基于双苯并咪唑及二羧酸配体配合物的合成、结构及抗菌活性

梁丽丽 刘从森 宗智慧 张曼丽 张冰源曹 睿 王子豪 庞苗苗 李玉杰 陶兆林

（蚌埠医学院，蚌埠 233030）

0 Introduction

With the increase of drug-resistant microbial strains,searching for new antibacterial and antifungal chemotherapeutics is becoming a formidable task for pharmaceutists and medicinal chemists. Since imidazoles are biocompatible and antimicrobial,many medicinal applications have been found.The imidazole derivatives are one of the important families in heterocyclic compounds,and many of them have recently been used in medicine and pesticide fields[1-3].The design and assembly of benzimidazole compounds have attracted great attention for their antifungal,antibacterial,antimicrobial,antiparasitic,antiviral and antitumor activities[4-10].Extensive efforts to develop new antibacterial metal-based benzimidazole compounds have been observed[11-16].Benzimidazole-1-ly-based ligands are also good candidates of N-donor linkers to construct coordination polymers of different configurations[17-18].Herein,we employed a linear benzimidazole-1-ly-based ligand 4,4′-bis（benzimidazol-1-ylmethy1）biphenyl）（bbmb）combined with a V-shaped dicarboxylates ligand 4,4′-dicarboxydiphenyl ether （H2dcpe）,and successfully synthesized two coordination polymers with different layer structures.

1 Experimental

1.1 Materials and instruments

The ligand bbmb 4,4′-bis（benzimidazole-1-ylmethyl）biphenyl （bbmb）was synthesized according to the reported method with a little modification[19].All other starting materials were commercially purchased and used as received.IR spectra were performed from KBr pellets in the range of 4 000～400 cm-1with a NICOLET iS50 spectrometer.C,H and N elemental analyses were carried out with an Elementar Vario-EL CHNS elemental analyzer.Solid-state UV-Vis diffuse reflectance spectra were obtained at room temperature on finely ground samples with Shimadzu UV-3600 double monochromator spectrophotometer using barium sulfate（BaSO4）as a 100%reflectance standard.Powder X-ray diffraction （XRD）intensities was measured on a Bruker D8 ADVANCE X-Ray Diffractometer （Cu Kα,λ=0.154 056 nm）in the 2θ range of 5°～50°in which the X-ray tube was operated at 40 kV and 40 mA.Thermogravimetrical （TG）analyses were performed from 25 to 700℃ at a heating rate of 10℃·min-1,under N2atmosphere with a flow rate of 50 mL·min-1on a simultaneous STA 449-F5 thermal analyzer.

1.2 Synthesis of{[Ni（bbmb）（dcpe）（H2O）]·2H2O}n（1）

A mixture of bbmb （21 mg,0.05 mmol）,H2dcpe（13 mg,0.05 mmol）and Ni（NO3）2·6H2O （29 mg,0.1 mmol）in 4 mL mixed solvent of DMF/H2O （1∶3,V/V）was placed in a 25 mL Teflon-lined stainless steel container and heated to 100℃for 48 h.The reaction system was cooled to room temperature.Green block crystals of 1 were collected by filtration and dried in air （Yield:48%based on bbmb）.Anal.Calcd.for C42H35N4NiO8（%）:C 64.47,H 4.51,N 7.16;Found（%）:C 64.41,H 4.54,N 7.12.IR:（KBr pellet,cm-1）:3 742（w）,3 423（s）,2 926（w）,2 363（w）,1 598（m）,1 548（m）,1508（w）,1 386（s）,1 240（w）,1 160（s）,1 116（w）,876（w）,792（w）,744（w）,658（w）,499（w）,419（w）.

1.3 Synthesis of{[Mn2（bbmb）（dcpe）2（H2O）]·1.5H2O}n （2）

A mixture of bbmb （21 mg,0.05 mmol）,H2dcpe（13 mg,0.05 mmol）and Mn（NO3）2（50%aq.0.1 mmol）in 4 mL mixed solvent of DMF/H2O （2∶2,V/V）was placed in a 25 mL Teflon-lined stainlesssteel container and heated to 110℃for 48 h.Then the reaction system was cooled to room temperature slowly.Colorless block crystals of 2 were collected by filtration and dried in air （Yield:61%based on H2dcpe）.Anal.Calcd.for C56H43Mn2N4O12.5（%）:C 62.17,H 4.01,N 5.18;Found（%）:C 62.12,H 4.05,N 5.13.IR:（KBr pellet,cm-1）:3 428（m）,3 099（w）,2 926（w）,1 667（w）,1 600 （s）,1 554 （m）,1 502 （s）,1 397 （s）,1 334（m）,1 242（s）,1 155（m）,1 010（w）,872（m）,792（m）,742（m）,702（m）,630（w）,513（w）.

1.4 Crystallography

Single crystals with suitable dimensions for 1 and 2 were selected for single crystal X-ray diffraction measurements and the data were collected at 296（2）K on a Bruker Apex Smart APEXⅡX-ray Single Crystal diffractometer.Data reductions and absorption corrections were performed using the SAINT and SADABS[21a]software packages,respectively.The structure was solved by direct methods and refined by full matrix least-squares methods on F2using the SHELXS-97 and SHELXL-97 programs[21b].The coordinates of the nonhydrogen atoms were refined anisotropically,and the positions of the H-atoms were generated geometrically.There are some highly disordered guest solvent molecules,which could hardly be located in the X-ray structure because of severe thermal disorder.The SQUEEZE subroutine of the PLATON software suit was used to remove the scattering from the highly disordered guest molecules[22].The resulting new files were used tofurtherrefinethe structures.The numbers of guest molecules in 1 and 2 were obtained by considering the number of electrons filtered by SQUEEZE combining with elemental analyses and TGA data.The result data reveal that 1 contains two H2O molecules,and 2 contains one and a half H2O molecules.Basic information pertaining to crystal parameters and structure refinement is summarized in Table 1.

CCDC:1525542,1;1525543,2.

Table 1 Crystal data and structure refinements for 1 and 2

1.5 Biological activity test

The antimicrobial activities of 1,2 and bbmb ligand were determined in vitro using agar well diffusion method[20].Growth inhibitory activity against S.aureus （MTCC 3160）,E.coli（MTCC 51）,dysentery bacillus,C.albicans and P.aeruginosa were measured.The bacterial strains grown on nutrient agar at 37℃for 18 h were suspended in saline solution（0.85%NaCl）and adjusted to a turbidity of 0.5 MacFarland standards.The suspension was used to inoculate sterile Petri plates of 9.0 cm diameter in which the test compounds were grown.Compounds 1,2 and bbmb ligand weredissolved in dimethylsulfoxide（DMSO）to prepare three different concentrations for evaluation of dose response.Antibacterial activities of the compounds were evaluated by measuring the inhibition zone diameters （IZD）.

2 Results and discussion

2.1 Crystal structures

Compound 1 crystallizes in the triclinic space group P1.The asymmetric unit consists of one Ni atom,two half bbmb ligands,one dcpe ligand and one coordinated water molecule.The Ni atom has an octahedral coordination sphere,which consists of four oxygen atoms （Ni-O 0.202 0（2）～0.219 9（2）nm）from two dcpe molecules and one water molecule,two nitrogen atoms （Ni-N 0.205 nm）from two bbmb molecules （Fig.1）.The two benzene rings of the dcpe ligand are crossed with a dihedral angle of 124.7°.The dcpe ligands connect Ni atoms through two carboxylates alternately to form wine chains （Fig.2,black color）.The wine chains are further connected by two kinds of bbmb ligands.Two bbmb ligands connect Ni atoms to form a helical chain.The bbmb ligands have similar configurations.The two center benzene rings of bbmb ligands are coplanar.The two benzimidazole rings of one bbmb ligand are parallel to each other,located on the opposite side of the two center benzene rings.There are π-π interactions between the benzimidazole rings of bbmb ligands.The two benzimidazole rings of one bbmb ligand are parallel to benzimidazole rings of other two bbmb ligands.The dihedral angle is 0°and the plane-to-plane distance is 0.334 and 0.362 nm,respectively[23]（Fig.2）.So the bbmb ligands are further connected through two kinds of π-π interactions.Each Ni atom is connected to two bbmb ligands and two dcpe ligands.Topologically,dcpe and bbmb ligands can be simplified into chains of different lengths and Ni atoms as four-connected nodes.The whole structure can be reduced to a 4-noded uninodal network.Analysis with Topos 4.0 software,the whole framework can be classified as sql topology with the Schlfli symbol of {44·62}.The wine chains formed by dcpe ligands and the helical chains formed by bbmb ligands are interwoven together by sharing Ni atoms and extended indefinitely （Fig.3a）.The whole framework is extended indefinitely along two directions to form a 2D thick layer structure （Fig.3b）.

Fig.1 Coordination environment of Ni atom showing the atom numbering scheme

Fig.2 Wine chains （black color）formed by dcpe ligands connecting Ni atoms and further connected by two kinds of bbmb ligands

Fig.3 （a）Extended 2D framework of 1 viewed along the b axis;（b）Two disconnected thick layer networks described in different colors

Compound 2 crystallizes in the monoclinic space group C2/c.The asymmetric unit consists of two crystallographically unique Mn atoms,one bbmb ligand,two dcpe ligands and one coordinated water molecule（Fig.4）.Mn1 and Mn2 atoms are both in an octahedral structure,coordinated by five oxygen atoms from two dcpe ligands and one water molecule （Mn-O 0.210 4（3）～0.238 4（3）nm）,one nitrogen atom from bbmb ligand（Mn-N 0.221 7（3）,0.222 7（4）nm）.Mn1 and Mn2 atoms are bridged by two carboxylate groups in μ2-η1∶η1fashion and a μ2-Owater.Mn2 and Mn2 atoms are bridged by two μ2-Ocarboxylto form a rhombus structure with Mn2…Mn2 separations of 0.357 3（1）nm.So Mn1-Mn2-Mn2-Mn1 is bridged together to afford a linear tetranuclear Mn4cluster.The Mn4cluster is connected by ten dcpe ligands and four bbmb ligands （Fig.5a）.The linear tetranuclear clusters are further connected through carboxylates to form a linear chain,which is further connected by dcpe ligands to form an infinite 2D network （Fig.5b）.The biphenyl rings of the bbmb ligand are not coplanar with the dihedral angle of 42.5（2）°.The two benzimidazole rings are in the same side of the biphenyl rings connecting Mn1 and Mn2 atoms,respectively.The linear tetranuclear chains of the 2D network are further connected by bbmb ligands in another direction to increase the thickness of the layer network.Fig.6a shows two disconnected 2D layer networks differentiated with different colors.The Mn4clusters chains are zigzag-shaped inside the network viewed along the c axis （Fig.6b）.

Fig.4 Coordination environments of Mn1 and Mn2

Fig.5 （a）Coordination environment of the linear Mn4cluster;（b）Linear Mn4clusters further connected through carboxylate to form a linear chain

Fig.6 （a）Two disconnected 2D layer networks;（b）Zigzag chains inside the layer networks viewed along the c axis

2.2 XRD and thermogravimetric analyses

Powder X-ray diffraction （XRD）experiments were carried out for the two compounds to confirm the phase purities of the bulk materials.The experimental and structure-simulated XRD patterns of the two compounds are compared （Fig.7）.The main peaks of the bulk synthesized materials and the simulated match well,indicating the purities of the two compounds.To estimate the stability of the coordination architecture,the thermal behaviors of the two compounds were investigated on crystalline samples by thermal gravimetric analysis （TGA）.The TGA curves （Fig.8）show compound 1 is thermally stable up to ca.385℃.The weight loss of 9.3%at about 140℃should be attributed to the loss of two guest H2O molecules（Calcd.4.6%）and adsorbed H2O molecules.An abrupt weight loss at about 385℃should be due to the pyrolysis of the main structure.For compound 2,the gradual weight loss of 5.0%at 230℃should be attributed to the loss of 1.5 guest H2O molecules （Calcd.2.5% ）.Decomposition of the framework occurred at 385℃,indicating that the main framework collapsed at a relatively high temperature under a nitrogen atmosphere.

Fig.7 Powder X-ray diffraction patterns of 1 and 2

Fig.8 TG curves of 1 and 2

2.3 Solid UV-Vis absorbance spectra

Fig.9 Solid-state UV-Vis absorbance spectra of bbmb,H2dcps and compound 1

The solid-state UV-Vis absorbance spectra of free bbmb,H2dcpe and compound 1 were measured at room temperature.Compound 1 exhibits three absorbance bands in the range of 200～850 nm （Fig.9）.The absorbance bands at 200～350 nm,similar with that of bbmb,a little red shift to that of H2dcpe,can be assigned to π→π*transitions of the phenyl ring ligands.The absorbance bands at about 400 nm and the broad bands at 600～700 nm of 1,can be attributed to[3T1g（p）→3A2g]and[3T1g（F）→3A2g]transitions of Niギcompounds[24-26].

2.4 Antimicrobial activities

The antimicrobial activities of 1,2 and bbmb ligand （DMSO solution）were tested with different bacteria using diffusion method.The diameters of the antibacterialrings were tested to evaluate the antimicrobial activities and the results were listed in Table 2.The results showed that compound 1 exhibited obviously fungicidal activity against S.aureus and E.coli.Compound 2 showed significant inhibitory effect on C.albicans,S.aureus,E.coli and dysentery bacillus.The bbmb ligand only showed very little inhibiting effect on dysentery bacillus,and no inhibitory effect on other bacteria.From thein vitro antibacterial assay,it is observed that compound 1 possesses exclusive inhibitory activities,while compound 2 shows extensive antibacterial effect.The coordination compounds showed enhanced antimicrobial activity in many cases over the free bbmb ligand.The results could be explained on the basis of chelation theory and the presence of suitable metal ions is essential for microbiological activity of the coordination polymer[27].Compound 2 has greater potential medical value worthy of further investigation.

Table 2 Antibacterial activities of bbmb ligand and compounds 1 and 2

3 Conclusions

Two coordination polymers were synthesized by hydrothermal methods with the benzimidazole ligand combined with a V-shaped dicarboxylates ligand.Both compounds possess unique 2D thick layer network.Compound 1 exhibits a rare layered 4-connected structure with sql topology.The biological activity test indicated that compound 2 showed enhanced antimicrobial activity to C.albicans,S.aureus,E.coli and dysentery bacillus compared to bbmb ligand.The coordination polymers were found to display considerable antimicrobial activity.

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