Zeolite-like Nanoporous Gadolinium Complexes Incorporating

Nov 17, 2005 - Tenerife, Spain, Departamento de Quı´mica Inorga´nica/Instituto de Ciencia ... Astrofı´sico Francisco Sa´nchez s/n, 38204 La Lagu...
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CRYSTAL GROWTH & DESIGN

Zeolite-like Nanoporous Gadolinium Complexes Incorporating Alkaline Cations

2006 VOL. 6, NO. 1 87-93

Laura O Ä scar Catalina Fernando S. Miguel Julve,# Marı´a Herna´ndez-Molina,‡ M. Milagros Laz,‡ and Pablo Lorenzo-Luis† Can˜adillas-Delgado,§

Fabelo,§

Ruı´z-Pe´rez,*,§

Delgado,§

Laboratorio de Rayos X y Materiales Moleculares, Departamento de Fı´sica Fundamental II, UniVersidad de La Laguna, AVda. Astrofı´sico Francisco Sa´ nchez s/n, 38206 La Laguna, Tenerife, Spain, Departamento de Quı´mica Inorga´ nica/Instituto de Ciencia Molecular, Facultad de Quı´mica de la UniVersitat de Vale` ncia, Dr. Moliner 50, 46100-Burjassot, Vale` ncia, Spain, Laboratorio de Rayos X y Materiales Moleculares, Departamento de Edafologı´a y Geologı´a, UniVersidad de La Laguna, AVda. Astrofı´sico Francisco Sa´ nchez s/n, 38204 La Laguna, Tenerife, Spain, and Laboratorio de Rayos X y Materiales Moleculares, Departamento de Quı´mica Inorga´ nica, UniVersidad de La Laguna, AVda. Astrofı´sico Francisco Sa´ nchez s/n, 38204 La Laguna, Tenerife, Spain ReceiVed April 21, 2005; ReVised Manuscript ReceiVed September 15, 2005

ABSTRACT: In this article, we describe the synthesis and single-crystal X-ray structural studies of two new lanthanide complexes of formula [MILnIII(bta)(H2O)3]‚nH2O, (M ) Na (1), K (2); Ln ) Gd; H4bta ) 1,2,4,5-benzenetetracarboxylic acid) to check the ability of rare earth ions to lead to high-dimensional materials. The crystal structures of 1 and 2 can be described as a succession of layers made up of chains with regular alternation of pairs of Gd3+ and Na+ or K+ ions that are connected by bta4- groups. Both structures contain a nine-coordinated gadolinium(III) cation ion and fully deprotonated bta4- anion. However, the alkaline cations exhibit different coordination numbers, seven (Na+) and nine (K+). The structures accommodate crystallization and coordination water molecules, and it was observed that the water molecules have a significant influence on the coordination geometry and on the overall extended structure. These compounds may be considered as novel nanocomposites of unusual structures within the benzenetetracarboxylate frameworks. Introduction The design of supramolecular materials from molecular building blocks has become a challenging field of research according to the new perspectives they open in materials science. A very promising approach to such functional systems involves coordination polymers.1,2 This approach also has been envisaged for the preparation of nanoporous materials.3-7 Several prototypical examples of such supramolecular nanoporous architectures have been reported and were shown to exhibit promising results in catalysis,8 gas sorption and storage,9 or separation.10 The vast majority of these open frameworks are prepared by the direct assembly of a metal ion with a bridging ligand, the resulting network relying on the formation during the association process of the so-called secondary building blocks. As compared to the reports on d-block transition metal polymers, lanthanide polymeric complexes are less studied. The higher coordination number of the lanthanide ions, when compared to the transition elements, makes more difficult the control of the synthetic reactions and thereby the structures of the resulting products.11 However, their fascinating coordination geometries and interesting structures, as well as the special properties of lanthanidecontaining complexes, have attracted the interest in materials science and the number of reports concerning them has greatly increased.11-15 An assembly of metal ions and ligands in polymeric complexes can be regarded as a programmed system in which the stereo and interactive information stored in the ligands is read by the metal ions through the algorithm defined by their * To whom correspondence should be addressed. E-mail: [email protected]. § Dpto. Fı´sica Fundamental II, Universidad de La Laguna. # Dpto. Quı´mica Inorga ´ nica/Instituto de Ciencia Molecular, Universitat de Vale`ncia. ‡ Dpto. Edafologı´a y Geologı´a, Universidad de La Laguna. † Dpto. Quı´mica Inorga ´ nica, Universidad de La Laguna.

Scheme 1

coordination geometry.16 Hence, the design or selection of a suitable ligand containing certain features, such as flexibility, versatile binding modes, and ability to form hydrogen bonds,17,18 is crucial in the building of polymeric complexes. In particular, multicarboxylate ligands13,19-24 are usually used in the architectures of the lanthanide polymeric complexes. 1,2,4,5-Benzenetetracarboxylic acid (H4bta), commonly known as pyromellitic acid, possesses several interesting characteristics: (a) it has four carboxylic groups, which after partial or full deprotonation, can coordinate to the metal ions in a wide variety of coordination modes leading to high-dimensional structures (see Scheme 1); (b) it can act not only as a hydrogenbond acceptor but also as a hydrogen-bond donor, depending upon the number of deprotonated carboxylic groups; (c) some of its carboxylic groups may not lie in the phenyl ring plane upon complexation to metal ions owing to geometrical constraints, and thus, the ligand may connect metal ions in different directions; (d) finally, the high symmetry that it exhibits may

10.1021/cg050170t CCC: $33.50 © 2006 American Chemical Society Published on Web 11/17/2005

88 Crystal Growth & Design, Vol. 6, No. 1, 2006

Can˜adillas-Delgado et al. Scheme 2

be helpful for the crystal growing of the product formed. Its diversity of coordination modes is depicted in Scheme 2. Previous works have proved that H4bta is a good building block for the construction of polymers with lanthanide15 or alkaline metal ions.22 Herein, following our systematic studies on carboxylate containing lanthanide complexes,23-25 and to check the ability of rare earth ions to afford high-dimensional materials, we have undertaken the study of two novel pyromellitate-containing gadolinium(III) complexes incorporating alkaline cations: [NaGd(bta)(H2O)3]‚2H2O (1) and [KGd(bta)(H2O)3]‚4H2O (2). Experimental Section Materials and Methods. Reagents and solvents used in the synthesis were purchased from commercial sources and used without further purification. Elemental analysis (C, H) were performed with an EA 1108 CHNS/0 automatic analyzer.

Synthesis of [NaGd(bta)(H2O)3]‚2H2O (1). Single crystals of 1 have been grown in silica gel medium, through the techniques described by Henisch.26 1,2,4,5-Benzenetetracarboxylic acid (0.5 g, 1.967 mmol) was poured into an aqueous solution (25 mL) containing sodium hydroxide (0.08 g, 2 mmol). The resulting clear solution was added dropwise to a warm (50 °C) aqueous solution (25 mL) of gadolinium(III) nitrate hexahydrate (0.902 g, 2 mmol) under continuous stirring and allowed to react during 15 min. Then, it was filtered, and the filtrate was allowed to evaporate at room temperature. Well-shaped colorless crystals were obtained after a few days. Anal. Calcd. for C10H10GdNaO13 1: C, 23.17; H, 1.94%. Found: C, 23.23; H, 1.78%. Synthesis of [KGd(bta)(H2O)3]‚4H2O (2). Aqueous solutions (9.5 mL) of potassium hydroxide (0.2 M) and 1,2,4,5-benzenetetracarboxylic acid (0.2 M) were mixed and the pH was adjusted to 4 by using 9 mL of tetramethoxysilane. The resulting mixture was introduced into test tubes, covered, and allowed to set for 1 day at room temperature. Finally, an aqueous solution (5 mL) of gadolinium(III) acetate monohydrate (0.2 M) was carefully layered on the gel, to prevent any damage of the surface of the gel, to prevent any damage of the surface

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Crystal Growth & Design, Vol. 6, No. 1, 2006 89

Figure 1. (a) Distorted brick-wall layer in 1, with bta4- units linking the inorganic chains of the edge sharing octahedra. (b) Detail of the strand of water molecules. Hydrogen bonds linking the water molecules are plotted in blue. Green, yellow, red and blue colors correspond to Gd, Na, carboxylate-O, and water-O atoms, respectively. Table 1. Summary of Crystallographic Data and Structure Refinement for 1 and 2 compound formula M crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z T (K) Fcalc (Mg m-3) λ (Mo KR Å) µ (Mo KR mm-1) R1a, I > 2σ(I) (all) wR2b, I > 2σ(I) (all) measured reflections independent reflections (Rint) a

1 C10H12GdNaO13 520.44 triclinic P1h 8.7673(4) 9.8149(4) 10.1743(4) 113.897(3) 105.754(3) 102.104(3) 717.74(5) 2 293(2) 2.408 0.71073 4.726 0.0426 (0.0583) 0.0958 (0.1012) 8343 4134 (0.0539)

2 C10H16GdKO15 572.58 triclinic P1h 7.1190(10) 8.783(2) 15.067(3) 79.61 (3) 87.52 (3) 83.21 (3) 919.9(3) 2 293(2) 2.067 0.71069 3.905 0.0265 (0.0320) 0.0649 (0.0665) 9097 4144 (0.0339)

R1) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(|Fo|2 - |Fc|2)2]/[∑w|Fo|2]1/2.

of the gel, and the tubes were stored at 30 °C. X-ray quality colorless crystals of 2 appeared after 6 days. Anal. Calcd. for C10H14GdKO15 2: C, 21.05; H, 2.47%. Found: C, 20.98; H, 2.56%. X-ray Data Collection and Structure Solution. Crystal data and details of the refinement for compounds 1 and 2 are listed in Table 1. X-ray diffraction data for single crystals were collected on a Nonius Kappa CCD diffractometer27 with graphite-monochromated Mo-KR radiation (0.71073 Å). All calculations for data reduction were done with standard procedures (WINGX).28 The structures of both compounds were solved by direct methods using the SHELXS9729 computational program. All non-hydrogen atoms were refined anisotropically by fullmatrix least-squares technique on F2 by using SHELXL97.30 The hydrogen atoms of the fully deprotonated bta4- ligand in 1 were set in calculated positions and refined as riding atoms with a common isotropic thermal parameter and in 2 were located from difference maps and refined with isotropic temperature factors. The final geometrical calculations and the graphical manipulations were carried out with PARST95,31 PLATON,32 and CRYSTALMAKER33 programs.

Results and Discussion Crystal Structure of 1. The crystal structure of 1 can be described as a succession of layers made up of chains with regular alternation of pairs of Gd3+ and Na+ ions along the [111] direction, which are connected by bta4- groups (Figure 1). The structure accommodates crystallization and coordination water

Figure 2. A view of a fragment of the structure of 1 showing the atom numbering. Symmetry code: (a1) -x, -y, -z; (b1) 1-x, -y, 1 z; (c1) x, 1 + y, z. Table 2. Intermolecular and Intramolecular Contacts (Å) in 1 Intramolecular D‚‚‚A O(2)‚‚‚O(2Wd1) O(3)‚‚‚O(1Wf1) O(7)‚‚‚O(3We1) O(7)‚‚‚O(3Wg1)

2.843(12) 2.6415(77) 2.9342(95) 2.9987(94) Intermolecular

D‚‚‚A O(5)‚‚‚O(5W) O(8)‚‚‚O(4W) O(2W)‚‚‚O(4Wd1) O(1W)‚‚‚O(4Wh1) O(2W)‚‚‚O(4Wc1) O(3Wf1)‚‚‚O(5W) O(4W)‚‚‚O(5Wj1)

2.822(13) 2.824(10) 2.897(15) 2.8908(77) 2.994(11) 2.717(18) 2.970(13)

molecules between the planes achieving a three-dimensional network through hydrogen bonding (see Table 2). The Gd(1) and Na(1) atoms are nine- and seven-coordinated, respectively (Figure 2 and Table 3), building a distorted monocapped square antiprism around the gadolinium atom and a distorted pentagonal bipyramid around the sodium atom. Two oxygen atoms [O(1) and O(1a1)] connect the two symmetry-related gadolinium atoms of the pair [Gd(1) and

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Can˜adillas-Delgado et al.

Table 3. Selected Bond Lengths (Å) and Angles (°) for Compounds 1a and 2b Gd(1)-O(1w) Gd(1)-O(3w) Gd(1)-O(1) Gd(1)-O(1a1) Gd(1)-O(2a1) Gd(1)-O(4) Gd(1)-O(5b1) Gd(1)-O(6b1) Gd(1)-O(8c1) Gd(1) O(4) Na(1) Gd(1b1) O(6) Na(1b1) Gd(1e1) O(8) Na(1e1) Gd(1)-O(1w) Gd(1)-O(2w) Gd(1)-O(1) Gd(1)-O(2) Gd(1)-O(3a2) Gd(1)-O(4a2) Gd(1)-O(11) Gd(1)-O(13b2) Gd(1)-O(14b2) Gd(1) O(2) K(1c2) Gd(1d2) O(3) K(1c2) Gd(1) O(11) K(1c2)

Compound 1 2.383(4) Na(1)-O(2w) 2.468(5) Na(1)-O(3) 2.512(4) Na(1)-O(4) 2.543(4) Na(1)-O(6b1) 2.512(4) Na(1)-O(6c1) 2.375(4) Na(1)-O(7b1) 2.437(4) Na(1)-O(8c1) 2.542(4) 2.418(4) 101.06(15) Na(1e1) O(6) Gd(1b1) 90.59(13) Gd(1) O(1) Gd(1a1) 97.66(14) Na(1e1) O(6) Na(1b1)

116.60(16) 115.04(14) 95.97(15)

Compound 2 2.369(3) K(1)-O(2wb2) 2.436(3) K(1)-O(3w) 2.491(3) K(1)-O(2c2) 2.447(3) K(1)-O(3c2) 2.578(3) K(1)-O(11c2) 2.416(3) K(1)-O(12) 2.311(3) K(1)-O(12c2) 2.588(3) K(1)-O(13d2) 2.454(3) K(1)-O(14) 98.85(9) Gd(1b2) O(13) K(1a2) 99.01(9) Gd(1b2) O(14) K(1) 94.19(9) Gd(1) O(2w) K(1b2) K(1) O(12) K(1c2)

2.974(3) 3.042(10) 2.788(3) 2.731(3) 3.079(3) 2.642(3) 2.775(3) 2.957(3) 3.059(3) 91.56(9) 93.54(10) 96.06(9) 99.10(10)

2.310(7) 2.501(5) 2.508(5) 2.758(5) 2.371(4) 2.360(6) 2.588(5)

a Symmetry code: (a1) -x, -y, -z; (b1) 1 - x, -y, 1 - z; (c1) x, 1 + y, z; (d1) 1 - x, -y, -z; (e1) x, -1 + y, z; (f 1) x + 1, y, z; (g1) -x, -y, 1 - z; (h1) -x, -y - 1, -z; (i1) 1 - x, -1 - y, -z; (j1) x - 1, y - 1, z - 1; (k1) 1 - x, 1 - y, 1 - z. b Symmetry code: (a2) -1 + x, y, z; (b2) 1 - x, 1 - y, 2 - z; (c2) 2 - x, 1 - y, 2 - z; (d2) 1 + x, y, z; (e2) 3 - x, 1 - y, 2 - z; (f2) -x, 1 - y, 1 - z; (g2) 1 - x, 1 - y, 1 - z; (h2) x - 1, y, z - 1; (i2) x - 1, y + 1, z; (j2) 1 - x, 2 - y, 2 - z; (k2) x, 1 + y, z; (l2) 2 - x, 2 - y, 2 - z; (m2) -x, 2 - y, 2 - z; (n2) 1 - x, 2 - y, 1 - z;(o2) 2 - x, 1 - y, 1 - z.

Figure 3. A view of a fragment of the inorganic chain in 1 showing (a) the edge sharing octahedral and (b) the ball-and-stick picture. Green, yellow, red and blue colors correspond to Gd, Na, carboxylate-O, and water-O atoms, respectively.

Gd(1a1)]. Other three oxygen atoms [O(4), O(8c1), and O(6b1)] act as bridges between the Gd(1) and the Na(1) atoms, and one of these oxygens [O(6b1)] also links the Gd(1) to another sodium atom [Na(1k1); (k1) ) 1 - x, 1 - y, 1 - z]. This sequence leads to a chain constituted of alternating couples of Gd3+ and Na+ cations where each sodium atom is finally connected by oxygen atoms to another sodium atom and to two gadolinium atoms, and each gadolinium atom is connected to another gadolinium and to two sodium atoms (Figure 3). The O(1) and O(1a1) oxygen atoms act as µ-oxo bridges linking Gd(1) and Gd(1a1), with a Gd‚‚‚Gd distance of 4.264(14) Å and a GdO-Gd angle of 115.04(14)°. There are also two oxygen atoms

Figure 4. Coordination mode of the fully deprotonated bta4- ligand in 1. Symmetry code: (a1) -x, -y, -z; (b1) 1 - x, -y, 1 - z; (e1) x, -1 + y, z.

[O(6b1) and O(6c1)] between the Na(1) and Na(1k1) atoms, which act as µ-oxo bridges, the Na‚‚‚Na distance and the NaO-Na angle being 3.820(8) Å and 95.97(15)°, respectively. Each chain is linked to another one by bta4- ligands (along the b-axis) leading to a sheetlike structure. The fully deprotonated bta4- group in 1 exhibits a surprising efficiency as a ligand toward the gadolinium and sodium atoms because it is coordinated to them through all its carboxylateoxygen atoms (Figure 4). The aromatic ring of this ligand is planar, and it forms a dihedral angle of 27.3° with the reference plane constituted by the ion chains and the ligands. The plane of the first carboxylate group [C(7), O(1), O(2)], which chelates Gd(1a1) and also adopts a bridging mode to connect with Gd(1), forms 62.5° with the layer. The second one [C(8), O(3), O(4)], which chelates Na(1) and also acts as a monodentate ligand toward the Gd(1) atom through one of its two oxygen atoms [O(4)], forms an angle of 118.6° with the layer. The third one [C(9), O(5), O(6)], which chelates Gd(1b1) and connects this atom with two sodium atoms [Na(1b1), Na(1e1); (e1) ) x, -1 + y, z] through the oxygen O(6), makes a dihedral angle of 41.7° with the layer. The last one [C(10), O(7), O(8)] forms an angle of 55° with the layer and it acts as a bridge connecting Na(1e1), Na(1b1), and Gd(1e1) atoms. Crystal Structure of 2. The crystal structure of complex 2 can be described as a succession of layers parallel to the (a,c)plane, which are made up of chains of Gd3+ and K+ cations growing along the a-axis and connected by bta4- ligands. The layers are connected to each other by another bta4- ligand forming a three-dimensional network [Figure 5]. The three-dimensional network has pores, which accommodate a cluster of eight crystallization water molecules, and they are shared with coordinated water molecules (Figure 5 and Table 4). The total solvent-accessible volume of the pore in the unit cell is about 273.8 Å3, which accounts for 29.8% of the total cell volume.32 The Gd(1) and K(1) atoms are nine- and seven-coordinated, respectively (Figure 6 and Table 3), building a distorted monocapped square antiprism around the Gd(1) atom. Three of the oxygen atoms [O(2), O(11), and O(13b2)] connect Gd(1) to K(1c2). Other two oxygen atoms [O(3) and O(14c2)] and one coordinated water [O(2wd2)] link K(1c2) to Gd(1d2), which in turn is also connected to K(1e2) [(e2) ) 3 - x, 1 - y, 2 - z] by other three oxygen atoms. This sequence leads to a chain constituted by Gd3+ and K+ ions. As K(1c2) is also connected to K(1) through O(12) and O(12c2), a double chain along the

Zeolite-like Nanoporous Gadolinium Complexes

Crystal Growth & Design, Vol. 6, No. 1, 2006 91

Figure 5. Distorted brick-wall layer in 2, with bta4- units linking the inorganic chains and detail of the interstitial strand of the water molecules. Hydrogen bonds linking the water molecules are plotted in blue. Green, violet, red, and blue colors correspond to Gd, K, carboxylate-O, and water-O atoms, respectively.

Figure 6. A view of a fragment of the structure of 2 showing the atom numbering. Symmetry code: (a2) -1 + x, y, z; (b2) 1 - x, 1 y, 2 - z; (c2) 2 - x, 1 - y, 2 - z; (d2) 1 + x, y, z; (j2) 1 - x, 2 - y, 2 - z; (o2) 2 - x, 1 - y, 1 - z. Table 4. Intermolecular and Intramolecular Contacts (Å) in 2 Intermolecular D‚‚‚A O(1)‚‚‚O(6W) O(1W)‚‚‚O(5W) O(1W)‚‚‚O(7W) O(2W)‚‚‚O(4W) O(1)‚‚‚O(5Wd2) O(14)‚‚‚O(7Wj2) O(3W)‚‚‚O(4Wj2) O(3W)‚‚‚O(5Wj2) O(4W)‚‚‚O(4Wm2) O(6W)‚‚‚O(6Wn2) O(6W)‚‚‚O(7Wn2)

3.0438(96) 2.7527(79) 2.6525(93) 2.7595(65) 2.8693(89) 2.8706(74) 2.8012(98) 2.722(14) 2.9664(85) 2.738(13) 2.6756(95) Intramolecular

D‚‚‚A O(13)‚‚‚O(2W)

2.9292(37)

a-axis results with each gadolinium atom connected to two potassium atoms, and each potassium atom connected to two gadolinium and one potassium atoms (Figure 7). The nearest intrachain Gd‚‚‚Gd distance is 6.723(6) Å, indicating the absence of a direct interaction. The O(12) and O(12c2) oxygen atoms act as µ-oxo bridges linking two potassium atoms, with a K‚‚ ‚K distance of 4.125(3) Å and a K-O-K angle of 99.1(1)°. Each double chain is linked to another one by bta4- ligands

Figure 7. View of a fragment of the inorganic chains of 2 as (a) edgesharing octahedra and (b) ball-and-stick picture. Green, violet, red, and blue colors correspond to Gd, K, carboxylate-O, and water-O atoms, respectively.

along the c-axis, leading to the layers in the (a,c)-plane. The layers are interconnected by other bta4- ligands along the b-axis achieving the final three-dimensional structure. There are two independent bta4- ligands in this structure (see Figure 8). In the first one (Figure 8a), each carboxylate group adopts a chelating-bridging mode, connecting four gadolinium atoms [Gd(1), Gd(1a2), Gd(1f 1), Gd(1g2); (f 2) ) -x, 1 - y, 1 - z and (g2) ) 1 - x, 1 - y, 1 - z] and two potassium [K(1b2), K(1h2); (h2) ) x - 1, y, z - 1] atoms. This bta4- ligand connects the chains along the c-axis. The aromatic part of this ligand is planar, and it is parallel to the (a,c)-plane. Two of the carboxylate groups are coplanar with the phenyl ring, whereas the other two ones are out of the plane, and they form a dihedral angle of 93° with it. In the second one (Figure 8b), the phenyl ring forms a dihedral angle of 100° with the (a,c)-plane. Two of its four carboxylate groups adopt bidentate [at K(1c2) and K(1i2); (i2) ) x - 1, y + 1, z] and bridging modes [connecting gadolinium Gd(1) and Gd(1j2) and K(1) and K(1j2)) atoms; symmetry code: (j2) ) 1 - x, 2 - y, 2 - z]. The planes of these two carboxylate groups form a dihedral angle of 66° with the (a,c)-plane. The other two carboxylate groups also adopt bidentate [at Gd(1b2) and Gd(1k2);(k2) ) x, 1 + y, z] and bridging modes [connecting two potassium atoms (K(1), K(1a2),

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The use of the gel synthetic route demonstrates its ability to generate novel complexes from well-exploited ligand and metal combinations. We are currently extending our study to incorporate other lanthanide and additional rigid spacer ligands. We wish to identify whether the weaker interactions found in the present examples might be transferable to new systems. The results from these studies will be reported in due course. Acknowledgment. Funding for this work is provided by the Ministerio Espan˜ol de Educacio´n y Ciencia and the Consejerı´a de Educacio´n, Cultura y Deportes (Gobierno Auto´nomo de Canarias) through projects MAT2004-03112 and PI2002/175, respectively. Predoctoral fellowships from CajaCanarias (L.C.D.) and Gobierno Auto´nomo de Canarias (F.S.D.) are acknowledged, We also thank the Consejerı´a de Industrı´a y Desarrollo Tecnolo´gico del Gobierno de Canarias for support to O.F. Supporting Information Available: Crystallographic data of the structures 1 and 2 in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org. Data for 1 and 2 are deposited with the Cambridge Crystallographic Data Centre, nos. CCDC 259229 and 259230, respectively.

References (1) (2) (3) (4)

Figure 8. (a, b) Coordination modes of the fully deprotonated bta4ligands in 2. Symmetry code: (a2) -1 + x, y, z; (b2) 1 - x, 1 - y, 2 - z; (c2) 2 - x, 1 - y, 2 - z; (f 2) -x, 1 - y, 1 - z; (g2) 1 - x, 1 y, 1 - z; (h2) -1+ x, y, -1+ z; (i2) -1 + x, 1 + y, z; (j2) 1 - x, 2 y, 2 - z; (k2) x, 1 + y, z; (l2) 2 - x, 2 - y, 2 - z.

(5)

K(1j2), K(1l2); (l2) ) 2 - x, 2 - y, 2 - z)]. These two carboxylate groups form a dihedral angle of 47° with the (a,c)plane. This last bta4- ligand links the layers along the b-axis leading to the three-dimensional network. Let us finish this structural part discussing briefly the different structural roles of the univalent alkaline cations in 1 and 2. Both structures contain nine-coordinated gadolinium(III) cation ion and fully deprotonated bta4- anion. However, the alkaline cations exhibit different coordination numbers, seven (Na+) and nine (K+). This has a strong influence on the resulting structures, which are two- (1) and three-dimensional (2). This noninnocent structural role of the alkaline cations was previously observed in other carboxylate-containing complexes such as the compounds of formula [NaCr(bpym)(ox)2]‚5H2O34 and [K(H2O)Cr(bpym)(ox)2]35 (bpym ) 2,2′-bipyrimidine and ox2- ) oxalate dianion). Neutral hexagonal (Na) and tetragonal (K) layered structures were found for these complexes, the sodium atom being six-coordinated (four oxalate-oxygen atoms from two ox2ligands and two bpym-nitrogen atoms) and the potassium one being eight-coordinated (one oxygen of a water molecule, two bpym-nitrogen atoms and five oxalate-oxygens from three ox groups).

(8)

Conclusions Two new bta-containing GdIII coordination polymers incorporating alkali cations [Na+ (1) and K+ (2)] have been prepared. The resulting structures are two- (1) and three-dimensional (2). The structures accommodate crystallization and coordination water molecules. These compounds may be considered as novel nanocomposites of unusual structures within the benzenetetracarboxylate frameworks.

(6) (7)

(9) (10) (11) (12)

(13)

(14)

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