YAO Hua-GangZHANG Jun-Jun CAI Zhang-Wei ZHANG Chen-Yang YOU Li-Jun ZHENG Shuang

a(School of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University, Zhongshan 528458, China)

A New Zn(II) Coordination Polymer Constructed by 1,4-Benzenedithiolate Dianion: [Zn(SC6H4S)(1,3-DPA)]n①

YAO Hua-Gang②ZHANG Jun-Jun CAI Zhang-Wei ZHANG Chen-Yang YOU Li-Jun ZHENG Shuang

a(School of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University, Zhongshan 528458, China)

A new one-dimensional polymer, [Zn(SC6H4S)(1,3-DPA)]n(1, SC6H4S = 1,4-benzenedithiolate and 1,3-DPA = 1,3-diaminepropane), has been synthesized and characterized by elemental analysis, PXRD, IR spectra, and single-crystal X-ray diffraction.The complex crystallizes in triclinic system, space group P1, with a = 6.7119(1), b = 9.0230(2), c = 10.4943(2) ?, α = 69.288(1), β = 75.848(1), γ = 81.513(1)o, V = 575.123(19) ?3, Dc= 1.615 g/cm3, Z = 2, F(000) = 288; the final S = 1.070, R = 0.0234, and wR = 0.0551.The compound consists of an infinite zigzag chain formed by [Zn(1,3-DPA)]2+units joined by SC6H4S ligands.Each chain interacts with neighboring chains via weak N–H··S hydrogen bonds to form an extended three-dimensional (3D) supramolecular network.The thermal and photoluminescent properties of 1 have also been investigated.

Zn(Ⅱ) coordination polymer, crystal structure, 1,4-benzenedithiol, zigzag chain;

1 INTRODUCTION

Coordination polymers are an important class of functional materials because of their intriguing structural features and potential applications in gas storage, luminescence, magnetism and catalysis[1-4].These compounds usually have strong coordinative chemical bonds between metal centers and organic bridging ligands, forming one-, two-, and threedimensional framework structures, and their structures and properties can be influenced by use of different organic ligands with a wide variety of types and shapes.

Recently, there is a steady increasing interest in the development of metal-organic solids with interesting optoelectronic properties and, in particular, with semiconductive behavior.The materials based on metal-sulfur bonds are more likely than those based on metal-oxygen bonds to be semiconducting by analogy with metal sulfides and metal oxides.As we know, it usually has two ways to construct coordination polymers containing metal-chalcogen bonds.The first one is cluster-organic frameworks formed by using chalcogenide nanoclusters as nodes and pyridyl molecules as linkers[5-10].The other is coordination polymers consisting of metal ions linked by thiolate ligands, such as chalcogenide-substituted aromatic polycarboxylates or arenepolythiols[11-16].However, compared to a large number of currently known metal-organic frameworks constructed by theformation of metal-oxygen and metal-nitrogen bonds, metal-organic frameworks containing metal-chalcogen bonds are still rarely explored.

Here we report the structure and properties of a new one-dimensional coordination polymer [Zn-(SC6H4S)(1,3-DPA)]n(1) prepared in the presence of 1,3-diaminepropane using 1,4-benzene- dithiolate as linker.

2 EXPERIMENTAL

2.1 Materials and physical measurements

All reagents were of analytical grade and used as obtained by commercial sources without further purification.The elemental analysis was carried out on an Elemental Vario EL III microanalyzer.EDS analysis of 1 was performed using JSM-5600LV (Japan).The Zn:S molar ratio in 1 is 1:2.05.Powder X-ray diffraction (PXRD) patterns were recorded on a Shimadzu XRD-7000 X-ray diffractometer with CuKa radiation (λ = 1.5406 ?).The thermal behavior (TGA) of 1 was carried out by Metter Toledo Star under a flow of nitrogen (40 mL/min) from 50 to 550 ℃ at a heating rate of 10 ℃/min.IR spectra were recorded on a Nicolet Avatar360 spectrometer USA) as KBr pellets in the 4000～400 cm-1region.The fluorescence spectra of 1 in solid state at room temperature were recorded using a HITACHIF-4500 (Fluorescence Spectrophotometer).

2.2 Synthesis of the title compound

The compound was prepared by Zn(NO3)2·6H2O (0.029 g, 0.10 mmol), 1,4-benzenedithiol (0.014 g, 0.10 mmol) and 0.5 mL of 1,3-diaminepropane.The mixture was sealed in a Pyrex glass tube with ca.10% filling at air atmosphere, placed in a stainlesssteel autoclave, and then heated at 140 ℃ for 5 days.After cooling down naturally to ambient temperature, the products were washed with ethanol and water, respectively, and well-formed pale yellow block crystals were obtained in 20% yield based on zinc.C, N and H analysis: calcd.: C, 38.64; N, 10.02; H, 5.05%.Found: C, 38.56; N, 9.97; H, 5.02%.IR (cm-1, KBr): 3420(vs), 3325 (m), 3275 (m), 2910 (m), 1580 (s), 1462 (w), 1125 (w), 1094 (s), 1081 (w), 1010 (s), 972 (m), 945 (s), 824 (s), 660 (w), 465 (w).

2.3 Crystal structure determination

A suitable single crystal of compound 1 with dimensions of 0.16mm × 0.12mm × 0.10mm was carefully selected under an optical microscope and glued to thin glass fiber with epoxy resin.The intensity data of the crystal were collected on a Bruker APEX CCD diffractometer with graphite-monochromated MoKα (λ = 0.71073 ?) using the SMART and SAINT programs[17].Absorption corrections were done using the SADABS program[18].The structure solution was performed with direct methods using SHELXS-97[19].Structure refinement was done against F2using SHELXL-97[19].All non-hydrogen atoms were refined with anisotropic displacement parameters.The C–H hydrogen atoms were positioned with idealized geometry and refined with isotropic displacement parameters using a riding model.A total of 5211 reflections of 1 were collected in the range of 2.42<θ<27.49° (–8≤h≤8,–8≤k≤11, –13≤l≤13) and 2610 were independent with Rint= 0.0170, of which 2315 with I > 2σ(I) were observed.The final R = 0.0234, wR = 0.0551 (w = 1/[σ2(Fo2) + (0.0273P)2+ 0.0798P], where P = (Fo2+ 2Fc2)/3), S = 1.070, (Δ/σ)max= 0.000, (Δρ)max= 0.279 and (Δρ)min= –0.235 e/?3.Selected bond distances and bond angles are listed in Table 1.

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

3 RESULTS AND DISCUSSION

3.1 Crystal structure of the complex

The polymer structure of 1 consists of an infinite zigzag chain formed by [Zn(1,3-DPA)]2+units joined by SC6H4S ligands (Fig.1a).Within the polymeric chain, the Zn atom is coordinated in a distorted tetrahedral geometry by two sulfur atoms from two bridging 1,4-benzenedithiolate dianion ligands and two nitrogen atoms from a 1,3-diaminepropane ligand (Fig.1b).The Zn–S bond lengths are 2.2893(5) and 2.3261(5) ?, slightly shorter than the average of 2.34 ? for the reported [Zn(en)3][Zn(SC6H4S)2] (en = ethylenediamine) complex[15], which consists of [Zn(en)3]2+cations within a two-dimensional anionic square grid of formula [Zn(SC6H4S)2]2-.

Fig.1.(a) Polymeric chain of 1 formed by [Zn(1,3-DPA)]2+units joined by the SC6H4S ligands; (b) 1,3-Diaminepropane molecules are on the top of the (ZnSC6H4S)nchain

The one-dimensional (ZnSC6H4S)nchain in 1 is different from the reported complex [Zn2(SC6H4S)5]6-containing substructures[15], in which one-dimensional ladders are formed, with Zn atoms at joints and a bare anionic charge on a terminal thiolate at each [ZnSC6H4S]-unit.Therefore, the Zn atom has diverse tetrahedral coordination environment between them, ZnS2N2and ZnS4, respectively.

It is noteworthy that the polymeric chain of 1 has the same linking mode as that found in [Hg(SC6H4S)(en)]n[16], but very different spatial conformation due to the presence of different organic amines.In [Hg(SC6H4S)(en)]n, the ethylenediamine molecules are between adjacent 1,4-benzenedithiolate ligands, while in 1, 1,3-diaminepropane molecules are on the top of the (ZnSC6H4S)nchain (Fig.1b).This arrangement favors the existence of N–H··S hydrogen bonds between adjacent chains and the formation of an extended three-dimensional (3D) supramolecular network (Fig.2).There are two types of hydrogen bonds in this structure between two sulfur atoms of 1,4-benzenedithiolate and two NH2groups of 1,3-diaminepropane (Table 2), with the N(1)–H(1B)··S(1) distance of 3.468(2) ? (Fig.3a) and N(2)–H(2C)··S(2) of 3.5275(19) ? (Fig.3b).

Table 2.Hydrogen-bond Geometry (?, °)

Fig.2.Formation of an extended three-dimensional supramolecular network by hydrogen bonding interactions.H atoms have been omitted for clarity

Fig.3.Two types of hydrogen bonds (dashed lines) between adjacent chains: (a) N(1)–H(1B)··S(1), (b) N(2)–H(2C)··S(2)

The reaction of several transition metals with 1,4-benzenedithiol by using en as the solvent leads to the formation of diverse microcrystalline powder[14-16].Their structures were solved by synchrotron X-ray powder diffraction.However, no hydrogen bonding interactions exist in these complexes.Compared with them, the packing arrangement of neutral [Zn(SC6H4S)(1,3-DPA)]nchains in 1 may be influenced by the N–H··S interactions between them.Moreover, the fact that the title complex grows in the form of single crystals demonstrates their significant role in both directing and stabilizing the final structure.To our knowledge, the title complex represents the first example of an extended, metal-sulfur-organic hybrid materials containing N–H··S hydrogen bonds constructed by arenepolythiol ligands and metal ions.

3.2 Powder XRD and thermogravimetric analysis

The XRD experimental and computer-simulated patterns of 1 are presented in Fig.4, where the main diffraction peaks of the experimental and simulated patterns match well in the key positions, confirming the purity of 1.To examine the thermal stability of 1, thermal gravimetric (TG) analyses were carried out for 1 between 50 and 550 ℃ (Fig.5).The sample was heated up under a flow of nitrogen (40 mL/min) at a heating rate of 10 ℃/min.The curve for 1 shows two steps of weight loss.The first one below 318 ℃can be attributed to liberation of one organic ligand (weight loss: calcd.22.9%; obsd.23.4%).In the following second step, 1 removes the remaining organic ligands between 357 and 462 ℃ gradually, and converts to zinc sulfide with a residual weight of 34.4% (calcd.: 34.8%).

3.3 Photoluminescent properties

The photoluminescent properties of 1 and free 1,4-benzenedithiol in the solid state at room temperature have also been studied.The emission maxima (λemmax) are shown in Fig.6.Upon excitation at 297 and 289 nm, 1 and free 1,4-benzenedithiol exhibit strong photoluminescence with emission maxima at 492 and 483 nm.The emission of 1 is neither metal-to-ligand charge transfer(MLCT) nor ligand-to-metal transfer (LMCT) in nature since the Zn(II) ion is difficult to oxidize or reduce due to its d10configuration.Therefore, the emission band may tentatively be assigned to the ligand-to-ligand charge transfer (LLCT).It is noteworthy that the emission of 1 is red shifted by 9 nm with respect to the band shown by the free ligand, which may be attributed to the coordination environment of Zn(II) ions.

Fig.4.Experimental and simulated XRD spectra of 1

Fig.5.TG curve of 1

Fig.6.Solid-state photoluminescent spectra of 1,4-benzenedithiol (black) and 1 (red)

4 CONCLUSION

In summary, a new one-dimensional compound, formed by [Zn(1,3-DPA)]2+units joined by SC6H4S ligand, is a member of the still small class of coordination polymers based on metal-sulfur or metal-selenium bonds, rather than the much more common metal-oxygen or metal-nitrogen bonds.While the materials described herein are not electrically conducting, the softer and more electropositive sulfur and selenium linkages are more likely to lead to semiconducting coordination polymers in the future.

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10.14102/j.cnki.0254-5861.2011-0625

4 January 2015; accepted 9 April 2015

① Supported by the National Natural Science Foundation of China (No.21301035)

② Corresponding author.Majoring in solid and coordination chemistry.E-mail: hgyao@gdpu.edu.cn