научная статья по теме SYNTHESIS, CRYSTAL STRUCTURE, AND LUMINESCENT PROPERTY OF [ZN2(OX)3]H2L · 4H2O (L = 2,2-(1,4-BUTANEDIYL)-BIS(1H-BENZIMIDAZOLE)) Химия

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SYNTHESIS, CRYSTAL STRUCTURE, AND LUMINESCENT PROPERTY OF [Zn2(Ox)3]H2L • 4H2O (L = 2,2'-(1,4-BUTANEDIYL)-£/s(1H-BENZIMIDAZOLE))

© 2012 L. Gou*, H. X. Zhang, X. Y. Fan, and D. L. Li

School of Materials Science and Engineering, Chang'an University, Xi'an, Shaanxi, 710061 P.R. China

*E-mail: leigou@chd.edu.cn Received June 23, 2011

A new complex [Zn2(Ox)3]H2L • 4H2O (L = 2,2'-(1,4-butanediyl)-bis(1H-benzimidazole)) (I) has been hy-drothermally synthesized and characterized by the elemental analysis, IR spectroscopy, and single crystal X-ray diffraction. It crystallizes in monoclinic space group P21/c with a = 10.108(2), b = 15.600(4), c = 9.768(2) Â, P = 105.289(3)°, V = 1485.7(6) Â3, Z = 4. Complex I is a 2D honeycomb-like polymer with protoned L and water molecules intercalating in the cavities. The luminescent spectra shows the emission peak of complex I is at 455 nm which is attributed to ligand-to-metal charge transfer.

INTRODUCTION

Interest in oxalate-bridged polymeric compounds is widespread, because of their intriguing variety of architectures and topologies [1—8], as well as their potential applications in diverse areas such as magnetism, photics, host-guest chemistry, catalysis [9—12]. The rational design and controllable preparation of such metal oxalate is highly influenced by several factors, for example, the coordination geometry of the central atom, the counter anion, the pH values, the reaction conditions and so on. Among these factors organic template reagent such as amines sometimes plays an important role in the construction of multidimensional architectures with channels or cavities [13-16].

In our attempt to construct oxalate based porous complexes, we introduced 2,2'-(1,4-butanediyl)-¿/s(1H-benzimidazole) (L) into the reaction system due to the following reasons: the protoned L could function as a structure-directing reagent as other protoned heterocycles [17]. In addition, L has potential to form intermolecular n—n interactions through benzimidazolyl rings to affect the packing arrangements of the supramolecular structure [18, 19]. As expected, we obtained a new coordination polymer [Zn2(Ox)3]H2L • 4H2O (I). Herein we report the synthesis, structure and fluorescent property of this complex.

EXPERIMENTAL

Reagents and physical measurements. Ligand L was synthesized according to literature [20]. All the other reagents and solvents were commercially available and used as purchased. Elemental analyses (C, H, N) were determined with a Vario EL III elemental analyzer. The FT-IR spectra were recorded from KBr pellets in

the range 4000-400 cm-1 on a Bruker EQUINOX-55 spectrometer. Fluorescence spectra were performed on a Hitachi F-4500 fluorescence spectrophotometer at room temperature.

Synthesis of I. A mixture of Zn(NO3)2 • 6H2O (59.6 mg, 0.20 mmol), L (28.8 mg, 0.10 mmol) and Na2C2O4 (39.9 mg, 0.3 mmol) in 15 mL water was stirred for 30 min, then sealed in a 25 mL Teflon-lined stainless steel container, which was heated to 160°C under autogenous pressure for 3 days and then cooled to room temperature at a rate of 2°C h-1 to give colorless crystals of I. The yield was 0.042 g (55%).

For C12HMN2O8Zn

anal. calcd., %: C, 37.96; H, 3.72; N, 7.38. Found, %: C, 38.01; H, 3.67; N, 7.44.

X-ray diffraction analysis. A single crystal with size of 0.19 x 0.17 x 0.15 mm was mounted on a glass fiber for data collection which was performed on a Bruker Smart Apex CCD diflractometer equipped with a graphite-monochromatic Mo^a radiation (X = 0.71073 A) at 296(2) K. A total of 8211 reflections were collected in the range of 2.09° < 0 < 26.72°. Corrections for Lp factors and empirical absorption were applied. The structure was solved by direct methods using SHELXTL-97 program [21]. All non-hydrogen atoms were refined with anisotropic thermal parameters. All hydrogen atoms were placed in the calculated positions with fixed isotropic thermal parameters and included in the structure factor calculations in the final cycle of full-matrix least-squares refinement. The final R = 0.0253, and wR = 0.0648 for 2686 observed reflections with I > > 2g(I), R = 0.0312 and wR = 0.0676 for 3135 inde-

pendent reflections. S = 1.054, w = 1/[a2(Fo2)

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Selected bond lengths and bond angles for complex I*

Bond d, A Bond d, A

Zn(1)-O(1) 2.1021(13) Zn(1)-O(2)#! 2.0769(12)

Zn(1)-O(3) 2.0723(13) Zn(1)-O(4)#1 2.0877(13)

Zn(1)-O(5) 2.1243(13) Zn(1)-O(6)#2 2.1070(13)

Angle ю, deg Angle ю, deg

O(3)Zn(1)O(2)#1 100.84(6) O(3)Zn(1)O(4)#! 94.61(5)

O(1)Zn(1)O(3) 80.28(5) O(2)#xZn(1)O(1) 96.82(5)

O(3)Zn(1)O(6)#2 92.77(5) O(2)#1Zn(1)O(6)#2 164.82(5)

O(4)#1Zn(1)O(6)#2 92.02(5) O(1)Zn(1)O(6)#2 92.03(5)

O(4)#1Zn(1)O(5) 95.03(6) O(1)Zn(1)O(5) 90.60(5)

O(2)#1Zn(1)O(4)#1 80.32(5) O(4)#1Zn(1)O(1) 173.63(5)

O(3)Zn(1)O(5) 167.25(5) O(2)#1Zn(1)O(5) 89.00(5)

O(6)#2Zn(1)O(5) 78.57(5)

* Symmetry transformations: #1 x, -y + 3/2, z + 1/2; #2 - x, -y + 1, — z + 2.

+ (0.0319P)2 + 0.3325P], where P = (Fo2 + 2Fc2 )/3, (A/a)max = 0.0044(5), (Ap) max = 0.368 and (Ap)min = = —0.287 e/A3. The selected bond lengths and bond angles are listed in table. Supplementary material has been deposited with the Cambridge Crystallographic Data Centre (no. 790587; deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).

RESULTS AND DISCUSSION

Single crystal X-ray diffraction analysis shows the crystal structure of I consists of [Zn2(Ox)3]2- anions, protonated cations (H2L)2+ and water molecules. As illustrated in Fig. 1, each Zn2+ center displays a distorted octahedral geometry, which is completed by six oxygen atoms from three oxalate groups. The Zn—O

Fig. 1. Coordination environment of zinc atoms in I (thermal ellipsoids are at 30% probability level, the hydrogen atoms are omitted for clarity).

Fig. 2. View of the 2D [Zn2(Ox)3]2- layer in the yz plane showing the honeycomb architecture with the protonated molecules intercalated in it (the water solvent and hydrongen atoms are omitted for clarity).

distances are in the range of 2.0723(13)-2.1243(13) A. The OZnO angles range from 78.57(5)° to 100.84(6)° and from 164.82(5)° to 173.63(5)°. Bond lengths and angles around Zn2+ in I compare well with those observed in the complex [Zn2(Ox)3] • • {[CuI(4,4-Bipy)]2} • C2H6O2 [22].

Each Zn2+ as three connected node is linked by three bridging oxalate groups to form the [Zn2(Ox)3]2-layers with 12-membered apertures in the yz plane, as shown in Fig. 2.

It is known that many transition metal oxalates including zinc oxalates often form the layered honeycomb architecture [22, 23]. Between the layers usually lie the solvent molecules or the charge-balancing cations. In compound I, protonated L molecules are intercalated in the pores, which connect adjacent layers through the face-to-face я—я interactions between the benzimidazol rings of protonated L from adjacent layers (3.788 A of centroid-centroid) to form a 3D su-pramolecular structure (Fig. 3).

The uncoordinated water molecules locate between the layers and form strong hydrogen bonding interactions with oxygen atoms from the oxalates and protonated nitrogen atoms from H2L to further stablize the 3D architecture (O(7)-H(74)™O(1)' 2.871 A,

173°; O(8)-H(8^)-O(4)i 2.871 A, 165°; O(7)-H(7P)-O(8)i 2.782 A, 155°; N(1)-H(1)-O(6)ii 2.733, 169°; N(2)-H(2)-O(7)iU 2.770 A, 174°. Symmetric codes: i x, 1.5 — y, —1.5 + z; ii -x + 1, y + 0.5, -z + 2.5; iii 1 - x, 2 - y, 1 - z).

In view of the fluorescent properties of d10 metal complexes, the luminescence of I was detected at room temperature in the solid-state and the result is depicted in Fig. 4. Compound I exhibits an intense emission band at ~455 under 390 nm excitation at room temperature, which has a large red-shift relative to that of organic ligands, since free oxalic acid exhibits weak emissions at 379 and 401 nm (^ex = 340 nm) [11] and L has a maximum emission at 303 nm (^ex = = 260 nm) [24]. The emission band of I might be attributed to ligand-to-metal charge transfer (LMCT) [16, 25].

ACKNOWLEDGMENTS

This work was financially supported by the National Natural Science Foundation of China (no. 21103013), the Natural Science Foundation of Shaanxi Province (no. 2010JQ2011), and the Special Fund for Basic Scientific Research of Central Colleg-

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Fig. 3. View of the 3D supramolecular structure of I formed through n—n interactions and hydrongen bonds (hydrongen atoms are omitted for clarity).

6000

5000

4000

§ 3000 te

5 2000 1000 0

400 450 500 550

Wavelength, nm

600

Fig. 4. Emission spectra of compound I in the solid state at room temperature (A,ex = 390 nm).

es, Chang'an University (nos. CHD2012ZD001 and CHD2012TD014)

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