KONG Chun-Yan（College of Chemistry and Chemical Engineering，Dezhou University，Dezhou 253023，China）

Hydrothermal Synthesis,Crystal Structure and Luminescent Property of a New Cd(II) Coordination Polymer with Four-fold Interpenetrated dia Topology

KONG Chun-Yan①
（College of Chemistry and Chemical Engineering，Dezhou University，Dezhou 253023，China）

A new Cd（ΙΙ）coordination polymer with 2-nitroterephthalic acid （H2npa）and 1，4-bis（2-methyl-imidazol-1-yl）butane （bib）has been prepared by hydrothermal synthesis and characterized by single-crystal X-ray diffraction，IR and EA.Complex ［Cd（npa）（bib）］n（1）is of orthorhombic system，space group Pcca with a = 16.1750（5），b = 9.8764（5），c = 15.5890（3）Å，V = 2490.4（2）Å3，Z = 4，Mr= 539.82，Dc= 1.440 g/cm3，F（000）= 1088，µ = 0.918 mm-1，the final R = 0.0320 and wR = 0.0775 for 2253 reflections with I ＞ 2σ（I）.X-ray diffraction analysis reveals that complex 1 displays a four-fold interpenetrated dia topology.Furthermore，the luminescent property for complex 1 is also investigated in solid state at room temperature.

Cd(II),coordination polymer,luminescence;

1　INTRODUCTION

The crystal engineering of coordination polymers （CPs）is currently of great interest not only because of their potential applications as functional materials in gas storage，magnetism，luminescence and so on［1-8］but also due to their intriguing variety of architectural features and fascinating new topologies［9，10］.In particular，the design and synthesis of3D CPs represent a quite area due to their undisputed beauty with more complicated architectures and intriguing topologies.Until now，although a number of3D CPs have been reported，the construction of new architectures and a systematic research still remain a large challenge.In order to construct highdimensional CPs，the crucial step is to choose multifunctional organic ligands［11，12］.According to literature，organic aromatic polycarboxylate ligands have been proved to be excellent structural constructors due to their various coordination modes to metal ions，which often generate multidimensional networks and interesting topologies［13，14］.Previous studies show that neutral bis（imidazole）ligands exhibit special ability to coordinate to various metal centers in multiform coordination fashions to formulate the compounds.The CPs constructed by 1，4-bis（2-methyl-imidazol-1-yl）butane with a-（CH2）4- spacer are less reported［15，16］.Taking the aforementioned idea into consideration，the reactions of cadmium（II）salts，long-chain 1，4-bis（2-methylimidazol-1-yl）butane together with dicarboxylateligand were carried out under hydrothermal conditions.One new complex ［Cd（npa）（bib）］n（1）was successfully obtained.

2　EXPERIMENTAL

2.1Materials and physical measurements

All reagents and solvents employed were commercially available and used without furtherPurification.Elemental analysis was carried out on a Carlo Erba 1106 full-automatic trace organic elemental analyzer.FT-IR spectra were recorded with a Bruker Equinox 55 FT-IR spectrometer as a dry KBr pellet in the 400～4000 cm-1range.Solidstate fluorescence spectra were recorded on a Hitachi F-4600 equipped with a xenon lamp and a quartz carrier at room temperature.The powder X-ray powder diffraction （XRPD）measurements were performed on a Bruker D8 diffractometer operated at 40 kV and 40 mA using Cu-Ka radiation.

2.2Preparation of [Cd(ata)(bib)]n(1)

The mixture of Cd（NO3）2·4H2O （0.5 mmol，0.145 g），H2ata （0.5 mmol，0.106 g），bib （0.109 g，0.5 mmol），NaOH （1 mmol，0.04 g）and 15 mL of water was placed in a 25 mL Teflon reactor which was heated to 120 ℃ for3 days and then cooled to room temperature.The colorless crystals were obtained and picked out，washed with distilled water and dried in air （Yield:51% based on Cd）.Elm.anal.Calcd.（%）for C20H21CdN5O6:C，44.50；H，3.92；N，12.97.Found:C，44.51；H，3.92；N，12.96.IR/cm-1（KBr）:1603 s，1448s，1342 m，1255 m，1172 m，1039 m，957 m，816 m，797 m.

2.3Structure determination

A suitable colorless block crystal with dimensions of 0.30mm × 0.25mm × 0.22mm was mounted on a glass fiber and the data were collected on a Bruker APEX2 CCD area-detector diffractometer with a Mo-Kα radiation （λ = 0.71073 Å）at 293（2）K by using an ω-scan mode in the range of 2.06＜θ＜27.53° （-16≤h≤22，-12≤k≤12，-16≤l≤20）.For the title complex 1，a total of 16515 reflections with 2871 unique ones （Rint= 0.027）were measured，of which 2253 were observed with I ＞ 2σ（I）to the final R = 0.0320 and wR = 0.0775 （w = 1/［σ2（Fo）2+ （0.0350P）2+ 2.9500P］，where P = （Fo2+ 2Fc2）/3，S = 1.005 and （Δ/σ）max= 0.000.All non-hydrogen atoms were located by successive difference Fourier syntheses and refined with anisotropic thermal parameters on F2.The hydrogen atoms were located by geometrical calculations，and their positions and thermal parameters were fixed during the structure refinement.The highest and lowest residual peaks in the final difference Fourier map are 0.804 and -0.311 e/Å3，respectively.The structure was solved by direct methods with SHELXS-97 and Fourier techniques and refined by the full-matrix leastsquares method on F2with SHELXL-97 program［17，18］.The selected bond lengths and bond angles are listed in Table 1.

Table 1.Selected Bond Lengths (Å) and Bond Angles (°)

3　RESULTS AND DISCUSSION

3.1Crystal structure description of [Cd(npa)(bib)]n(1)

Single-crystal X-ray diffraction analysis reveals that complex 1 is a3D four-fold interpenetrated dia topology and crystallizes in the orthorhombic space group Pcca.The Cd（II）ion lying on the crystallographic inversion is six-coordinated by four carboxylate oxygen atoms （Cd（1）-O（1）= 2.487（3）Å and Cd（1）-O（2）= 2.288（2）Å）and two nitrogen atoms （Cd（1）-N（1）= 2.232（2）Å），showing a distorted octahedral geometry （Fig.1）.In 1，the carboxylate groups adopt chelating coordination mode and connect the CdIIions to form a one-dimensional chain.Furthermore，the bib ligands connect the 1D chains to form a3D framework （Fig.2）.Each CdIIion links other four CdIIions by two npa2-and two bib ligands in the formation of a diamondoid cage with diamondoid type windows （Fig.3）.From thetopological point of view by topos software，the whole framework of complex 1 can be described as a uninodal 4-connected dia net with the point symbol of 66.Owing to the spacious nature of the single network，the potential channels in 1 are filled by interpenetration of three independent identical nets，generating a fourfold interpenetrated dia net （Fig.4）.It belongs to the class Ia interpenetration.Full interpenetration vectors are ［0，1，0］ （9.88 Å）.

Fig.1.Coordination environment of Cd(II) ion in 1 (Symmetric mode:(a) x,1 - y,0.5 + z).All hydrogen atoms are omitted for clarity

Fig.2.View of the three-dimensional framework structure of 1

Fig.3.View of a single diamondoid cage generated through bib ligands and bridging CdII

The intermolecular π-π stacking interactions further assemble the architecture to form a supramolecular framework.The interplanar Cg（1）rings defined by N（1），C（1），N（2），C（4）and C（3）has the centroid-to-centroid distance to be3.6024（19）Å （symmetric mode:-x，1-y，1-z），as shown in Fig.5.

3.2Luminescent properties

X-ray power diffraction （XRPD）was used toconfirm the phase purity of bulk materials of compound 1 at room temperature.The XRPD pattern of 1 has been matched with the simulated patterns （Fig.6）.The photoluminescence spectra of complex 1 and bib are shown in Fig.7.Complex 1 exhibits intense blue luminescent properties with emission maximum at ca.457 nm （λex=365 nm）.The free ligand bib displays photoluminescence with emission maxima at 465 nm.The emission of 1 is neither metal-to-ligand charge transfer nor ligandto-metal transfer in nature，since the CdIIion is difficult to oxidize or reduce due to their d10configuration.In comparison to that of free bib ligand，most of the emission maxima of complex 1 are shifted.The shifts of the emission bands are attributed to both the deprotonated effect of dicarboxylate and the coordination interactions of organic ligands to the metal center［19-21］.

Fig.5.Supramolecular structure for complex 1

Fig.6.XRPD for the title complex 1

Fig.7.Solid-state emission spectra for bib and complex 1 at room temperature

4　CONCLUSION

In summary，we have synthesized a new3D Cd（II）coordination polymer which displays a four-fold interpenetrated topology.The solid state luminescent emission of complex was also investigated and assigned tentatively to the ligand-to-ligand charge transfer effect.

REFERENCES

（1）Yang，H.；Wang，F.；Kang，Y.；Li，T.H.；Zhang，J.Chiral assembly of dodecahedral cavities into porous metal-organic frameworks.Chem.Commun.2012，48，9424-9426.

（2）Liao，P.Q.；Zhou，D.D.；Zhu，A.X.；Jiang，L.；Lin，R.B.；Zhang，J.P.；Chen，X.M.Strong and dynamic CO2sorption in a flexible porous framework possessing guest chelating claws.J.Am.Chem.Soc.2012，134，17380-17383.

（3）Jia，Q.X.；Tian，H.；Zhang，J.Y.；Gao，E.Q.Diverse structures and magnetism of cobalt（II）and manganese（II）compounds with mixed azido and carboxylato bridges induced by methylpyridinium carboxylates.Chem.Eur.J.2011，17，1040-1051.

（4）Zhang，X.T.；Sun，D.；Li，B.；Fan，L.M.；Li，B.；Wei，P.H.Unusual high thermal stability of a 2D →3D polycatenated Fe（II）metal-organic framework showing guest-dependent spin-crossover behavior and high spin-transition temperature.Cryst.Growth Des.2012，12，3845-3848.

（5）Qin，J.；Qin，C.；Wang，C.X.；Li，H.；Cui，L.；Li，T.T.；Wang，X.L.A lacuna in reticular chemistry:an unprecedented binodal （6，10）-connected network based on two distinct zinc clusters.CrystEngComm.2010，12，4071-4073.

（6）Wang，L.Y.；Fan，R.Q.；Wang，P.；Yang，Y.L.Synthesis and structure of a novel blue luminescent coordination polymer possessing3D network with mirror symmetry triple-interpenetrated sixteen-membered rings.Inorg.Chem.Commun.2012，23，54-58.

（7）Liu，Y.；Pan，M.；Yang，Q.Y.；Fu，L.；Li，K.；Wei，S.C.；Su，C.Y.Dual-emission from a single-phase Eu-Ag metal-organic framework:an alternative way to get whitelight phosphor.Chem.Mater.2012，24，1954-1960.

（8）Han，Z.P.；Li，Y.H.Solvothermal synthesis，structure and catalytic activity of a mixed-valence CuI/CuIIcomplex with 1-D chain structure.Inorg.Chem.Commun.2012，22，73-76.

（9）Zhang，Y.；He，X.；Zhang，J.；Feng，P.CuI cluster-based organic frameworks with unusual 4- and 5-connected topologies.Cryst.Growth Des.2011，11，29-32.

（10）Wang，X.L.；Qin，C.；Wang，E.B.；Su，Z.M.；Xu，L.；Batten，S.R.An unprecedented eight-connected self-penetrating network based on pentanuclear zinc cluster building blocks.Chem.Commun.2005，4789-4791.

（11）Wang，J.J.；Tang，L.；Hou，X.Y.；Gao，L.J.；Fu，F.；Zhang，M.L.Synthesis and characterization of a new 2D Ca（II）coordination polymer containing 1D calcium-oxygen chains.Chin.J.Struct.Chem.2014，33，1069–1073.

（12）Wang，D.Z.；Sun，X.S.；Zhang，J.B.；Liu，C.J.Metal-organic coordination architectures of triazole-ligands:syntheses，structures and luminescent properties.Chin.J.Struct.Chem.2013，32，1236–1244.

（13）Yang，Q.X.；Chen，X.Q.；Chen，Z.J.；Hao，Y.；Li，Y.Z.；Lu，Q.Y.；Zheng，H.G.Metal-organic frameworks constructed from flexible V-shaped ligands:adjustment of the topology，interpenetration and porosity via a solvent system.Chem.Commun.2012，48，10016-10018.

（14）Lu，Z.Y.；Du，L.T.；Zheng，B.S.；Bai，J.F.；Zhang，M.X.；Yun，R.R.A highly porous agw-type metal-organic framework and its CO2and H2adsorption capacity.CrystEngComm.2013，15，9348-9351.

（15）Guo，F.；Wang，F.；Yang，H.；Zhang，X.L.；Zhang，J.Tuning structural topologies to three photoluminescent metal-organic frameworks via isomeric biphenyldicarboxylates.Inorg.Chem.2012，51，9677-9682.

（16）Xu，G.L.；Guo，F.Topological diversification of two new Cd（II）photoluminescent coordination polymers via auxiliary N-donor ligands.J.Coord.Chem.2013，66，2398-2404.

（17）Sheldrick，G.M.SHELXS-97.Program for the Solution of Crystal Structure.University of Göttingen，Germany 1997.

（18）Sheldrick，G.M.SHELXL-97.Program for the Refinement of Crystal Structure.University of Göttingen，Germany 1997.

（19）Wang，F.；Jing，X.；Zheng，B.；Li，G.；Zeng，G.；Huo，Q.；Liu，Y.Four Cd-based metal-organic frameworks with structural varieties derived from the replacement of organic linkers.Cryst.Growth Des.2013，13，3522-3527.

（20）Zheng，S.L.；Yang，J.H.；Yu，X.L.；Chen，X.M.；Wong，W.T.Syntheses，structures，photoluminescence，and theoretical studies of d10metal complexes of 2，2΄-dihydroxy-［1，1΄］binaphthalenyl-3，3΄-dicarboxylate.Inorg.Chem.2004，43，830-838.

（21）Wang，J.J.；Zhang，R.C.；Zhang，D.J.；Zhang，C.；Zhang，Y.H.A two-dimensional anthracene-9，10-dicarboxylate Zinc（II）coordination polymer based on binuclear ［Zn2Cl2］ nodes:synthesis，characterization and luminescent properties.Chin.J.Struct.Chem.2014，33，695-700.

10.14102/j.cnki.0254-5861.2011-0477

2 August 2014；accepted 21 October 2014 （CCDC 994981）

① Corresponding author.E-mail:dzkongcy@163.com