XIAO Guo-Bin FANG Zi-Han YAO Xiao-Qiang LIU Jia-Cheng

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A Three-dimensional Self-penetrating Co(II) Coordination Polymer Containing a 2→ 3Parallelly Polycatenated Subnet①

XIAO Guo-Bin FANG Zi-Han YAO Xiao-Qiang②LIU Jia-Cheng

(730070)

Hydrothermal assembly of Co2+ion, a bis-imidazole ligand BIMB (BIMB = 1,4-bis(imidazol-1-yl)benzene) and a rigid bidentate linker 2,6-naphthalenedicarboxylic acid (H2ndc), yields a novel three-dimensional (3) self-penetrating coordination polymer {[Co(BIMB)(ndc)]?H2O}n(1). Complex 1 exhibits {65.8} topology and contains a2→3parallel polycatenated substructure. In addition, solid-state UV-vis absorptionspectra of 1 were also investigated.

2,6-naphthalenedicarboxylic acid, 1,4-bis(imidazol-1-yl)benzene, topology, crystal structure, subnet;

1 INTRODUCTION

In recent years, construction and characterization of high-dimension coordination polymers (CPs) have attracted significant interest, not only for their aesthetic structures and interesting topologies, but also for their potential applications as functional materials[1-3]. The mixed ligand assembly strategy was adopted to construct new CPs. The bis-imidazole ligand, 1,4-bis(imidazol-1-yl)benzene (BIMB), has been proved to be a good organic build block to construct CPs with intriguing structures. Many CPs based on BIMB ligand have been reported[4-6]. In general, the incorporation of auxiliary acid ligands to the synthetic procedure can yield more CPs[7-9]. 2,6-Naphthalenedicarboxylic acid (H2ndc) as a linear rigid aromatic dicarboxylate ligand not only possess good coordination ability to metal ions, but also contain-conjugated naphthalene ring motif which usually can enhance the stability of the resultant CPs[10-12]. Therefore, H2ndc acid was chosen as coligand to construct high dimensional CP with high stability. Here, we report the synthesis and crystal structure analysis of a new coordination polymer {[Co(BIMB)(ndc)]?H2O}n(1) obtained by the reac- tion of BIMB with Co(NO3)2?6H2O in the presence of H2ndc acid under hydrothermal conditions.

2 EXPERIMENTAL

2. 1 Materials and physical measurements

All chemicals of analytical reagent grade were commercially purchased and used as received. BIMB was prepared according to the previously reported method[13]. Elemental (C, H, N) analyses were performed on a Perkin-Elmer 2400 element analyzer. The phase purity of the synthesized complex has been examined by powder X-ray diffraction (PXRD). PXRD pattern was collected using a Philips PW 1710-BASED diffractometer. IR spectra were recorded with a Perkin-Elmer Spectrum One FT-IR spectrophotometer on KBr pellets in the range of 4000～400 cm–1. The UV-vis absorption spectra were measured on a Varian Cary 100 UV-Vis spec- trophotometer equipped with an integrating sphere attachment and a standard BaSO4plate used as reference. The thermal analysis was performed under nitrogen with a Netzsch STA449C thermal analyzer.

2. 2 Synthesis of {[Co(BIMB)(ndc)]?H2O}n

A mixture of BIMB (0.1 mmol, 21.0 mg), H2ndc (0.1 mmol, 21.6 mg), Co(NO3)2?6H2O(0.1 mmol, 29.1 mg), H2O (6 mL) and N,N-dimethylformamide (DMF, 2 mL) was sealed in a Teflon-lined stainless- steel vessel and heated to120 ℃ for 72 h, and then cooled to room temperature naturally. Purple block- shaped crystals were obtained(yield: 48% based on Co). Analysis calculated forC48H34Co2N8O9: C, 58.55; H, 3.48; N, 11.38%. Found: C, 58.68; H, 3.37; N, 11.24%. IR (cm?1, KBr): 3455 (s), 3145 (m), 3127 (w), 3100 (w), 3045 (w), 1606 (s), 1575 (s), 1529 (s), 1492 (w), 1391 (s), 1356 (s), 1306 (m), 1246 (m), 1189 (w), 1123 (w), 1067 (s), 960 (w), 927 (w), 831 (m), 794 (s), 652 (m).

2. 3 X-ray structure determination

A purple crystal with dimensions of 0.26mm × 0.22mm × 0.21mm was selected for X-ray analyses. Crystallographic data of the complex were collected on a Bruker Apex Smart CCD diffractometer equip- ped with a graphite-monochromatized Moradia- tion (= 0.71073 ?) at room temperature.The structure of the complex was resolved by direct methods, and then refined by full-matrix least- squares technique on2using the SHELX-97 pro- gram[14]. The hydrogen atom positions were fixed geometrically at the calculated distances and allowed to ride on the parent atoms. Complex 1 crystallizes in monoclinic space group2/, with= 22.7753(14),11.1584(7),= 18.4834(11) ?,106.101(3)o,4513.0(5) ?3,4,D1.449 g/cm3,= 0.801 mm–1,(000) = 2016, the final= 0.0334 and= 0.0959 with> 2() and= 1.02. The selected bond lengths and bond angles are shown in Tables 1 and 2, respectively.

Table 1. Selected Bond Lengths (?) for Complex 1

Table 2. Selected Bond Angles (°) for Complex 1

3 RESULTS AND DISCUSSION

3. 1 Description of the structure

Single-crystal X-ray crystallographic analysis reveals that complex 1 crystallizes in monoclinic space group2/The asymmetric unit consists of one Co2+ion, one BIMB ligand (marked in blue), half a normal ndc2–anion (marked in magenta), half a disordered ndc2–anion (marked in green) and one lattice water molecule. As shown in Fig. 1, the Co2+ion is five-coordinated by two N atoms (N(1), N(3)) from two individual BIMB ligands and three O atoms (O(1), O(2), O(4)) from two carboxylate groups of two ndc2–ligands in a distorted tetragonal pyramid geometry. The Co?N bond lengths are 2.017 and 2.054 ? and the Co?O bond lengths fall in the 1.979～2.398 ? range, which are similar to those in other cobalt complexes[15, 16].

Fig. 1. Coordination environments of Co(II) in complex 1. The hydrogen atoms are omitted for clarity (30% ellipsoids probability). Symmetry codes: a = 0.5 –, 2.5 –, 1 –; b = 1 –, 1 –, 1 –; c = 0.5 +, 1.5 –, 0.5 +, d = –0.5 +, 1.5 –, –0.5 +

Each Co2+ion is connected by two BIMB ligands and two ndc2–anions, yielding a complicated 3network (Fig. 2). Using topological analysis method, we can better understand the structural characteristics of complex 1. The BIMB and ndc2–ligands joining neighboring two Co2+ions can be simplified as a rod and the Co2+ion can be regarded as a four-connector. Thus, we obtain a self-penetrating 3network (Fig. 3a).As determined by TOPOS software[17], the Schl?fli symbol for this four-connected uninodal network is {65.8}, representing a simple yet unreported topology. A better insight into the nature of this complicated architecture can be achieved if the non-disordered ndc2–ligands (marked in magenta) are neglected from the structure. Elimination of the non-disordered ndc2–ligands leaves a 2→ 3parallel polycatenated subnet (Fig. 3b). Within each layer, the large rhomboid window is composed of four Co2+ions, four BIMB ligands and two disordered ndc2–ligands (marked in green), which has a dimension of 25.03 × 12.88 ?2and an angle of 79.77o(defined by Co···Co distance and Co···Co···Co angle). These parallel layers with 44-sql topology are highly undulating, resulting in the interpenetration between adjacent layers.

Fig. 2. 3framework of complex 1

Fig. 3. (a) Topology of complex 1. (b) 2→ 3parallel polycatenated subnet of complex 1

3. 2 Phase purity and thermogravimetric analysis

The measured and simulated PXRDs of complex 1 are shown in Fig. 4. The result confirms that the measured PXRD pattern basically matches the simulated pattern based on the single-crystal X-ray data, which demonstrate the phase purity of the bulk samples.

Fig. 4. Experimental and simulated PXRD patterns of complex 1

The thermogravimetric analysis (TGA) was per- formed to investigate the thermal stability of com- plex 1.The polycrystalline samples were heated from room temperature to 750 ℃ under a flow of nitrogen at a heating rate of 10 ℃×min-1(Fig. 5). The TG curve of 1 shows the first weight loss of 1.87% (calcd. 1.83%) in the temperature range of 20～119 ℃, which corresponds to the loss of one lattice water molecule. Then, its framework is stable up to ca. 370 ℃, indicating that the framework of 1 is thermally stable. Then, as the temperature continued to rise, the rapid decomposition occurs.

3. 3 UV-vis absorption spectra

In order to further characterize the complex, the solid-state UV-vis absorption spectra were also investigated. The UV-vis absorption spectra of free ligands BIMB, H2ndc and complex 1 are shown in Fig. 6. We observed broad intense absorption peaks at 230～360 nm, which can be ascribed to-* transitions of the ligands. In addition, a peak at 530 nm [41g(F) →41g(P)] is typical for the Co(II) complexes[18, 19].

Fig. 5. TG curve of complex 1

Fig. 6. UV-vis absorption spectra of BIMB and H2ndc ligands and complex 1

4 CONCLUSION

In summary, a new Co(II) coordination polymer has been synthesized and structurally characterized. Complex 1 features an unprecedented 34-connec- ted {65.8} topological framework. The ndc2–ligandplays two different roles in the assemble procedure, leading to the formation of a 2→ 3parallelly polycatenated subnet. Besides, this coordination polymer displays high thermal stability.

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30 October 2017;

30 January 2018 (CCDC 1567202)

the National Natural Science Foundation of China (Nos. 21361023 and 21461023)

. Yao Xiao-Qiang, associate professor. E-mail: yxq@nwnu.edu.cn

10.14102/j.cnki.0254-5861.2011-1877