基于雙咪唑基配體的兩個鎘(Ⅱ)配位聚合物合成、晶體結構和表征

張衛國崔廣華焦翠歡耿建琛

(1河北科技師范學院理化學院，秦皇島 066004)

(2河北聯合大學化學工程學院，唐山 063009)

基于雙咪唑基配體的兩個鎘(Ⅱ)配位聚合物合成、晶體結構和表征

張衛國＊,1崔廣華2焦翠歡2耿建琛2

(1河北科技師范學院理化學院，秦皇島 066004)

(2河北聯合大學化學工程學院，唐山 063009)

水熱條件下，合成了兩個新的配位聚合物[Cd(PhCOO)2(bmix)]n(1)和{[Cd(chdc)(bmix)]·C2H5OH}n(2)(bmix=1，4-雙(2-甲基咪唑基-1-甲基)苯，H2chdc=1，4-環己二酸)。單晶結構分析表明，配合物1為一維鋸齒狀鏈結構平行于[001]平面；配合物2為層狀結構，鎘原子通過雙配體橋連形成四連接的二維(4，4)網絡。兩個配合物中鎘原子均具有6配位的畸變八面體幾何構型，另外，測定了兩個配合物的熱穩定性。

鎘(Ⅱ)配位聚合物；晶體結構；柔性雙咪唑；(4，4)網絡

0 Introduction

Metal-organic coordination polymers comprised of metal ions and bridging ligands have received much attention due to their potential applications as functional materials ranging from catalysis,gas adsorption,molecular recognition,optics,and so on[1-5]. The structuralmotifs of coordination polymers rest on several factors,such as the central atoms,the performance of the ligands,the coordinated and/or non-coordinated counter ions,the solvent systems and the reaction conditions.The choice of appropriate ligands is no doubt the key factor because it has an obvious influence on the topologies of the coordinationpolymers and behavior of the molecules[6-8].Some flexible bis(imidazole)bidentate ligands,which can adopt various conformations to bend and rotate when coordinating to metal centers so as to conform to the coordination geometries of metal ions.We and other groups have focused on the synthesis and structural exploration of novel coordination polymers with mixed carboxylates and flexible di(imidazole)ligands[9-14],with a view tomaking good progress in understanding how the nature of metal ions and the structures of the organic ligands affect the architectures assembled via coordination bonds properties.

In this paper,we report the synthesis,structures and thermal properties of two interesting coordination polymers:1D zigzag chain[Cd(PhCOO)2(bmix)]n(1) and 2D(4,4)sheet{[Cd(chdc)(bmix)]·C2H5OH}n(2) (bmix=1,4-bis(2-methylimidazole-1-ylmethyl)benzene, H2chdc=1,4-cyclohexanedicarboxylic acid).This work shows that different organic carboxylates used in self assembly processmay play a crucial role in the topology diversity of the cadmium coordination polymers.

1 Experimental

1.1 M aterials and generalmethods

All starting regents are commercially available, analytical grade and used in the experiment without further purification.The ligand bmix was prepared according to the literaturemethod[15].Elementalanalyses were made on a Perkin-Elmer automatic analyzer.IR spectra were recorded on a FT-IR Avatar 360 (Nicolet)spectrophotometer in 4 000～400 cm-1region by using KBr pellets method.The TG measurements were carried out on a NETZSCH TG 209 thermal analyzer from room temperature to 800℃under N2atmosphere with a heating rate of 10℃·min-1.

1.2 Synthesis of coordination polymers

1.2.1 Synthesis of[Cd(PhCOO)2(bmix)]n(1)

A mixture of cadmium acetate dihydrate(1.0 mmol,266.5 mg),bmix ligand(1.0 mmol,266.3mg), PhCOOH(1.0 mmol,122.1 mg),NaOH(2.0 mmol, 80.0 mg),H2O(4 mL)and ethanol(2 mL)was placed in a Teflon-lined stainless vessel and heated to 140℃for 3 d under autogenous pressure,and then cooled to room temperature at a rate of 5℃·h-1.The colorless crystal of 1 was obtained in 83%yield based on Cd. Element anal.calcd.for C30H28CdN4O4(%):C 58.03,H 4.54,N 9.02;found(%):C 58.31,H 4.49,N 9.16. FT-IR(KBr pellet,cm-1):3 130(m),3 060(m),1 600 (vs),1550(vs),1390(vs),1280(vs),1140(s),1070(m), 1000(m),849(s),721(vs),496(w).

1.2.2 Synthesis of{[Cd(chdc)(bmix)]·C2H5OH}n(2)

2 was prepared using a similar method as for 1 with replacement of H2chdc with PhCOOH.The colorless crystal of 2 was obtained in 78%yield based on Cd.Element anal.calcd.for C24H28CdN4O4(%):C 52.51,H 5.14,N 10.21;found(%):C 52.25,H 5.52, N 9.65.FT-IR(KBr pellet,cm-1):3440(m),3120(m),2 940(m),1 550(vs),1 410(vs),1 340(s),1 280(s),1 140 (m),1040(m),935(m),849(m),725(s),588(w).

Both complexes are stable in air and insoluble in common solvents such as water,ethanol,methanol, and acetone.

1.3 Crystallography data and crystal structure determ ination of 1 and 2

The suitable single crystals of title coordination polymers were mounted on the top of a glass fiber with epoxy cement for the X-ray measurement.The crystallographic data collections for 1 and 2 were carried out on a Bruker Smart 1000 CCD diffractometer with graphite-monochromated Mo Kαradiation (λ=0.071 073 nm)andω-2θscanmode at 296 K.The absorption corrections were applied using SADABS program[16].The structurewas solved by directmethods and refined anisotropically by the full-matrix leastsquares technique using the Bruker′s SHELXTL program package[17].Anisotropic thermal parameters were applied to all nonhydrogen atoms.The organic hydrogen atoms were generated geometrically(C-H= 0.096 nm).In the structure of 2,the one ethanol latticemolecule is disordered,thus this structure was refined by theSQUEEZE routineofPLATON program[18]. A summary of crystallography data is given in Table 1.The selected bond lengths and angles are listed in Table 2.

CCDC:842711,1;842712,2.

Table 2 Selected bond lengths(nm)and angles(°)for 1 and 2

2 Results and discussion

2.1 Description of the crystal structures of complexes 1 and 2

[Cd(PhCOO)2(bmix)]n(1):X-ray diffraction analysis indicates that the structure of complex 1 is a 1D zigzag chain and the asymmetric unit contains one Cd2+cation,one bmix ligand and two PhCOO-ligands. The Cd1 center locates in a distorted octahedral geometry defined by three O(O1,O2 and O4)atoms from two PhCOO-ligands and one N(N1i,i-0.5+x, 1.5-y,1+z)atom from one bmix ligand locate in the equatorial positions,while two apical sites are occupied by one O(O3)atom from one PhCOO-ligand and one N(N3)atom from another bmix ligand.The coordination environment of Cd atom in complex 1 is shown in Fig.1,and selected bond lengths and angles are listed in Table 2.The Cd-O bond lengths range from 0.231 9(3)to 0.252 7(4)nm,and the two Cd-N bond lengths amount 0.2257(3)and 0.2265(3)nm, respectively.The coordination angles range from 51.87(12)°to 141.76(12)°,showing the distortion of octahedral geometry in 1.

Fig.1 Coordination environmentaround Cd(Ⅱ)center in 1

In 1,each Cd(PhCOO)2unit is linked to adjacent Cd(Ⅱ)center through the bridging bmix,forming a 1D zigzag chain structure(Fig.2),where the Cd1-Cd1i(Cd1-Cd1ii)distance and the Cd1i-Cd1-Cd1iiangle (Symmetry transformations codei-0.5+x,-y+1.5,z+1;ii0.5+x,-y+1.5,z-1),defined by the orientation of the bmix ligands in the chain,are 1.436 19(7)nm and 144.771(2)°,respectively.The carboxylate group of PhCOO-ligand shows a chelating coordination mode to cadmium ion.The dihedral angles between the mean-planes of the benzene ring and the imidazole rings are 77.110°and 88.899°in the same bmix ligand,respectively.

Fig.2 1D zigzag chain connected by bmix in 1

[Cd(chdc)(bmix)]n(2):Single-crystal X-ray analysis shows that the structure of 2 is a 2D layer framework possessing a(4,4)network and the asymmetric unit consists of one cadmium ion,one chdc ligand,one bmix ligand.As displayed in Fig.3,each Cd(Ⅱ)ion with a distorted octahedral coordination geometry is coordinated by four oxygen atoms(O1ii,O2ii,O3,O4,i-1.5-x,y-0.5,-z-0.5;ii0.5+x,-y+1.5,z+0.5.)from two chdc ligands and two N atoms(N1,N3i)from two different bmix ligands.The N3i,O1ii,O2ii,and O4 atoms comprise the equatorial plane,and the axial positions are occupied by N1 and O3.The Cd-O distances range from 0.222 0(2)to 0.225 6(2)nm,and the Cd-N distances are 0.227 5(2)and 0.227 7(2) nm,respectively(Table 2).(Fig.4).The 21helical chains are further connected by the bridging chdc dianions ligands to give rise to a 2D layer structure with the nearest Cd-Cd distance between the helical chains of 0.889 99(5)nm(Fig.5). Since the 21left-and right-handed helical chains are alternant and equal in the layer,thus,the whole structure is achiral.The dihedral angles between the mean-planes of the benzene ring and the imidazole rings are 88.493°and 88.365°in the one bmix ligand, respectively.Furthermore,the interesting feature in the structure of 2 is that the flexible chdc ligand possesses only one kind of e,a-cis-form and each carboxylate group of chdc ligand exhibits chelating coordinationmode.

Fig.3 Coordination environmentaround Cd(Ⅱ)center in 2

In 2,the bmix ligand adopt bis-monodentate bridgingmode to connect the cadmium ion.Thus,the cadmium ions are infinitely connected by bmix ligands to generate a 21helical chain with the nearest Cd-Cd distance in the chain being 1.466 88(7)nm(Fig.4). The 21 helical chains are further connected bythe bridging chdc dianions ligands to give rise to a 2Dlayer structure with the nearest Cd-Cd distancebetween the helical chains of 0.889 99(5) nm (Fig.5).Since the 21 left- and right-handed helical chains arealternant and equal in the layer, thus, the wholestructure is achiral. The dihedral angles between themean-planes of the benzene ring and the imidazolerings are 88.493° and 88.365° in the one bmix ligand,respectively. Furthermore, the interesting feature inthe structure of 2 is that the flexible chdc ligandpossesses only one kind of e,a-cis-form and eachcarboxylate group of chdc ligand exhibits chelatingcoordination mode.

Fig.4 Left- and right-handed Cd-bmix helical chains of 2

Fig.5 2D layer of 2

The layer can also be viewed as ladders sharing legs,in which the vertical bar are formed by Cd-bmix 21helical chains and rungs by the bridging chdc ligands.It is interesting to note that the 2D layer contains two different metallo-macrocycles.Although both are 44-membered metallo-macrocycles made up of two bmix ligands,two chdc ligands and four cadmium ions,there are slight difference due to the imidazole rings of bmix ligands pointing to different directions.One adopts head-to-head mode,in which the two bmix ligands locate inside the metallomacrocycles with the size of themetallomacrocycles being 2 nm×0.6 nm(Fig.6);the other one adopts tail-to-tail mode,in which the two bmix ligands locate outside the metallomacrocycles with the size of the metallomacrocycles being 1.1 nm×1.4 nm(Fig.7).If the bmix and chdc ligands can be considered as linear linkers and the cadmium ion as single node,then complex 2 possesses a 2D undulated(4,4)net,as shown in Fig.8.

Fig.6 44-membered metallo-macrocycles with the two imidazole rings of the two bmix ligands adopting head-to-head arrangement of 2

Fig.7 44-membered metallo-macrocycles with the two imidazole rings of the two bmix ligands adopting tail-to-tail arrangement of 2 2498

Fig.8 2D undulated (4,4) network of 2

2.2 IR spectral characterization of com plexe 1 and 2

The IR spectra of the title complexes show broad bands at 3 440 cm-1for 2 can be attributed to the stretching vibrations of O-H.The two absorption bands of 1 280 and 1 070 cm-1in complex 1(1 280 and 1 040 cm-1in complex 2)can be assigned to the vibrations of imidazole rings of bmix ligand.In complex 1,the absorption band for stretching carboxylate vibrations appear at 1 550 cm-1for asymmetry (νas),at 1 390 cm-1for symmetry(νs).For complex 2, the absorption for antisymmetric stretching carboxylate vibrationνasappears at 1 550 cm-1.The corresponding symmetric stretching vibrationνsappearsat1 410 cm-1. The separation ofνasandνs(Δν=160 cm-1for 1 and 140 cm-1for 2)imply the presence of chelating coordinationmode of the carboxylic groups.

2.3 Thermal properties of com plexe 1 and 2

The TG analyses for the two complexes have been investigated under N2.1 has two weight-loss processes.Firstly,1 is stable up to about 289.5℃and with further heating to 379℃,a gradual weight loss occurs,which is due to the departure of PhCOO-ligand(Obsd.38.33%;Calcd.39.01%).Secondly,the mass loss of 41.11%was observed in the temperature range of 393.9～459.8℃,which is attributed to the releaseofbmix ligand(Calcd.42.88%).The remaining weight corresponds to the formation of CdO(Obsd. 20.56%;Calcd.20.68%).2 can be divided into three steps from the TG curve.The firstmass loss of 7.62% between 99.3 and 127.2℃corresponds to the release of the uncoordination ethanolmolecule(Calcd.7.74%). The second weight loss of 28.09%is observed from 316.6 to 394.2℃,assigned to the decomposition of chdc ligand(Calcd.28.6%).The third mass loss of 42.79%from 401.4 to 496.6℃is ascribed to the loss of bmix ligand(Calcd.44.75%)leading to the decomposition of the complex to CdO with a residual mass of 21.50%(Calcd.21.58%).

3 Conclusions

Two new cadmium coordination polymers with di(imidaozle)and organic carboxylate ligand, [Cd(PhCOO)2(bmix)]n(1)and{[Cd(chdc)(bmix)]· C2H5OH}n(2),were obtained by hydrothermal reaction under similar conditions.The complex 1 exhibits a 1D zigzag chain united by bmix ligand while the 2 displays a 2D(4,4)-connected net.The different complexity in the structures of coordination architectures is due to variation of organic carboxylate part.

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Synthesis,Crystal Structures and Characterization of Two Cadm ium Coordination Polymers Based on a Bis(im idazole)Ligand

ZHANGWei-Guo＊,1CUIGuang-Hua2JIAO Cui-Huan2GENG Jian-Chen2
(1Departmentof Chemistry,Hebei Normal University of Science and Technology,Qinhuangdao,Hebei 066004,China)
(2College of Chemical Engineering,HebeiUnited University,Tangshan,Hebei 063009,China)

The two Cdcoordination polymers,[Cd(PhCOO)2(bmix)]n(1)and{[Cd(chdc)(bmix)]·C2H5OH}n(2) (bmix=1,4-bis(2-methylimidazole-1-ylmethyl)benzene,H2chdc=1,4-cyclohexanedicarboxylic acid)were hydrothermally synthesized and characterized by elemental analysis,IR spectroscopy,TG and X-ray single crystal diffraction.1 possesses a one-dimensional zigzag chain structure parallel to[001];2 displays a two-dimensional undulated(4,4)network constructed with bmix and chdc dianion bridge ligands.Each cadmium(Ⅱ)ion in 1 and 2 has distorted octahedral coordination geometry.In addition,the thermal properties of two coordination polymers have been presented.CCDC:842711,1;842712,2.

coordination polymer;crystal structure;flexible di(imidazole);(4,4)network

book=1507,ebook=9

O614.24+2

A

1001-4861(2012)11-2494-07

2012-02-20。收修改稿日期：2012-07-09。

河北科技師范學院科研創新團隊和重點學科建設經費(No.CXTD2010-02)資助項目。

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