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| Author(s): |
Tereza da Silva Martins
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2004-11-25 |
| Examining board members: |
Paulo Celso Isolani;
Alcídio Abrão;
Jivaldo do Rosario Matos;
Viktoria Klara Lakatos Osorio;
Elizabeth Berwerth Stucchi
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| Advisor: | Paulo Celso Isolani |
| Abstract | |
A study involving the interaction of rare-earth (III) hydrated picrates and amino acids is reported in this work. The addition compounds with L-arginine (Arg), L-Iysine (Lys) and L-Ieucine (Leu) were prepared and characterized by severaI common techniques. The compounds were prepared in the molar ratio 1:2 (hydrated salts: ligands, Arg, Lys and Leu) using specific synthetic routes for each amino acid. The Arg and Lys complexes are partially soluble in water and insoluble in ethanol, methanol,acetonitrile and nitromethane. The Leu complexes are soluble in water, acetone, ethanol, methanol and nitromethane; they are partially soluble in acetonitrile and they are non-electrolytes in acetone and nitromethane. The general formulae for the complexes, determined by EOTA titrations, elemental analyses and thermogravimetry, are RE(pic) 3.2AA.2H2O and RE(pic) 3.2Leu.5H2) (RE =La-Lu and Y, pic =picrate, AA =Arg and Lys). In all compounds, the amino acids are bonded to RE(III) ions through the αaminogroup nitrogen atom and picrates, at least partially, are coordinated as bidentate ligands, through the phenoxy oxygen and one o-nitrogroup oxygen atom, as evidenced by IR absorption spectra. The Arg and Lys complexes display only one isomorphous series, but the Leu compounds present three isomorphous series. Parameters obtained from visible absorption spectra of the Nd complexes indicate that ligand-metal bonds are weakly covalent. Eu complexes are luminescent, both at room temperature and at 77K. Tb complexes are not luminescent, since their upper emitting state is above the Iigand\'s triplet state. The position of this state was determined by the picrate phosphorescence spectra of the Gd compound. Spectral characteristics, as well as the biexponential decay of Eu luminescence suggest that there is more than one coordination environment around the Eu(III) ion and that these complexes have polymeric structures. The stability and thermal behavior of these compounds were studied by thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). In the three series of complexes thermal stability is similar, but the Lys complexes are the most stable and the Arg complexes the least stable ones. Thermal decompositions differ, but in each series the decomposition is similar. From TG curves it was possible also to determine water contents and the RE percent compositions. (AU) | |