Synthesis, Crystal Structure and Thermal Stability of a New Cadmium(II) Polymer Based on 1H-pyrazole-3-carboxylic Acid Ligand 1

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1 34 卷 4 期结构化学 (JIEGOU HUAXUE) Vol. 34, No Chinese J. Struct. Chem Synthesis, Crystal Structure and Thermal Stability of a New Cadmium(II) Polymer Based on 1H-pyrazole-3-carboxylic Acid Ligand 1 GAO Gui-Yuan a SUN Li-Na a FENG Chao a QU Zhi-Rong b2 FAN Yan b ZHAO Hong a2 a (School of Chemistry and Chemical Engineering, Southeast University, Nanjing , China) b (Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou , China) ABSTRACT A novel Cd(II) coordination polymer, [CdCl(Hpc)H 2 O] n (1, H 2 pc = 1H-pyrazole-3- carboxylic acid), was synthesized by the reaction of CdCl 2 2.5H 2 O with H 2 pc, and structurally characterized by IR spectrum, UV-Vis spectrum, elemental analysis, single-crystal X-ray diffraction, as well as thermal analysis. Compound 1 crystallizes in monoclinic, P2 1 /n space group with a = (3), b = (3), c = (4) Å, β = (4)º, V = (5) Å 3, Z = 4, C 4 H 5 CdClN 2 O 3, M r = , D c = g/cm 3, F(000) = 528.0, µ = mm -1, R = and wr = The central metals adopt distorted octahedral geometry. Carboxyl groups of the ligand connect Cd(II) into a one-dimensional chain, which further constructs a two-dimensional network by halogen bridging. Such two-dimensional structures are finally connected into a three-dimensional supramolecular architecture due to the hydrogen bonds and intermolecular π-π interactions. In addition, complex 1 has high thermal stability. Keywords: Cd(II) coordination polymer, pyrazolecarboxylic acid, crystal structure, supramolecular architecture, thermal stability; DOI: /j.cnki INTRODUCTION Diverse derivatives of the pyrazole carboxylic acid can form different kinds of complexes due to pyrazole N atoms and carboxyl O atoms [1-3]. Besides, suitable substitutions together with their positions on pyrazole play an important role [4-7]. And so such, the multifunctional ligand, pyrazole dicarboxylic acid, especially 3,5-pyrazoledicarboxylic acid (H 3 pdc), has received much attention in recent years [8-13]. Recently, 3,4-pyrazoledicarboxylic acid has been reported [14]. Their three different protons can easily lose though adjusting the ph value to coordinate with transition, lanthanide and alkaline earth metals to construct novel 1D-, 2D- and 3D-structures [15-17]. 1H-pyrazole-3-carboxylic acid (H 2 pc) has similar coordination sites involving both pyrazole nitrogen atoms and carboxylate oxygen atoms with H 3 pdc [8, 14]. The two protons which come from the pyrazole ring and carboxyl group can be easily deprotonated to get Hpc 1- and pc 2-. So, it is very useful to synthe- size and build these new complexes. However, to the best of our knowledge, less attention has been paid to compounds containing 1H-pyrazole-3-carboxy- Received 23 October 2014; accepted 11 December 2014 (CCDC ) 1 This work was supported by the National Natural Science Foundation of China (No ) and New Energy Technology Co. Ltd. of Ai Naji of Jiangsu Province (No ) 2 Corresponding authors. Born in 1976, professor. zhaohong@seu.edu.cn and born in 1971, professor. quzr@hznu.edu.cn

2 GAO G. Y. et al.: Synthesis, Crystal Structure and Thermal Stability of a New 612 Cadmium(II) Polymer Based on 1H-pyrazole-3-carboxylic Acid Ligand No. 4 lic acid (H 2 pc). In this paper, a new two-dimensional cadmium(ii) complex with 1H-pyrazole-3-carboxylic acid which acts as a tridentate ligand has been prepared, charac- terized by IR spectra, X-ray diffraction and UV-Vis spectrum method. Meanwhile, we have also studied its thermal stabilities. 2 EXPERIMENTAL 2. 1 Material All chemicals and solvents purchased were of analytical grade and used without further purifica- tion. 1H-pyrazole-3-carboxylic acid and cadmium(ii) chloride hemi(pentahydrate) were purchased from Aldrich. Crystal structure was determined on an Xcalibur, Atlas, Gemini ultra diffractometer. Ele- mental analyses for carbon, hydrogen, and nitrogen were performed on a Perkin Elmer 240C elemental analyzer. IR spectra were obtained with KBr pellets from 400 to 4000 cm -1 using a Shimadzu Irpre- stige-21 spectrophotometer. The UV-vis spectrum was recorded on a UV-2450 spectrophotometer. Thermogravimetric Analysis (TGA) data were recor- ded on a SDT-Q600 analyser from TA instruments Synthesis of the title complex A solution of 1H-pyrazole-3-carboxylic acid ( g, 0.2 mmol) in 8 ml of methanol was added to a solution of cadmium(ii) chloride he- mi(pentahydrate) ( g, 0.2 mmol) in 8 ml distilled water. The resulting colorless solution was allowed to stand at ambient temperature for several days. The colorless crystals of 1 suitable for X-ray diffraction analysis were obtained. Yield: g (58.9% based on Cd). Anal. Calcd. (%) for C 4 H 5 CdClN 2 O 3 : C, 17.35; H, 1.82; N, Found (%): C, 17.37; H, 1.85; N, IR data (KBr pellet, cm -1 ): 3487(w), 3242(m), 3139(m), 3125(w), 1671(m), 1577(vs), 1508(w), 1485(m), 1376(s), 1241(w), 1210(s), 1072(s), 998(s), 813(m), 783(s), 684(m), 615(w), 559(m), 492(m) Single-crystal structure determination A colorless block crystal of complex 1 with dimensions of 0.20mm 0.25mm 0.30mm was selected for measurement. The data were collected at 293(2) K by an Xcalibur, Atlas, Gemini ultra diffractometer equipped with a graphite-mono- chromatized MoKα radiation (λ = Å). The data sets were corrected for absorption by multi-scan technique in the range of 3.10 θ 24.96º ( 8 h 8, 12 k 12, 12 l 12). A total of 5867 reflections were collected, of which 1299 were unique with R int = and 1168 were observed with I > 2σ(I). The crystal is of monoclinic group, P2 1 /n space group with a = (3), b = (3), c = (4) Å, β = (4)º, V = (5) Å 3, Z = 4, D c = g/cm 3, F(000) = 528.0, the final R = , wr = (w = 1/[σ 2 (F o 2 ) + (0.0197P) P], where P = (F o 2 + 2F c 2 )/3), S = 1.06, ( /σ) max = 0.002, ( ρ) max = 0.38 and ( ρ) min = 0.31 e/å 3. The structure was solved with the ShelXS [18] structure solution program using direct methods and refined with the ShelXL [19] refine- ment package using Least-Squares minimisation. All H atoms were placed in the calculated positions and refined constrained to ride on their parent atoms, with C H = 0.93 Å, N H = 0.80 Å, O H = 0.80~ 0.85 Å, and U iso (H) = 1.2U eq (C, N) for pyrazole H atoms and 1.5U eq (O) for the aqua. The selected bond lengths and bond angles are listed in Table 1. Rele- vant hydrogen bonding parameters of 1 are provided in Table 2. 3 RESULTS AND DISCUSSION 3. 1 Crystal structural description of the title complex 1 Single-crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the monoclinic space group P2 1 /n and exhibits a 2D network. The asymmetric unit of 1 contains one Cd(II), one Hpc -1 ligand, one Cl anion and one coordinated water molecule. The molecular structure (Fig. 1) exhibits that each six-coordinated Cd(1) atom is defined by one N atom (N(2)) and two carboxyl O atoms (O(1), O(2B)) from two Hpc -1 ligands, one O atom from

3 2014 Vol. 33 结构化学 (JIEGOU HUAXUE)Chinese J. Struct. Chem. 613 coordinated water (O(3)) and two bridging Cl atoms (Cl(1), Cl(1A)), leading to a distorted octahedral coordination geometry. O(1), N(2), O(2B) and Cl(1) atoms form the equator plane of the distorted octahedron, while O(3) and Cl(1A) occupy two apical positions with the angle O(3) Cd(1) Cl(1A) of (5)º. The Cd O bond lengths range from (17) to (18) Å, the Cd N bond length is 2.258(2) Å, and the Cd Cl bond lengths are (7) and (7) Å, respectively. The selected bond lengths and bond angles for 1 are given in Table 1. Table 1. Selected Bond Distances (Å) and Bond Angles ( ) for 1 Bond Dist. Bond Dist. Bond Dist. Cd(1) O(1) Cd(1) N(2) (18) (2) Cd(1) O(3) Cd(1) Cl(1) (2) (7) Cd(1) O(2B) Cd(1) Cl(1A) (17) (7) Angle ( ) Angle ( ) Angle ( ) Cl(1) Cd(1) O(1) Cl(1) Cd(1) N(2) Cl(1) Cd(1) O(2B) Cl(1) Cd(1) O(3) Cl(1) Cd(1) Cl(1A) Cl(1A) Cd(1) O(3) 88.38(4) (5) 98.96(5) 85.70(5) 84.69(2) (5) Cl(1A) Cd(1) N(2) Cl(1A) Cd(1) O(2B) Cl(1B) Cd(1) O(1) O(1) Cd(1) O(2B) O(1) Cd(1) O(3) O(1) Cd(1) N(2) (6) 92.93(5) 99.32(5) (7) 87.18(7) 70.67(6) O(2B) Cd(1) N(2) O(2B) Cd(1) O(3) O(3) Cd(1) N(2) Cd(1) Cl(1) Cd(1A) 99.97(7) 81.86(7) 84.78(7) 95.31(2) Symmetry transformation: A: x, y, 2 z; B: 0.5+x, 0.5 y, 0.5+z Table 2. Hydrogen Bond Lengths (Å) and Bond Angles ( ) D H A d(d H) d(h A) d(d A) DHA O(3) H(3V) Cl(1D) O(3) H(3W) O(2E) C(1) H(1) O(3F) 0.80(4) 0.85(3) (4) 1.92(3) (2) 2.753(3) 3.423(4) 151(3) 167(3) 149 Symmetry codes: D: 1 x, y, 2 z; E: 0.5 x, 0.5+y, 1.5 z; F: 1 x, 1 y, 2 z Fig. 1. Coordination environments of the Cd(II) centers in compound 1 (Thermal ellipsoids are drawn at the 50% level). Symmetry codes: A: x, y, 2 z; B: 0.5+x, 0.5 y, 0.5+z; C: 0.5 x, 0.5+y, 1.5 z As shown in Fig. 2, the carboxyl of each tridentate ligand connects with two Cd(II) atoms to form a 1D chain. In each chain, the adjacent Cd(II) atoms are bridged through two Cl anions to form a 2D coor- dination polymer (Fig. 3). The distances between two neighbouring Cd atoms are (4) and

4 GAO G. Y. et al.: Synthesis, Crystal Structure and Thermal Stability of a New Cadmium(II) Polymer Based on 1H-pyrazole-3-carboxylic Acid Ligand 614 [20-22] (3) Å, respectively (Fig. 4). The complexes in atoms are quite rare which Cd(II) coordinates with two bridging halogen broadens the compound of this kind. Fig. 2., and polymer 1 further A view of 1D chain of compound 1 connected by Hpc-1 and Cd(II) center along the a-axis Fig. 3. Fig. 4. No. 4 Adjacent 1D chains bridged by two Cl-1 to form a 2D structure A view of the 2D network of compound 1 without organic ligands, Cl-1 and H2O, showing the distances of the inorganic Cd(II) centers along the a-axis

5 2014 Vol. 33 结 构 化 学 JIEGOU HUAXUE Chinese J. Struct. Chem. 615 In the crystal structure of 1, the coordinated water C(1) H(1) O(3F) (3.423(4) Å). Owing to the molecules take part in the formation of three dif- existence of multiple intermolecular hydrogen bonds, ferent intermolecular hydrogen bonds (Table 2). The the 2D nets construct a 3D supramolecular architec- O H Cl hydrogen bond is formed by O(3) and ture (Fig. 5). In addition, intermolecular π-π interac- coordinated Cl(1) anion (O(3) H(3V) Cl(1D): tion existing between the pyrazole rings (centroid (2) Å); the O H O hydrogen bond is built by centroid separation is (17), (17) Å, -1 O(3) and carboxylate O2 from ligand Hpc (O(3) respectively) plays an important role in forming the H(3W) O(2E): 2.753(3) Å). The O atom acts as supramolecular structure of 1 (Fig. 6). both proton donor and acceptor in hydrogen bond Fig. 5. 3D supramolecular network in compound 1 linked by 2D nets by hydrogen-bonding interactions. Symmetry codes: B: 0.5+x, 0.5 y, 0.5+z; D: 1 x, y, 2 z; E: x, 1+y, z Fig. 6. π-π stacking in complex 1

6 GAO G. Y. et al.: Synthesis, Crystal Structure and Thermal Stability of a New 616 Cadmium(II) Polymer Based on 1H-pyrazole-3-carboxylic Acid Ligand No FT-IR spectra IR spectrum exhibits a strong broad band around 3000~3500 cm -1 region which can be assigned to the characteristic peaks of OH vibration of coor- dination water. This band overlaps the N H and C H stretching vibration absorption of pyrazole rings at 3487 and 3139 cm -1, respectively. No absorption band was detected between 1690 and 1730 cm -1, indicating the carboxylic group was deprotonated [23]. Furthermore, strong peak appearing at 1577 cm -1 was attributed to the asymmetric stretching vibration of ν as(coo - ), while the absorption peaks at 1367 cm -1 match to the symmetric stretching vibration of ν s(coo - ). The new absorption bands were observed at 559 and 492 in the IR spectrum of complex 1, which may be due to the metal-nitrogen and metal-oxygen interactions [24] UV-Vis spectra analysis The liquid-states of UV-Vis spectra of free H 2 pc ligand and its complex 1 were measured at room temperature. In the recorded wavelength region of 200~700 nm, the ligand shows one main absorption peak at 221 nm (Fig. 7), owing to the π-π transition of the pyrazole ring. The peak of complex 1 is at 205 nm. The difference may be due to the π-π transition of pyrazole ring slightly shifted by the coordination between the H 2 pc ligand and Cd(II) ion. Fig. 7. UV-Vis absorption spectra of complex 1 and H 2 pc which were dissolved in methanol at room temperature 3. 4 Thermal analysis To examine the thermal stability of the title complex, thermal gravimetric (TG) and differential thermal gravimetry (DSC) were carried out by heating [CdCl(Hpc)(H 2 O)] n from 50 to 600 under nitrogen flow at the heating rate of 15 min -1. TG curve (Fig. 8) exhibits two main weight loss steps. The first one starts from 50 to 195 with a mass loss of 6.62%, which might correspond to the release of coordinate water (Calcd. 6.50%). The second degradation stage in the tem- perature range of 195~425 with weight loss of 39.04% is presumably owing to the decom- position of Hpc - (Calcd %). As shown in Fig. 8, the product is thermally stable from 220 to 330 in this stage, which may attribute to the stronger coordination bond. Above 330, Hpc - begins to decompose. The final experimental residual percentage (54.34%) is consistent with the calculated value of 53.38%, which reveals that the final product is CdCl 2.

7 2014 Vol. 33 结构化学 (JIEGOU HUAXUE)Chinese J. Struct. Chem. 617 Fig. 8. TG curve of complex 1 under a nitrogen atmosphere 4 CONCLUSION By using 1H-pyrazole-3-carboxylic acid as the pyrazolecarboxylate ligand, we have successfully synthesized a novel two-dimensional Cd(II) polymer: [CdCl(Hpc)H 2 O] n (1), which has been characterized by X-ray structural analysis and also supported by thermal analysis. The structure of 1 contains distorted octahedral Cd (II) centers coordinated by one water molecule, two Hpc -1 ligands and two Cl anions to form a 2D network, and a 3D supramolecular framework is further construct though intermolecular hydrogen bonds and π-π interactions. Owing to the π-π transition shifted of pyrazole ring, the UV absorption peak of complex 1 is at 205 nm. Thermal analysis reveals the skeleton of 1 collapses above 330, indicating its high thermal stability. REFERENCES (1) Han, W.; Cheng, M. L.; Liu, Q.; Wang, L. D.; Wu, Y. J. Syntheses, crystal structures and electrochemical properties of cobalt and nickel complexes based on 5-methyl-1H-pyrazole-3-carboxylic acid ligand. Chin. J. Inorg. Chem. 2012, 9, (2) Hu, F. L.; Yin, X. H.; Mi, Y.; Zhang, Y.; Zhang, S. S.; Huang, Z. J. Synthesis and crystal structures of supramolecular compounds: [Cu(mpca) 2(H 2O)] 3H 2O and [Cu 2(mpca) 2(pyr) 4]. J. Coord. Chem. 2009, 22, (3) An, C. X.; Lu, Y. C.; Shang, Z. F.; Zhang, Z. H. Syntheses and crystal structures of the metal complexes based on pyrazolecarboxylic acid ligands. Inorg. Chem. Acta 2008, 9/10, (4) Kazuki, U.; Shigeki, K.; Takao, I. N N bond cleavage of hydrazines with a multiproton-esponsive pincer-type iron complex. J. Am. Chem. Soc. 2013, 18, (5) Liu, L. F.; Cai, B.; He, C. S.; Wu, J. Z.; Wang, Q. M.; Yu, Y. Coordination and topology versatility of metal-organic frameworks based on cadmium iodide and 5-azaarylpyrazole-3-carboxylic acids. Inorg. Chem. Comm. 2013, 30, (6) Tian, W.; Han, G. Q.; Zhu, J.; Qi, J. J.; Chen, Q. Q.; Zhao, J. T.; Zheng, C. H.; Zhang, L.; Zhou, Y. J.; Lv, J. G. Synthesis and acrosin inhibitory activities of 5-phenyl-1Hpyrazole-3-carboxylic acid amide derivatives. Bioorg. Med. Chem. Lett. 2013, 14, (7) Chen, Y.; Liu, C. B.; Gong, Y. N.; Zhong, J. M.; Wen, H. L. Syntheses, crystal structures and antibacterial activities of six cobalt(ii) pyrazole carboxylate complexes with helical character. Polyhedron 2012, 1, (8) King, P.; Clerac, R.; Anson, C. E.; Powell, A. K. The building block approach to extended solids: 3,5-pyrazoledicarboxylate coordination compounds of increasing dimensionality. J. Chem. Soc., Dalton Trans. 2004, 6, (9) Xia, J.; Zhao, B.; Wang, H. S.; Shi, W.; Ma, Y.; Song, H. B.; Cheng, P.; Liao, D. Z.; Yan, S. P. Two- and three-dimensional lanthanide complexes: synthesis, crystal structures, and properties. Inorg. Chem. 2007, 9,

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