Syntheses, Crystal Structure and Properties of a Cadmium Complex containing 2, 5-Thiophene Dicarboxylic Acid and 1, 1'-(1, 4-Butanediyl)Bis(imidazole)

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	2016-05-13 收稿

	2016-06-20 接受



本文作者相关文章
	李佳

	刘博

Li Jia, Liu Bo

College of Chemistry, Jilin Normal University, Siping 136000

Abstract: A mononuclear cadmium compound, [Cd(bbi)(tdc)(H₂O)]_n·nH₂O [bbi:1, 1'-(1, 4-butanediyl)bis(imidazole); H₂tdc: 2, 5-thiophene dicarboxylic acid] was synthesized at room temperature in the mixed solvent. Its structure was determined by single-crystal X-ray diffraction analysis, and further characterized by IR spectra and elemental analysis. In addition, the thermal stability and the luminescent property of [Cd(bbi)(tdc)(H₂O)]_n·nH₂O have been investigated in detail. The titled complex crystallizes in orthorhombic system, space group Fdd2 with a=20.945(2) Å, b=32.309(4) Å, c=12.1084(14) Å, α=90°, β=90°, γ=90°, V=8194.1(16)Å³, C₁₆H₂₀CdN₄O₆S, M_r=508.82, Z=16, D_c=1.650 g·cm^-³, F(000)=4096, the final R1=0.0186, wR2=0.0491. The Cd ion was coordinated with carboxyl oxygen atoms from H₂tdc ligands to form a one-dimensional (1D) linear chain, and ultimately formed a 3D structure by bbi ligands.

Key words: Crystal structure Thermal stability analysis Luminescent property

由1, 4-双(咪唑-1-基)丁烷配体和2, 5-噻吩二羧酸构筑的镉配合物的合成、结构和性质研究

李佳, 刘博

吉林师范大学化学学院四平 136000

2016-05-13 收稿, 2016-06-20 接受

作者简介: 李佳, 女, 28岁, 助理实验师, 从事多功能材料研究, E-mail:lijia@jlnu.edu.cn

摘要：常温下，以溶液法合成了一个单核结构的镉配合物[Cd（bbi）（tdc）（H₂O）]_n·nH₂O（bbi：1，4-双（咪唑-1-基）丁烷；H₂tdc：2，5-噻吩二羧酸），通过单晶X-射线衍射、红外光谱、元素分析对其进行了结构表征，并研究了配合物的热稳定性和荧光性质。配合物属于正交晶系，空间群Fdd2，晶胞参数：a=20.945（2）Å，b=32.309（4）Å，c=12.1084（14）Å，α=90°，β=90°，γ=90°，V=8194.1（16）Å³，C₁₆H₂₀CdN₄O₆S，M_r=508.82，Z=16，Dc=1.650 g·cm^-3，F（000）=4096，R1=0.0186，wR2=0.0491。来自tdc配体的羧基氧原子与Cd离子配位形成1D直线型链，并通过含氮配体bbi与Cd离子配位最终形成了3D结构。

关键词：晶体结构热稳定分析荧光

The designed synthesis and characterization of metal-organic coordination polymers have achieved considerable progress in supramolecular chemistry and material chemistry^[1-8]. The synthetic strategy for the coordination polymers networks is mainly dependent on the ligands selected with both flexible and long rigid characters. Therefore, H₂tdc (2, 5-thiophene dicarboxylic acid) and bbi (1, 1’- (1, 4-butanediyl) bis (imidazole) ) were used as the bridging ligands for building coordination polymer. So far, a large number of mixed-ligand metal organic frameworks (MOFs) with versatile dimensional structures have been rationally designed and physically characterized^[9]. A similar compound had been reported by our group^[10]. In this paper, a new cadmium compound [Cd (bbi) (tdc) (H₂O) ]_n·nH₂O was synthesized. They are quite different in synthetic methods, structures and properties.

1 Experimental

1.1 Materials and physical measurements

All reagents and solvents were purchased from commercial sources and used as received. The ligand bbi was synthesized according to the reported procedure^[11]. The crystal structure was determined on a Bruker SMART APEX II CCD X-ray diffractometer. Infrared spectra (KBr pellets) were recorded on a Perkin-Elmer 2400LS IIspectrometer, and elemental analyses for C, H, and N were performed on a Perkin-Elmer 240C analyzer. Thermogravimetric (TG) analysis was performed with a Perkin-Elmer TGA7 analyzer at 10℃·min^-¹ in nitrogen. Fluorescence spectra were recorded on a computer-controlled JY Fluoro-Max-3 spectrometer at room temperatrue.

1.2 Synthesis

A mixture of Cd (NO₃) ₂·4H₂O (0.154g, 0.5mmol) , bbi (0.5mmol，0.095g) and H₂tdc (0.25mmol，0.043g) were dissolved in 10mL distilled water and 10mL ethanol. The solution was stirred for 30min at room temperature and fitered. The filtrate was allowed to evaporate in air at room temperature. After one week, white block crystals of the titled compound were isolated (41% yield based on Cd) . Anal. Calcd. (%) for C₁₆H₂₀CdN₄O₆S: C 37.77；H 3.96；N 11.01; Found: C 37.76；H 3.97；N 11.02。IR (KBr, cm^-1) :1562m, 1400s，1235m, 1104s, 1088w, 938s, 841m, 806w, 785s, 659w, 471s。

1.3 X-ray structure determination

A single crystal with dimensions of 0.69 mm×0.47mm×0.28mm was selected and mounted on a Bruker CCD diffractometer equipped with a graphite-monochromatized MoK_α (λ=0.071073 Å) radiation for cell determination and subsequent data collection．The reflection intensities in the range of 2.04°＜θ＜26.06° were collected at 293 (2) K using the w scan technique. The structure was solved by direct methods with SHELXS-97 program^[12] and refined with SHELXL-97^[13] by full-matrix least-squares techniques on F². All non-hydrogen atoms were refined anisotropically and hydrogen atoms of the ligands were refined as rigid groups. Detailed information about the crystal parameters, data collection and refinements for the compound were summarized in Tab. 1. Selected bond lengths and angles for the compound were given in Tab. 2.

Table 1 Crystal data and refinement details for [Cd (bbi) (tdc) (H₂O) ]_n·nH₂O 表 1 配合物的晶体学数据及结构精修数据

Table 2 Selected bond lengths (Å) and angles (°) of the compound 表 2 配合物的部分键长 (Å) 和键角 (°)

2 Results and Discussion

2.1 Description of crystal structure

X-ray single-crystal diffraction analysis revealed that the compound crystallizes in orthorhombic system with space group Fdd2. The asymmetric unit contains one Cd (II) ion, one complete bbi ligand and one tdc anion, one coordinated water molecule and one free water molecule as shown in Fig. 1, each Cd (II) ion is seven-coordinated by two nitrogen atoms (Cd (1) -N (1) =2.302 (3) Å and Cd (1) -N (4) #1=2.318 (3) Å) from two different bbi ligands and four oxygen atoms from four different tdc anions and one coordinated water molecule in a pentagonal bipyramid arrangement. The Cd-O bond lengths are in the range of 2.325 (2) Å to 2.540 (2) Å. The Cd ion was coordinated with the carboxyl oxygen atoms from H₂tdc ligands to form a one-dimensional (1D) linear chain, and ultimately formed a 3D structure by bbi ligands (as shown in Fig. 2) . Topologically, each Cd (II) ion can be considered as a 4-connected node, and the compound is triple interspersed with topology {4²·8⁴} (as shown in Fig. 3) .

Fig. 1 Asymmetric unit of the compound (All H atoms are omitted for clarity) 图 1 配合物的不对称单元图

Fig. 2 3D structure of compound viewed along c-direction 图 2 配合物沿c轴方向的三维立体图

Fig. 3 The triple interspersed of the compound

2.2 Thermogravimetric analysis

Thermal gravimetric analysis (TGA) was performed to examine the thermal stability of the compound. The crushed single crystal sample was heated up to 800℃ under N₂ gas at a heating rate of 10℃·min^-¹. As shown in Fig. 4, the TG curve revealed that the first weight loss of 3.00% (Calcd. 3.48%) occurs between 130℃ to 210℃ corresponding to the loss of water molecules, afterward, the continuous weight loss of 62.00% (Calcd. 61.90%) from 210℃ to 470℃ is due to the removal of bbi ligand. No weight loss is observed after 470℃, and the resulting residue corresponds to CdO (Obsd. 35.00%, Calcd. 34.62%) .

Fig. 4 配合物的热重曲线图图 4 TG curve for the compound

2.3 Luminescent property

The lumine-scent property of the compound was investigated at room temperature in solid state (as shown in Fig. 5) . The Cd (II) ion is belong to d¹⁰ valence electron structure, and is difficult to be oxidized or reduced. The emission of this compound is neither MLCT nor LMCT in nature. As a result, the emission can be assigned to intraligand transitions. It is shown that the compound exhibits photoluminescence with maximum emission at 376 nm (Ex=325 nm) .

Fig. 5 配合物的荧光光谱图图 5 Solid-state luminescent emission spectra of the compound

3 Conclusion

In conclusion, a mononuclear cadmium compound was synthesized at room temperature and characterized by single-crystal X-ray diffraction analysis, infrared spectra, and elemental analysis. The single-crystal X-ray diffraction revealed that the center Cd (II) atom is in a pentagonal bipyramid arrangement. Moreover, the compound exhibits better thermal stability and fluorescent property.

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