Syntheses and Crystal Structures of Cd(II) and Ni(II) Complexes Containing Flexible Sulfide and Nitrogen Heterocyclic Ligands①

HAO Xio-Min GU Chng-Sheng HAN Si-YinMIAO Yn-Li LI Yong SONG Wen-Dong

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Syntheses and Crystal Structures of Cd(II) and Ni(II) Complexes Containing Flexible Sulfide and Nitrogen Heterocyclic Ligands①

HAO Xiao-MinaGU Chang-Shenga②HAN Si-YinbMIAO Yan-LiaLI YongaSONG Wen-Dongc②

a(524088)b(524088)c(,150001)

Two new coordination polymers [Cd(EBLA)(ip)(H2O)] (1) and [Ni(EBSA) (im)2(H2O)](2) were synthesized by hydrothermal and solution methods using 2,2?-dithio- salicylicacid (EBSA), 1-imidazo[4,5-][1,10]phenanthroline (ip), imidazole (im), Cd(NO3)2·4H2Oand Ni(NO3)2·6H2O. The complexes were characterized by elemental analysis and FT-IR. Meanwhile, the crystal structures, fluorescence properties of complex 1 and thermogravimetrie analysis of complex 2 have been studied. In complex 1, 2,2?-dicarboxydiphenylthioether (EBLA) was prepared with 2,2?-dithiosalicylicacid (EBSA)reaction by hydrothermal method. Complex 1 is a dinuclear structure and Cd2+is five-coordinated in a distorted trigonal bipyramidal geometry. Complex 2 is a one-dimensional infinite linear chain and Ni2+is six-coordinated to form a distorted octahedral geometry. Hydrogen bonding andinteractions are observed in these complexes.

2,2?-dithiosalicylicacid,reaction, crystal structure;

1 INTRODUCTION

The coordination polymers including metal-orga- nic frameworks or inorganic-organic hybrid mate- rials are a significant field in chemical researchbecause of the realization of interesting architec- tures and potential properties such as gas storage, nonlinear optics, magnetism, luminescence, cata- lysis[1-5]and so on. To dominate and adjust the structures and properties, more attention has been paid to the design of organic ligand and the selec- tion of suitable metal ion[6, 7]. Aromatic-carboxylic ligand can provide various coordination modes and widely used for building various structural and topological coordination polymers with metal ions. It is well known that flexible EBSA is a preeminent candidate for constructing novel structures[8-10]. Moreover, disulfides have proven to be desirable objects for thereactions because of versatile S–S transformations through the facile cleavage of S–S which can occur both reductively and oxida- tively[11-14]. In this study, we introduced EBSA with nitrogen heterocyclic ligands in order to assemble Cd(II) and Ni(II) coordination polymers. Unexpec- tedly, the 2,2?-dicarboxydiphenylthioether (EBLA) ligand isgenerated from 2,2?-dithio- salicylicacid. In addition, thermal stability and luminescent property of the complexes were mea- sured and discussed.

2 EXPERIMENTAL

2. 1 Generals

The chemicals were purchased from commercial suppliers and used without further purification. Elemental analyses were performed on a Carlo Erba 1106 analyzer. It shows the percentage of carbon, hydrogen and nitrogen of the complexes. The FT-IR spectra were recorded on a BRUKER EQUINOX 55 FT-IR spectrometer using KBr pellet at a resolution of 0.5 cm-1(400～4000 cm-1). Luminescence spectra for crystal solid samples were recorded at room temperature on a PERKIN ELMER LS 55 phosphorimeter. Thermogravimetry analyses were performed on an automatic simul- taneous thermal analyzer (PE TG/DTA 6300) under a flow of N2at a heating rate of 10 ℃·min-1between ambient temperature and 800 ℃.

2. 2 Synthesis of the complexes

[Cd(EBLA)(ip)(H2O)] (1) The EBSA (0.3043 g, 1.0 mmo1), 1-imidazo[4,5-][1,10]-phenanthroline (0.228 g, 1.0 mmo1) and Cd(NO3)2·4H2O (0.2364 g, 1.0 mmo1) were added in a mixing solution of DMF (,?-dimethylformamide), water and methanol (1:8:1, V/V, 20 mL). The vial was sealed and heated at 160 ℃ for three days. After being cooled to room temperature, dark yellow crystals were obtained in 38% yield. Analysis calculated for C27H18N4O5SCd (%): C, 51.92; H, 2.91; N, 8.98. Found (%): C, 51.09, H, 2.49, N, 9.01. IR(KBr pellet, cm-1): 3391(m), 3139(m), 1576(s), 1553(m), 1448(m), 1436(m), 1391(s), 1374(s), 1357(w), 1312(w), 1280(m), 1078(s), 945(m), 851(m), 822(m), 749(s), 636(s), 544(m), 449(m).

[Ni(EBSA)(im)2(H2O)](2): Complex 2 was prepared by the addition of stoichiometric amounts of Ni(NO3)2·6H2O (0.2908 g, 1.0 mmol), 2,2?- dithiosalicylicacid (0.3043 g, 1.0 mmol) and imidazole (0.1361 g, 2.0 mmol) dissolved in 1:5 methanol/water solution (25 mL) and the pH was adjusted to 7 with 0.1 mol/L potassium hydroxide solution. After the mixture was stirred for 30 min, green crystals were obtained by evaporation of the solution for 10 days at room temperature in 34% yield. Analysis calculated for C20H18N4O5S2Ni (%): C, 46.51; H, 3.52; N, 10.85. Found (%): C, 47.09; H, 3.87; N, 10.77. IR(KBr pellet, cm-1): 3407(s), 3114(w), 1644(s), 1615(s), 1576(m), 1524(m), 1386(w), 1326(w), 1279(w), 1162(w), 1133(s), 1068(m), 989(w), 868(w), 740(w), 612(w), 483(m).

2. 3 X-ray structure determination

Single-crystal X-ray diffraction measurements were carried out on a Bruker SMART APEXII CCD diffractometer. The diffraction data were collected with Moradiation (= 0.71073 ?). Empirical absorption corrections were carried out by using the SADABS program[15]. The unit cell dimensions were determined by direct methods using the SHELXS program and refined with SHELXL[16]. All non-hydrogen atoms were refined anisotro- pically. The hydrogen atoms were added theore- tically, riding on the concerned atoms and refined with fixed thermal factors. The crystal structure data of complexes 1 and 2 are listed in Table 1.

3 RESULTS AND DISCUSSION

3. 1 Crystallographic analysis

3. 1. 1 Crystallographic analysis of complex 1

The molecular structure of complex 1 is shown in Fig. 1 and the selected bond distances and bond angles are listed in Table 2. X-ray diffraction analy- sis shows that this complex has a dinuclear structure. Each EBLA2–ligand has one coordination type of monodentate mode. The Cd(II) ion is five-coor- dinated bytwo carboxylate O atoms from two dif- ferent EBLA2–groups, and two N atoms from one 1-imidazo[4,5-][1,10]-phenanthroline (ip) ligand as well as one water molecule, and the local coordination sphere around the Cd(II) ion can be described as a distorted trigonal bipyramid with a CdO3N2chromophore. Atoms OW, O(3)iand N(4) define the equatorial plane, while O(1) and N(3) atoms occupy the apical sites (O(1)–Cd(1)–N(3) = 155.04(6)o). Two Cd(II) atoms are double-bridged by two EBLA2–ligands, generating a macrocyclic ring with the Cd···Cd separation of 8.3519 ?. The dihedral angle between two benzene ring planes of EBLA2–ligand is 87.42(0.07)o, and the bond angle (C(7)–S(1)–C(8)) is 102.66(10)o. There are two kinds of intramolecular hydrogen bonds in the com- pound: O–H···O (OW–H(2W)···O(2) =2.842(3) ?) and C–H···O(C(3)–H(3)···O(2)= 2.754(3)? and C(21)–H(21)···O(1)=3.087(3)?), as shown in Fig. 1 and Table 3.

Table 1. Crystal Data and Structure Refinement Parameters for 1 and 2

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

Table 3. Hydrogen Bond Lengths (?) and Bond Angles (°) for 1 and 2

Symmetry codes: ii –+ 2, –+ 1, –+ 2; iii+ 1,,; iv,,+ 1; v –+ 2, –+ 1, –+ 1 for 1;iii –+ 1, –+ 1, –+ 1; iv– 1, –+ 1/2,+ 1/2; v– 1,,+ 1; vi,,– 1 for 2

Fig. 1 . Dual-molecular structure of complex 1 (Symmetry code:i –x+1, –y+1, –z+1)

The two-dimensional layer structure of the com- pound is formed through intermolecular non-cova- lent bonding interactions including intermolecular hydrogen bonds,···and C–H···. There are three kinds of intramolecular hydrogen bonds: O–H···O (OW–H(1W)···N(1)ii= 2.855(2) ? and OW– H(2W)···O(3)iii= 2.831(2) ?), N–H···O (N(2)– H(2N)···O(4)iv= 2.817(2) ?) and C–H···O (C(23)– H(23)···O(4)iv= 3.295(3) ? and C(15)–H(15)···O(2)v= 3.408(3) ?). In addition, the 2D layer structure in complex 1 is further linked through···interactions (Cg3···Cg1 = 3.706 ? and Cg2···Cg1 = 3.530 ?) and C–H···(C(16)– H(16)···Cg3 = 3.466 ?), as depicted in Fig. 2. Thereinto, the centroids Cg1 and Cg2 are made up of atoms N(4), C(20), C(21), C(22), C(23) and C(24). Moreover, the centroid Cg3 is built by atoms C(18), C(19), C(20), C(24), C(25) and C(26). With the help of C–H···(C(22)–H(22)···= 3.466 ?)interactions between adjacent 2D sheets, the poly- meric sheets are assembled to form a supramo- lecular 3-D network structure (Fig. 3). Considering that the crystal packing results from many different contributions of directional and nondirectional inter- molecular interactions, it is important to consider jointly different types of interactions in structure analysis, contributing to the stabilization of the crystal structures.

Fig. 2 . 2-D structure of complex 1

Fig. 3 . 3-D structure of complex 1

3. 1. 2 Crystallographic analysis of complex 2

As shown in Fig. 4, X-ray crystal structure of complex2comprises one Ni complex, [Ni(EBSA)- (im)2(H2O)].Each Ni(II) atom exists in a distorted octahedral coordination environment, defined by three carboxyl O atoms from two different EBSA2–groups and two N atoms from two imidazole ligands as well as one coordination water molecule. Its equatorial plane is defined by the atoms of O(2), O(3), O(4)iand N(3). The axial positions are occupied by atoms O(1W) and N(1), with an angle of 175.44(18)o. The imidazole molecules act as typical monodentate ligands terminally coordinated to the metal center. The Ni–O(carboxyl) distances (Table 2) fall in the range of corresponding bond distances of Ni-terephthalate complexes (2.047(4)～2.179(3) ?). In the former (O(1)–C(1)–O(2)), the carboxyl group is in a monodentate mode through the O(2) atom, and the other carboxyl group (O(3)–C(14)–O(4)) is in a bidentate chelating mode through atoms O(3) and O(4). The dihedral angles between two imidazoles as well as between two benzene ring planes of EBSA are 83.53(0.31) and 85.15(0.25)o, respectively. The difference for tor- sion angle C(7)–S(1)–S(2)–C(8), 82.9(3)o, may be attributed to the remarkable conformational flexi- bility of EBSA2–ligand. Three kinds of intramo- lecular hydrogen bonds are observed in the com- pound: O–H···O (O(1W)–H(1W1)···O(1) = 2.591(6) ?), C–H···O (C(3)–H(3)···O(2) = 2.780(7) ?, C(12)–H(12)···O(4) = 2.782(8) ? and C(15)– H(15)···O(2) = 3.038(8) ?) and C–H···S (C(6)– H(6)···S(2) = 3.168(7) ? and C(9)–H(9)···S(1) = 3.215(6) ?), as shown in Table 3.

Fig. 4 . Coordination environment of Ni(1I) in complex 2 (Symmetry code:ix–1, y, z)

Each EBSA2–group adopts a tridentate coordina- tion mode to link two Ni(II) atoms into a one- dimensional infinite linear chain. In the chain, the adjacent Ni···Ni distance is 12.4490(71) ?. The two-dimensional layer structure of the compound is formed through intermolecular hydrogen bond. There are two kinds of intramolecular hydrogen bonds: N–H···O (N(2)–H(2N)···O(4)iv= 2.818(7) ? and N(4)–H(4N)···O(4)v= 3.093(7) ?) and C–H···S (C(11)–H(11)···S(2)vi= 3.630(7) ?) (Fig. 5). Fur- thermore, such layers are connected through inter- molecular hydrogen bonds (O(1W)–H(2W1)···O(3)iii= 2.809(6) ? and O(1W)–H(2W1)···S(2)iii= 3.473(4) ?), yielding a three-dimensional supra- molecular network (Fig. 6).

Fig. 5 . 2-D structure of complex 2

Fig. 6 . 3-D structure of complex 2

3. 2 IR spectrum

The absorption bands at 3391, 3139 cm-1in complex 1 and 3407, 3114 cm-1in complex 2 mean the O–H and N–H characteristic stretching vibra- tions, respectively, corresponding to the known structure. The IR spectra of complex 1 exhibit typi- cal antisymmetric 1576, 1553 cm-1and symmetric 1357, 1312 cm-1stretching bands of two carboxy groups. The values Δ(ν(COO-) –ν(COO-)) of 219 and 241 cm-1, respectively indicate that EBLA2-(2,2?-dicarboxydiphenylthioether) is monodentate. In complex 2, the absorptions at 1615, 1524 cm-1and 1386 cm-1correspond to asymmetricas(COO-) and symmetricals(COO-) stretching vibrations of the coordinated carboxy groups, with the Δ(as(COO-) –s(COO-)) values to be 229 and 138 cm-1, respectively. We can infer that the two car- boxy groups show monodentate and bidentate- chelating coordination modes. Meanwhile, charac- teristic bands 1448 cm-1in 1 and 1576 cm-1in 2 belong to the stretching vibration of -N=C- of ip and imidazoleligands, respectively. The charac- teristic bands 1374 and 822 cm-1in complex 1 belong to the stretching vibration of -S-(aromatic) of EBLA ligand[17]. In addition, the weak absorp- tions at 1162, 1133 and 483 cm-1in complex 2 belong to the stretching vibration of -S-S-(aroma- tic) of EBSA ligand[18]. The IR spectra analysis results are in consistent with that of single-crystal X-ray analyses.

3. 3 Thermal analysis

The thermal stability and thermal decomposition behavior of complex 2 were studied by thermal analysis in a static N2atmosphere in the temperature range of 30～800 ℃, as shown in Fig. 7. The weight-loss step occurred from 145 to 431 ℃ (Obsd. 62.65%, Calcd. 62.77%) due to the decomposition of one coordinated water molecule and EBSA2+ligand. Complex 2 starts to slowly decompose above 431 ℃, and this structure is similarly adopted by [Co(bpp)(H2O)(nip)][19].

Fig. 7 . Thermogravimetric curves (TG) for complex 2

3. 4 Photoluminescence properties

Coordination polymers based on10metal centers and organic ligand are promising candidates for photoactive materials with potential applications. In this study, fluorescent property of complex 1 has been investigated in the solid state. The ip(1- imidazo[4,5-][1,10]phenanthroline) shows strong emission peak centered at 460 nm upon excitation at 315 nm[20]and the emission peaks were not observed for free EBLA ligand since it was obtained as hydrothermalligand syntheses. On complexation of these ligands with Cd(II) atoms, fluorescence with emission peak centered at 499 nm (ex= 391nm) for complex 1 was observed at room temperature (Fig. 8), which may originate from theL-L* transition emission of ligand-to-ligand charge transfer (LLCT) in aromatic rings of the two ligands[21].

Fig. 8 . Solid-state photoluminescent spectrum for complex 1

4 CONCLUSION

In conclusion, two new Cd(II) and Ni(II) com- plexes, [Cd(EBLA)(ip)(H2O)] and [Ni(EBSA)(im)2-(H2O)], have been synthesized and structurally characterized. Complexes 1 and 2 are a dinuclear and a one-dimensional infinite linear chainstructures, respectively. The EBSA turns to be EBLA ligand viareaction at 160 ℃.Complex 1 emits intense luminescence with the fluorescence of 499 nm in the solid state at room temperature.

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9 September 2014; accepted 18 November 2014 (CCDC 998514 and 1000617)

① The authors thank the Foundation of Guangdong Province (No. S2012020011054 and 2011B090400415) and Zhanjiang Municipality(No. 2011C3108001)

. Gu Chang-Sheng, assistant professor, majoring in coordination compound. E-mail: gcsheng1968@126.com; Song wen-dong, professor, majoring in functional material. E-mail: swd60@163.com

10.14102/j.cnki.0254-5861.2011-0501