1028-novo.cdr ECLÉTICA química www.scielo.br/eq Volume 35, número 4, 2010 93 Artigo/ArticleArtigo/Article Ecl. Quím., São Paulo, 35 - 4: 93 - 100, 2010 SYNTHESIS, CHARACTERIZATION AND THERMAL BEHAVIOUR OF HEAVY TRIVALENT LANTHANIDE MALONATES 1 2 3 30J. R. Locatelli , C. T. Carvalho , F. J. Caires , M. Ionashiro 1Academia da Força Aérea (AFA), Pirassununga, SP, Brazil. 2Universidade Federal da Grande Dourados, CEP 79.804-970, Dourados, MS, Brazil. 3Instituto de Química, UNESP, CP 355, 14801-970, Araraquara, SP, Brazil Abstract: Solid-state Ln-L compounds, where Ln stands for heavy trivalent lanthanides (Tb-Lu) and L is malonate, have been synthesized. Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy, TG-FTIR system, elemental analysis and complexometry were used to characterize and to study the thermal behaviour of these compounds. The dehydration of the compounds begins at 303 K and the anhydrous compounds are stable up to 548 K. The results also provided information concerning the ligand’s denticity, thermal behaviour and identification of some gaseous products evolved during the thermal decomposition of these compounds. Keywords: heavy lanthanides, malonate, thermal behaviour. Introduction Lanthanide compounds have a numerous applications in various industrial and technological fields, in materials science, principally due to luminescence and/or magnetic properties. In search of new materials the malonate ions arouse a great interest because it exhibits a rather flexible stereo- chemistry at variable mode of binding with metal ion [1]. The malonate ions are employed in the controlled assembly of malonates and ions into strategies for supramolecular synthesis and crystal engineering purposes [2, 3], for designing complexes with desired magnetic properties [3, 4] and so on. Preparation and investigation of several metal-ion malonates have also been investigated in the solid-state using thermoanalytical techniques, X- ray diffractometry and infrared spectroscopy. The papers published are concerned with the influence of the lanthanide contraction in the dehydration of malonates in solid state, discussed on the basis of TG curves [5]; The onset temperatures of dehydration and decomposition which measures the relative stability of anhydrous and hydrated compounds varying according to some physical parameters of lanthanides and lanthanide malonates [6]; studies on double malonates (potassium rare earth malonates) K Ln(C H O ) of gadolinium to holmium and 5 3 2 4 4 yttrium [7]; study of thermal decomposition of transition metal malonates [8,9]. In this paper, the object of the present research was to prepare solid state compounds of heavy trivalent lanthanide ions (i.e. Tb to Lu) with malonate and to characterize and to investigate by means of complexometry, elemental analysis, X-ray powder diffractometry, infrared spectroscopy, simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC) and TG-FTIR system. The thermal studies were performed in dynamical air atmosphere. 94 Artigo Article Experimental The sodium malonate monohydrated, Na CH C O .H O with 99.6% purity was obtained 2 2 2 4 2 -1from Sigma, and aqueous solution of 0.1 mol L was prepared, by direct weighing of the salt. Lanthanide(III) chlorides were prepared from the corresponding metal oxides by treatment with concentrated hydrochloric acid. The resulting solutions were evaporated to near dryness; the residues were again dissolved in distilled water, transferred to a volumetric flask and diluted in order -1to obtain ca. 0.1 mol L solutions, whose pH were adjusted to 5.0 by adding diluted sodium hydroxide solution. The solid state compounds were prepared by adding slowly, with continuous stirring, the aqueous solutions of the ligand (Na CH C O ) to the respecti-2 2 2 4 ve metal chloride solutions until total precipitation of the metal ions. The precipitates were washed with distilled water until elimination of chloride ions, filtered through and dried on Whatman no. 42 filter paper and kept in desiccator over anhydrous calcium chloride. In the solid state compounds hydration water, ligand and metal ion contents were determined from TG curves. The metal ions were also determined by complexometric tritrations with standard EDTA solution using xylenol orange, as indicator [10]. Carbon and hydrogen contents were determi- ned by microanalytical procedures, with an EA 1110 CHNS-O Elemental Analyser from CE Instruments. X-ray powder patterns were obtained using a Siemens D-5000 X-ray diffractometer, employing CuKá radiation (ë = 1.541Å) and a setting of 40 kV and 20 mA. The attenuate total reflectance infrared spectra for sodium malonate, as well as for its metal-ion compounds were run on a Nicolet iS10 FTIR spectrop- hotometer, using an ATR accessory with Ge window. Simultaneous TG-DTA and DSC curves were obtained with two thermal analysis system, model SDT 2960 and DSC Q10, both from TA Instruments. The purge gas was an air with a flow rate of 100 mL -1 -1min for TG-DTA and 50 mL min for DSC experi- -1ments. A heating rate of 20 K min was adopted, with sample masses about 7 mg for TG-DTA and 2 mg for DSC runs. Alumina and aluminium crucibles, the latter with perforated cover, were used for TG-DTA and DSC, respectively. The measurements of the gaseous products were carried out using a Thermogravimetric Analyzer Mettler TG-DTA coupled to a FTIR spectrophotometer Nicolet with gas cell and DTGS KBr detector. The furnace and the heated gas cell (523 K) were coupled through a heated (T = 473 K) 120 cm stainless steel line transfer with diameter 2 -1mm both purged with dry air (50 mL min ). The FTIR spectra were recorded with 32 scans per spectrum at a -1 resolution of 4 cm . Results and Discussion The analytical and thermoanalytical (TG) results of the synthesized compounds are shown in Table 1. These results permitted to establish the stoichiometry of these compounds, which is in a g r e e m e n t w i t h t h e g e n e r a l f o r m u l a : Ln (CH C O ) ·nH O, where Ln = Tb to Lu and 2 2 2 4 3 2 CH C O is malonate, with n = 7.5 (Tb, Dy, Ho) and 7 2 2 4 (Er, Tm, Yb, Lu). X-Ray Diffractometry The X - ray powder patterns Fig. 1 show that all the compounds have a crystalline structure without evidence for formation of an isomorphous series. The X-ray powder patherns also show that the final residues of these compounds are: Tb O and 4 7 Ln O (Ln = Dy to Lu).2 3 FTIR of the compounds in the solid state The attenuate total reflectance spectroscopic data on malonate and its compounds with the metal ions considered in this work are shown in Table 2. The investigation was focused mainly within 1700- -11400 cm range because this region is potentially most informative in attempting to assign coordinati- on sites. -1In Na CH C O , strong band at 1582 cm and 2 2 2 4 -1a medium intensity band located at 1352 cm are attributed to the anti-symmetrical and symmetrical frequencies of the carboxylate groups, respectively. The band assigned to the anti-symmetrical stretching carboxylate frequencies are shifted to lower values relative to the corresponding frequencies in CH C O 2 2 4 itself (sodium salt) and Dn(OCO) significantly less than ionic value. This behavior indicates that the coordination carried out through the carboxylate group [11] and the infrared spectra data suggests that the bonding of the carboxylate group to the metal is chelating bidentate and/or bridging in these com- Ecl. Quím., São Paulo, 35 - 4: 93 - 100, 2010 Artigo Article 95 Table 1. Analytical data for the Ln2L3·nH2O compounds Ln: trivalent lanthanides, L: malonate. Compounds Lanthanide oxide (%) Ligand lost (%) Water (%) Carbon (%) Hydrogen (%) Final Residue Calcd. TG EDTA Calcd. TG Ca lcd. TG Calcd. EA Calcd. E. A. Tb2L3·7.5H2O 49.25 48.89 49.40 32.95 33.38 17.80 17.73 14.24 14.01 2.26 2.52 Tb4O7 Dy2L3·7.5H2O 48.68 48.33 49.01 33.68 34.15 17.64 17.52 14.11 14.32 2.24 2.46 Dy2O3 Ho2L3·7.5H2O 49.00 48.95 48.65 33.47 34.00 17.53 17.05 14.02 13.80 2.23 2.11 Ho2O3 Er2L3·7H2O 49.88 49.38 49.50 33.67 33.85 16.45 16.77 14.10 13.89 2.11 2.34 Er2O3 Tm2L3·7H2O 50.10 49.85 49.80 33.52 33.56 16.38 16.59 14.03 14.35 2.10 2.35 Tm2O3 Yb2L3·7H2O 50.63 49.98 49.70 33.16 33.41 16.21 16.61 13.89 14.30 2.08 1.95 Yb2O3 Lu2L3·7H2O 50.87 50.09 50.62 33.00 33.53 16.13 16.38 13.82 13.50 2.07 1.90 Lu2O3 pounds [12]. The appearance of two n (OCO) sym bands in the spectrum of these compounds probably is due to different types of interaction between the carboxylate groups of malonate and lanthanide ions. This conclusion is supported at least in the case of the Dy compound by the results of the crystal structure determination [13]. Simultaneous TG-DTA curves of the compounds are shown in Fig.2. These curves exhibit mass losses in three or four consecutive steps and thermal events corresponding to these losses. A close similarity is noted concerning the TG-DTA profiles of these compounds. These curves also show that the first mass loss occurs within the same temperature range for Tb, Dy, Ho and Tm compounds (i.e. 303 – 473 K) and for Er, Yb and Lu ones (i.e. 303 – 453 K), in spite of the compounds have been maintained in a forced circulation oven at 323 K during 12 h and removed to a desiccator over anhydrous calcium chloride. The second mass loss for all the compounds also begins at the same temperature (548 K), showing that the thermal behaviour up to this step is not dependent on the nature of the lanthanide ion. However the temperature range as shown by the next steps of thermal decomposition, as well as the mass lost in each step are characteristic of each compound. For all the compounds the first mass loss that begin through a slow process followed by a fast one, associated to endothermic peak at 409 – 413 K, is attributed to dehydration, which occurs in a single step. Once dehydrated, the anhydrous compounds are stable up to 548 K, and above this temperature up to 653 K (Tb), 673 K (Dy, Ho, Er) and 693 K (Tm to Lu), the mass losses corresponding to exothermic events are attributed to the oxidation of the organic matter. The similarity of the TG-DTA curves up to this point suggests that the decomposition mecha- nism is the same for these compounds. For each of the considered compounds, the oxidation of the organic matter yields on intermedia- te derivative of carbonate, accompanied by a carbonaceous residue. The intermediate is probably the corresponding dioxycarbonate, as already observed for the compounds of phenyl-substituted derivatives of benzalpyruvates with trivalent lanthanides [14] and lanthanide malonates [6]. Tests with hydrochloric acid solution on samples heated up to the temperatures of formation of these intermedia- tes, as indicated by the corresponding TG-DTA curves, confirmed in all cases evaluation of CO and 2 presence of the carbonaceous residues. The small mass loss observed above 673 K (Dy, Ho, Er) or 693 K (Tm, Yb, Lu), that occurs slowly, is attributed to the thermal decomposition of the carbonaceous residues. The small mass gain observed between 823 – 898 K (Er), 813 – 943 K (Tm), 798 – 910 K (Yb) and 803 – 948 K (Lu) is Ecl. Quím., São Paulo, 35 - 4: 93 - 100, 2010 96 Artigo Article Figure 1. X - ray - Tb(L) ·7.5H O, Dy(L) ·7.5H O, 3 2 3 2 Ho(L) ·7.5H O, Er(L) ·7H O, Tm(L) ·7H O, 3 2 3 2 3 2 Yb(L) ·7H O and Lu(L) ·7H O. (L = malonate).3 2 3 2 1 0 2 0 3 0 4 0 5 0 6 0 7 0 T b D y H o E r T m Y b L u 2 è I/I 0 attributed to the formation of more derivative of carbonate due to the carbon dioxide evolved during the oxidation of the carbonaceous residues. No peak corresponding to the mass loss or gain is observed in the DTA curve, which is probably due to the small heat effect of these steps. The mass loss above 793 K (Tb), 873 K (Dy, Ho), 898 K (Er), 910 K (Yb) and 948 K (Tm, Lu), corresponding to the exothermic followed by endothermic events (Tb-Er) or endothermic one (Tm-Lu) is attributed to the oxidation of the remai- ning carbonaceous residues and thermal decomposi- tion of the intermediate derivative of carbonate, with formation of the respective oxides, Tb O and Ln O 4 7 2 3 (ln = Dy to Lu). For Tm to Lu, no exothermic event is observed, probably because of the small amount of carbonaceous residues remaining. The mass losses or gain, temperature ranges and the peak or thermal event temperatures observed for each step of the TG-DTA curves are shown in Table 3. The TG-DTA profiles, as well as the tempera- ture range and the mass losses observed in each step of the TG curve are in disagreement with the results reported by Muraishi and co-workers [6]. These disagreements undoubtedly are due to the different experimental conditions, principally the static air atmosphere used to obtain the TG and DTA curves. For the dynamic atmosphere the evolved products of the thermal decompositions are continuously changed while in the static atmosphere the same is Table 2. Spectroscopic data for sodium malonates (Na CH C O ) and compounds with heavy trivalent 2 2 2 4 lanthanides. - -1 - -1Compound n (COO ) cm (COO ) cm ( - )as sym as sym Na L·H O 1582(vs) 1352(m) 2302 2 Tb L ·7.5H O 1568 1378 1902 3 2 f m Dy L ·7.5H O 1565 1376 1892 3 2 f m Ho L ·7.5H O 1567 1375 1922 3 2 f m Er L ·7H O 1569 1378 1912 3 2 f m Tm L ·7H O 1570 1378 1922 3 2 f m Yb L ·7H O 1572 1378 1942 3 2 f m Lu L ·7H O 1573 1379 1942 3 2 f m L = malonate s = strong; m = médium; vs = very strong as (coo-) and ísym (coo-); anti-symmetrical and symmetrical vibrations of the coo- group, respectively n nnnD Ecl. Quím., São Paulo, 35 - 4: 93 - 100, 2010 Artigo Article 97 not observed. On that account the disagreements are observed. The DSC curves of the compounds are shown in Fig. 3. These curves show endothermic and exothermic peaks that all are in agreement with the mass losses observed in the TG curves. Small differences observed concerning the peak temperatu- res obtained by TG-DTA and DSC are undoubtedly due to the perforated cover used to obtain the DSC curves, while TG-DTA ones are obtained without cover, beyond other experimental conditions that was not the same. Compound Steps First Second Third Fourth Tb(L)3 . 7.5H2O è K 303-473 548-653 793-1023 - loss (%) 1.73 20.97 12.41 - Peak (K) 413(endo) 638(exo) 853(exo) - Dy(L )3 .7.5H2O è K 303-4733 548-673 673-823 873-1053 loss (%) 17.52 21.11 2.92 10.12 Peak (K) 413(endo) 648(exo) - 908(exo), 917(endo) Ho(L)3 . 7.5H2O è K 303 - 473 548 - 673 673 - 783 873 -1048 loss (%) 17.05 22.28 2.57 9.15 Peak (K) 410(endo) 648(exo) - 926(exo), 1013(endo) Er (L)3 . 7H2O è K 303-473 548-673 673-898 898-1023 loss (%) gain(%) 16.67 - 23.86 - 2.13 0.11 7.96 - Peak (K) 412(endo) 648(exo) - 941(exo), 1019(endo) Tm(L)3 . 7H2O è K 303-473 548-693 693-943 943-1053 loss (%) gain(%) 16.59 - 24.76 - 1.59 0.33 7.21 - Peak (K) 410(endo) 655(exo) - 1023(endo) Yb(L)3 . 7H O è2 K 303-453 548-693 693-910 910-1033 loss (%) gain(%) 16.61 - 25.48 - 0.98 0.52 6.95 - Peak (K) 409(endo) 648(exo) - 1012(endo) Lu(L)3 . 7H O è2 K 303-453 548-693 693-948 948-1053 loss (%) - 16.38 - 26.15 - 1.11 0.66 6.27 - Peak (K) 410(endo) 655(exo) - 1033(endo) Table 3. Temperature ranges ? , mass losses or gain (%) and peak temperatures observed for each step of the TG-DTA curves of the compounds Ln (L) ·nH O, where Ln = heavy 2 3 2 trivalent lanthanides and L is malonate. Ecl. Quím., São Paulo, 35 - 4: 93 - 100, 2010 98 Artigo Article . Figure 2. TG-DTA curves of the compounds: Tb(L)3 . 7.5H O (m = 5.26 mg), Dy(L) 7.5H O (m = 5.09 2 3 2 . . mg), Ho(L) 7.5H O (m = 5.04 mg), Er(L) 7H O (m 3 2 3 2 . . = 5.16 mg), Tm(L) 7H O (m = 5.87 mg), Yb(L)3 2 3 . 7H O (m = 5.02 mg) and Lu(L) 7H O (m = 5.22 2 3 2 mg). (L = malonate) 50 75 100 00 3 66 12731073973873773673573373473 M as s lo ss ( % ) Temperature / K 373 Ä T ( K /m g) TG DTA exo up Tb 50 75 100 0 5 M as s lo ss ( % ) Ä T ( K /m g) 373 473 373 573 673 773 873 973 1073 1273 Temperature/ K TG DTA exo up Dy 50 75 100 0 5 M as s lo ss ( % ) Temperature / K Ä T ( K /m g) 373 473 373 573 673 773 873 973 1073 1273 TG DTA exo up Ho 50 75 100 0 5 373 473 373 573 673 773 873 973 1073 1273 exo up Ä T ( K /m g) Temperature /K M as s lo ss ( % ) Er TG DTA 50 75 100 0 5 Temperature/K 373 473 373 573 673 773 873 973 1073 1273 Ä T ( K /m g) M as s lo ss ( % ) Tm exo up TG DTA 50 75 100 0 3 6 M as s lo ss ( % ) Temperature/ K 373 473 373 573 673 773 873 973 1073 1273 TG DTA exo up Ä T ( K /m g) Yb 50 75 100 0 5 M as s lo ss ( % ) Temperature/K 373 473 373 573 673 773 873 973 1073 1273 exo up Ä T ( K /m g) Lu TG DTA Ecl. Quím., São Paulo, 35 - 4: 93 - 100, 2010 The endothermic peaks within 420-430 K range are due to dehydration, which occurs in a single step. The dehydration enthalpies found for Tb to Lu compounds were: 357.2, 366.3, 369.4, 363.5, 336.3, -1368.8 and 388.1 kJ mol , respectively. Monitoring of gaseous products by TG-FTIR system The gaseous products evolved during the thermal decomposition in an air atmosphere of the compounds studied in this work were monitored by FTIR, and it has acetone and carbon dioxide as main product due to decarboxylation and oxidation of the organic matter. The IR spectra of the gaseous products evolved during the thermal decomposition of ytterbium malonate as representative of all the compounds are shown in Fig. 4. The spectra of the -1gaseous products evolved show peaks at 2360 cm , -1 -12345 cm and 666 cm , being the first two due to anti- symmetrical stretching and scissoring (degenerated), respectively attributed to carbon dioxide. The peaks -1 -1 -1at 1737 cm , 1366 cm and 1215cm , corresponding to axial deformation of C = O, angular symmetric deformation of CH and axial and angular deformati-3 on of C – CO – C, respectively are attributed to acetone. Conclusion From TG, complexometry and elemental analysis data, a general formula could be established for the compounds involving heavy lanthanides ions. The X-ray powder patterns pointed out that the synthesized compounds have a crystalline structure and the infrared spectroscopic data suggests that CH C O acts as a chelating bidentate and/or briding 2 2 4 bidentate ligand towards the metal ions considered in this work. The TG-DTA and DSC curves provided previously unreported information about the thermal stability and thermal decomposition of these compounds in dynamic air atmosphere. The gaseous evolved during the thermal decomposition of the compounds have acetone, CO 2 and CO as main products. Acknowledgements The authors thank, AFA, FAPESP, CNPq and CAPES Foundations for financial support. Artigo Article 99 100 200 300 400 500 600 Dy Tb Ho H ea t fl o w /( W /g ) Er Tm Yb Lu Temperature/ºC exo up Figure 3. DSC curves of the compounds: Tb(L) ·7.5H O (m = 2.17 mg), Dy(L) ·7.5H O 3 2 3 2 (m = 2.08 mg), Ho(L) ·7.5H O (m = 2.40 mg), 3 2 Er(L) ·7H O (m = 2.00 mg), Tm(L) ·7H O 3 2 3 2 (m = 2.22 mg), Yb(L) ·7H O (m = 2.09 mg) and 3 2 Lu(L) ·7H O (m = 2.10 mg). (L = malonate)3 2 Ecl. Quím., São Paulo, 35 - 4: 93 - 100, 2010 100 Artigo Article Ecl. Quím., São Paulo, 35 - 4: 93 - 100, 2010 Resumo: Compostos Ln-L no estado sólido, em que Ln representa os lantanídeos trivalentes (Tb – Lu) e L é malonato, foram sintetizados neste trabalho. A termogravimetria e análise térmica diferencial simultânea (TG- DTA), calorimetria exploratória diferencial (DSC), difratometria de raios X pelo método do pó, espectroscopia na região do infravermelho (FTIR), TG-FTIR, análise elementar e complexometria foram utilizadas para caracterizar e estudar o comportamento desses compostos. A desidratação desses compostos começa em 303 K e os compostos anidros são estáveis até 548 K. Os resultados também proporcionaram informações com respeito à denticidade do ligante, comportamento térmico e a identificação de alguns produtos gasosos eliminados durante a decomposição térmica desses compostos. Palavras-chave: lantanídeos pesados, malonato, comportamento térmico. 4000 3500 3000 2500 2000 1500 1000 500 66 6 12 15 13 66 17 37 23 4 5 23 60 Wavernumber / cm -1 T ra ns m it ta nc e / % 4000 3500 3000 2500 2000 1500 1000 500 66 6 23 4 5 2 36 0 Wavernumber / cm -1 Figure 4. FTIR spectra of gaseous products evolved during the decomposition of the ytterbium malonate, as representative of the all compounds. References [1] A. Karipides, J. Ault, A. Thomas Reed, Inorg Chem. 16 (1977) 3299. [2] H-Y. Shen, W-M. Bu, D-Z. Liao, J-H Jiang, SP. Yan, G-L. Wang, Inorg Chem Commun. 3 (2000) 497. [3] Rodriguez-Martin Y, Ruiz-Pérez C, Sanchiz J, Lloret F, Julve M, Inorg Chim Acta 318 (2001)159. [4] Y. Rodriguez-Martin, M. Hernandez-Molina, F. S. Delgado, J. Pasan, C. Ruiz- Perez, J. Sanchiz , F. Lloret , M. Julve, Cryst Eng Comm. 4 (2002) 522. [5] K. Muraishi, K. Nagase , M. Kikuchi, K. Sone, N. Tanaka, Cryst Eng Comm. 55 (1982) 1845. [6] K. Muraishi, Thermochim. Acta 182 (1991) 209. [7] M. A. Nabar , B. N. Jukar, T Bull Chem Soc Jpn. 58 (1985) 3582. [8] F. J. Caires, L. S. Lima, C. T. Carvalho, M. Ionashiro, Thermochim. Acta 497 (2010) 35. [9] B. S. Randhawa, K. Gandotra, J. Therm. Anal. Cal. 85 (2006) 417. [10] M. Ionashiro, C. A. F. Graner, J. Zunon Netto, Eclet. 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