for the perchlorate adducts suggests that the anion is uncoordinated, and the alteration of the Td symmetry of the ion can be attributed to solid effects. There is no indication of the ionic nitrate for any compound, but alI the nitrate group bands are observed, suggesting the coordination of alI three nitrates. The molar conductance data indicates that the perchlorate compounds have 1:3 electrolyte behaviour in nitromethane and acetonitrile, while the nitrates behave as non electrolytes in the same solvents. The chemical compsition of the rare earth complexes has only on limited value in determining the coordination number, because there are several factors which seriously hinder that task. However, based on vibrational spectrum analysis, on molar conductance for alI the compounds and on PMR data for Ln(CIO4)3.4AAPH and La(NO3)3.2AAPH compounds it is consistent to suppose a coordination number eight for the adducts of perchlorates. For the nitrates this supposition turns out to be difficult, because, even though the presence of the three coordinated anions in alI the compounds is indicated, there is no exact knowledge about the mode(s) of coordination of them.

ASSUNTO(S)

nitratos solução (quimica) metais de terras raras

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