杜晓迪 李春阳 王振领 常加忠 金 刚

基于双核铜簇和[β-Mo8O26]4-阴离子的杂化化合物的合成及结构

杜晓迪＊,1李春阳2王振领1常加忠2金 刚2

(1周口师范学院化学系，周口 466001)
(2周口师范学院物理系，周口 466001)

通过水热合成方法得到了一个基于双核铜簇[Cu2(1，4-bth)3]4+和[β-Mo8O26]4-阴离子的有机-无机杂化化合物，[Cu2(1，4-bth)3(H2O)(β-Mo8O26)](1)(1，4-bth=4-(6-(1H-1，2，4-三氮唑-1-基)正己烷)-4H-1，2，4-三氮唑)，并通过元素分析、红外光谱、X-射线单晶衍射、热分析等测试对其进行了表征。晶体数据表明该化合物属于三斜晶系，P1空间群。在化合物1中，1，4-bth配体都以三齿配体的形式与3个铜离子相连，形成双核铜簇[Cu2(1，4-bth)3]4+，每个簇单元进一步和其相邻的4个同类型单元相连形成了相互平行的层状结构[Cu2(1，4-bth)3]n4n+，层与层之间又通过[β-Mo8O26]4-阴离子相连构筑成1个三维框架结构，其拓扑类型为pcu alpha-Po简单立方格子；热分析表明该化合物具有相对较高的热稳定性。

有机-无机杂化物；柔性配体；八钼酸盐；晶体结构

0 Introduction

Design and synthesis of organic-inorganic hybrid have recently aroused much interest owning to the possibility of combining the different characteristics of the components to get unusual structures or properties[1].Polyoxometalates (POMs),as one of the most widely used inorganic components,posses extreme variability of composition,structure,electronic properties and applications in many areas,such as catalysis,material science and biology,medicine[2].Octamolybdates(Mo8),as an important member of POM family,have been extensively studied due to its diverse structures and intriguing properties.Up to date,eight isomeric forms of octamolybdates have been explored,that is,the α-,β-,γ-,δ-,ε-,ζ-,η-and θ-isomers[3].Su and coworkers have synthesized several hybrids based on Mo8polyanions and Cu-bis(imidazole)ligands.The supramolecular isomerism[4]and the influence of the organic amine on the charge of the Cu ions in these systems were also studieded[5].

In this work, we use the octamolybdate polyanions as the inorganic building block and the bis(triazole)ligand,4-(6-(1H-1,2,4-triazol-1-yl)hexyl)-4H-1,2,4-triazole)as organic unit to construct organicinorganic hybrid.The selection of the ligand is based on the following considerations: (i)N-heterocycle ligands play the important role during the construction of metal-organic frameworks (MOFs),owing to strong metal binding capability and versatile coordination modes[6-7];(ii)The bis(triazole)ligand combine the coordination geometry of both imidazoles and pyrazoles to provide more potential coordination sites;(iii)The ligand can act as bridges to construct high dimensional framework;(iv)The ligand has different flexibility and conformational freedom,which may providedifferentcapacitiesforspatialextension.These characteristics may result the construction of diversified attractive frameworks[8].

Herein,by utilizing the octamolybdate as inorganic building block and the flexible bis(triazole)ligand as organic unit,a three-dimensional(3D)hybrid,[Cu2(1,4-bth)3(H2O)(β-Mo8O26)](1)(1,4-bth=4-(6-(1H-1,2,4-triazol-1-yl)hexyl)-4H-1,2,4-triazole))has been synthesized.Thermal analysis for the compound was also performed.

1 Experimental

1.1 Materials and general methods

The 1,4-bth ligand was synthesized according to the literature method[9].All other chemicals were of reagentgrade and used asreceived.Elemental analyses for C,H and N were performed on a Perkin-Elmer 240C analyzer.Infrared spectrum was recorded on a Vector22 Bruker Spectrophotometer with KBr pellets in the 400～4 000 cm-1region.The powder XRD pattern was recorded on a Shimadzu XD-3A X-ray diffractometer.Thermogravimetric analyses(TGA)was collected on a Perkin-Elmer Pyris 1 TGA analyzer from room temperature to 800℃with a heating rate of 10 ℃·min-1under nitrogen.

1.2 Synthesis of[Cu2(1,4-bth)3(H2O)(β-Mo8O26)]

A mixture of Cu(NO3)2·3H2O(2 mmol,480 mg),(NH4)6Mo7O24·4H2O (0.2 mmol,240 mg),1,4-bth(0.2 mmol,44 mg)and H2O(15 mL)(pH=2.93)was sealed in a 30 mL Teflon-lined bomb and heated at 175℃for 3 d.The reaction mixture was slowly cooled to room temperature.Green virgulate crystals of 1 suitable for X-ray diffraction analysis were isolated in 41%yield.Anal.Calcd.for C30H50Cu2Mo8N18O27(%):C,18.11;H,2.53;N,12.67.Found(%):C,18.24;H,2.39;N,12.58.IR for 1(KBr)/cm-1:3 404(m),3 119(w),1 639(m),1556(m),1527(m),1460(m),1279(m),1217(m),1125(m),1087(w),1057(w),944(s),910(s),893(s),839(m),712(m),660(m),646(m),559(w),520(w),450(w).

1.3 X-ray crystallography

A green single crystal of 1 with dimensions of 0.23 mm×0.20 mm×0.18 mm was mounted on a Bruker Smart Apex CCD diffractometer equipped with a graphite-monochromatic Mo Kα radiation(λ=0.071 073 nm)using the φ-ω scan mode in the range 1.83°≤θ≤25.10° at298(2)K.A totalof13 655 reflections were collected and 9 593 were independent with Rint=0.054 4,of which 6 507 were observed with I＞2σ(I).Raw frame data were integrated with theSAINT program[10].The structure was solved by direct methods and refined by full-matrix least-squares on F2using SHELX-97[11].An empirical absorption correction was applied with the program SADABS[12].All nonhydrogen atoms were refined anisotropically.All the hydrogen atoms were set in calculated positions and refined by a riding mode,with a common thermal parameter.The final cycle of refinement converged to R=0.087 6 and wR=0.163 8(w=1/[σ2(Fo2)+(0.076 8P)2]where P=(Max(Fo2,0)+2Fc2)/3).(Δ/σ)max=0.000,S=1.001,(Δρ)max=1732 and(Δρ)min=-862 e·nm-3.Crystallographic details have been summarized in Table 1.Selected bond lengths and angles for 1 are listed in Table 2.

Table 1 Crystallographic data for complex 1

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

CCDC:865416.

2 Results and discussion

2.1 Synthesis and general characterization

Complex 1 was obtained under hydrothermal condition.The complex is stable in air and insoluble in water and common organic solvents.And all the Cu2+ions in the compound were not reduced and retained their oxidation state.Comparing with the observation of Cu+ions in the other system[13-14],it can be concluded that the 1,4-bth ligand in the system only acted as the tridentate-linker but not reductant,possibly due to the relatively lower molar ratio(1∶10)of 1,4-bth ligand to Cu2+ion[15].

In the IR spectrum of 1,the bands in the range of 600～1 000 cm-1show the characteristic vibrational features similar to the known [β-Mo8O26]4-anion.The strong bands from 944 to 893 cm-1(944(s),910(s),893(s))are attributed to the νas(Mo=O),while multiple bands attributed to the bridging (Mo-O-Mo(Cu))groups′absorptions are found in 839～646 cm-1region(839(m),712(m),660(m),646(m)).Bands in the regions of 1 450～1 650 cm-1(1639(m),1 556(m),1 527(m),1460(m))can be assigned to the skeletal vibrations of the aromatic rings of 1,4-bth ligands.In addition,the broad band around 3 404 cm-1indicates the presence of ν(O-H)stretching of water molecules.The powder X-ray diffraction pattern for 1 is displayed in Fig.1.The diffraction peaks of the experimental and simulated patternsmatch wellin key positions,indicating the phase purities of complex 1.

2.2 Structure analysis

Compound 1 crystallizes in the triclinic,P1 space group.The asymmetric unit of 1(Fig.2)contains two Cu2+ions,three 1,4-bth ligands,one [β-Mo8O26]4-anion and one coordinated water molecule.The[β-Mo8O26]4-anion consists of eight distorted edge-and/or corner-sharing{MoO6}octahedra,with four kinds of O atoms,two μ5-O,four μ3-O,six μ2-O,and fourteen terminal oxygen atoms (Ot).The bond valence sum calculations[16]reveal that all Mo atoms are in the+6 oxidation state and Cu atoms are in the+2 oxidation state.The Mo-O bond lengths(0.168 1(6)～0.252 0(6)nm)all fall in the regular range[17].

In 1,there are two crystallographically unique Cu2+ions in the asymmetric unit.The Cu(1)ion is sixcoordinated by five nitrogen atoms((N(1),N(7),N(12),N(14),N(18))from five 1,4-bth ligands,and one terminal oxygen atoms(O(1))from one[β-Mo8O26]4-polyanion.The Cu(2)ion is also six-coordinated by four nitrogen atoms((N(2),N(6),N(8),N(13))from four 1,4-bth ligands,one terminal oxygen atom(O(4e))from one [β-Mo8O26]4-polyanion and one oxygen atom from coordinated water molecule (Symmetry code:e:x,y+1,z).Both of the coordination geometry around the copper ions can be described as the distorted octahedra.The bond distances around the Cu2+ions are in the range of 0.200 8(9)～0.232 5(8)nm(Cu-N)and 0.202 7(7)～0.251 4(7)nm(Cu-O).

Interestingly,the coordination mode of the 1,4-bth ligand in complex 1 is different from those of the other bis(triazole)ligands[18].Each 1,4-bth ligand in 1 utilizes its three apical N atoms as the tridentatelinker to bridge three Cu2+ions,and Cu(1)and Cu(2)ions are chelated by three N-N bonds from three 1,4-bth ligands to form a dimeric copper cluster[Cu2(1,4-bth)3]4+with the Cu…Cu distance of 0.376 2 nm(Fig.3a).Then each copper cluster is connected to four same clusters in its neighborhood by the 1,4-bth bridges forming a 2D[Cu2(1,4-bth)3]n4n+sheet with the dimensions of 1.274 nm×1.424 nm(Fig.3b).The sheet can be rationalized as a 4-connected uninodal(44·62)topologicalnetwork (Fig.3c)by considering the dimeric copper clusters as 4-connected nodes,1,4-bth ligandsaslinkers. In addition,three kindsof conformation of 1,4-bth ligand were observed in 1:gauch-trans-trans-trans-gauche (a),gauch-trans-transgauch-trans (b)and trans-gauche-gauche-gauchegauche(c)(Scheme 1),resulting three kinds of-(CH2)-lengths for 1,4-bth ligand,1.237,1.191 and 1.328 nm,respectively.And such diverseconformation results the flexibility of positive framework ([Cu2(1,4-bth)3]4+),to make sure the matching of the [Mo8O26]4-polyanions.

The neighboring [Cu2(1,4-bth)3]4+sheets are parallel,and are further linked by the[β-Mo8O26]4-anions through bonded to the Cu2+ions as the pillars to construct the 3D framework (Fig.4).From the topological view,the 3D framework can be considered as a pcu alpha-Po primitive cubic,with the topological symbol (412·63),by considering the dimeric copper clusters as 6-connected nods,1,4-bth ligands and[β-Mo8O26]4-anions as linkers.In addition,the existence of the intermolecular hydrogen bonds(Table 3)O(27)-H(27C)…O(8e)and O(27)-H(27D)…O(9f))(Symmetry code:f:-x+1,-y,-z+1),with the average distance of donor and acceptor(d(D…A))0.275 2 nm,further strengthen the interaction between the coordinated water molecules(O(27))and[β-Mo8O26]4-anions,and enhance the stability of the whole framework.

Table 3 Hydrogen bond lengths and bond angles for complex 1

2.3 Thermal property

The thermogravimetry (TG)experiment was also performed for complex 1.As shown in Fig.5,the TG curve displays two distinct weight loss steps with a total loss of 34.36% (Calcd.34.12%)in the 28～800 ℃.The first weight loss,0.92% (Calcd.0.90%)in the range of 28～285 ℃,is ascribed to the release of the one coordinated water molecule in 1.The second weight loss,33.44% (Calcd.33.12%)in the range of 285～654℃,corresponds to the combustion of all the organic ligands in 1.All the data above illustrate that complex 1 retains a comparatively good thermal stability.

3 Conclusions

In summary,a new hybrid based on flexible bis(triazole)ligands and[β-Mo8O26]4-polyanions has been synthesized.In this complex,the 1,4-bth ligands acted as tridentate-linkers and dimeric copper clusters[Cu2(1,4-bth)3]4+were observed.The whole framework showed the pcu alpha-Po primitive cubic topology.The thermal analysis illustrates that complex 1 retains a comparatively good thermal stability.

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Synthesis and Structure of One Hybrid Constructed by Dimeric Copper Clusters and[β-Mo8O26]4-Polyanions

DU Xiao-Di＊,1LI Chun-Yang2WANG Zhen-Ling1CHANG Jia-Zhong2JIN Gang2
(1Department of Chemistry,Zhoukou Normal University,Zhoukou,Henan 466001,China)
(2Department of Physics,Zhoukou Normal University,Zhoukou,Henan 466001,China)

An organic-inorganic hybrid[Cu2(1,4-bth)3(H2O)(β-Mo8O26)](1)(1,4-bth=4-(6-(1H-1,2,4-triazol-1-yl)hexyl)-4H-1,2,4-triazole))based on dimeric copper clusters[Cu2(1,4-bth)3]4+and[β-Mo8O26]4-polyanions has been synthesized and characterized by element analysis,IR spectra,single-crystal X-ray diffraction,thermal analysis.The crystallographicdatashowsthatcomplex 1crystallizesintriclinicspacegroup P1witha=1.1951(2)nm,b=1.2520(2)nm,c=2.146 0(4)nm,α=85.893(3)°,β=76.229(3)°,γ=62.714(3)°,V=2.769 0(8)nm3,C30H50Cu2Mo8N18O27,Mr=1989.48,Dc=2.386 g·cm-3,μ(Mo Kα)=2.598 mm-1,F(000)=1 932,GOF=1.001,Z=2,the final R1=0.062 0 and wR2=0.153 4 for I>2σ(I).In complex 1,each 1,4-bth ligand acted as a tridentate-linker to bridge three Cu2+ions and dimeric copper clusters[Cu2(1,4-bth)3]4+were formed.Each dimeric copper cluster is connected to four same clusters forming parallel two dimensional(2D)sheets[Cu2(1,4-bth)3]n4n+.Then the[β-Mo8O26]4-anions through bonded to the Cu2+ions as the pillars to construct a three dimensional(3D)framework,with the pcu alpha-Po primitive cubic topology;the thermal analysis illustrate that compound 1 retains a comparatively good thermal stability.CCDC:865416.

organic-inorganic hybrid;flexible ligand;octamolybdate;crystal structure

O614.121

A

1001-4861(2012)11-2419-06

2012-02-13。收修改稿日期：2012-07-11。

国家自然科学基金(No.21171179)，河南省自然科学基金(No.112300410291)，河南省教育厅自然科学基金(No.2011B140025，12A150028，12A140017)以及周口师范学院博士启动基金资助项目。

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