1,3-二(4-吡啶基)丙烷Cd（Ⅱ）配合物的合成、晶體結構及發光性質研究

江 晶 王冬杰 劉志鵬 汪俊龍 李 星

(寧波大學材料科學與化學工程學院，寧波 315211)

0 Introduction

In the field of supramolecular chemistry,great interest has recently been focused on the crystal engineeringof coordination frameworksdueto their new topologies, intriguing architectures, intertwining phenomena, and potential applications in microelectronics,nonlinear optics,molecular selection,ion exchange,and catalysis[1-3].What is particularly attractive is the novel types of structural motifs observed in these species.Supramolecular chemistry has advanced to a stage at which it is possible to select molecular building blocks that will assemble into structures with specific and desired network topologies,so that a rational design of frameworks with potentially interesting properties is possible[4-7]．Flexible ligands were used often to obtain new frameworks such as 1,3-di(4-pyridy)propane(L),which is an important highly flexible N-donor bridging ligand．The ligands exhibit a special ability to formcompoundsand play an important role in bridging metal cations．The frameworks constructed from metals and 1,3-di(4-pyridy)propane ligands have been widely reported[8-10]．In this paper,we report the synthesisand crystal structure of a new Cd（Ⅱ）complex with 1,3-di (4-pyridy)propane and 5-(3-aminophenyl)tetrazole,the complex is prepared in the solvothermal condition．

1 Experimental

1.1 Materialsand measurement

All commercially available chemicals are of reagent grade and were used as received without further purification．The FTIR spectra were recorded from KBr pellets in the range of 4 000～400 cm-1on a Shimadzu FTIR-8900 spectrometer． All fluorescence measurements were carried out on a LS 50B Luminescence Spectrometer(Perkin-Elmer,Inc．,USA)．Thermogravimetric analyses(TGA)were carried out in an N2atmosphere with a heating rate of 10℃·min-1on a TG/DTA7300 integration thermal analyzer．Powder X-ray diffraction (PXRD)data were collected on a Bruker D8 Focus X-ray diffractometer using Cu Kα radiation．Thecalculated PXRDpatternswereproduced using the SHELXTL-XPOW program and single crystal reflection data．

1.2 Synthesisof thecomplex

A mixture of 5-(3-aminophenyl)tetrazole(0．02 mmol,3 mg),Cd(NO3)2·4H2O(0．04 mmol,12．3 mg)and 1,3-di(4-pyridy)propane (0．04 mmol,7．9 mg)were placed in a small vial including H2O (0．5 mL),DMF(0．5 mL)and ethanol(0．5 mL)．The vial was sealed and heated at 332 K for two days,then allowed to cool to room temperature．Colorless block-like crystals suitable for X-ray diffraction were collected and dried in air．Yield:75% (based on Cd)．Anal．Calcd． (%)for C40H44N14O2Cd:C,55．52;H,5．12;N,22．7;Found (%):C,56．24;H,5．25;N,22．9．

1.3 Crystal structuredetermination

A suitable crystal with dimension of 0．34 mm×0．28 mm ×0．16 mm for the complex was carefully selected under a polarizing microscope and glued at the tip of a thin glass fiber with cyanoacrylate adhesive．X-ray single-crystal diffraction data for Cd（Ⅱ）complexe were collected on a BRUKER SMART APEX II CCD diffractometer equipped with a graphite-monochromatic Mo Ka radiation (λ=0．071 073 nm)using an ω scan mode at 173(2)K．Empirical absorption corrections were applied using SADABSprogram[11]．The structure was solved by direct methods and refined with a fullmatrix least-squares technique using SHELXTL-97 program package[12]．All hydrogen atoms were placed geometrically and were subsequently refined in ariding-model approximation.The crystallographic data as well as details of the data collection and refinement for the complex are listed in Table 1.Selected bond lengthsand angles are given in Table 2.

Table 1 Crystal data and structure refinement for the title complex

CCDC:908806.

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

Table 3 Hydrogen bond lengths and bond angles for the title complex

2 Resultsand discussion

2.1 Crystal structureof{[CdL 2(H 2O)2]·2(C7H 6N5)}n

Single-Crystal X-ray diffraction analysis reveals that the complex crystallizes in monoclinic system with C2/c space group.The asymmetry unit of the complex consistsof one Cd（Ⅱ）ion together with two L molecules,two coordinate water molecules and two free 5-(3-aminophenyl)tetrazoleions(C7H6N5).The Cd（Ⅱ）complex is a one-dimensional coordination polymer,the Cd（Ⅱ）ion is six-coordinated by four nitrogen and two oxygen atoms,of which four nitrogen atoms from four different L molecules(N1,N1i,N2ii,N2iii),two oxygen atoms from coordinate water molecules(O1,O2),as shown in Fig.1.Thebond anglesaround Cd atomrange from83.47(7)to 180.0°,the bond angle of O-Cd-O is 180.0°indicating the three atoms are in a line.The Cd-O bond distances are almost similar(Cd1-O1 0.2309(3)nm and Cd1-O2 0.2301(3)nm).The Cd-Nbond distances are 0.234 83(19)and 0.237 1(2)nm.In the crystal,adjacent Cd（Ⅱ）centers are bridged by L molecules to generate a infiniteone-dimensional chain structure(Fig．2)．

Fig.1 Coordination environment of Cd（Ⅱ）in the title complex with 30%probability displacement ellipsoids

Fig．2 A view of 1D chain structure of the Cd（Ⅱ） complex

It is successfully leads to the assembly of the onedimensional units by intermolecular hydrogen bonds because of the introducing 5-(3-aminophenyl)tetrazole molecular in the complex,the units are linked by intermolecular hydrogen bonding(N3-H3A…N5v;N3-H3B…N5vi)(Table 3)to generate a one-dimensional chain．The chains are further assembled into a threedimensional supramolecular framework by the other intermolecular hydrogen bonding(O1-H1A…N4iv)(Fig．3)．

Fig．3 Packing diagram of the Cd（Ⅱ） complex

2.2 Power X-ray diffraction analysis

In an attempt to confirm the homogeneity of the material synthesized under the hydrothermal condition,we have analyzed the PXRD pattern of the complex and correlated the result with the simulated powder pattern obtained from the single crystal data．As depicted in Fig．4,the basic featuresof the PXRD patternsresemble the simulated from single crystal data for the complex,indicating that the bulk products obtained are homogenous in nature．

2.3 IR spectrum

In the IR spectra, the complex exhibits characteristic N-H stretching bands at 3 338 and 3 226 cm-1because of the stretching vibration coupling of the two N-H,which 3 338 cm-1for an asymmetric stretching and 3 226 cm-1for a symmetric stretching．The very strong absorption bandsof 1 614 cm-1were attributed to C=N stretching contributions,the strong absorption bands at 1 473 and 1 429 cm-1and the bands in the rang 3 100～3 000 cm-1stretching vibration of benzene ring were assigned to pyridine ring stretching vibration．The strong bands at ca．3 431 cm-1are corresponding to the vibration of the coordinate water molecules in the complex．

Fig．4 Experimental and simulated powder XRD patterns of the Cd（Ⅱ）complex

2.4 Thermogravimetric analyses

Thermogravimetric analyses (TGA)experiments were conducted to determine the thermal stability of the title complexes,which is an important aspect for metalorganic frameworks[13-14].TGA was performed on crystalline samples of the complex under an N2atmosphere from 30 to 800°C.In the complex,the first weight loss of 64.36%(Calcd.64.10%),corresponding to an endothermic peak,which implying removal of two guest 5-(3-aminophenyl)tetrazole ions (C7H6N5), two coordinate water molecules and one L molecule per formula unit{[CdL2(H2O)2]·2(C7H6N5)}nfrom 105 to 340.3℃.Then a drop of weigh is observed after 444℃,indicating the decomposition of the framework of the complex(Fig.5).

Fig.5 TGA curve of the Cd（Ⅱ）complex

2.5 Fluorescent emission

Previous studies have shown that compounds containing cadmium could exhibit fine photoluminescent properties[15-17].Hence,we also investigated the photoluminescent properties of the Cd（Ⅱ）complex (Fig.6).In the solid state,strong photoluminescence emission bands at 358 nm is observed for the complex, respectively, upon photoexcitation at 335 nm.Since L molecules and the free 5-(3-aminophenyl)tetrazole molecules exhibit weak photoluminescence emission at 384 and 390 nm,which may originate from the ligand-to-ligand πL-πL*charge transfer(LLCT)transition emission.The position blueshift (comparing with L molecules and 5-(3-aminophenyl)tetrazole molecules)of the strong emission peak (358 nm)and the fluorescent enhancement of the complex,may be assigned to the effect of ligand-tometal or metal-to-ligand charge transfer (LMCT or MLCT)transition emission similar topreviousreports.

Fig.6 Solid-state emission spectra of the title complex at room temperature

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