Coordination polymers incorporating light lanthanide ions

Coordination polymers incorporating light lanthanide ions

Journal of Alloys and Compounds 344 (2002) 179–185 L www.elsevier.com / locate / jallcom Coordination polymers incorporating light lanthanide ions ...

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Journal of Alloys and Compounds 344 (2002) 179–185

L

www.elsevier.com / locate / jallcom

Coordination polymers incorporating light lanthanide ions a ´ C. Daiguebonne a , Y. Gerault , F. Le Dret a , O. Guillou a , *, K. Boubekeur b a

´ , INSA-Rennes, 20 Avenue des Buttes de Coesmes, 35043 Rennes Cedex, France Groupe de Recherches en Chimie et Metallurgie b ´ Laboratoire des Sciences Moleculaires aux Interfaces, FRE 2068, Nantes, France

Abstract The reaction, in a gel medium, of Sm(III) chloride with the trisodium salt of benzene-1,3,5-tricarboxylic acid (H 3 TMA) yielded three different kinds of crystals. All three have been structurally characterized. 1, namely SmTMA(H 2 O) 6 crystallizes in Cc with ˚ b518.062(2) A, ˚ c57.219(1) A, ˚ b 5118.5432(11)8 and Z54. Its crystal structure has been found to be isostructural to a511.4818(12) A, the Y(III) complex already reported. It consists of juxtaposed ribbon-like molecular motifs. 2, namely SmTMA(H 2 O) 5 ?H 2 O has been ˚ b59.9654(15) A, ˚ found to be isostructural to the Er(III) complex already reported. It crystallizes in P-1 with a57.6305(15) A, ˚ a 5106.988, b 5103.52(2)8, g 5107.50(2)8 and Z52. Its structure consists of juxtaposed chains. 3, namely c511.219(2) A, ˚ b510.020(1) A, ˚ c515.294(2) A, ˚ b 5125.53(1) and Z58. Its Er 3 TMA 3 (H 2 O) 3 ?1.5H 2 O crystallizes in C2 /c with a520.511(2) A, structure consists of parallel double-sheet networks based on honeycomb-like motifs. Heating 1 liberates water molecules and finally leads to SmTMA, namely 4, which can reversibly bind water reforming 1.  2002 Elsevier Science B.V. All rights reserved. Keywords: Coordination polymers; Light lanthanide ions; Crystals

1. Introduction The assembly of metal–organic infinite frameworks via coordination of metal ions with multifunctional organic ligands is a field of increasing interest [1]. Work along this line is motivated by the concept that molecular-based coordination polymers have potential technological applications such as opto-electronic devices and microporous materials for shape- and size-selective separations and catalysis [2]. The advantage of this metal–organic open framework is to allow a wide choice in various parameters including diverse electronic properties and coordination geometry of the metal ions as well as versatile functions and topologies of organic ligands. So, specific electronic or structural characteristics of the metal ion can be translated into bulk properties for solid-state properties. In this context, there has been current interest in using polycarboxylate as anionic linking groups to support stable polymeric coordination open frameworks with transition metal ions [3]. The lanthanide ions, owning to their very *Corresponding author. Tel.: 133-2-99-286-549; fax: 133-2-99-636705. E-mail addresses: [email protected] (O. Guillou), [email protected] (K. Boubekeur).

similar chemical and structural properties but very different physical properties from one to the other, could lead to materials exhibiting tunable properties via the choice of the rare earth ion. That is why rather numerous coordination polymers, resulting from the copolymerization of lanthanide ions and polycarboxylate anions, have been described [4]. All of them have been obtained with rare earth belonging to the second half of the lanthanide family that is for the smallest lanthanide ions. We report herein the synthesis and crystal structures of the first three coordination polymers incorporating a light lanthanide, namely, the Sm(III) ion. These three compounds have similar chemical formula: SmTMA?nH 2 O with n equal to 6 for two of them and 4.5 for the third one and where TMA32 stands for benzene-1,3,5-tricarboxylate. All three have been obtained by slow diffusion through gels at room temperature and crystallize as 1-D or 2-D molecular frameworks. The 1-D or 2-D layers are held together by numerous hydrogen bonding interactions to yield tightly held 3-D molecular solids. The guest water molecules, when they exist, are localized inside the cavities and are linked to the molecular skeleton via a complex hydrogen bond network. These water molecules progressively leave the molecular framework when heated. An elemental analysis reveals that in many cases the resulting powder chemical formula is

0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 02 )00336-5

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SmTMA. This compound can reversibly bind water when exposed to a wet atmosphere. The anhydrous materials have a reasonable degree of thermal stability and the lability of the water molecules allows their replacement by other molecules.

2. Experimental

2.1. Synthesis of the micro-crystalline powder of SmTMA( H2 O)6 (1) Trimesic acid and samarium(III) oxide were respectively purchased from Acros Organics and Strem Chemicals. They were used without further purification. Subsequently, 20 ml of aqueous solutions containing 1 mmol of hexahydrated samarium(III) chloride and 1 mmol of the sodium salt of trimesic acid were mixed. An abundant precipitation immediately occurs. The mixture was then left under stirring for half an hour in order to allow the completion of the reaction. The crystalline powder was then filtrated and dried in air. Anal. calc. for 1 (found): Sm 32.3% (32.5); C 23.2% (23.0); O 41.2% (41.4); H 3.2% (3.4).

2.2. Synthesis of the anhydrous phase SmTMA (4) The polycrystalline powder obtained by direct precipitation (1) was heated under nitrogen to 300 8C for 2 h. The resulting polycrystalline white powder was rather well crystallized and exhibited an original X-ray diffraction pattern. IR spectra clearly shows the TMA32 ligand had not been destroyed during the thermal treatment and the elemental analysis results fit well with the chemical formula SmTMA. Anal. calc. for (4) (found): Sm 42.0% (42.1); C 30.3% (30.0); O 26.9% (27.1); H 0.8% (0.7). Despite great efforts we have not succeeded, until now, in obtaining single crystals.

2.3. Synthesis of the single crystals of SmTMA( H2 O)6 (1), SmTMA( H2 O)5? H2 O (2) and SmTMA( H2 O)3?1.5 H2 O (3) Agarose was purchased from Prolabo and used without further purification. Dilute aqueous solutions of hexahydrated samarium(III) chloride and sodium salt of trimesic acid were allowed to slowly diffuse, in an U-shaped tube, across agar–agar gel media at room temperature. After a few weeks of diffusion, single crystals of 1, 2 or 3 were obtained depending on the strength of the gel medium. Single crystals of 1 were obtained in pure water or very liquid gel medium. This can be related to the direct precipitation in water where a pure polycrystalline powder of the phase 1 is obtained.

Anal. calc. for 1 (found): Sm 32.3% (32.5); C 23.2% (23.0); O 41.2% (41.4); H% 3.2 (3.4). Anal. calc. for 2 (found): Sm 32.3% (32.0); C 23.2% (23.2); O 41.2% (41.5); H% 3.2 (3.3). Anal. calc. for 3 (found): Sm 35.3% (35.5); C 24.3% (24.3); O 37.7% (37.8); H% 2.7 (2.6). All crystals are fragile and tend to decompose in air at room temperature.

2.4. X-ray data collection and structure determination of SmTMA( H2 O)6 (1), SmTMA( H2 O)5? H2 O (2) and SmTMA( H2 O)3?1.5 H2 O (3) A transparent plate-like single crystal of SmTMA(H 2 O) 3 ?1.5H 2 O (3) and transparent needle-like crystals of SmTMA(H 2 O) 6 (1) and SmTMA(H 2 O) 5 ?H 2 O (2) were sealed in glass capillaries and mounted on a STOE IPDS single f -axis diffractometer with a 2D area detector based on Imaging Plate Technology. For all three crystals 130 images were recorded by using the rotation method (0#f #2608) with Df 52.08 increments, an exposure time of 3 min and a crystal to plate distance of 60 mm ( EXPOSE [5]). The images were processed with the set of programs from STOE [5] ( DISPLAY, PROFILE, INDEX, CELL and INTEGRATE ) and the data were corrected by an empirical absorption correction [5] (ABSORB ). The structures were solved by direct method and difference Fourier techniques and refined (on F 2 s) by full matrix least squares calculations using the software package SHELXS-97 [6] and SHELXL97 [7].

2.5. Thermal analysis TGA curve was recorded using TGA Linseis L81 / 064. A microcrystalline powder of the compound 1 sample (1000 mg) was heated under nitrogen flow in quartz (TGA) crucible to 900 8C at a heating rate of 6 8C h 21 . The TGA performed shows a first loss of mass between ambient temperature and 150 8C which corresponds to the departure of the six water molecules. The compound 4 thus obtained is then stable over a large range of temperatures (between 150 and 480 8C). Then a decomposition occurs that finally leads to a microcrystalline powder. X-ray powder diffraction analysis revealed that this powder is Sm 2 O 3 .

2.6. Description of the structure of SmTMA( H2 O)6 (1), SmTMA( H2 O)5? H2 O (2) and SmTMA( H2 O)3?1.5 H2 O (3) All three compounds revealed were isostructural to already described structures with heavier lanthanide ions. Compound 1 is isostructural to the compound YTMA(H 2 O) 6 [4a], compound 2 to ErTMA(H 2 O) 5 ?H 2 O [4c] and compound 3 to GdTMA(H 2 O) 3 ?1.5H 2 O [4b]. The asymmetric units, along with the atomic numbering schemes, and a view of the corresponding molecular

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Fig. 1. Right: extended asymmetric unit of SmTMA(H 2 O) 6 . Left: molecular motif.

motifs are depicted in Figs. 1–3 for compounds 1 to 3, respectively. Selected experimental data are listed in Table 1. The crystal structure of SmTMA(H 2 O) 6 (1) can be depicted as parallel ribbon-like molecular motifs spreading along the a¢ axis. These mono dimensional molecular motif stack in such a way that phenyl groups of TMA32 ligands superimposed along the c¢ axis. Free carboxylate groups are facing Sm atoms belonging to adjacent ribbons forming a strong hydrogen bond network with coordinated water molecules. This hydrogen bond network yields a 3D framework as can be seen in Fig. 4. The lack of guest water molecules in this crystal structure may be noticed because it is fairly rare in that sort of compound. It could be related to the simultaneous departure of all the water molecules during the thermogravimetric analysis. In this compound, all the coordination water molecules are linked, via hydrogen bonds to oxygen atoms belonging to a carboxylate. This suggests that during the dehydration process the Sm(III) ions could lose their coordination molecule and establish a bond with the corresponding carboxylato group. The crystal structure of SmTMA(H 2 O) 5 ?H 2 O (2) can be described as parallel chains spreading along the b¢ axis. These mono dimensional molecular motifs stack in such a way that phenyl groups of TMA32 ligands superimposed along the b¢ axis. The guest water molecule (O6) is localized inside inter-chain space and is involved in a hydrogen bond network with water molecules coordinated to Sm(III) ions belonging to neighboring chains (O3 and O5). All the coordinated water molecules are involved in a

Fig. 2. Right: extended asymmetric unit of SmTMA(H 2 O) 5 ?H 2 O. Left: molecular motif.

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Fig. 3. Right: extended asymmetric unit of SmTMA(H 2 O) 3 ?1.5H 2 O. Left: molecular motif.

strong hydrogen bond network leading as well to a 3D molecular network (see Fig. 5). Lastly, the crystal structure of SmTMA(H 2 O) 3 ?1.5H 2 O (3) consists of parallel double sheet networks based on molecular honeycomb-like motifs where one corner out of two is occupied by an Sm(III) ion and the other corner is occupied by a TMA32 ligand. Molecular bidimensional ¢ a¢ 1 c¢ ) plane in a step like motifs spread parallel to the (b, manner. Cohesion between adjacent layers is ensured by

strong hydrogen bonds involving one of the crystallization water molecules (O4), the coordinated water molecules and oxygen atoms from carboxylato groups. All these intermolecular interactions lead, once more, to a 3D molecular network (see Fig. 6). The other crystallization water molecule is affected by an occupancy factor of 1 / 2 and is weakly bonded to the rest of the structure by a weak hydrogen bond with a coordinated water molecule. More accurate details about these three structures can be

Table 1 Experimental data for the X-ray diffraction studies of SmTMA(H 2 O) 3 ?1.5H 2 O, SmTMA(H 2 O) 6 and SmTMA(H 2 O) 5 ?H 2 O

Molecular formula Crystal system Space group ˚ a (A) ˚ b (A) ˚ c (A) a (8) b (8) g (8) ˚ 3) V (A Z Observed data (Fobs $2s (F 2obs )) Parameters refined R a (%) R w b (%)

SmTMA(H 2 O) 3 ?1.5H 2 O

SmTMA(H 2 O) 6

SmTMA(H 2 O) 5 ?1H 2 O

SmC 9 O 10.5 H 12 monoclinic C2 /c (n815) 20.511(2) 10.020(1) 15.294(2) 106.98(2) 125.53(1) 107.50(2) 2558.0(4) 8 1441 187 3.4 3.6

SmC 9 O 12 H 15 monoclinic Cc (n89) 11.4818(12) 18.062(2) 7.219(1)

SmC 9 O 12 H 8 triclinic P-1(n82) 7.6305(15) 9.9654(15) 11.219(2)

118.5432(11)

103.52(2)

1315(2) 4 874 94 4.0 3.9

728.2(2) 2 2680 194 5.06 8.13

w 5 1 / [s 2 (F 2o ) 1 (0.0443*P)2 1 0.00*P] where P 5 (F 2o 1 2*F 2c ) / 3. a R 5 S iFo u 2 uFc i /S uFo u. b R w 5 [S [w(F 2o 2 F 2c )2 ] /S [w(F 2o )2 ]] 0.5 .

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Fig. 4. Projection along the c-axis of SmTMA(H 2 O) 6 . Dotted lines symbolize strong hydrogen bonds.

obtained in Ref. [4a–c], where isostructural compounds have already been described.

3. Discussion The only compound obtained as a microcrystalline powder is the SmTMA(H 2 O) 6 (1). The other two have been obtained in gel media as single crystals with a weak yield. So it has not been possible to study their thermal behavior. However, an isostructural compound involving Er has been obtained for SmTMA(H 2 O) 3 ?1.5H 2 O (3) and its thermal behavior has been studied (see Ref. [4f]). Its thermal decomposition was a two step process. First was observed the departure of the crystallization water molecule which presents an occupancy factor of 0.5 and the cyclization of the planes to lead to molecular tubes with hexagonal sections. Then, the remaining water molecules left and a microcrystalline powder with chemical formula ErTMA was obtained. The comparison of the X-ray powder diagram of ErTMA and SmTMA (4) reveal that these two compounds are isostructural. We have also studied the rehydration process of

SmTMA and it clearly appears that this anhydrous compound can reversibly bind water and compound 1 is finally obtained. This reversible process of dehydration / rehydration related to the great thermal stability (over more than 300 8C) of the anhydrous phase make this microporous solid particularly interesting.

4. Conclusion and outlook We have here reported the first three coordination polymers with a light lanthanide and trimesate ligand. These compounds obtained in very similar conditions are structurally identical to already reported compounds with heavy lanthanide. We are currently trying to extend our study in order to obtain for all lanthanides all the possible crystal structures. We especially focus on two lanthanide ions: Er(III) and Dy(III) ions. The former because of its obvious interest in laser fiber amplification and the latter because it is the only lanthanide ion which leads, when mixed with sodium trimesate to DyTMA(H 2 O) 3 ?1.5H 2 O (3) as a microcrystalline powder. We are currently inves-

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tigating the different thermal behavior of all these compounds.

5. Supplementary material Full details of the X-ray structure determination of SmTMA(H 2 O) 5 ?H 2 O has been deposited with the Cambridge Crystallographic Data Center under the depository number CCDC-151348 and can be obtained, on request, from the authors and the reference to this publication.

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Fig. 5. Projection along the a-axis of SmTMA(H 2 O) 5 ?H 2 O. Dotted lines symbolize strong hydrogen bonds.

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Fig. 6. Projection along the c-axis of SmTMA(H 2 O) 3 ?1.5H 2 O. Dotted lines symbolize strong hydrogen bonds.

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