WU Qi-Ting WU Li-Bin LI Guo-Bi LIU Sheng-GuiPAN Rong-Kai SU Wen-Yi HUANG Qian-Wen（School of Chemistry and Chemical Engineering，Lingnan Normal University，Zhanjiang 524048，China）

Synthesis,Crystal Structure and Luminescent Property of a Dinuclear Cadmium Complex Based on 1,2,3,4-Tetra(1H-benzo[d]imidazol-2-yl)butane①

WU Qi-Ting WU Li-Bin LI Guo-Bi LIU Sheng-Gui②
PAN Rong-Kai SU Wen-Yi HUANG Qian-Wen
（School of Chemistry and Chemical Engineering，Lingnan Normal University，Zhanjiang 524048，China）

A complex ［Cd2（tbb）Cl4］·4DMF·3H2O，where tbb is 1，2，3，4-tetra（1H-benzo［d］imidazol-2-yl）butane，was synthesized and characterized by X-ray single-crystal structure analyses.For this complex:C44H49Cd2Cl4N12O7，Mr= 1224.55，monoclinic system，space group C2/c，a = 29.563（3），b = 14.2580（17），c = 26.355（3）Å，β = 97.036（2）°，V = 11025（2）Å3，Z = 8，Dc= 1.475 g/cm3，λ = 0.71073 Å，μ（MoKα）= 1.021 mm-1，F（000）= 4936，S = 1.047，R = 0.0680 and wR = 0.1832 for 11812 observed reflections with I ＞ 2σ（I）.It is a neutral dinuclear complex.One 1，2，3，4-tetra（1H-benzo［d］imidazol-2-yl）butane coordinates to two cadmium ions.Each cadmium ion is coordinated by two nitrogen atoms of tbb and two chloride ions.The complex emits blue luminescence in DMF solution as well as in solid powder state.

benzimidazole,cadmium complex,crystal structure,luminescence

1　INTRODUCTION

Cadmium is widely used in industry，agriculture，and many other fields［1］.Cadmium is a very toxic element and easily absorbed and accumulated by plants and other organisms［2，3］.It causes many serious diseases such as lung，prostatic，and renal cancers，even at very low concentrations［4-6］.Due to the toxicity of cadmium，it is in great need for the development of methods to detect and monitor cadmium levels［7-9］.Luminescence analysis is a powerful tool to detect cadmium ion for simplicity and high sensitivity.It is important to investigate that how luminescent chromophore coordinates to the cadmium ion and what its luminescent property is，which contributes to set up luminescent method of cadmium.Benzimidazole derivatives are important pharmacophores in drugs that display a diversity of pharmacological activities，such as anti-inflammatory，antioxidant，gastroprotective and antiparasitic activities［10-13］.We have paid attention to luminescent cadmium complexes based on organic ligand containing benzimidazole rings［14-16］.In our extended efforts to design and synthesize new luminescent cadmium complexes based on benzimidazole chromophore，herein we synthesize a new dinuclear cadmium complex based on 1，2，3，4-tetra（1H-benzo-［d］imidazol-2-yl）butane （tbb）to investigate its luminescent property.

2　EXPERIMENTAL

2.1Materials and instrument

o-Phenylenediamine and 1，2，3，4-butane tetracarboxylic acid were purchased from ACROS company.All chemicals and solvents were analytically pure and used without further purification.The analyses （C，H and N）were made on a Perkin-Elmer 240C elemental analyzer.1HNMR spectroscopic measurements were carried out on a Bruker AM-300 NMR spectrometer，using TMS （SiMe4）as an internal reference.The solid infared spectra （IR）were obtained from a Bruker IFS66V vacuum-type FT-IR spectrophotometer by using KBr pellets.The UV absorption spectra were recorded on a model UV-240 spectrophotometer （Shimazu，Janpan）.Fluorescence measurements were measured with an EDINBURGH FLS 920 Combined Fluorescence.Thermogravimetric analysis （TGA）was carried out up to 750 ℃ at a heating rate of 10.0 K/min in atmosphere on an NETZSCH TG-209 Thermogravimetric Analyzer after vacuum drying under 60 ℃for 24 h.

2.2Synthesis of tbb

1，2，3，4-Butane tetracarboxylic acid （2.34 g，0.01 mol）and o-phenylenediamine （4.32 g，0.04 mol were added to phosphoric acid （20 mL），and the mixture was stirred at 180 ℃ for3 h.The resulting dark brown solution was allowed to cool to room temperature and poured into water with vigorous stirring.The precipitate was filtered off.The pure product was recrystalized from DMF solution.Yield:5.2 g，58.6%.Anal.Calcd.for C44H62N12O8（tbb·4DMF·4H2O）:C，59.58；H，7.05；N，18.95%.Found:C，59.48；H，7.01；N，18.93%.Selected IR data （KBr，cm-1）:3593，3150，1644，1531，1440 1386 1274，1030，839，746.1HNMR:（300MHz d6-DMSO）:2.50（water-H），2.72（s，1H），2.88（s，1H）2.95（s，1H），3.00（s，1H），3.32（DMSO-CH3）3.53（DMF-CH3），4.26 （d，1H），4.44 （d，1H），6.99 （m，4H），7.06 （m，4H），7.35 （s，4H），7.44 （s，4H）8.29 （DMF-CHO），12.16 （s，2H），12.61（s，2H）.

2.3Synthesis of [Cd2(tbb)Cl4]·4DMF·3H2O

CdCl2（0.366 g，0.02 mol）was added to tbb （886 g，0.01 mol）dissolved in DMF solution （30 mL）.The reaction mixture was stirred for 20 minutes at room temperature.White block crystals were obtained in three days under air evaporation.Yield:0.82 g，67.1%.Anal.Calcd.for C44H49Cl4Cd2N12O7｛［Cd2（tbb）Cl4］·4DMF·3H2O｝:C，43.16；H，4.03；N，13.73%.Found:C，43.29；H，4.01；N，13.53%.Selected IR data （KBr，cm-1）:3518，3025，1655，1537，1426，1395，1324，1270，1206，1086，1034，971，743.

2.4Structure determination

A white single crystal of the title compound with dimensions of 0.14mm × 0.17mm × 0.28mm was selected for X-ray diffraction analysis.Data collection was performed on a Bruker P4 CCD diffractometer equipped with a graphite-monochromatic MoKα radiation （λ = 0.71073 Å）by an ω scan mode at 173（2）K.The empirical absorption was applied to the intensity data.A total of 26832 reflections were collected in the range of 1.59＜θ＜27.10º，of which 11812 were independent with Rint= 0.0777 and 11812 were observed with I ＞ 2σ（I）.The structure was solved by direct methods with SHELXS-97 and refined by full-matrix least-squares techniques on F2with SHELXL-97［17，18］.H atoms were positioned geometrically and constrained with riding model position parameters together with fixed isotropic thermal parameters.The final R = 0.0680，wR = 0.1832 （w = 1/（σ2（Fo2）+ （0.1126P）2+ 0.0000P），where P = （Fo2+ 2Fc2）/3）.（Δ/σ）max= 0.00，S = 1.047，（Δρ）max= 2.345 and （Δρ）min= -0.996 e/Å3.All calculations were performed on a computer with SHELXTL-97 program package.

在泵站封闭圈大体积砼浇筑时，特别委托南京水科院为该项目“量身定制”混凝土配合比，在混凝土中添加使用矿粉、粉煤灰，C30混凝土使用水泥192 kg，C40使用的水泥是234 kg，极大地节约了建设成本，防止了温度裂缝的产生，保证了封闭圈砼浇筑的一次性成功，并取得了良好效果。

3　RESULTS AND DISCUSSION

3.1Synthesis and thermal stability for the complex

1，2，3，4-Tetra（1H-benzo［d］imidazol-2-yl）butane was synthesized from the traditional condensation reaction of 1，2，3，4-butane tetracarboxylic acid and o-phenylenediamine （Fig.1）.The reaction tempera-ture is controlled above 170 ℃ so that the four carboxylic acid groups can react completely with ophenylenediamine.1，2，3，4-Tetra（1H-benzo［d］imidazol-2-yl）butane coordinates easily with CdCl2to form the complex in solution at room temperature.In the IR spectrum of the complex，the peaks3518（N-H），1537（C=C），1426（C=N）and 1270（C-N）cm-1show absorption bands resulting from the skeletal vibration of benzimidazole rings.The strong peak at 1655 cm-1is from C=O of DMF solvent.In the'H NMR spectrum of free ligand （Fig.2），the NH hydrogen atom appears at δ = 12.16 and 12.61 ppm.The signals of δ = 6.99，7.06，7.35 and 7.44 are from phenyl rings hydrogen atoms.The peaks at δ = 2.72，2.88，2.95 and3.00 are attributed to four hydrogen atoms of -CH2-.The peak of two hydrogen atoms attached to tertiary carbon occurs at δ= 4.26 and 4.44.The H atom signals of the free ligand are all in good agreement with the assumed structure.

Fig.1.Synthesis route of the ligand and complex

Fig.2.1HNMR spectrum of the ligand (tbb)

The complex was performed on thermogravimetric analysis after vacuum drying under 60 ℃ for 24 h.Thermogravimetric analysis （TGA）showed that the complex has much high thermal stability.The decomposition temperature is up to320 ℃ （Fig.3）.The lost weight of 25.5% under 204 ℃ is due to theloss of crystallized solvents DMF，which is consistent with the theoretical weight-loss value of 27.9%.The weight of crystallized water was lost when vacuum drying of the sample.

3.2Crystal structure

Fig.3.Thermogravimetric analysis of the complex

The ORTEP drawing of the complex is shown in Fig.4.The complex is a dinuclear cadmium complex.One tbb ligand molecule simultaneously coordinates with two cadmium ions.The central cadmium ion is four-coordinated and surrounded by an N2Cl2environment，adopting distorted tetrahedron geometry.The ligand （tbb）affords two N atoms to coordinate to each cadmium ion.The other sites were occupied by two chloride ions.Selected bond lengths and bond angles for the complex are listed in Table 1.The bond lengths of Cd（1）-Cl（1），Cd（1）-Cl（2），Cd（2）-Cl（3）and Cd（2）-Cl（4）are respectively 2.3902（2），2.461（2），2.407（2），and 2.444（3）Å，averaged by 2.425 Å.The bond distances of Cd（1）-N（1）， Cd（1）-N（7），Cd（2）-N（3）and Cd（2）-N（5）are 2.223（6），2.243（6），2.226（6）and 2.251（6）Å，respectively，with the average to be 2.236 Å.The bond angles related to Cd（1）and Cd（2）show that two cadmium coordination configurations are both distorted tetrahedral geometry.Each Cd2+coordinates to the N atoms of tbb to form an eight-membered ring.

Fig.4.Molecular structure of the complex

Table 1.Selected Bond Lengths (Å) and Bond Angles (°)

The 2D net structure of the complex was formed by three kinds of π··π stacking interactions between benzimidazole rings.The distances of π··π interactions between benzimidazoles are respectively3.879，3.544 and3.757 Å （Fig.5）.The hydrogen bond between the O2atom of solvent DMF and the non-coordinated N4atom of tbb，N（4）-H（4B）··O（2）（2.741（1）Å），links the DMF solvent with the complex molecule.The DMF solvent molecules further stabilize the 2D net structure formed by π··π stacking interactions.O2W/O2'W and O3W/O3'W are in disorder states.The details of hydrogen bonds are given in Table 2.

3.3Absorption spectra and luminescent property

Fig.5.π··π stacking interactions of the adjacent molecules

Fig.6.UV-Visible absorption spectra of the ligand and complex (a stands for ligand;b shows the complex)

Fig.7.Photoluminenscence spectra of the ligand and complex (λex=310 nm,λem= 410 nm) in the DMF solution (a stands for excitation of the ligand;b is the excitation of complex;c means the emission of ligand;d shows the emission of complex)

Fig.8.Photoluminenscence spectra of the ligand and complex (λex= 280 nm,λem= 490 nm) in solid powder.(a stands for excitation of the ligand;b is the excitation of complex;c means the emission of ligand;d shows the emission of complex)

Table 2.Hydrogen-bonding Geometry (Å,°)

4　CONCLUSION

A new dinuclear cadmium complex，Cd2（tbb）Cl4· 4DMF·3H2O，based on 1，2，3，4-tetra（1H-benzo-［d］-imidazol-2-yl）butane（tbb）was synthesized and characterized by X-ray single-crystal structure analysis.In the complex molecule，one tbb molecule coordinated to two cadmium ions. Each cadmium ion in distorted tetrahedral geometry is coordinated by two nitrogen atoms of 1，2，3，4-tetra（1H-benzo-［d］imidazol-2-yl）butane and two chloride ions.The complex emits blue luminescence in DMF solution and solid powder.

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10.14102/j.cnki.0254-5861.2011-0464

Received30 July 2014；accepted 15 October 2014 （CCDC 1015790）

①This work was financially supported by the Natural Science Foundation of Guangdong Province （No.1414050000021），the National Natural Science Foundation of China （（NO.21403191））and the State Undergraduate Training Programs for Innovation

②Corresponding author.Liu Sheng-Gui，born in 1970，Professor，E-mail:lsgui@sohu.com