Preparation and thermal behavior of mixture of basic carbonate and 4-dimethylaminocinnamylidenepyruvate with lanthanides ( III ) and yttrium ( III ) in the solid state

Solid Ln-OHCO3-DMCP compounds, where Ln represents lanthanides (III) and yttrium (III) ions and DMCP is the anion 4-dimethylaminocinnamylidenepyruvate, have been prepared. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC), x-ray diffraction powder patterns and elemental analysis have been used to characterize the compounds. The thermal stability as well as the thermal decomposition of these compounds were studied using an alumina crucible in an air atmosphere.


Introduction
Several metal ion complexes with 4-dimethylaminobenzylidenepyruvate (DMBP), 2-chloro-4dimethylaminobenzylidenepyruvate (2-Cl-DMBP), 4-methoxybenzylidene-pyruvate (4-MeO-BP) and cinnamylidenepyruvate (CP) have been investigated in aqueous solution [3][4][5][6]12 . Thefactors that govern the thermodynamic stability and selectivity of these ligands towards metal ions, as well as analytical applications of the corresponding complexation reactions have been the main purposes of the studies.Solid state compounds of several metal ion with DMBP and 4-MeO-BP, have also been prepared and studied using TG, DTG, DSC, DTA and X-ray powder diffractometry.7,[9][10][11] The establishment of the stoichiometry, thermal stability and thermal decomposition mechanism have been the main objective of these studies.
In this study, solid state compounds of lanthanide (III) and yttrium (III) with characterized and studied by complexometric titration, TG, DTG, DSC, elemental analysis and X-ray powder difractometry.The data obtained allowed us to acquire new information concerning these compounds.

Experimental
The sodium salt of DMCP was prepared following the same procedure for the 4dimethylaminobenzylidenepyruvate, as previously describe 4 .The neutralization of aqueous suspension of the acid HDMCP in excess, was made with sodium hydrogen carbonate.The excess of the acid was separed by centrifugation.Lanthanides (III) and yttrium (III) chlorides were prepared in accordance with Giesbretch et al. 1 The solid compounds of trivalent lanthanides and yttrium with DMCP were prepared following the procedure as previously described. 7 the solid compounds, the anions contents were determined from the TG curves and elemental analysis and the lanthanide and yttrium contents were determined by complexometric titrations with standard EDTA solutions, using xylenol orange as indicator 2 and from the TG curves.
The TG, DTG and DSC curves were obtained using a Mettler TA-4000 thermoanalyser system with an air flux of » 150 mL min -1 , a heating rate of 10°C min -1 and with samples weighing about 7 mg.An alumina crucible was used for the TG, DTG curves and an aluminium crucible with a perforated cover was used for the DSC curves.
Diffraction patterns were obtained using an HGZ 4/B horizontal diffractometer (Germany), equipped with a proportional counter and pulse-heigh discriminator.The Bragg-Brentano arrangement was adapted using CuKa radiation (l = 1.541Å ) and settings of 38 KV and 20 mA.

Results and discussion
Table 1 presents the analytical and thermoanalytical (TG) data and Table 2 presents the elemental analysis results for the prepared compounds of general formula Ln(DMCP) 3 .LnOHCOFor the dysprosyum -lutetium and yttrium compounds the TG-DTG curves, Figure 1(i) -(o), also show that this intermediate, Ln 2 O 2 CO 3 is not formed, probably because the thermal stability of this intermediate decrease with the increase of the atomic number of the lanthanide ion. 8hydrous compounds the mass loss begins with a slow process, followed by a fast process.
Although the DTG curves show mass losses in several steps, the TG curves suggest two or three mass losses except for the cerium compound.The mass losses and the corresponding temperature ranges, for the partial thermal decompositions for all the compounds are shown in Table 3.
The DSC curves of these compounds (Figure 2) show endothermic and exothermic peaks up to 600°C, in correpondence with the mass losses observed in the TG curves.The broad endothermics that occur in all the compounds between 30 and 200°C, are due to the loss of hydration water.The sequence of broad exotherms observed after the dehydration between 200 and 600°C are attributed to the thermal decomposition of these compounds.
3 .nH 2 O,where Ln represents lanthanides and yttrium, DMCP is 4-dimethylaminocinnamylidenepyruvate, and n = 3-4.5.The X-ray powder patterns showed that all the compounds are amorphous.The TG and DTG curves of the compounds are shown in Figure1.These curves show mass losses in steps between 30 and 730°C.In all the curves a great similarity are observed and the first mass loss observed up to 150°C is due to hydration water.The formation of the intermediate dioxycarbonate, Ln 2 O 2 CO 3 , is observed only for La, Nd -Gd, compounds, Figure1(a), (d-g).In the cerium, praseodymium and terbium compounds, the TG, DTG curves, Figure1(b), (c) and (h), show that this intermediate is not formed, probably because the exothermic oxidation reaction that results in the formation of the respective oxides (CeO 2 , Pr 6 O 11 and Tb 4 O 7 ), as already observed7 .

For
the anhydrous cerium compound, the TG and DTG curves show mass losses in two consecutive steps between 150 and 450°C.Calculations based on the mass losses observed in the TG curves are in agreement with the losses of 3(CH 3 ) 2 -N; 0.5H 2 O (first step) and the rest of the ligand DMCP and the thermal decomposition of the cerium monoxycarbonate formed during the dehydration of basic carbonate with formation of 2CeO 2 (second step).For the anhydrous lanthanium compound, the TG curve indicates that the thermal decomposition occurs in three steps with losses of (first step), rest of the ligand DMCP and thermal decomposition of the lanthanium monoxycarbonate formed during the dehydration of basic carbonate with formation of the dioxycarbonate (second step) and elimination of CO 2 with formation of La 2 O 3 (last step).For the anhydrous neodymium -gadolinium compounds, the TG curves also show mass losses in three steps with osses of of the ligand DMCP and thermal decomposition of the respective monoxycarbonate formed during the dehydration of basic carbonate with formation of the dioxycarbonate (second step) and elimination of CO 2 with formation of Ln 2 O 3 .Finally, for the anhydrous praseodimium, terbium -lutetium and yttrium compounds, the TG curves show mass losses in two steps with losses of (first step), rest of the ligand DMCP and thermal decomposition of the respectives monoxycarbonates formed during the dehydration of basic carbonate with formation of the oxides, Pr 6 O 11 , Tb 4 O 7 and Ln 2 O 3 (second step).