HOU Xiang-Yang WANG Xiao REN Yi-Xia TANG Long JU Ping WANG Ji-Jiang KANG Wei-Wei LIU Xiao-Li

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Two New Silver Coordination Polymers Constructed from 3,3-Azodibenzoic Acid and Different Pyridine Derivatives: Syntheses, Structures and Fluorescent Properties①

HOU Xiang-Yang WANG Xiao②REN Yi-Xia TANG Long JU Ping WANG Ji-Jiang②KANG Wei-Wei LIU Xiao-Li

(716000)

silver, CPs, synthesis, structure, fluorescence properties;

1 INTRODUCTION

In recent years,the construction of CPs mainly depends on balance on metal ions and multidentate ligands under suitable reaction conditions,including reaction temperature, pressure, solvent,[1-3]. How- ever, the structures of CPsbased on flexible ligandsare difficult to predict because of the conformational diversity of different reaction conditions, and theligands influencethe architectures which are largely considered to be serendipitous[4, 5]. In fact, it is important that the architectures of CPs areachieved via the ligandswith some flexible structure units, such as“-X-X-”(X = C, N, Oor). So far, many kinds of flexible ligands with “-X-X-” type unit with metal ionshave beenreported. There are CPs of ligands with flexible “-C-C-” types documented[6]. A series of CPs have been synthesized via 3,3?- and 4,4?-dithiobisbenzoic acid ligands with “-S-S-” type unit[7], as the biphenylethene-4,4?- dicarboxylate ligands containing “-C=C-” type unit bridge the Zn2+or Cd2+centers to produce CPs in the previous researches[8]. A sequence of compounds with flexible ligands containing “-N=N-” type unit has been reported recently[9]. Especially, the imidazole and pyridine flexible ligands containing “-X-X-” or “-X-X-X-” units bridging the metal ion centers in the synthesis of complexes have been reported[10-15]. The ligand with flexible unit can give rise to the construc- tion of frameworks with different structures.

Metallic silver and its complexes as new func- tional materials have potential applications, such as medical, fluorescence, ion exchange, catalysis, gas adsorption and separation, and so on[16-19]. Recently, the study of fluorescent properties about silver com- plexes has relatively extensive research. To achieve useful luminescent Ag-CPs, an effective method is to use the ligand-based strategy, arising from-conju- gated rigid organic ligands. To date, a variety of luminescent Ag-CPs have been reported on organic molecules, however, most of them were focused on the rigid ligands. Only several Ag-CPs have been investigated based on the ligands containing flexible “-X-X-” structure unit.

Bearing the aforementioned ideas and taking advantages of the structures and properties of Ag-CPs, the ligand of 3,3-azodibenzoic acid, and/or 1,2-di(4-pyridyl)ethylene, 4,4?-bipyridine was selec- ted in this work. Fortunately, solvothermal reactions to the mixed ligand with AgNO3in different mixed solvent system, pressure and temperature produced two new CPs {[Ag(ADA)0.5(DPE)]·H2O}n(1) and {[Ag(ADA)0.5(Bipy)0.5]·H2O}n(2), which were characterized by elemental analyses, single-crystal diffraction analysis, IR spectroscopy, and thermogra- vimetric analyses. In addition, the fluorescence properties of 1 and 2 under solid powder state have been investigated at room temperature.

2 EXPERIMENTAL

2. 1 Materials and methods

All available solvents and starting materials of analytical grade in the experiments were purchased and used without further purification. Elemental analysis (C, H, N) was determined on a Perkin-Elmer 2400 type elemental analyzer. The infrared spectra were measured between 4000～400 cm-1on a Bruker EQUINOX-55 spectrophotometer using KBr pellets. Thermal decomposition behaviors were performed under nitrogen at a heating rate of 10 °C·min-1using a NETZSCH STA 449C thermogravimetric analyzer. The photoluminescence of the solid samples was performed on an Edinburgh Instrument FLS920 fluorescence spectrometer at ambient temperature.

2. 2 Syntheses of {[Ag(ADA)0.5(DPE)]·H2O}n (1) and {[Ag(ADA)0.5(Bipy)0.5]·H2O}n (2)

{[Ag(ADA)0.5(DPE)]·H2O}n(1) H2ADA (0.1 mmol), DPE (0.13 mmol), AgNO3(0.2 mmol), and 15 mL deionized water were sealed in a 25 mL Te?on-lined stainless-steel autoclave reactor. After stirring for 30 min at room temperature and heated at 160 °C for 96 hours under autogenous pressure, the reaction system was cooled to room temperature at a cooling rate 2 °C·h-1. The colorless bulk crystals were collected in 43% yield (based on Ag).H, C and N elemental analyses Calcd. (%) for C13H11AgN2O3(1): H, 3.16; C, 44.47; N, 7.98. Found (%): H, 3.12; C, 44.52; N, 7.87.

{[Ag(ADA)0.5(Bipy)0.5]·H2O}n(2) A mixture of H2ADA (0.1 mmol), Bipy (0.13 mmol), AgNO3(0.2 mmol), and H2O (15 mL)was sealed in a Te?on- lined stainless-steel vessel (25 mL) and heated to 170 ?C for 3 days under autogenous pressure and cooled to room temperature at a rate of 5 ?C·h-1. Colorless bulk crystals of 2 were obtained in the yield of 30% based on Ag. Elemental analysis calcd. (%) for C12H10AgN2O2. 5: C, 43.66; H, 3.05; N, 8.49. Found (%): C, 43.70; H, 3.10; N, 8.43.

2. 3 X-ray crystal structure determination

Crystallographic data for CPs 1 and 2 were collected on a Bruker Smart CCD X-ray diffracto- meter equipped with graphite-monochromatized Moradiation with an-scan mode. A semi-empi- rical absorption correction was applied using the SADABS program[20]. The structures were solved by direct methods and re?ned on2by full-matrix least-squares using SHELX-97[21, 22]. All non-hydro- gen atoms were re?ned anisotropically. Hydrogen atoms of coordinated and uncoordinated water molecules were located in a difference Fourier map, while other hydrogen atoms were included in the calculated positions and re?ned with isotropic thermal parameters riding on the parent atoms. Selected bond lengths and bond angles for CPs 1 and 2 are listed in Table 1.

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

Symmetry codes of 1: #1: –, 2–, 1–; #2: 1–, 2–, 1–. Symmetry codes of 2: #1: 1–, 1–, –; #2:, 1–, –0.5+

3 RESULTS AND DISCUSSION

3. 1 Crystal structure of CP {[Ag(ADA)0.5(DPE)]·H2O}n (1)

3. 2 Crystal structure of {[Ag(ADA)0.5(Bipy)0.5]·H2O}n (2)

X-ray single-crystal diffraction analysis shows that CP 2 is a 2D structure, and it extends into a 3D supramolecular compound via hydrogen bonding andinteraction. CP 2 crystallizes in the monoclinic crystal, space group2/. The asymmetric unit of CP 2 consists of one Ag+, one half ADA2-, one Bipy ligand,and one uncoordinated water molecule (Fig. 2a). EachAg+ion is five-coordinatedby one N(2) atom from one Bipy ligand, three carboxylate oxygen atoms (O(1), O(1)#2, O(2)#1)from three ADA2-, and one Ag(1)#1ion. The coordination geometry of each Ag+ion can be described as a slightly distorted tetragonal pyramid, and four atoms (O(1)#1, O(2)#1, Ag(1)#1, N(2)) locate at the plane positions.The Ag–O/N bondlengths vary from 2.234(8) to 2.913(2) ?, and the Ag–Ag bond length is 2.892(2) ?, which are all in agreement with the corresponding values of reported CPs[23]. As shown in Fig. 2b, the Ag–Ag units are bridged by carboxyl oxygen atoms (O(1)–C(1)–O(2)) of ADA2-ligands to form 1D chains with the 8-membered rings in the-axis direction, and the shortest distance for the 8-membered rings is 14.6184(61) ? on the same plane.Adjacent 1D chains of 1 are linked by the ADA2-and Bipy ligand using6-O,O:O:O:O,O:O:O and2-O:O coordination modes to generate a 2D structure (Fig. 2c). The hydrogen bonding and···stacking exist in the neighboring 2D structure of CP 2, which play a critical role in the formation and stabilization of the 3D supramolecular structure(Fig. 2d). The geometrical parameters of all hydrogen bond and···stacking are listed in Table 2.

Fig. 1a. Asymmetric unit of complex 1. Symmetry codes: #1: –, 2–, 1–; #2: 1–, 2–, 1–

Fig. 1b. 2D network of complex 1 in the-plane

Fig. 1c. 3D network of complex 1

Fig. 2a. Asymmetric unit of CP 2. Symmetry codes: #1: –, 1–, –; #2: –, 1–, –

Fig. 2b. 1D chain structure of CP 2

Fig. 2c. 2D structure of CP 2

Fig. 2d. 3D structure of CP 2

Table 2. Geometrical Parameters of All Hydrogen Bonds and π-πInteractions for CP 2

Symmetry codes: #1: –3–, –2–, –4–; #2: –3+, –2–, –3.5+. Cg(1, light blue): C(2)C(3)C(4)C(5)C(6)C(7); Cg(2, light blue):N(2)C(8)C(9)C(10)C(11)C(12); Cg(3, pink): C(2)C(3)C(4)C(5)C(6)C(7); Cg(4, pink): N(2)C(8)C(9)C(10C(11)C(12)

3. 3 IR spectra

The IR spectra display characteristic absorption bands for water molecules, carboxylate, and phenyl units. As shown in Fig. 3, CPs 1 and 2 show broad absorption bands at 3405 and 3472 cm?1, respec- tively, indicating the presence ofO?Hstretching frequencies of coordinated water molecules. The strong bands at 1690 and 1677 cm-1are the charac- teristic stretching vibration of COO-of CPs 1 and 2. The characteristic IR bands of the phenyl ring bands at 813 and 826 cm?1are due to the=C?Hvibrations for 1 and 2, respectively.

Fig. 3. IR spectra of CPs 1 and 2

3. 4 Thermogravimetric analyses

The thermal analysis curves of 1 and 2 were investigated. The ?rst weight loss of 5.20% observed from 70 to 240 °C for 1 corresponds to the release of water molecule (calculated 5.13%). It keeps losing weight from 260 to 410 °C due to the departure of ADA2-and DPE ligands. The final residue of 33.71% is close to the calculated value of 33.00% based on Ag2O. The first weight loss of 5.53% below 220 °C of 2 results from the loss of water molecules (calculated 5.45%). Above 470 °C, a plateau region is observed, implying that the ADA2-and Bipy ligands are decomposed, with the final residue to be Ag2O (found 35.19%, calcd. 35.10%).

3. 4 Photoluminescence properties

The fluorescence properties of CPs 1 and 2 were examined at room temperature in the solid state. As shown in Fig. 4, an intense emission of the H2ADA ligand occurs at 415 nm with an excitation wave- length of 360 nm, which can be attributed to*→n or*→transitions. CPs 1 and 2 exhibit the maximum emission peaks at 421 and 419 nm in broad bands when excited at 376 and 359nm, and which are red-shifted by 6 and 4 nm for the H2ADA ligand, respectively. However, the emissions of CPs 1 and 2 can be attributed to neither metal-to-ligand nor ligand-to-metal charge transfer because the Ag+ion is in10configuration and difficult to oxidize or reduce[24].Therefore, this may be assigned to intraligand*→ n or*→transitions.

Fig. 4. Solid-state emission spectra of CPs 1 and 2

4 CONCLUSION

Two new CPs, {[Ag(ADA)0.5(DPE)]·H2O}n(1) and {[Ag(ADA)0.5(Bipy)0.5]H2O}n(2), have been synthesized by hydrothermal method, and their structures were determined and characterized by single-crystal X-ray diffraction analysis, elemental analysis, IR spectroscopy, and thermal behaviors. The crystal structure of CP 1 is a 3D framework consisting of Ag+centers, 6-connected ADA2-anionic ligand (6O,O:O:O:O,O:O:O) and 2-connected DPE ligands (2O:O). CP 2 is a 3D supramolecular structure. The Ag-Ag subunits are bridged to form 1D chains, and adjacent 1D chains are linked by the ADA2-(6-O,O:O:O:O,O:O:O) and Bipy (2-O:O) ligand to generate 2D structures. The hydrogen bonding and···stacking interac- tions existing in the neighboring 2D structures play a critical role in forming and stabilizing the 3D supra- molecular structure(Fig. 2d). Furthermore, solid- state photoluminescence measurements show that CPs 1 and 2 produce strong emissions at room tem- perature.

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31 March 2017;

20 July 2017 (CCDC 1546854-1546855)

① This work was supported by the National Natural Science Foundation of China (21503183, 21663031, 21373189), and the provincial level innovation programs funds of undergraduate for 2017 (1573)

. Wang Xiao (1977-), majoring in functional materials. E-mail: wx2248@126.com

10.14102/j.cnki.0254-5861.2011-1737