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Synthesis, crystal structures and photoluminescence of Zn–Ln heterometallic polymers based on pyridine-2,3-dicarboxylic acid
Inorganic Chemistry Communications 12 (2009) 761–765
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Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, crystal structures and photoluminescence of Zn–Ln heterometallic polymers based on pyridine-2,3-dicarboxylic acid Li Chen a, Xiao-Ming Lin a, Yin Ying a, Qing-Guang Zhan a, Ze-Hong Hong a, Jun-Yong Li a, Ng Seik Weng b, Yue-Peng Cai a,* a
Key Lab of Technology on Electrochemical Energy Storage and Power Generation in Guangdong Universities, School of Chemistry and Environment, South China Normal University, Guangzhou 510006, PR China b Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
a r t i c l e
i n f o
Article history: Received 20 May 2009 Accepted 8 June 2009 Available online 10 June 2009 Keywords: 3d–4f heterometallic complex Pyridine-2,3-dicarboxylic acid Synthesis and characterization Crystal structures Luminescence
a b s t r a c t Three new two-dimensional 3d–4f isostructural heterometallic coordination polymers, namely [Ln2Zn(2,3-pydc)4(H2O)44H2O]n (Ln = Sm (1), Eu (2), Gd (3), 2,3-pydcH2 = pyridine-2,3-dicarboxylic acid) have been successfully synthesized by the hydrothermal reactions of Ln2O3, Zn(NO3)26H2O, H2pydc and H2O. X-ray diffraction analyses reveal that they possess a 2D heterometallic framework containing 1D lanthanide chains based on dimeric [Ln(2,3-pydc)2(H2O)2]2 unit. The Zn(II) ion, which is six-coordinated by four oxygen and two nitrogen atoms from four 2,3-pydc2 ligands, as a bridge, links the lanthanide chains to make the 1D chains further extend into 2D layer framework. Furthermore, the neighboring layers are assembled into three-dimensional supramolecular network through inter-layer O–H O and C– H O hydrogen-bond interactions. In addition, the solid-state luminescent property of complex 2 was investigated. Ó 2009 Elsevier B.V. All rights reserved.
Recently, the design and synthesis of heterometallic complexes, such as 3d–4f or 4d–4f organic-metal systems, have received intense interest [1,2], not only because their fascinating structural topology, but also the potential applications as functional materials in magnetism, molecular adsorption, fluorescence, catalysis and chemical separation [3,4]. Up to now, the preparation of extended structures with the 3d–4f heterometallic coordination frameworks by selecting the organic ligands and mixed metal ions is still a challenge to chemists [5,6], owing to the variable and flexible coordination behavior of 4f metal ions, which have different coordination characteristics from transition metals. Therefore, choice of suitable ligands play an important role in determining the topologies and properties of coordination networks [7,8]. In these studies, pyridyl carboxylic acids are good choices for constructing heterometal-organic frameworks (HMOFs) due to the existence of both N and O atoms in the ligands, which can link both 3d and 4f metal ions [9–11]. However, compared with other pyridine-dicarboxylic acids, the use of 2,3-pydc2 ligand in HMOFs chemistry has been very limited and only one example of the three-dimensional La– Zn compound was reported so far [12,13]. It is probably due to the following reasons: First, it often behaves like picolinic acid, acting as a chelating bidentate ligand through the nitrogen atom and one oxygen atom of the 2-position carboxylate group [14], and the
* Corresponding author. Tel.: +86 20 33033475; fax: +86 20 85215865. E-mail address: [email protected] (Y.-P. Cai). 1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2009.06.009
3-position carboxyl group remains idle. Second, it prefers decarboxylation of the 2-position carboxylate group and transforms to nicotinic acid under hydrothermal conditions [1,15]. In the past few years, we have prepared a series of new MOFs in the presence of heterocyclic multi-carboxylic acids via the hydrothermal synthesis and their intriguing architectures have also been investigated [16–18]. In order to continue and extend our research work, we chose 2,3-pyridinedicarboxylic acid as the bridging ligand to prepare 3d–4f heterometallic coordination polymers. Since the hydrothermal synthesis technique has proved to be a powerful method for preparation of polymeric coordination complexes, take advantage of this method, three isostructural 3d–4f heterometallic complexes [Ln2Zn(2,3-pydc)4(H2O)44H2O]n [Ln = Sm (1), Eu (2), Gd (3)], have been successfully synthesized based on 2,3-pyridinedicarboxylic acid, which show interesting two-dimensional layerlike structures. Herein reported are synthesis, characterization and photoluminescence of three 2D Zn–Ln complexes. The three compounds were obtained by the reactions of Ln2O3, Zn(NO3)26H2O, 2,3-pydcH2 and H2O in hydrothermal condition at 130 °C for 3 days [19]. The formulae of three complexes were identified by elemental analysis, IR and X-ray diffraction. In the IR spectra of 1–3, the strong and broad absorption bands in the rage of 3200–3500 cm1 are assigned as the characteristic peak of OH vibration from the water molecules. Moreover their IR spectra also shows characteristic bands of carboxyl groups at near 1578 cm1 for the antisymmetric stretching and at near 1467 and 1396 cm1 for the symmetric stretching [20].
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The structural analysis [21] reveals that these complexes are isostructural (Table S1), accordingly, the structure of 2 is described representatively here in detail. Complex 2 exhibits a 2D layer-like coordination framework constructed from 1D lanthanide-carboxylate chains and zinc(II) centers as inter-chain spacers, in which the asymmetric unit contains two europium ions, one zinc ion, four crystallographically unique 2,3-pydc2 ligands, four coordinated water and four lattice water molecules. As shown in Fig. 1, Each Eu (III) ion is nine-coordinated by seven oxygen atoms from four 2,3-pydc2 ligands and two coordinating water molecules to furnish a tricapped trigonal prism geometry (Fig. S1a). The distances of Eu–O range from 2.347(3) to 2.553(3) Å (average value 2.450(3) Å) (Table S2), comparable to those in other Eu(III) carboxylate complexes observed in our previous work [16,18]. The O–Eu– O bond angles fall in the range of 51.24(10)–143.37(11)°. Each Zn(II) center is six-coordinated by two nitrogen and four oxygen atoms from four 2,3-pydc2 ligands to form a slightly distorted octahedral geometry with two nitrogen atoms at the axial positions and the other four oxygen atoms are located on the plane (Fig. S1b). The0 average distances of Zn–O and Zn–N are 2.156(3) and 2.070(4) Å A. The angles of N(1)–Zn(1)–N(1)#3, O(2)#3–Zn(1)– O(2) and O(6)#4–Zn(1)–O(6)#5 are 180°, N(1)–Zn(1)–O(2) and N(1)–Zn(1)–O(6)#4 are 79.60(13)° and 90.44(14)°, respectively (Table S2), which are similar to those found in the related Ln–Zn complexes [22]. The four 2,3-pydc2 anions in the asymmetric unit of 1–3 adopt two coordination modes as depicted in Scheme 1, in which two carboxyl groups of each 2,3-pydcH2 ligand are deprotonated. In both coordination modes, two carboxyl groups of each 2,3-pydc2 ligand have the different relationship of configurations relevant to the pyridine core in 1–3, the 2-carboxyl group is almost coplanar with the pyridyl ring (dihedral angles 7.35(6)–10.32(6)°), however the 3-position results bent by the dihedral angles of 80.58(3)– 82.76(3)°, a conformation already observed in a series of transition/lanthanide metal complexes formed with pyridinedicarboxylic acids [12]. In coordination mode a, the nitrogen atoms and one of the 2-carboxylate oxygen atoms of 2,3-pydc2 ligand chelate one Zn2+ ion, and the other of the 2-carboxylate oxygen atoms and one of the 3-carboxylate oxygen atoms coordinate to one Eu(III) ion in a chelating fashion, whereas the other of the 3-carboxylate oxygen atoms is bonded to another Eu(III) ion. In mode b, in addition to the 2-carboxylate group chelating
Scheme 1. Two coordination modes of 2,3-pydc2 ligand in complexes 1–3, where coordination mode b was observed for the first time in 3d–4f complexes.
coordinated to one Eu(III) ions, one of the 2-carboxylate oxygen atoms cooperating with one of the 3-carboxylate oxygen atoms are chelated to another Eu(III) ion, and the other 3-carboxylate oxygen atom adopts a monodentate coordination mode, connecting one Zn(II) ion, leaving the remaining nitrogen atom alone. The coordination mode b of 2,3-pydc2 in 3d–4f complexes is reported for the first time. On the basis of such coordination modes of 2,3-pydc2 ligands and the characteristics of lanthanide ions with the affinity of oxygen, each pair of Eu(III) ions are combined by the two l2-bridging oxygen atoms from two 2,3-pydc2 ligands with a Eu Eu interatomic distance of 4.1839(5) Å, forming a basic binuclear structure unit [Eu(pydc)2(H2O)2]2 as secondary building units (SBUs) with a planar square Eu2O2 core. Two neighboring SBU units are further connected together through two carboxylate groups in bidentate bridging mode, giving rise to a 1D a zigzag chain along a-axis, as illustrated in Fig. S2. The Zn(II) ion as a bridging spacer, is coordinated by four 2,3-pydc2 ligands from two neighboring lanthanide chains, and makes the 1D chain further extend into the 2D layer in the ac plane (Fig. 2). Furthermore, these layers are assembled 3D supramolecular network via inter-layer O–H O and C–H O hydrogen-bond interactions between the lattice/coordinated water molecules and the carboxylate oxygen atoms/C–H bonds of pyridine rings from two adjacent layers (Fig. 3 and Table S3), obviously existence of which will contribute to the additional stability of these structures [23,24]. Compounds 1 and 3 are isomorphous of 2, and selected distances are listed in Table S2. Because the radii of Sm(III), Eu(III)
Fig. 1. Viewing plot of compound [Eu2Zn(pydc)4(H2O)44H2O]n, (2), all organic hydrogen atoms and uncoordinated water molecules were omitted for clarify.
L. Chen et al. / Inorganic Chemistry Communications 12 (2009) 761–765
and Gd(III) ions are very close to each other, the obvious effect of lanthanide contraction have not observed in the three Ln–Zn compounds. To examine the thermal stability of the complexes, the thermogravimetric analysis (TGA) of complexes 2–3 was carried out in nitrogen from 20 to 800 °C. The TGA curves of 2–3 were shown
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in Fig.S3, the thermogravimetric analysis (TGA) shows that compounds 2 and 3 have three steps of weight loss. The first weight loss (6.24% below 175 °C for 2 and 6.18% below 181 °C for 3) is assigned to the liberation of four free water molecules, which is in agreement with the calculated value of 6.13% for 2 and 6.08% for 3. The second weight loss (6.32% for 2 and 6.45% for 3) is in the
Fig. 2. 2D network representation of complex 2 along ac plane.
Fig. 3. 3D packing diagram through inter-layer O–H O and C–H O hydrogen bonding interactions.
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range of 180–250 °C, corresponding to the thermal decomposition and loss of three coordinated water molecules (calcd.: 6.18% for 2 and 6.08% for 3). The third stage occurs above 330 °C, corresponding to the thermal decomposition and loss of 2,3-pydc2 ligand in two compounds 2–3. The TG analysis results of 2–3 are almost identical, indicating that the thermal behaviors of the two compounds are very similar because of isostructuralism. Taking into account the excellent luminescent properties of Eu(III) ions, the luminescent properties of solid-state powder sample for 2 was qualitatively studied at room temperature. As shown in Fig. 4, compound 2 in the solid-state displays an intense red photoluminescence with emission at 580, 593,619, 652 and 695 nm, upon excitation at 338 nm. These emission bands were attributed to the 5D0 ? 7FJ (J = 0–4) transitions of the Eu(III)-centerd luminescence, respectively [25,26]. The small emission band, 5 D0–7F0 at 580 nm belongs to a symmetry-forbidden emission of the Eu(III) ions in 2, indicating Eu(III) ions with low symmetry and without an inversion center. The intensity of the 5D0–7F2 transition to the 5D0–7F1 transition is widely used as a measure of the coordination state and the site symmetry of the europium ion, since the emission band 5D0–7F1 at 593 nm is a magnetic dipole transition and its intensity should vary with the crystal field strength acting on the Eu(III) ion, while the strongest 5D0–7F2 transition is essentially purely electric dipole in character, and its intensity is extremely sensitive to the crystal field symmetry. This is consistent with the result of the single-crystal X-ray analysis. As far the luminescent properties of the ligand center could not be observed from emission spectra, it is probably due to the strong luminescent properties of the Eu(III) ion that may cover ligand-centered weak luminescence. In summary, three isostructural Zn–Ln heterometallic compounds 1–3 are successfully constructed from a hydrothermal reaction system containing organic ligand 2,3-pydcH2 with mixed-donor atoms (O and N). These compounds show an interesting 2D layer framework containing 1D lanthanide chains based on dimeric [Eu(2,3-pydc)2(H2O)2]2 units and the Zn(II) ions as interchain spacers. Most of the previously reported high dimensional metal-coordination polymer compounds are composed of either d-block metals or rare-earth metals with pyridine-2,3-dicarboxylatic acid, while 3d–4f heterometallic compounds with high dimensional structures are less common in the literature, in particular, three heterometallic compounds reported here are the second example of 2D Zn–Ln compounds containing 2,3-pydcH2 ligand. At the same time, the successful preparation of the three coordination polymers 1–3 provides valuable information for further construction of other 2D/3D 3d–4f frameworks. Clearly, the use of ligands with mixed-donor atoms is a key strategy in the crystalli-
Fig. 4. Solid-state emission spectrum of complex 2 at room temperature (excited at 338 nm).
zation of 3d–4f frameworks. Upon the addition of lanthanide ions, the luminescent property of the pydc2 ligand is affected. The intense red luminescence properties of the complexes 2 at room temperature suggest that the compound has great potential application as luminescent materials. Acknowledgements We are grateful to the National Natural Science Foundation of PR China (Grant No. 20772037), Science and Technology Planning Project of Guangdong Province (Grant No. 2006A10902002) and the N.S.F. of Guangdong Province (Grant No. 06025033) for financial support. Appendix A. Supplementary material CCDC 725551, 725552 and 725553 contains the supplementary crystallographic data for complexes 1–3. These data can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2009.06.009. References [1] W. Chen, H.-M. Yuan, J.-Y. Wang, Z.-Y. Liu, M.-Y. Yang, J.-S. Chen, J. Am. Chem. Soc. 125 (2003) 9266. [2] Y.-C. Liang, R. Cao, W.-P. Su, M.-C. Hong, W.J. Zhang, Angew. Chem., Int. Ed. 39 (2000) 3304. [3] F. Mori, T. Nogami, K.Y. Choi, H. Nojin, J. Am. Chem. Soc. 128 (2006) 1440. [4] F.-C. Liu, Y.-F. Zeng, J. Jiao, J.-R. Li, X.-H. Bu, J. Ribas, S.R. Batten, Inorg. Chem. 45 (2006) 6129. [5] Y.-O. Yang, W. Zhang, N. Xu, G.-F. Xu, D.-Z. Liao, K. Yoshimura, S.P. Yan, P. Cheng, Inorg. Chem. 46 (2007) 8454. [6] Y.-F. Zhou, F.-L. Jiang, D.-Q. Yuan, B.-L. Wu, R.-H. Wang, Z.-Z. Lin, M.-C. Hong, Angew. Chem., Int. Ed. 43 (2004) 5665. [7] M. Hong, Y. Zhao, W. Su, R. Cao, M. Fujita, Z. Zhou, A.S.C. Chan, J. Am. Chem. Soc. 122 (2000) 4819. [8] M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M.O. Keeffe, O.M. Yaghi, Science 295 (2002) 469. [9] B. Zhao, X.-Y. Chen, P. Cheng, D.-Z. Liao, S.-P. Yan, Z.-H. Jiang, J. Am. Chem. Soc. 126 (2004) 15394. [10] Y.-C. Liang, R. Cao, W.-P. Su, M.-C. Hong, W.-J. Zhang, Angew. Chem., Int. Ed. 39 (2000) 3304. [11] Y.-L. Liu, V.C. Kravtsov, D.A. Beauchamp, J.F. Eubank, M. Eddaoudi, J. Am. Chem. Soc. 127 (2005) 7266. [12] Q. Yue, J. Yang, G.-H. Li, G.-D. Li, W. Xu, J.-S. Chen, S.-N. Wang, Inorg. Chem. 44 (2005) 5241. [13] M. Li, J.-F. Xiang, L.-J. Yuan, S.-M. Wu, S.-P. Chen, J.-T. Sun, Crys. Growth Des. 6 (2006) 2036. [14] P. Sengupta, S. Ghosh, T.C.W. Mark, Polyhedron 20 (2001) 975. [15] L.A. Gerrard, P.T. Wood, Chem. Commun. (2000) 2107. [16] M.-S. Liu, Q.-Y. Yu, Y.-P. Cai, C.-Y. Su, X.-M. Lin, X.-X. Zhou, J.-W. Cai, Cryst. Growth Des. 8 (2008) 4083. [17] X.-X. Zhou, M.-S. Liu, X.-M. Lin, H.-C. Fang, J.-Q. Chen, D.-Q. Yang, Y.-P. Cai, Inorg. Chim. Acta 362 (2009) 1441. [18] X.-M. Lin, L. Chen, H.-C. Fang, Z.-Y. Zhou, X.-X. Zhou, J.-Q. Chen, A.-W. Xu, Y.-P. Cai, Inorg. Chim. Acta 362 (2009) 2619. [19] Synthesis of complexes Ln2Zn(2,3-pydc)4(H2O)44H2O]n (Ln = Sm (1), Eu (2), Gd (3), 2,3-pydcH2 = pyridine-2,3-dicarboxylic acid) are as follows: A mixture of Zn(NO3)26H2O (0.059 g, 0.2 mmol), pyridine-2,3-dicarboxylic acid (0.167 g, 1.0 mmol), distilled water (10 mL) and Ln2O3 (0.2 mmol, Sm2O3, 70 mg; Eu2O3, 70 mg; Gd2O3, 73 mg) was sealed in a 23-mL stainless steel reactor with a Teflon liner and heated directly at 130 °C from temperature for 72 h under autogenous pressure. The mixture was cooled to room temperature at a rate of 5 K/h. Crystals of 1, 2 and 3 were isolated by filtration, washed with distilled water, and dried in air (135, 106 and 109 mg for 1, 2 and 3, respectively). Anal. Calcd. for 1 C28H28Sm2ZnN4O24: C, 28.71; H, 2.41; N, 4.78. Found: C, 28.67; H, 2.43; N, 4.81%. FI-IR data (KBr, cm1): 3399 (vs), 1578 (s), 1467 (s), 1435 (m), 1395(m), 1109 (m), 879 (s), 727 (s). Anal. Calcd. for 2 C28H28Eu2Zn2N4O24: C, 28.65; H, 2.40; N,4.77. Found: C, 28.69; H, 2.42; N, 4.74%. IR (KBr, cm1): 3408 (vs), 1582 (s), 1469 (s), 1439 (m), 1396(m), 1114 (m), 881 (s), 725 (s). Anal. Calcd. for 3 C28H28Gd2ZnN4O24: C, 28.39; H, 2.38; N, 4.73; Found: C, 28.42; H, 2.36; N, 4.70%. FI-IR data (KBr, cm1): 3410 (vs), 1576 (s), 1470 (s), 1440 (m), 1398(m), 1117 (m), 883 (s), 723(s). [20] Y.-C. Liang, M.-C. Hong, R. Cao, W.-P. Su, Y.-J. Zhao, J.-B. Weng, R.-G. Xiong, Bull. Chem. Soc. Jpn. 75 (2002) 1521.
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0
a = 7.5966(9) Å [21] Crystal data for 01: triclinic space group P 1, A, b = 9.8980(11) Å A, c = 12.4518(14) A, a = 73.6030(10)°, b = 79.5310(10)°, c = 86.4160(10)°, V = Å 0 3 Z = 1, F(0 0 0) = 570, GOF = 1.038, final R1 = 0.0386, 883.17(17) Å A , 0 a = 7.6099(8) Å all data; 2: triclinic space group P 1, A, wR2 = 0.0818 for 0 0 A, a = 73.6220(10)°, b = 79.5370(10)°, c = Å b = 9.9213(10) Å A, c = 12.4617(13) 0 86.4080(10)°, V = 887.61(16) Å A3, Z = 1, F(0 0 0) = 572, GOF = 1.035, final R1 0= a = 7.5975(4) Å A, 0.0332, wR2 = 00.0724 for all data;0 3: triclinic space group P 1, A, a = 73.6190(10)°, b = 79.5310(10)°, c = Å b = 9.9065(6) Å A, c = 12.4583(7) 0 3 86.4460(10)°, V = 884.57(9) Å A , Z = 1, F(0 0 0) = 574, GOF = 1.049, final R1 = 0.0326, wR2 = 0.0746 for all data; Data collections of 1–3 were performed on a Bruker Apex II CCD diffractometer operating at 50 kV and 30 mA using Mo Ka radiation (k = 0.71073 nm). Multi-scan absorption corrections were applied for all the data sets using the APEX II program. All structures were solved by direct methods and refined by full-matrix least squares on F2 using the SHELXTL program package. All C-bound H atoms were geometrically positioned and allowed to ride on their parent atoms and refined isotropically. The C2 and N2,
[22] [23] [24] [25] [26]
C3 and N3 atoms of one pyridyl ring in one asymmetrical unit of compounds 1–3 possess the same position, and each atom has a site occupancy factor of 0.5. Two hydrogen atoms of each water molecule including the coordinated and lattice ones were restrained in idealized positions and isotropically refined with the O–H and H H distances restrained to 0.84(1) Å and 1.43(2)°, respectively, and Uiso values were set equal to 1.5Ueq (parent atom) for water H atoms. X.L. Wang, C. Qin, E.B. Wang, Y.G. Li, N. Hao, C.W. Hu, L. Xu, Inorg. Chem. 43 (2004) 1850. L. Pan, N.W. Zheng, Y.G. Wu, S. Han, R.Y. Yang, X.Y. Huang, J. Li, Inorg. Chem. 40 (2001) 828. Y.-L. Shen, J.-G. Mao, Inorg. Chem. 44 (2005) 5328. H.-X. Li, Z.-G. Ren, Y. Zhang, W.-H. Zhang, J.-P. Liang, Q. Shen, J. Am. Chem. Soc. 127 (2005) 1122. M.R. George, C.A. Golden, M.C. Grossel, Inorg. Chem. 45 (2006) 1739.
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Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, crystal structures and photoluminescence of Zn–Ln heterometallic polymers based on pyridine-2,3-dicarboxylic acid Li Chen a, Xiao-Ming Lin a, Yin Ying a, Qing-Guang Zhan a, Ze-Hong Hong a, Jun-Yong Li a, Ng Seik Weng b, Yue-Peng Cai a,* a
Key Lab of Technology on Electrochemical Energy Storage and Power Generation in Guangdong Universities, School of Chemistry and Environment, South China Normal University, Guangzhou 510006, PR China b Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
a r t i c l e
i n f o
Article history: Received 20 May 2009 Accepted 8 June 2009 Available online 10 June 2009 Keywords: 3d–4f heterometallic complex Pyridine-2,3-dicarboxylic acid Synthesis and characterization Crystal structures Luminescence
a b s t r a c t Three new two-dimensional 3d–4f isostructural heterometallic coordination polymers, namely [Ln2Zn(2,3-pydc)4(H2O)44H2O]n (Ln = Sm (1), Eu (2), Gd (3), 2,3-pydcH2 = pyridine-2,3-dicarboxylic acid) have been successfully synthesized by the hydrothermal reactions of Ln2O3, Zn(NO3)26H2O, H2pydc and H2O. X-ray diffraction analyses reveal that they possess a 2D heterometallic framework containing 1D lanthanide chains based on dimeric [Ln(2,3-pydc)2(H2O)2]2 unit. The Zn(II) ion, which is six-coordinated by four oxygen and two nitrogen atoms from four 2,3-pydc2 ligands, as a bridge, links the lanthanide chains to make the 1D chains further extend into 2D layer framework. Furthermore, the neighboring layers are assembled into three-dimensional supramolecular network through inter-layer O–H O and C– H O hydrogen-bond interactions. In addition, the solid-state luminescent property of complex 2 was investigated. Ó 2009 Elsevier B.V. All rights reserved.
Recently, the design and synthesis of heterometallic complexes, such as 3d–4f or 4d–4f organic-metal systems, have received intense interest [1,2], not only because their fascinating structural topology, but also the potential applications as functional materials in magnetism, molecular adsorption, fluorescence, catalysis and chemical separation [3,4]. Up to now, the preparation of extended structures with the 3d–4f heterometallic coordination frameworks by selecting the organic ligands and mixed metal ions is still a challenge to chemists [5,6], owing to the variable and flexible coordination behavior of 4f metal ions, which have different coordination characteristics from transition metals. Therefore, choice of suitable ligands play an important role in determining the topologies and properties of coordination networks [7,8]. In these studies, pyridyl carboxylic acids are good choices for constructing heterometal-organic frameworks (HMOFs) due to the existence of both N and O atoms in the ligands, which can link both 3d and 4f metal ions [9–11]. However, compared with other pyridine-dicarboxylic acids, the use of 2,3-pydc2 ligand in HMOFs chemistry has been very limited and only one example of the three-dimensional La– Zn compound was reported so far [12,13]. It is probably due to the following reasons: First, it often behaves like picolinic acid, acting as a chelating bidentate ligand through the nitrogen atom and one oxygen atom of the 2-position carboxylate group [14], and the
* Corresponding author. Tel.: +86 20 33033475; fax: +86 20 85215865. E-mail address: [email protected] (Y.-P. Cai). 1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2009.06.009
3-position carboxyl group remains idle. Second, it prefers decarboxylation of the 2-position carboxylate group and transforms to nicotinic acid under hydrothermal conditions [1,15]. In the past few years, we have prepared a series of new MOFs in the presence of heterocyclic multi-carboxylic acids via the hydrothermal synthesis and their intriguing architectures have also been investigated [16–18]. In order to continue and extend our research work, we chose 2,3-pyridinedicarboxylic acid as the bridging ligand to prepare 3d–4f heterometallic coordination polymers. Since the hydrothermal synthesis technique has proved to be a powerful method for preparation of polymeric coordination complexes, take advantage of this method, three isostructural 3d–4f heterometallic complexes [Ln2Zn(2,3-pydc)4(H2O)44H2O]n [Ln = Sm (1), Eu (2), Gd (3)], have been successfully synthesized based on 2,3-pyridinedicarboxylic acid, which show interesting two-dimensional layerlike structures. Herein reported are synthesis, characterization and photoluminescence of three 2D Zn–Ln complexes. The three compounds were obtained by the reactions of Ln2O3, Zn(NO3)26H2O, 2,3-pydcH2 and H2O in hydrothermal condition at 130 °C for 3 days [19]. The formulae of three complexes were identified by elemental analysis, IR and X-ray diffraction. In the IR spectra of 1–3, the strong and broad absorption bands in the rage of 3200–3500 cm1 are assigned as the characteristic peak of OH vibration from the water molecules. Moreover their IR spectra also shows characteristic bands of carboxyl groups at near 1578 cm1 for the antisymmetric stretching and at near 1467 and 1396 cm1 for the symmetric stretching [20].
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The structural analysis [21] reveals that these complexes are isostructural (Table S1), accordingly, the structure of 2 is described representatively here in detail. Complex 2 exhibits a 2D layer-like coordination framework constructed from 1D lanthanide-carboxylate chains and zinc(II) centers as inter-chain spacers, in which the asymmetric unit contains two europium ions, one zinc ion, four crystallographically unique 2,3-pydc2 ligands, four coordinated water and four lattice water molecules. As shown in Fig. 1, Each Eu (III) ion is nine-coordinated by seven oxygen atoms from four 2,3-pydc2 ligands and two coordinating water molecules to furnish a tricapped trigonal prism geometry (Fig. S1a). The distances of Eu–O range from 2.347(3) to 2.553(3) Å (average value 2.450(3) Å) (Table S2), comparable to those in other Eu(III) carboxylate complexes observed in our previous work [16,18]. The O–Eu– O bond angles fall in the range of 51.24(10)–143.37(11)°. Each Zn(II) center is six-coordinated by two nitrogen and four oxygen atoms from four 2,3-pydc2 ligands to form a slightly distorted octahedral geometry with two nitrogen atoms at the axial positions and the other four oxygen atoms are located on the plane (Fig. S1b). The0 average distances of Zn–O and Zn–N are 2.156(3) and 2.070(4) Å A. The angles of N(1)–Zn(1)–N(1)#3, O(2)#3–Zn(1)– O(2) and O(6)#4–Zn(1)–O(6)#5 are 180°, N(1)–Zn(1)–O(2) and N(1)–Zn(1)–O(6)#4 are 79.60(13)° and 90.44(14)°, respectively (Table S2), which are similar to those found in the related Ln–Zn complexes [22]. The four 2,3-pydc2 anions in the asymmetric unit of 1–3 adopt two coordination modes as depicted in Scheme 1, in which two carboxyl groups of each 2,3-pydcH2 ligand are deprotonated. In both coordination modes, two carboxyl groups of each 2,3-pydc2 ligand have the different relationship of configurations relevant to the pyridine core in 1–3, the 2-carboxyl group is almost coplanar with the pyridyl ring (dihedral angles 7.35(6)–10.32(6)°), however the 3-position results bent by the dihedral angles of 80.58(3)– 82.76(3)°, a conformation already observed in a series of transition/lanthanide metal complexes formed with pyridinedicarboxylic acids [12]. In coordination mode a, the nitrogen atoms and one of the 2-carboxylate oxygen atoms of 2,3-pydc2 ligand chelate one Zn2+ ion, and the other of the 2-carboxylate oxygen atoms and one of the 3-carboxylate oxygen atoms coordinate to one Eu(III) ion in a chelating fashion, whereas the other of the 3-carboxylate oxygen atoms is bonded to another Eu(III) ion. In mode b, in addition to the 2-carboxylate group chelating
Scheme 1. Two coordination modes of 2,3-pydc2 ligand in complexes 1–3, where coordination mode b was observed for the first time in 3d–4f complexes.
coordinated to one Eu(III) ions, one of the 2-carboxylate oxygen atoms cooperating with one of the 3-carboxylate oxygen atoms are chelated to another Eu(III) ion, and the other 3-carboxylate oxygen atom adopts a monodentate coordination mode, connecting one Zn(II) ion, leaving the remaining nitrogen atom alone. The coordination mode b of 2,3-pydc2 in 3d–4f complexes is reported for the first time. On the basis of such coordination modes of 2,3-pydc2 ligands and the characteristics of lanthanide ions with the affinity of oxygen, each pair of Eu(III) ions are combined by the two l2-bridging oxygen atoms from two 2,3-pydc2 ligands with a Eu Eu interatomic distance of 4.1839(5) Å, forming a basic binuclear structure unit [Eu(pydc)2(H2O)2]2 as secondary building units (SBUs) with a planar square Eu2O2 core. Two neighboring SBU units are further connected together through two carboxylate groups in bidentate bridging mode, giving rise to a 1D a zigzag chain along a-axis, as illustrated in Fig. S2. The Zn(II) ion as a bridging spacer, is coordinated by four 2,3-pydc2 ligands from two neighboring lanthanide chains, and makes the 1D chain further extend into the 2D layer in the ac plane (Fig. 2). Furthermore, these layers are assembled 3D supramolecular network via inter-layer O–H O and C–H O hydrogen-bond interactions between the lattice/coordinated water molecules and the carboxylate oxygen atoms/C–H bonds of pyridine rings from two adjacent layers (Fig. 3 and Table S3), obviously existence of which will contribute to the additional stability of these structures [23,24]. Compounds 1 and 3 are isomorphous of 2, and selected distances are listed in Table S2. Because the radii of Sm(III), Eu(III)
Fig. 1. Viewing plot of compound [Eu2Zn(pydc)4(H2O)44H2O]n, (2), all organic hydrogen atoms and uncoordinated water molecules were omitted for clarify.
L. Chen et al. / Inorganic Chemistry Communications 12 (2009) 761–765
and Gd(III) ions are very close to each other, the obvious effect of lanthanide contraction have not observed in the three Ln–Zn compounds. To examine the thermal stability of the complexes, the thermogravimetric analysis (TGA) of complexes 2–3 was carried out in nitrogen from 20 to 800 °C. The TGA curves of 2–3 were shown
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in Fig.S3, the thermogravimetric analysis (TGA) shows that compounds 2 and 3 have three steps of weight loss. The first weight loss (6.24% below 175 °C for 2 and 6.18% below 181 °C for 3) is assigned to the liberation of four free water molecules, which is in agreement with the calculated value of 6.13% for 2 and 6.08% for 3. The second weight loss (6.32% for 2 and 6.45% for 3) is in the
Fig. 2. 2D network representation of complex 2 along ac plane.
Fig. 3. 3D packing diagram through inter-layer O–H O and C–H O hydrogen bonding interactions.
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range of 180–250 °C, corresponding to the thermal decomposition and loss of three coordinated water molecules (calcd.: 6.18% for 2 and 6.08% for 3). The third stage occurs above 330 °C, corresponding to the thermal decomposition and loss of 2,3-pydc2 ligand in two compounds 2–3. The TG analysis results of 2–3 are almost identical, indicating that the thermal behaviors of the two compounds are very similar because of isostructuralism. Taking into account the excellent luminescent properties of Eu(III) ions, the luminescent properties of solid-state powder sample for 2 was qualitatively studied at room temperature. As shown in Fig. 4, compound 2 in the solid-state displays an intense red photoluminescence with emission at 580, 593,619, 652 and 695 nm, upon excitation at 338 nm. These emission bands were attributed to the 5D0 ? 7FJ (J = 0–4) transitions of the Eu(III)-centerd luminescence, respectively [25,26]. The small emission band, 5 D0–7F0 at 580 nm belongs to a symmetry-forbidden emission of the Eu(III) ions in 2, indicating Eu(III) ions with low symmetry and without an inversion center. The intensity of the 5D0–7F2 transition to the 5D0–7F1 transition is widely used as a measure of the coordination state and the site symmetry of the europium ion, since the emission band 5D0–7F1 at 593 nm is a magnetic dipole transition and its intensity should vary with the crystal field strength acting on the Eu(III) ion, while the strongest 5D0–7F2 transition is essentially purely electric dipole in character, and its intensity is extremely sensitive to the crystal field symmetry. This is consistent with the result of the single-crystal X-ray analysis. As far the luminescent properties of the ligand center could not be observed from emission spectra, it is probably due to the strong luminescent properties of the Eu(III) ion that may cover ligand-centered weak luminescence. In summary, three isostructural Zn–Ln heterometallic compounds 1–3 are successfully constructed from a hydrothermal reaction system containing organic ligand 2,3-pydcH2 with mixed-donor atoms (O and N). These compounds show an interesting 2D layer framework containing 1D lanthanide chains based on dimeric [Eu(2,3-pydc)2(H2O)2]2 units and the Zn(II) ions as interchain spacers. Most of the previously reported high dimensional metal-coordination polymer compounds are composed of either d-block metals or rare-earth metals with pyridine-2,3-dicarboxylatic acid, while 3d–4f heterometallic compounds with high dimensional structures are less common in the literature, in particular, three heterometallic compounds reported here are the second example of 2D Zn–Ln compounds containing 2,3-pydcH2 ligand. At the same time, the successful preparation of the three coordination polymers 1–3 provides valuable information for further construction of other 2D/3D 3d–4f frameworks. Clearly, the use of ligands with mixed-donor atoms is a key strategy in the crystalli-
Fig. 4. Solid-state emission spectrum of complex 2 at room temperature (excited at 338 nm).
zation of 3d–4f frameworks. Upon the addition of lanthanide ions, the luminescent property of the pydc2 ligand is affected. The intense red luminescence properties of the complexes 2 at room temperature suggest that the compound has great potential application as luminescent materials. Acknowledgements We are grateful to the National Natural Science Foundation of PR China (Grant No. 20772037), Science and Technology Planning Project of Guangdong Province (Grant No. 2006A10902002) and the N.S.F. of Guangdong Province (Grant No. 06025033) for financial support. Appendix A. Supplementary material CCDC 725551, 725552 and 725553 contains the supplementary crystallographic data for complexes 1–3. These data can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2009.06.009. References [1] W. Chen, H.-M. Yuan, J.-Y. Wang, Z.-Y. Liu, M.-Y. Yang, J.-S. Chen, J. Am. Chem. Soc. 125 (2003) 9266. [2] Y.-C. Liang, R. Cao, W.-P. Su, M.-C. Hong, W.J. Zhang, Angew. Chem., Int. Ed. 39 (2000) 3304. [3] F. Mori, T. Nogami, K.Y. Choi, H. Nojin, J. Am. Chem. Soc. 128 (2006) 1440. [4] F.-C. Liu, Y.-F. Zeng, J. Jiao, J.-R. Li, X.-H. Bu, J. Ribas, S.R. Batten, Inorg. Chem. 45 (2006) 6129. [5] Y.-O. Yang, W. Zhang, N. Xu, G.-F. Xu, D.-Z. Liao, K. Yoshimura, S.P. Yan, P. Cheng, Inorg. Chem. 46 (2007) 8454. [6] Y.-F. Zhou, F.-L. Jiang, D.-Q. Yuan, B.-L. Wu, R.-H. Wang, Z.-Z. Lin, M.-C. Hong, Angew. Chem., Int. Ed. 43 (2004) 5665. [7] M. Hong, Y. Zhao, W. Su, R. Cao, M. Fujita, Z. Zhou, A.S.C. Chan, J. Am. Chem. Soc. 122 (2000) 4819. [8] M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M.O. Keeffe, O.M. Yaghi, Science 295 (2002) 469. [9] B. Zhao, X.-Y. Chen, P. Cheng, D.-Z. Liao, S.-P. Yan, Z.-H. Jiang, J. Am. Chem. Soc. 126 (2004) 15394. [10] Y.-C. Liang, R. Cao, W.-P. Su, M.-C. Hong, W.-J. Zhang, Angew. Chem., Int. Ed. 39 (2000) 3304. [11] Y.-L. Liu, V.C. Kravtsov, D.A. Beauchamp, J.F. Eubank, M. Eddaoudi, J. Am. Chem. Soc. 127 (2005) 7266. [12] Q. Yue, J. Yang, G.-H. Li, G.-D. Li, W. Xu, J.-S. Chen, S.-N. Wang, Inorg. Chem. 44 (2005) 5241. [13] M. Li, J.-F. Xiang, L.-J. Yuan, S.-M. Wu, S.-P. Chen, J.-T. Sun, Crys. Growth Des. 6 (2006) 2036. [14] P. Sengupta, S. Ghosh, T.C.W. Mark, Polyhedron 20 (2001) 975. [15] L.A. Gerrard, P.T. Wood, Chem. Commun. (2000) 2107. [16] M.-S. Liu, Q.-Y. Yu, Y.-P. Cai, C.-Y. Su, X.-M. Lin, X.-X. Zhou, J.-W. Cai, Cryst. Growth Des. 8 (2008) 4083. [17] X.-X. Zhou, M.-S. Liu, X.-M. Lin, H.-C. Fang, J.-Q. Chen, D.-Q. Yang, Y.-P. Cai, Inorg. Chim. Acta 362 (2009) 1441. [18] X.-M. Lin, L. Chen, H.-C. Fang, Z.-Y. Zhou, X.-X. Zhou, J.-Q. Chen, A.-W. Xu, Y.-P. Cai, Inorg. Chim. Acta 362 (2009) 2619. [19] Synthesis of complexes Ln2Zn(2,3-pydc)4(H2O)44H2O]n (Ln = Sm (1), Eu (2), Gd (3), 2,3-pydcH2 = pyridine-2,3-dicarboxylic acid) are as follows: A mixture of Zn(NO3)26H2O (0.059 g, 0.2 mmol), pyridine-2,3-dicarboxylic acid (0.167 g, 1.0 mmol), distilled water (10 mL) and Ln2O3 (0.2 mmol, Sm2O3, 70 mg; Eu2O3, 70 mg; Gd2O3, 73 mg) was sealed in a 23-mL stainless steel reactor with a Teflon liner and heated directly at 130 °C from temperature for 72 h under autogenous pressure. The mixture was cooled to room temperature at a rate of 5 K/h. Crystals of 1, 2 and 3 were isolated by filtration, washed with distilled water, and dried in air (135, 106 and 109 mg for 1, 2 and 3, respectively). Anal. Calcd. for 1 C28H28Sm2ZnN4O24: C, 28.71; H, 2.41; N, 4.78. Found: C, 28.67; H, 2.43; N, 4.81%. FI-IR data (KBr, cm1): 3399 (vs), 1578 (s), 1467 (s), 1435 (m), 1395(m), 1109 (m), 879 (s), 727 (s). Anal. Calcd. for 2 C28H28Eu2Zn2N4O24: C, 28.65; H, 2.40; N,4.77. Found: C, 28.69; H, 2.42; N, 4.74%. IR (KBr, cm1): 3408 (vs), 1582 (s), 1469 (s), 1439 (m), 1396(m), 1114 (m), 881 (s), 725 (s). Anal. Calcd. for 3 C28H28Gd2ZnN4O24: C, 28.39; H, 2.38; N, 4.73; Found: C, 28.42; H, 2.36; N, 4.70%. FI-IR data (KBr, cm1): 3410 (vs), 1576 (s), 1470 (s), 1440 (m), 1398(m), 1117 (m), 883 (s), 723(s). [20] Y.-C. Liang, M.-C. Hong, R. Cao, W.-P. Su, Y.-J. Zhao, J.-B. Weng, R.-G. Xiong, Bull. Chem. Soc. Jpn. 75 (2002) 1521.
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0
a = 7.5966(9) Å [21] Crystal data for 01: triclinic space group P 1, A, b = 9.8980(11) Å A, c = 12.4518(14) A, a = 73.6030(10)°, b = 79.5310(10)°, c = 86.4160(10)°, V = Å 0 3 Z = 1, F(0 0 0) = 570, GOF = 1.038, final R1 = 0.0386, 883.17(17) Å A , 0 a = 7.6099(8) Å all data; 2: triclinic space group P 1, A, wR2 = 0.0818 for 0 0 A, a = 73.6220(10)°, b = 79.5370(10)°, c = Å b = 9.9213(10) Å A, c = 12.4617(13) 0 86.4080(10)°, V = 887.61(16) Å A3, Z = 1, F(0 0 0) = 572, GOF = 1.035, final R1 0= a = 7.5975(4) Å A, 0.0332, wR2 = 00.0724 for all data;0 3: triclinic space group P 1, A, a = 73.6190(10)°, b = 79.5310(10)°, c = Å b = 9.9065(6) Å A, c = 12.4583(7) 0 3 86.4460(10)°, V = 884.57(9) Å A , Z = 1, F(0 0 0) = 574, GOF = 1.049, final R1 = 0.0326, wR2 = 0.0746 for all data; Data collections of 1–3 were performed on a Bruker Apex II CCD diffractometer operating at 50 kV and 30 mA using Mo Ka radiation (k = 0.71073 nm). Multi-scan absorption corrections were applied for all the data sets using the APEX II program. All structures were solved by direct methods and refined by full-matrix least squares on F2 using the SHELXTL program package. All C-bound H atoms were geometrically positioned and allowed to ride on their parent atoms and refined isotropically. The C2 and N2,
[22] [23] [24] [25] [26]
C3 and N3 atoms of one pyridyl ring in one asymmetrical unit of compounds 1–3 possess the same position, and each atom has a site occupancy factor of 0.5. Two hydrogen atoms of each water molecule including the coordinated and lattice ones were restrained in idealized positions and isotropically refined with the O–H and H H distances restrained to 0.84(1) Å and 1.43(2)°, respectively, and Uiso values were set equal to 1.5Ueq (parent atom) for water H atoms. X.L. Wang, C. Qin, E.B. Wang, Y.G. Li, N. Hao, C.W. Hu, L. Xu, Inorg. Chem. 43 (2004) 1850. L. Pan, N.W. Zheng, Y.G. Wu, S. Han, R.Y. Yang, X.Y. Huang, J. Li, Inorg. Chem. 40 (2001) 828. Y.-L. Shen, J.-G. Mao, Inorg. Chem. 44 (2005) 5328. H.-X. Li, Z.-G. Ren, Y. Zhang, W.-H. Zhang, J.-P. Liang, Q. Shen, J. Am. Chem. Soc. 127 (2005) 1122. M.R. George, C.A. Golden, M.C. Grossel, Inorg. Chem. 45 (2006) 1739.