YANG Xin FU Rui-Bio HU Sheng-Min HUANG Yi-Hui SHENG Tin-Lu WU Xin-To② (Stte Key Lortory of Structurl Chemistry, Fujin Institute of Reserch on the Structure of Mtter, Chinese Acdemy of Sciences, Fuzhou 350002, Chin) (Grdute University of Chinese Acdemy of Sciences, Beijing 100049, Chin)

1 INTRODUCTION

The increasing interest of researchers in the syntheses of metal-organic coordination polymers during the past decades has led to the emergence of a variety of new hybrid materials with intriguing structure diversities and multi-kinds of properties such as photoluminescence, electric conductivity,magnetism, gas adsorption, catalytic activity and so forth[1-7]. In particular, the research of metal complexes based on H2mna has been developed rapidly owing to its complicated and flexible coordination modes resulted from three potential donors known as nitrogen, oxygen and sulfur atoms[8-16]. However,among a number of metal coordination polymers,assembled by mna ligand, which have been already reported, the Zn(II)/Cd(II) complexes with bridging ligands introduced as building blocks are still rare[16-22]. To further explore the coordination chemistry of mna ligand with transitional metals,recently we have figured out a strategy by introducing dpe, a well known flexible dipyridyl bridging ligand which can be used to form a higher-dimensional structure, into the Zn(II)/Cd(II)complexes constructed with mna ligand based on the previous work. Herein, we report the syntheses and crystal structures of three new metal-organic coordination polymers 1, 2 and 3. The coordination of mna ligands to transitional metal ions in these compounds adopt five distinct chelating modes indicated in Scheme 1, which are rarely documented according to the Cambridge Structural Database[9].

Scheme 1. 5 types of chelating modes of mna ligands in compounds 1-3

2 EXPERIMENTAL

a) Materials and methods

All chemicals of AR grade were commercially available and used without further purification.Elemental analyses were carried out with a Vario ELIII elemental analyzer. Infrared spectra were obtained on a Perkin-Elemer Spectrum-one FT-IR instrument.

b) Syntheses

[Zn2(dpe)0.5(mna)2] (1)The mixture of Zn(CH3COO)2·2H2O (0.1098 g, 0.5 mmol), dpe(0.0910 g, 0.5 mmol), H2mna (0.0776 g, 0.5 mmol)and 10 mL H2O was stirred homogeneously in a 25 mL Parr Teflon-lined autoclave, and then heated at 160 °C for 4 days. After slowly cooling to room temperature at a rate of 2 °C/h, colorless blockshaped crystals could be obtained with the yield of about 27% based on Zn(CH3COO)2·2H2O. The pattern of experimental powder XRD was in agreement with that of simulated from single-crystal X-ray data, which proved the homogeneous phase of the product. Anal. Calcd. for C18H11N3O4S2Zn2(%):C, 40.93; H, 2.10; N, 7.96. Found (%): C, 40.83; H,2.20; N, 8.02. IR (KBr pallet, cm-1): 3039w, 2938w,1629s, 1615s, 1588s, 1557s, 1438m, 1391s, 1347m,1215m, 1153m, 1096m, 1074w, 1058w, 1030m,1015w, 865m, 834m, 765m, 752m, 684w, 574m,552m, 484w.

[Zn4(dpe)4(mna)4] (2)The Zn(CH3COO)2·2H2O(0.1098 g, 0.5 mmol), dpe (0.0910 g, 0.5 mmol),H2mna (0.0776 g, 0.5 mmol) and 10 mL H2O were mixed and stirred homogeneously in a 25 mL Parr Teflon-lined autoclave, and then heated at 110 °C for 4 days. After slowly cooling to room temperature at a rate of 2 °C/h, colorless block-shaped crystals could be obtained with the yield of about 23% based on Zn(CH3COO)2·2H2O. The pattern of experimental powder XRD was in agreement with that of simulated from single-crystal X-ray data, which proved the homogeneous phase of the product. Anal.Calcd. for C72H52N12O8S4Zn4(%): C, 53.95; H, 3.27;N, 10.49. Found (%): C, 52.46; H, 3.38; N, 10.26. IR(KBr pallet, cm-1): 3432w, 3053m, 1636s, 1611s,1553s, 1499m, 1421m, 1397s, 1387s, 1335s, 1222m,1198m, 1152m, 1096w, 1061m, 1028m, 972m, 863m,834m, 823m, 778m, 752m,735w, 682w, 636w, 587w,551s, 485w.

[Cd2(dpe)0.5(mna)2]·H2O (3)The mixture of Cd(CH3COO)2·2H2O (0.1331 g, 0.5 mmol), dpe(0.0910 g, 0.5 mmol), H2mna (0.0776 g, 0.5 mmol)and 10 mL H2O was stirred homogeneously in a 25 mL Parr Teflon-lined autoclave, and then heated at 130 °C for 4 days. After slowly cooling to room temperature at a rate of 2 °C/h, colorless blockshaped crystals could be obtained with the yield of about 19% based on Cd(CH3COO)2·2H2O. The pattern of experimental powder XRD was in agreement with that of simulated from single-crystal X-ray data,which proved the homogeneous phase of the product.Anal. Calcd. for C18H13N3O5S2Cd2(%): C, 33.77; H,2.05; N, 6.56. Found (%): C, 33.93; H, 2.09; N, 6.65.IR (KBr pallet, cm-1): 3458m, 3058w, 1606s, 1567s,1425m, 1392s, 1364s, 1236m, 1157w, 1129w,1083m, 1063w, 1014w, 981w, 855m, 828w, 766m,748m, 667w, 559w, 547w, 489w.

c) Structure determination

X-ray data of 1 were collected at 293(2) K on a Rigaku Saturn724 diffractometer equipped with a graphite- monochromatic Mo-Kα radiation (λ =0.71073 ?) as light source. Crystal data for 2 and 3 were collected with a Rigaku Mercury CCD/AFC diffractometer using a graphite-monochromatic Mo-Kα radiation (λ = 0.71073 ?) at 293(2) K. All structures were solved by direct methods and refined by full-matrix least-squares techniques on F2with SHELXS-97 and SHELXL-97 programs[23-24]. All non-hydrogen atoms were refined anisotropically.Hydrogen atoms were generated according to coordination geometries and interactions of hydrogen bonds. Crystallographic data and relevant bond information for 1–3 are summarized in Tables 1–4.

Table 1. Crystallographic Data and Structural Refinements for Compounds 1–3

Table 2. Selected Bond Lengths (?) and Bond Angles (°) for 1

Table 3. Selected Bond Lengths (?) and Bond Angles (°) for 2

Table 4. Selected Bond Lengths (?) and Bond Angles (°) for 3

3 RESULTS AND DISCUSSION

3.1 Crystal structure of [Zn2(dpe)0.5(mna)2] (1)

The single-crystal X-ray crystallographic diffraction result suggests that compound 1 crystallizes in triclinic space group Pwith the asymmetry unit containing two Zn(II) ions, half a dpe ligand and two mna ligands. As shown in Fig. 1a, there exist two Zn(II) centers possessing different coordination geometries in the asymmetry unit of complex 1.Zn(1) is five-coordinated by two mercapto sulfur atoms from different mna ligands, one carboxylate oxygen atom, one nitrogen atom of dpe ligand and one nitrogen atom from mna ligand to form a distorted tetragonal-pyramidal construction. Zn(2) is four-coordinated by one mercapto sulfur atom, two oxygen atoms from different carboxylate groups and one nitrogen atom of mna ligand giving rise to a tetrahedronal configuration. According to the coordination environment of mna ligands, we can conclude that the mna ligands in compound 1 adopt two types of intriguing coordination modes denoted in Scheme 1a and 1b, which are rarely reported in the previous work.

Structure analysis reveals that the coordination of Zn(II) ions with mna ligands results in a one-dimensional cylindrical structure (Fig. 1b) with a 12-membered ring composed of four Zn(II) ions, two bridging mercapto sulfur atoms and two carboxylate groups as a repeating unit. The 1D cylinders are then bridged by dpe ligands to form a 2D network.Furthermore, the 2D sheets of complex 1 are arranged in a staggered way under the influence of intermolecular interactions which contain hydrogen bonds, C–H··π and π··π interactions to give rise to a three-dimensional network seen as Fig. 2. The geometric parameters of hydrogen bonds, C–H··π and π··π interactions for compound 1 are listed in Table 5.

Table 5. Geometric Parameters of the Hydrogen bonds, C–H··π and π··π Interactions of Compound 1

Fig. 1. (a) Coordination environment of Zn(II) ions in compound 1; (b) 1D cylindrical structure bridged by mna ligands. All hydrogen atoms have been omitted for charity

Fig. 2. 3D structure of compound 1 formed by hydrogen bonds, C–H··π and π··π interactions between the 2D sheets. Hydrogen bonds are indicated by green dashed lines, while black dashed lines represent the C–H··π interactions with pink dashed lines corresponding to the π··π interactions

3.2 Crystal structure of [Zn4(dpe)4(mna)4] (2)

The single-crystal X-ray crystallographic diffraction result suggests that compound 2 crystallizes in monoclinic space group P21/c, of which the asymmetry unit consists of two atom-groups with each group containing two Zn(II) ions, two dpe ligands and two mna ligands. As shown in Fig. 3a, there exist four Zn(II) centers possessing different coordination geometries in the asymmetry unit of complex 2. In the bottom right atom-group, Zn(1) is five-coordinated by two mercapto sulfur atoms from different mna ligands, one carboxylate oxygen atom,one nitrogen atom of dpe ligand and one nitrogen atom from mna ligand to form a distorted tetragonal-pyramidal construction. Zn(2) is four-coordinated by one mercapto sulfur atom, one carboxylate oxygen atom, one nitrogen atom of mna ligand and one nitrogen atom from dpe ligand giving rise to a tetrahedral configuration. For the top left atom-group, Zn(3) adopts a similar coordination configuration to that of Zn(1), and the coordination environment of Zn(4) is approximate to that of Zn(2).The two atom-groups possess approximate geometries to each other, only differing slightly in bond lengths and bond angles. Considering the coordination environment of mna ligands, we find that the mna ligands in compound 2 adopt two types of intriguing chelating modes (Scheme 1b and 1c),which are rarely documented.

Fig. 3. (a) Coordination environment of Zn(II) ions in complex 2; (b) Structure of the tetra-nuclear cluster of compound 2. All hydrogen atoms are omitted for clarity

Structural analysis reveals that the structure of compound 2 can be classified as a tetra-nuclear cluster, in which four Zn(II) ions, four mercapto sulfur atoms, two nitrogen atoms from mna ligands and two carbon atoms of mna ligands are connected to form a 12-membered ring (Fig. 3b). It is revealed in Fig. 4a that there exist two kinds of clusters with Zn(1) and Zn(2) ions as the metal centers of cluster A, while cluster B is based on Zn(3) and Zn(4) ions.According to the environment of Zn(II) ions in compound 2, the two types of clusters are geometrically similar to each other with small difference in their bond lengths and bond angles. The geometrical arrangement of the clusters of complex 2 in 3D space have been explored and the intramolecular interactions are discussed with the geometric parameters of hydrogen bonds, C–H··π and π··π interactions of compound 2 are noted in Table 6.

Fig. 4. (a) Two types of clusters named as A and B in compound 2; (b) Perspective views of the geometrical arrangement of the two kinds of clusters for complex 2 along the c axis. Cluster A is indicated in bright green, while the red clusters belong to the type of cluster B. Some atoms are omitted for clarity

Table 6. Geometric Parameters of the Hydrogen bonds, C–H··π and π··π Interactions of Compound 2

3.3 Crystal structure of[Cd2(dpe)0.5(mna)2]·H2O (3)

The single-crystal X-ray crystallographic diffraction result suggests that compound 3 crystallizes in monoclinic space group P21/c with the asymmetry unit composed of two Cd(II) ions, one dpe ligand and two mna ligands. As shown in Fig. 5a, there exist two Cd(II) centers possessing different coordination geometries in the asymmetry unit of complex 3. Cd(1) is six-coordinated by three mercapto sulfur atoms from different mna ligands, one carboxylate oxygen atom, one nitrogen atom of dpe ligand and one nitrogen atom from mna ligand to form a highly distorted octahedral construction.Cd(2) is six-coordinated by two mercapto sulfur atoms from different mna ligands, three oxygen atoms from different carboxylate groups and one nitrogen atom of mna ligand giving rise to a distorted octahedronal configuration. Exploring of the coordination environment of mna ligands revealed that the mna ligands in compound 3 adopt two types of uncommon chelating modes indicated as Scheme 1d and 1e, which have not been referred to so far.

Fig. 5. (a) Coordination environment of Cd(II) ions in complex 3; (b) Side view of the 2D metal sheet formed by the coordination of Cd(II) with mna ligands. Some atoms are omitted for clarity

Structure analysis reveals that the Cd(II) ions are coordinated by mercapto sulfur atoms giving rise to a 1D chain-like structure. And then, with the bridging of carboxylate groups, the 1D Cd–S chains are connected to result in a 2D network (Fig. 5b)which contains only Cd(II) and mna ligands.Furthermore, the 2D metal sheets are bridged by dpe ligands to form a 3D porous network (Fig. 6) with free water molecules filled in the certain pores. The hydrogen bonds are indicated in Fig. 6 with the geometric parameters summarized in Table 7.

Fig. 6. Perspective view of the 3D network of compound 3 along the b axis. Hydrogen bonds are indicated by bright green dashed lines. Some atoms are omitted for clarity

Table 7. Geometric Parameters of the Hydrogen Bond of Compound 3

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