Synthesis, Crystal Structure and Luminescence of a Cadmium(II) Coordination Polymer with 3,6-Connected rtl Topology 1

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1 35 卷 2 期 结构化学 (JIEGOU HUAXUE) Vol. 35, No Chinese J. Struct. Chem Synthesis, Crystal Structure and Luminescence of a Cadmium(II) Coordination Polymer with 3,6-Connected rtl Topology 1 XUE Li-Ping 2 SHAN Li-Li FENG Wen-Jing (College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang , China) ABSTRACT A new cadmium(ii) coordination polymer, [Cd(Hcna) 2 ] n (1), was hydrothermally synthesized based on 5-(4-carboxyphenoxy)nicotinic acid (H 2 cna) organic linker. X-ray singlecrystal diffraction determination reveals that 1 crystallizes in the monoclinic P2 1 /c space group, with a = (2), b = (17), c = (3) Å, β = (3), V = (4) Å 3, Z = 2, M r = , D c = Mg/m 3, μ = mm -1, F(000) = 628, the final R = and wr = for 2263 observed reflections with I > 2σ(I). In 1, the Cd(II) cations are connected by nicotiniate units to form a two-dimensional (2D) layer, and it is further linked through benzoate units to form a three-dimensional (3D) structure. Topologically, the structure of 1 represents a 3,6-connected 3D rtl topology. Furthermore, thermal stability and photoluminescent property of 1 have also been investigated. Keywords: cadmium coordination polymer, crystal structure, 5-(4-carboxyphenoxy)nicotinic acid, rtl topology, luminescence; DOI: /j.cnki INTRODUCTION The recent exponential growth in the synthesis and structural characterization of coordination polymers (CPs) has been driven in part by their fascinating structural diversities, functional properties and a wide range of potential applications [1-3]. Although significant progress in this area has presently been achieved, the rational design and synthesis of CPs with desired structures and properties still remain a grand challenge, in view of many factors affecting the synthetic procedure [4-7]. Especially, the molecule size, backbone rigidity and coordination ability of organic ligands are among the very key factors for the assembly of topologically new CPs with functional properties. On the other hand, organic ligands based on ether-linked benzene polycarboxylates have drawn increasing focus because the freely-rotating ether bond may lead to structural diversity for the construction of CPs [8-12]. Here, we have selected tritopic Y-shaped 5-(4-carboxyphenoxy)nicotinic acid (H 2 cna) as a functional building block on account of the following considerations: (a) H 2 cna is a flexible ligand allowing the rotation of two aromatic rings around the O bond, thus making H 2 cna a versatile flexible and semirigid pyridine-dicarboxylate building block; (b) H 2 cna is endowed with nicotiniate and benzoate groups, in which the cooperation of benzoate groups and the functional nicotinic moiety may exhibit collaborative coordination ability with the metal ions during the self-assembly process; (c) Received 15 June 2015; accepted 6 September 2015 (CCDC ) 1 This work was supported by the Natural Science Foundation of China ( ) for the financial support. 2 Corresponding authors. Doctor, majoring in material chemistry. lpxue@163.com

2 XUE L.P. et al.: Synthesis, Crystal Structure and Luminescence of a 294 Cadmium(II) Coordination Polymer with 3,6-Connected rtl Topology No. 2 H 2 cna possesses two carboxyl groups that may be partially or completely deprotonated, depending on the ph. In addition, to our knowledge, H 2 cna has not been adequately explored in the construction of CPs. Taking into account these factors, we herein report the synthesis, crystal structure and luminescent property of a Cd(II) CP constructed from H 2 cna ligand. The compound exhibited 3,6-connected 3D rtl topology. Furthermore, the thermal stability and photoluminescent property of the compound have also been investigated 2 EXPERIMENTAL All chemicals for the syntheses were purchased from commercial sources and used without further purification. The hydrothermal reaction was performed in a 30 ml Teflon-lined autoclave under autogenous pressure. Elemental analyses for C, H, and N were carried out on a Flash 2000 elemental analyzer. The IR spectra were recorded as KBr pellets on a Nicolet Avatar-360 spectrometer in the range of 4000~400 cm 1. Thermogravimetric analyses (TGA) were carried out on a SDTQ600 thermogravimetric analyzer. A platinum pan was used for heating the sample at a heating rate of 10 /min under N 2 atmosphere. Powder X-ray diffraction (PXRD) measurements were performed on a Bruker D8- ADVANCE X-ray diffractometer with CuKα radiation (λ = Å). Fluorescence measurements were recorded with a Hitachi F4500 fluorescence spectrophotometer Synthesis of compound [Cd(Hcna) 2 ] n A mixture of H 2 cna (25.9 mg, 0.1 mmol), Cd(NO 3 ) 2 4H 2 O (30.8 mg, 0.1 mmol), NaOH (4.0 mg, 0.1 mmol) and 8 ml deionized water was sealed in a 30 ml Teflon-lined stainless steel vessel and heated at 140 C for five days under autogenous pressure, followed by cooling to room temperature. Colourless block crystals of 1 were collected by filtration (yield: 29% based on H 2 cna). Elemental analysis calcd. (%) for C 26 H 16 N 2 O 10 Cd: C, 49.62; H, 2.55; N, Found: C, 49.71; H, 2.57; N, IR data (KBr, cm -1 ): 3051(w), 2987(w), 1714(s), 1605(m), 1586(m), 1551(s), 1504(m), 1453(m), 1276(m), 1247(m), 1206(m), 1159(s), 1100(m), 1064(m), 979(w), 959(m), 886(w), 848(m), 813(m), 786(m), 766(m), 757(m), 686(s) X-ray structure determination The structure of 1 was determined by singlecrystal X-ray diffraction technique. Diffraction data were collected on a Bruker SMART Apex CCD diffractometer with MoKa radiation (λ = Å) at 293 K. Data reduction and absorption correction were made with SADABS software [13]. The structure was solved by direct methods with SHELXS-97 [14] and refined by full-matrix least-squares methods on F 2 using the program SHELXL-97 [15]. All non-hydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms were placed at the calculation positions. Selected bond distances and bond angles of 1 are summarized in Table 1. Crystal data for 1: monoclinic, space group P2 1 /c, a = (2), b = (17), c = (3) Å, β = (3), V = (4) Å 3, Z = 2, M r = , D c = Mg/m 3, μ = mm -1, F(000) = 628, the final R = and wr = for 2263 observed reflections with I > 2σ(I) and R = and wr = for all data. (Δρ) max = and (Δρ) min = e/å 3. The goodness-of-fit indicator (S) is Table 1. Selected Bond Lengths (Å) and Bond Angles ( ) Bond Dist. Bond Dist. Bond Dist. Cd(1) O(2) (12) Cd(1) O(3)# (14) Cd(1) N(1)# (15) Angle ( ) Angle ( ) Angle ( ) O(2)#3 Cd(1) O(2) O(2) Cd(1) O(3)# (5) O(2) Cd(1) N(1)# (5) O(2) Cd(1) N(1)# (5) N(1)#1 Cd(1) N(1)# O(2) Cd(1) O(3)# (5) N(1)#1 Cd(1) O(3)# (5) N(1)#2 Cd(1) O(3)# (5) O(3)#4 Cd(1) O(3)# Symmetry transformation: #1: x, 0.5 y, z; #2: 1 x, y 0.5, 0.5 z; #3: 1 x, y, 1 z; #4: x 1, 0.5 y, z; #5: 2 x, y 0.5, 0.5 z

3 2016 Vol. 35 结构化学 (JIEGOU HUAXUE)Chinese J. Struct. Chem RESULTS AND DISCUSSION in Fig. 1, the Cd(II) cation shows a distorted octahedral geometry, coordinated by four oxygen atoms of X-ray crystallographic data show that 1 crystallizes in the monoclinic space group P2 1 /c and forms a 3D framework. The asymmetric unit of 1 contains one independent Cd(II) cation in a inversion centre carboxyl groups and two nitrogen atoms from H 2 cna ligands. The Cd N distance is (15) Å and the distances of Cd O are (12) and (14) Å, respectively. and one monodeprotonated H 2 cna anion. As shown Fig. 1. Coordination environment of Cd 2+ ion in 1. Symmetry transformation used to generate the equivalent atoms: (#1) x, 0.5 y, z; (#2) 1 x, y 0.5, 0.5 z In 1, the partly deprotonated Hcna ligand adopts a µ 3 -coordination mode, in which two carboxylate groups exhibit the same monodentate coordination mode, and attain orientations with a (58) dihedral angle. Noticeably, the Hcna ligand here is not only a simple multicarboxylate ligand, but also can afford a nitrogen atom to bond the Cd(II) cation. The interlinkage between the nicotiniate units and Cd(II) cations generates a 2D grid layer parallel to the bc plane, and it further joins the adjacent layers through benzoate units of Hcna along the a axis, leading to a 3D framework (Fig. 2a and Fig. 2b). To get further insight into the structure of 1, a topological analysis of the 3D framework was performed using a topological approach [16]. From the topological viewpoint, the overall network topology can be described as a rutile (rtl)-type 3,6-connected topology with the Schläfli symbol of (4 6 2 ) 2 - ( ), in which the Hcna ligands are considered as 3-connected nodes and the Cd(II) cations as 6- connected nodes (Fig. 3). Fig. 2. 2D layer structure connected by nicotiniate units (a) and view of the 3D net (b) Fig. 3. Chematic representation of the 3D rtl framework

4 XUE L.P. et al.: Synthesis, Crystal Structure and Luminescence of a 296 Cadmium(II) Coordination Polymer with 3,6-Connected rtl Topology No. 2 The underprotonation of 1 is confirmed by IR spectral data, since a strong band at 1714 cm -1 from COOH was observed. Strong absorption bands between 1247 and 1605 cm -1 can be assigned to the coordinated carboxylate groups. The IR spectrum of compound 1 is consistent with its single-crystal X-ray analysis. Moreover, 1 exhibits excellent stability in air and is insoluble in various solvents such as methanol, ethanol, toluene, acetonitrile and N,N-dimethylformamide. To evaluate the thermal stability of 1, thermogravimetric analysis was performed under N 2 atmosphere in the temperature range of 30~800 at a heating rate of 10 C min -1. As shown in Fig. 4a, the thermogravimetric curve shows high stability of 1, which is evident from the beginning loss in 340. In addition, PXRD technique has been used to check the phase purity of the bulky samples in the solid state. The experimental PXRD patterns of 1 agree with the simulated patterns from the single-crystal structures to confirm the phase purity of 1 (Fig. 4b). Fig. 4. (a) TGA curve for 1. (b) XRD patterns of 1 simulated from X-ray single-crystal diffraction data and the experimental data Recently, photoluminescence research of many cadmium(ii) coordination polymers constructed from conjugated organic linkers has attracted increasing attention [17-19]. Therefore, solid-state photoluminescent properties of free H 2 cna ligand and 1 have been investigated at room temperature. As illustrated in Fig. 5, the free H 2 cna ligand is emissive showing a band at 502 nm (λ ex = 420 nm), since the Cd(II) cation is difficult to oxidize or reduce due to its d 10 configuration. Obviously, the fluorescent emission band of 1 (λ em = 514 nm, λ ex = 356 nm) can be attributed to the intraligand π* π charge transitions of H 2 cna owing to their close emission bands. Fig. 5. Solid-state emission spectrum of 1

5 2016 Vol. 35 结构化学 (JIEGOU HUAXUE)Chinese J. Struct. Chem CONCLUSION has been synthesized and characterized. The complex is a 3D structure with 3,6-connected rtl topo- In conclusion, a new cadmium coordination polymer based on 5-(4-carboxyphenoxy)nicotinic acid logy. Furthermore, luminescence property of the complex is also investigated. REFERENCES (1) Du, M.; Li, C.; Chen, M.; Ge, Z.; Wang, X.; Wang, L.; Liu, C. Divergent kinetic and thermodynamic hydration of a porous Cu(II) coordination polymer with exclusive CO 2 sorption selectivity. J. Am. Chem. Soc. 2014, 136, (2) Xu, B.; Li, Z.; Jiang, Y.; Li, C. A luminescent Cd(II) coordination polymer constructed from isophthalic acid and 1,3-bis-(4-pyridyl)propane. Chin. J. Struct. Chem. 2015, 34, (3) Wang, G. X.; Wu, H. X.; Li, Z. H.; Zhao, B. T. Controlled self-assembly of two coordination polymers via subtly varying bis(2-methyl imidazole) ligands: from 3-connected (6,3) net to 4-connected sql net. Chin. J. Struct. Chem. 2014, 7, (4) Zhang, X.; Fan, L.; Sun, Z.; Zhang, W.; Li, D.; Dou, J.; Han, L. Syntheses, structures, and properties of a series of multidimensional metal-organic polymers based on 3,3,5,5 -biphenyltetracarboxylic acid and N donor ancillary ligands. Cryst. Growth Des. 2013, 13, (5) Yuan, S.; Wang, H.; Wang, D.; Lu, H.; Feng, S.; Sun, D. Reactant ratio-modulated six new copper(i)-iodide coordination complexes based on diverse [Cu m I m ] aggregates and biimidazole linkers: syntheses, structures and temperature-dependent luminescence properties. CrystEngComm. 2013, 15, (6) Wu, Y.; Li, D.; Zhao, J.; Fang, Z.; Dong, W.; Yang, G.; Wang, Y. Isomeric phenylenediacetates as modular tectons for a series of Zn II /Cd II coordination polymers incorporating flexible bis(imidazole) co-ligands. CrystEngComm. 2012, 14, (7) Xue, L. P.; Chang, X. H.; Ma, L. F.; Wang, L. Y. Four d 10 metal coordination polymers based on bis(2-methyl imidazole) spacers: syntheses, interpenetrating structures and photoluminescence properties. RSC Adv. 2014, 4, (8) Liu, G.; Li, X.; Xin, L.; Wang, L. Two topologically new trinodal cobalt(ii) metal-organic frameworks characterized as a 1D metallic oxide and a 2D 3D penetrated porous solid. CrystEngComm. 2012, 14, (9) Li, S.; Han, M.; Liu, G.; Ma, L.; Wang, L. Guest-induced single-crystal-to-single-crystal transformations of a new 4-connected 3D cadmium(ii) metal-organic framework. RSC Adv. 2015, 5, (10) Han, Z.; Cheng, X.; Chen, X. Effect of the size of aromatic chelate ligands on the frameworks of metal dicarboxylate polymers: from helical chains to 2-D networks. Cryst. Growth Des. 2005, 5, (11) Yang, J.; Zhang, X.; Cheng, J.; Zhang, J.; Yao, Y. ph influence on the structural variations of 4,4 -oxydiphthalate coordination polymers. Cryst. Growth Des. 2012, 12, (12) Xu, J.; Su, W.; Hong, M. Two lanthanide-natrium pillared-layer frameworks constructed from 4,4 -oxybis(benzoic acid) and oxalate. Inorg. Chem. Commun. 2011, 13, (13) Sheldrick, G. M. SADABS, University of Göttingen, Göttingen, Germany (14) Sheldrick, G. M. SHELXS-97. Program for the Solution of Crystal Structures. University of Göttingen: Germany (15) Sheldrick, G. M. SHELXL-97. Program for the Refinement of Crystal Structures. University of Göttingen: Germany (16) Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. Interpenetrating metal-organic and inorganic 3D networks: a computer-aided systematic investigation. Part I. Analysis of the Cambridge structural database. CrystEngComm. 2004, 6, (17) Guo, Q.; Xu, C.; Zhao, B.; Jia, Y.; Hou, H.; Fan, Y. Syntheses, characterizations, and properties of five interpenetrating complexes based on 1,4-benzenedicarboxylic acid and a series of benzimidazole-based linkers. Cryst. Growth Des. 2012, 12, (18) Zheng, S.; Yang, J.; Yu, X.; Chen, X.; Wong, W. Syntheses, structures, photoluminescence, and theoretical studies of d 10 metal complexes of 2,2 -dihydroxy-[1,1 ]binaphthalenyl-3,3 -dicarboxylate. Inorg. Chem. 2004, 43, (19) Xue, L.; Li, Z.; Li, S.; Wang, J. Synthesis, crystal structure and fluorescent property of a new one-dimensional cadmium(ii) coordination polymer based on 3,4-thiophenedicarboxylic acid and 1,10-phenanthroline. Chin. J. Struct. Chem. 2013, 32,