Solvothermal Synthesis,Crystal Structure and Photoluminescence Property of a Coordination Polymer Based on 1,1′-Ethynebenzene-3,3′,5,5′-tetracarboxylate

WANG Li-FengHU Yun-XiaZHANG Wen-Wei＊,REN Xiao-Ming(Department of Applied Chemistry,College of Science,Nanjing University of Technology,Nanjing 0009,China)(State Key Laboratory of Coordination Chemistry,School of Chemistry and Chemical Engineering,Nanjing University,Nanjing 0093,China)

Solvothermal Synthesis,Crystal Structure and Photoluminescence Property of a Coordination Polymer Based on 1,1′-Ethynebenzene-3,3′,5,5′-tetracarboxylate

WANG Li-Feng1,2HU Yun-Xia2ZHANG Wen-Wei＊,2REN Xiao-Ming＊,1
(1Department of Applied Chemistry,College of Science,Nanjing University of Technology,Nanjing 210009,China)(2State Key Laboratory of Coordination Chemistry,School of Chemistry and Chemical Engineering,Nanjing University,Nanjing 210093,China)

A novel Zn2+coordination polymer,[Zn2(EBTC)(BPDO)(DMSO)(H2O)2]n(1)(EBTC=1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate;BPDO=4,4′-bipyridine 1,1′-dioxide)has been synthesized and characterized.1 has the three-leg-ladder-like architecture along the crystallographic a-axis direction,in which the adjacent three-legladder-like chains are linked together to build 3D supermolecules via intermolecular hydrogen bond and π…π stacking interactions.It displays fluorescent emission at room temperature.CCDC:806016.

coordination polymer;hydrogen bond interaction;solvothermal synthesis;photoluminescence property

0 Introduction

Coordination polymers have been flourishing in the recent years[1].The majority of the numerous coordination polymers reported are normally constructed by linking metal ions with multidentate bridging ligands,and a great numerous of one-,two-and threedimensional(1D,2D and 3D)coordination polymers have been synthesized through the judicious selection of versatile organic ligands,appropriate metal ions and reaction conditions[2-5].Aromatic polycarboxylates have been found to be favorable ligands since the multipotential oxygen donors after deprotonation can adopt different coordination modes and lead to diverse coordination networks as well as interesting optical,magnetic and hydrogen storage properties[6-8].

Up to now,even if many metal carboxylate frameworks have been reported in literatures,thecoordination chemistry of the 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate acid(H4EBTC,Scheme 1)remains largely unexplored[9-10].Most recently,we have successfully synthesized one microporous cupric MOFs based on H4EBTC,which exhibits excellent uptake of H2,CH4,CO2and C2H2[9].Taking advantages of structures and properties of H4EBTC and BPDO,we expect to design and synthesize new functional metal-organic frameworks.Herein we present the solvothermal synthesis,crystal structure and photoluminescence property of a novel Zn2+coordination polymer[Zn2(EBTC)(BPDO)(DMSO)(H2O)2]n(1)based on the molecular building blocks(MBBs).

1 Experimental

1.1 Materials and measurements

All commercially available chemicals were of analytical grade and used as received without further purification.Elemental analyses(C,H,S and N)were carried out on a Perkin-Elmer 240 analyzer.The FTIR spectra were obtained on a VECTOR TM 22 spectrometer with KBr pellets in the 400～4 000 cm-1region.TGA-DTA diagrams were recorded by a CA Instruments DTA-TGA 2960 type simultaneous analyzer heating from 293 to 1073 K in nitrogen atmosphere at a rate of 20 K·min-1.Powder X-ray diffraction(PXRD)data were recorded on a Shimadzu XRD-6000 diffractometer with Cu Kα (λ=0.154056 nm)radiation at room temperature with a scan speed of 5°·min-1and a step size of 0.02°in 2θ.Photoluminescence spectra in the solid state were recorded with a Hitachi 850 fluorescence spectrophotometer.

1.2 Preparation of complex 1

Zn(NO3)3·6H2O(15 mg,50.4 mmol),H4EBTC,(5.0 mg,0.014 mmol),DMF(0.15 mL),DMSO (0.15 mL)and BPDO (1.3 mg,0.007 mmol)were heated at 65 ℃for 24 h to give a pellucid solution,then 0.4 mL water was added to the clear solution,and the mixture was heated at 120 ℃ for 12 h.Colorless block-shaped[Zn2(EBTC)(BPDO)(DMSO)(H2O)2]nwas achieved after slowly cooling down to room temperature(yield ca.36%based on Zn(NO3)3·6H2O).Elemental analysis calcd.for C30H24N2O13SZn2(%):C 45.96,H 3.06,N 3.57,S 4.08;Found(%):C 46.20,H 3.10,N 3.59,S 4.11.Selected IR data(cm-1):3 408(b),1 573(s),1 363(s),1 492(s),1 010(w),721(w).

1.3 X-ray crystallography

Single crystal X-ray diffraction data were collected on a Bruker Smart ApexⅡCCD diffractometer at 153 K using graphite monochromated Mo Kα radiation(λ=0.071 073 nm).The structure was solved by direct method and refined with full-matrix least squares technique using the SHELXTL package[11].All nonhydrogen atoms were refined anisotropically,and all hydrogen atoms were put in calculated positions.Main data of collection and refinement details of 1 are summarized in Table 1.Selected bond lengths and angles are listed in Table 2.Hydrogen bond distances and angle are listed in Table 3.

CCDC:806016.

Table 1 Crystal data and structure refinement for complex 1

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

Table 3 Hydrogen bond distances and angles

2 Results and discussion

2.1 IR spectra and PXRD data

IR spectra of 1 showing strong absorption bands around 1 362,1 578 and 1 627 cm-1can be assigned to coordinated carboxylate groups[12].The broad and strong absorption bands in the range of 3 350～3 500 cm-1correspond to the presence of water molecules in 1.The experimental and stimulated powder X-ray diffraction(PXRD)patternsaregiven in Fig.1,which are consistent with each other to indicate the good purity of sample.

Fig.1 Experimental and simulated PXRD patterns of 1

2.2 Crystal structure description

Crystal of 1 belongs to triclinic system with space group P1.Its asymmetric unit consists of two different Zn2+ions,one deprotonated EBTC4-,one BPDO,one coordinated DMSO molecule and two coordinated H2O molecules as shown in Fig.2.Two crystallographically independent Zn2+ions exhibit different coordination geometries.Zn1 is coordinated by five oxygen atoms from H2O(O11),DMSO(O13)and EBTC4-(O1,O3iand O4i)to form a distorted trigonal bipyramidal coordination environment with τ=0.543(τ=(β-α)60,α and β are the bigger bond angles around Zn1 center,which are 125.9(2)°and 158.5(2)°,respectively.Usually,τ=0 for idealsquare pyramid and τ=1 for ideal trigonal bipyramid)[13],in which O4i,O11 and O13 atoms are lying on the equatorial plane and O1 and O3iatoms are on the axial positions.The Zn-O distances are in the range of 0.1949(4)～0.2034(5)nm.Zn2 coordinates five oxygen atoms from H2O(O12),BPDO(O9)and EBTC4-(O5i,O7iiand O8),where a distorted trigonal bipyramidal coordination geometry with τ=0.627 was formed(α and β are 137.61(18)°and 175.20(17)°,respectively[13]).The distorted trigonal bipyramidal geometry of Zn2 atoms is composed of O5i,O7ii,O8,O12 and O9 atoms with O5i,O7iiand O8 atoms lying the equatorialplane and the axial positions being occupied by O12 and O9 atoms.The Zn-O distances around Zn2 are in the range of 0.199 4(4)～0.223 2(5)nm.

Fig.2 ORTEP plot of 1 showing the local coordination environment of Zn1 and Zn2 ions with thermal ellipsoids at 50%probability

As illustrated in Fig.3,each EBTC4-ligand bridges five Zn2+ions via four carboxylate groups in monodentate and bidentate coordination modes,respectively.The oxygen atoms(O2,O6)of EBTC4-are uncoordinated.The two neighboring trigonal bipyramids comprising of Zn2 atoms are connected through two carboxylate groups (O7ii,O8)into a 8-membered ring dinucler subunit with Zn-Zn distance of 0.3431 nm.Each dinuclear Zn2 subunit is coordinated by four EBTC4-ligands,and every Zn1-type coordination polyhedron is connected by two EBTC4-ligands to form three-legladder-like architecture along the crystallographic b axis direction.

Fig.3 Perspective view of stacking along b direction

The adjacent three-leg-ladder-like chainsare linked together to build 3D supermolecules via intermolecular hydrogen bond interactions between O10/O5iand O11 with O11-H11A…O10 0.2732(8)nm,O11-H11B…O5i0.2961(7)nm in the ac plane as well as between O10 and O12 with O12-H12B…O10 0.269 8(7)nm along the b direction.Besides the intermolecular hydrogen bond interactions,1 also has intramolecular hydrogen bond interaction between O12 and O6 with O12-H12A…O6 0.273 6(7)nm in the ac plane (Table 3).Moreover it is worth noting that a shorter contact of 0.356 8 nm between the center of the ethynyl fragment and the center of the phenyl ring is observed in the ac plane(Fig.4).Therefore,it is highly probable that there exists π…π stacking interactions between the superimposed phenyl ring and the ethynyl fragment.Moreover,slipped π…π interactions are also found between the offset face-to-face phenyl rings in the ac plane due to its centroid-centroid distance of 0.3653 nm.In the meanwhile,shorter distances of 0.333 5 nm within adjacent BPDO molecules with dihedral angle of 11.768°and 0.328 0 nm between the BPDO and the EBTC4-ligands with dihedral angle of 12.697°are also observed in the ac plane,respectively.They can be considered as aromatic interactions which are intermediate between slipped π…π interactions and edge-on C-H…π interactions[14].

Fig.4 Perspective view of π…π stacking interactions along the b direction

2.3 Thermal analysis

Thermal gravimetric analysis (TGA)experiment was conducted to determine the thermal stability of 1,which isan importantaspectformetal-oraganic frameworks.As shown in Fig.5,1 shows three steps of weight loss.The first weight loss of 4.5%in the temperature of 40～100℃ corresponds to the liberation of two coordinated water molecules(calculated as 4.6%).The second weight loss of 9.2%in the temperature of 100～200℃is attributed to the removal of coordinated DMSO molecule(calculated as 9.7%).The third weight loss of 22.0%is assigned to the loss of coordinated BPDO ligand (calculated as 21.7%).The coordination framework is collapsed when the temperature is higher than 440℃.

Fig.5 TGA plot of 1 in the temperature range of 25～750 ℃

2.4 Photoluminescence

The luminescent property of 1 was investigated in the solid state at room temperature(25℃),as depicted in Fig.6.It displays fluorescent emission bands at about 431 nm upon excitation at 365 nm.This band is probably assigned to the π-π*fluorescent emission since similar emission is observed at 420 nm upon excitation at 342 nm for H4EBTC.Compared with the emission of H4EBTC,the emission band of 1 is shift to low energy region.Due to its remarkable luminescence,it appears to be good candidate of novel hybrid inorganic-organic optic materials.

Fig.6 Emission spectra of 1 in the solid state at ambient temperature

Acknowledgments:We thank the Nature Science Foundation of China for financial support(Grant No.20871068)and the Center of Analysis and Determining of Nanjing University for their assistances.We also appreciate Dr.WANG Fang-Ming and Dr.KANG Ling-Chen for their kind help.

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基于 1，1′-苯乙炔-3，3′，5，5′-四羧酸的配位聚合物：水热合成、结构和荧光性质

王立锋1,2胡云霞2章文伟＊,2任小明＊,1

(1南京工业大学应用化学系，南京 210009)(2配位化学国家重点实验室，南京大学化学化工学院，南京 210093)

合成并表征了配合物 1，[Zn2(EBTC)(BPDO)(DMSO)(H2O)2]n，其中 EBTC 为 1，1′-苯乙炔-3，3′，5，5′-四羧酸根，BPDO 为 4，4′-二吡啶基1，1′-二氧化物，DMSO为二甲亚砜。1沿着b轴的方向具有类似于三腿梯子状的链状结构，链与链之间通过氢键作用和π-π堆积作用形成了三维超分子结构。在室温条件下1表现出了荧光性质。

配位聚合物；氢键作用；溶剂热合成；荧光性质

O614.24+1

：A

：1001-4861(2011)03-0542-05

2010-09-10。收修改稿日期：2010-11-25。

国家自然科学基金资助项目(No.20871068)。

＊通讯联系人。 E-mail：wwzhang@nju.edu.cn