李秀梅 紀(jì)建業(yè)牛艷玲 王志濤

(通化師范學(xué)院化學(xué)系，通化 134002)

由吡嗪二甲酸及雙咪唑基配體構(gòu)筑的鋅配位聚合物的合成、晶體結(jié)構(gòu)及熒光性質(zhì)

李秀梅 紀(jì)建業(yè)＊牛艷玲 王志濤

(通化師范學(xué)院化學(xué)系，通化 134002)

通過(guò)水熱法合成了一個(gè)新的金屬-有機(jī)配位聚合物[Zn(pzdc)(bix)0.5(H2O)]n(1)(H2pzdc=吡嗪-2,3-二甲酸，bix=1，4-雙(咪唑基1-甲基)-苯)。并對(duì)其進(jìn)行了元素分析、紅外光譜、紫外光譜和X-射線單晶衍射測(cè)定。該配合物屬于三斜晶系，P1空間群。晶體學(xué)數(shù)據(jù)：a=0.737 27(8)，b=1.004 45(12)，c=1.079 10(13)nm，α=113.771(2)，β=102.005(2)，γ=93.586(2)°，V=0.705 71(14)nm3，C13H11N4O5Zn，Mr=368.63，Dc=1.735 g·cm-3，μ(Mo Kα)=1.773 mm-1，F(xiàn)(000)=374，Z=2，最終 R=0.027 6，wR=0.067 7 用于 2 460 個(gè)可觀測(cè)點(diǎn)。在晶體結(jié)構(gòu)中，鋅離子通過(guò)吡嗪-2，3-二甲酸和1，4-雙(咪唑基1-甲基)-苯)配體橋聯(lián)成二維層狀結(jié)構(gòu)。而且該配合物通過(guò)氫鍵和π-π堆積作用擴(kuò)展成三維超分子網(wǎng)狀結(jié)構(gòu)。此外還研究了它的熒光性質(zhì)。

鋅配合物；晶體結(jié)構(gòu)；熒光

0 Introduction

Recently, the effective combination of coordination bond and hydrogen bond hasbeen applied in the engineering study of inorganic-organic hybrid material and the construction of metal-organic coordination supramolecular complexes.The suitable organic ligand makes the complex not only possess novel structure but also produce unique optical,electric and magnetic properties.Pyrazine-2,3-dicarboxylic acid(H2pzdc)has been proved to be well suited for the construction of multidimensional frameworks due to the presence of two adjacent carboxylate groups(O donor atoms)as substituents on the N-heterocyclic pyrazine ring (N donor atoms).A series of one-,two-and three-dimensional metalorganic coordination supramolecular complexes have been synthesized and characterized[1-8].On the other hand,the employment of mixed ligands during the self-assembly process has gradually become an effective approach,which isexpected to obtain frameworks with more diverse structuralmotifs compared to using only one type of ligands.Therefore,the auxiliary ligands such as imidazole-containing ligands,are introduced into the reaction systems so as to tune up the metal coordinated sites[9-11].Taking all the above discussion into account,we utilized the pyrazine-2,3-dicarboxylic acid(H2pzdc)and polycyclic aromatic bidentate bridging ligands,bix,to generate coordination polymers.In this communication,we reportthe hydrothermalsynthesisand structural characterization of[Zn(pzdc)(bix)0.5(H2O)]n(1).It shows a two-dimensional layer structure bridged by pzdc and bix ligands.Moreover,their luminesent properties have been investigated in the solid state.

1 Experimental

1.1 General procedures

All reagents were purchased commercially and used without further purification.Elemental analyses(C,H and N)were measured on a Perkin-Elmer 2400 CHN Elemental Analyzer.IR spectrum was recorded in the range of 4 000～400 cm-1on an Alpha Centaurt FT/IR Spectrophotometer using a KBr pellet.The fluorescent studies were carried out on a computercontrolled JY Fluoro-Max-3 spectrometer at room temperature.

1.2 Synthesis

The title complex was prepared from a mixture of Zn(OAc)2·2H2O(0.2 mmol,0.044 g),H2pzdc(0.4 mmol,0.068 g),bix(0.2 mmol,0.048 g)and H2O(18 mL)in a 30 mL Teflon-lined autoclave under autogenous pressure at 150 ℃ for 7 d.After cooling to room temperature,pale yellow block crystals were collected by filtration and washed with distilled water in 37%yield (based on Zn).Anal.Calcd.(%)for C13H11N4O5Zn:C,42.35;H,3.00;N,15.20.Found(%):C,41.89;H,2.31;N,14.96.IR (KBr,cm-1):3 253m,3093w,2362w,1660m,1626m,1571w,1532m,1451 w,1430w,1388s,1365s,1282w,1244m,1197w,1173 w,1125m,1112w,1090m,1063w,1028w,952w,890 w,859w,840w,771m,752m,720m,659w,627w,612 w,545w,467w.

1.3 Structure determination

A single crystalofthe titlecomplexwith dimensions of 0.389 mm×0.285 mm×0.244 mm was mounted on a Bruker Smart ApexⅡCCD diffractometer equipped with a graphite-monochromatic Mo Kα (λ=0.071 073 nm)radiation using an φ-ω scan mode at 292(2)K.In the range of 4.26°＜2θ＜52.06°,a total of 3 905 reflections were collected and 2 734 were independent with Rint=0.010 9,of which 2 460 were observed with I＞2σ(I).The correction for Lp factors was applied.The structure was solved by direct methods with SHELXS-97 program[12]and refined by full-matrix least-squares techniques on F2with SHELXL-97[13].All non-hydrogen atoms were refined anisotro-pically and hydrogen atoms isotropically.All H atoms were placed in calculated positions and refined as riding with Uiso(H)=1.2Ueq(C).The final R=0.027 6 and wR=0.0677(w=1/[σ2(Fo2)+(0.0345P)2+0.2643P],where P=(Fo2+2Fc2)/3).S=1.084,(Δρ)max=341 e·nm-3,(Δρ)min=-389 e·nm-3and(Δ/σ)max=0.001.The selected important bond parameters are given in Table 1.

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

CCDC:878878.

2 Results and discussion

2.1 IR spectrum

The COO-is coordinated with its asymmetric and symmetric stretching appearing at 1 660 cm-1(Ⅴ(OCO)assym)and 1 365 cm-1(Ⅴ(OCO)sym)[14],respectively.The ΔⅤ(Ⅴ(OCO)assym-Ⅴ(OCO)sym)is 295 cm-1(＞200),showing the presence of monodentate linkage of carboxylates in the dianions.Thus the carboxylates coordinate to the metal as monodentate ligands via the carboxylate groups[15].The absence of the characteristic bands at abound 1 700 cm-1in compound 1 attributed to the protonated carboxylic group indicates that the complete deprotonation of cbba ligand upon reaction with Zn ions[16].In addition,X-ray diffraction analysis further indicates the existence of monodentate coordination manners of the carboxylate groups and prence deprotonation of pzdc ligands.

2.2 Description of the structure

Complex 1 crystallizes in P1 space group.The molecular structure of 1 is shown in Fig.1.There are one Zn（Ⅱ）ion,one pzdc ligand,half bix ligand and one coordinated water molecule in the asymmetric unit.Each Zn（Ⅱ） ion is five-coordinated by two carboxylate oxygen atom from two different pzdc ligands,one nitrogen atom from bix ligand,one nitrogen atom from pzdc ligand and one coordinated water molecule to form distorted square-pyramidal coordination architecture.Itsequatorialplane is occupied by two carboxylate oxygen atoms,O1,O3A,one nitrogen atom,N3,and one coordinated water molecule,O5,while the apical position is occupied by one nitrogen atom,N1.The Zn-O bond lengths are in the range of 0.200 39(17)～0.205 40(16)nm,the Zn-N bond lengths are 0.202 68(19)～0.211 83(18)nm.The N(O)-Zn-O(N)anglesrangefrom78.06(6)°to164.29(7)°.The bix ligand adopts trans-conformation with a dihedral angle between the two imidazole rings of 0°.The pzdc anions adopt μ3coordination mode and linked Zn（Ⅱ） ions to form a one-dimensioal chain.The distance of neighboring Zn （Ⅱ） ions is about 0.737 3 nm as illustrated in Fig.2.The neighboring chains are bridged by bix ligands to afford a 2D sheet with(4,4)topology (Fig.2).The Zn…Zn distances separated by bix ligands are 1.429 7 nm.The resulting layers are packed in a paralled fashion and stacked along the c axis.

Hydrogen bonding interactions are usually important in the synthesis of supramolecular architectture[17].There are persistent O-H…O hydrogen bonding interactions between carboxylate oxygen atom and coordinated water molecule (O5…O4A(0.266 7 nm,151.32°,A-x+1,-y,-z+1);O5…O2B(0.262 8 nm,155.32°,Bx+1,y,z))in complex 1.Moreover,there are π-π interactions in complex 1(Fig.3)between bix ligands from adjacent chains and pzdc ligands from adjacent chains too.The centroid-to-centroid distances between adjacent aromatic rings are 0.378 5 nm for N1C1N2C3C2 and N1′C1′N2′C3′C2′(2-x,1-y,2-z)and 0.369 2 nm for N3C8C9N4C10C11 and N3′C8′C9′N4′C10′C11′ (1-x,1-y,1-z)aromatic rings.Theperpendicular distances are 0.368 6 nm for N1C1N2 C3C2 and N1′C1′N2′C3′C2′ (2-x,1-y,2-z)and 0.352 6 nm for N3C8C9N4C10C11 and N3′C8′C9′N4′C10′C11′(1-x,1-y,1-z)aromatic rings.Therefore,through hydrogen bonds and π-π interactions,the two-dimensional layers are further extended into a three-dimensional supramolecular framework.

2.3 Photoluminescent properties

The emission spectrum of complex 1 in the solid state at room temperature is shown in Fig.4.It can be observed that complex 1 exhibits green photoluminescence with an emission maximum at ca.531 nm upon excitation at 325 nm.In order to understand the nature of these emission bands,we first analyzed the photoluminescence properties of free pyrazine-2,3-dicarboxylic acid,and confirmed that it does not emit any luminescence in the range of 400～800 nm.And then we investigated the emission spectrum of bix itself and the result indicated that it does not emit any luminescence in the range 400～800 nm,which has also been confirmed previously[18].Thus,according to the previous literature[19],the emission band could be assigned to the emission of ligand-to-metal charge transfer (LMCT).For possesses strong fluorescent intensity,it appears to be good candidates for novel hybrid inorganic-organic photoactive materials.

2.4 UV spectrum

The UV spectra for the title compound,H2pzdc and bix ligands have been investigated in the solid state (Fig.5).For bix ligand,there is no absorption band,while both the title compound and H2pzdc have one absorption band at about 274 nm,which should be assigned to the n→π*[20]transition of H2pzdc.However,after H2pzdc coordinating to the Zn2+ion,the absorption intensity slightly decreases.It is clearly that the absorption band in H2pzdc remains in the same position with that in the title compound,showing that they are not affected basically by the metal coordination.

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Synthesis,Crystal Structure and Fluorescent Property of Zinc Coordination Polymer Assembled by Pyrazine-2,3-dicarboxylic Acid and Bis(imidazol)Ligands

LI Xiu-MeiJI Jian-Ye＊NIU Yang-Ling WANG Zhi-Tao
(Department of Chemistry,Tonghua Teachers College,Tonghua,Jilin 134002,China)

A new metal-organic coordination polymer[Zn(pzdc)(bix)0.5(H2O)]n(1)(H2pzdc=pyrazine-2,3-dicarboxylic acid,bix=1,4-bis(imidazol-1-ylmethyl)-benzene)has been hydrothermally synthesized and structurally characterized by elemental analysis,IR spectrum,UV spectrum and single-crystal X-ray diffraction.The complex crystallizes in triclinic,space group P1 with a=0.737 27(8),b=1.004 45(12),c=1.079 10(13)nm,α=113.771(2),β=102.005(2),γ=93.586(2)°,V=0.705 71(14)nm3,C13H11N4O5Zn,Mr=368.63,Dc=1.735 g·cm-3,μ(Mo Kα)=1.773 mm-1,F(000)=374,Z=2,the final R=0.027 6 and wR=0.067 7 for 2 460 observed reflections (I＞2σ (I)).In the crystal structure,1 shows a two-dimensional layer structure bridged by pzdc and bix ligands.Furthermore,it exhibits a 3D supramolecular network through hydrogen bonding and π-π stacking interactions.Moreover,its luminesent property has been investigated in the solid state.CCDC:878878.

Zn（Ⅱ）complex;crystal structure;fluorescence

O614.24+1

A

1001-4861(2012)08-1712-05

2011-11-29。收修改稿日期：2012-03-28。

吉林省教育廳科學(xué)技術(shù)研究(吉教科合字[2012]第358號(hào))和吉林省科技發(fā)展計(jì)劃(No.201205080)資助項(xiàng)目。

＊通訊聯(lián)系人。E-mail：lixm20032006@yahoo.com.cn