Syntheses and Crystal Structures of Three Ag(I) Complexes with Chloro-phenylacetic Acid and Nitrogen Heterocyclic Ligand①

HAO Xio-Min GU Chng-Sheng② JI Li-Li HU Shi-Wei LI Yong SONG Wen-Dong②

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Syntheses and Crystal Structures of Three Ag(I) Complexes with Chloro-phenylacetic Acid and Nitrogen Heterocyclic Ligand①

HAO Xiao-MinaGU Chang-Shenga②JI Li-LibHU Shi-WeibLI YongaSONG Wen-Dongb②

a(524088)b(,316022)

Three new coordination polymers {[Ag2(2,4-DCPA)(4,4?-bipy)2(NO3)]·(H2O)}(1), [Ag(2,4-DCPA)(bpp)](2) and {[Ag(4-DCPA)(bpp)]·(H2O)}(3), were synthesized by evaporation methods using 2,4-dichlorophenylacetic acid (2,4-DCPA), 4-chlorophenylacetic acid (4-DCPA), 4,4?-dipyridyl (4,4?-bipy), 1,3-bis(4-pyridyl)propane(bpp) and AgNO3. Compound 1 crystallizes in monoclinic, space group21/with= 10.035(2),= 17.796(3),= 16.448(2) ?,= 104.086(2)o,= 2705.9(2) ?3,D= 1.893 g/cm-3, C28H23Cl2N5O6Ag2,M= 812.15,(000) = 1608,(Mo) = 1.615 mm-1,= 4,= 0.0310,= 0.0832 for 4357 observed reflections (> 2()), and= 0.0362,= 0.0873 for all data. Compound 2 crystallizes in monoclinic, space group21/with= 9.840(2),= 24.971(5),= 9.3301(2) ?,= 117.504(2)o,= 2033.5(7) ?3,D= 1.666 g/cm-3, C21H19Cl2N2O2Ag,M= 510.15,(000) = 1024,(Mo) = 1.273 mm-1,= 4,= 0.0315 and= 0.0680 for 2853 observed reflections (> 2()) and= 0.0454,= 0.0736 for all data. Compound 3 crystallizes in monoclinic, space group21/with= 15.472(4),= 9.000(2),= 16.262(4) ?,= 112.049(4)o,= 2099.0(8) ?3,D= 1.562 g/cm-3, C21H22ClN2O3Ag,M= 493.73,(000) = 1000,(Mo) = 1.111 mm-1,= 4,= 0.0296,= 0.0821 for 3059 observed reflections (> 2()), and= 0.0398,= 0.0986 for all data. The complexes were characterized by elemental analysis, FT-IR, thermogravimetrie analysis (TGA) and X-ray single-crystal structure analysis. Fluorescence properties of complex 3 and PXRD of 1 and 2 have been studied. As a result, in complex 1, the Ag(I) ion is surrounded by two nitrogen atoms from two bipy ligands to form an infinite chain, and adjacent Ag-bipy chains produce “” of a ladder by silver ions contact. And in complexes 2 and 3, the two-dimensional-sheet like layersare obtained by Ag···Ag interactions.

silver complex, chloro-phenylacetic acid, crystal structure;

1 INTRODUCTION

The rational design and construction of metal- organic frameworks (MOFs) are rapidly expanding in crystal engineering and materials chemistry because of their large numbers of promising applica-tions in many areas, such as luminescence, catalysis, gas storage, ion exchange and so on, as well as for their diverse architectures and topology[1-4]. Con- trolling the structure and property of MOFs still remains a major challenge in this field because many factors such as organic ligands and central metal ions, temperature, pH value of solution, solvent, hydrogen bonding and-stacking interactions also have an efficient effect on assembling the final structure[5-8]. The basic design strategies used for constructing MOFs are based on the nature of interactions between the organic ligand and metal center. Considering the10closed-cell electronic configuration of silver ions, the preparations of silver complexes have attracted much attention[9]. Furthermore, silver ions have a flexible coordination number and irregular coordination spheres which may lead to the discovery of fascinating structures[10]. Chloro-benzene carboxylic acids have rich coordination modes such as terminal monodentate, chelating or bridging to more than one metal cation, and therefore they have been extensively employed in the preparation of complexes[11-13]. Heterocyclic nitrogen donors, such as 4,4?-bipyridine and 1,3- bis(4-pyridyl)propane, have also been proved to be among the most important types of organic ligands for the design and construction of coordination polymers exhibiting remarkable properties for their excellent coordinating ability[14-16]. In this study, we introduced chloro-phenylacetic acid with the nitro- gen heterocyclic ligands in order to assemble three Ag(I) coordination polymers. In addition, thermal stability, PXRD and fluorescence of the polymers were measured and discussed.

2 EXPERIMENTAL

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 PerkinElmer Spectrum 100 FT-IR spectrometer using KBr pellet at a resolution of 0.5 cm–1(400～4000 cm–1). Thermogravimetry analyses were performed on an automatic simultaneous thermal analyzer (PE TG/DTA 6300) under a flow of N2at a heating rate of 10 ℃·min–1between ambient temperature and 800 ℃. Luminescence spectra for crystal solid samples were recorded at room temperature on a PERKIN ELMER LS 55 luminance meter. X-ray powdered diffraction pattern of the sample was recorded by an X-ray diffractometer (Rigaku D8) equipped with a graphite-monochromatic Curadiation.

2. 1 Synthesis of the complexes

{[Ag2(2,4-DCPA)(4,4?-bipy)2(NO3)]·(H2O)}(1): Complex 1 was prepared by the addition of stoichiometric amounts of silver nitrate (0.1699 g, 1 mmol), 2,4-DCPA (0.2050 g, 1 mmol) and 4,4?-bipy(0.3124 g, 2 mmol) dissolved in a 1:1 metha- nol/water solution (35 mL) and the pH was adjusted to 7 with 0.1 mol/L potassium hydroxide solution. After the mixture was stirred for 30 min, the precipitate was dissolved in the aqueous solution of NH3(25%) which was added drop by drop. Colorless crystals of the compound were obtained by evaporation of the solution for 15 days at room temperature in 52% yield(based on Ag). Analysis calculated for C28H23Cl2N5O6Ag2(%): C, 41.41; H, 2.85; N, 8.62. Found (%): C, 41.70; H, 2.90; N, 8.77. IR (KBr pellet, cm-1): 3206(m), 1601(s), 1527(m), 1477(m), 1410(w), 1375(s), 1225(m), 1106(m), 1068(m), 865(m), 801(m), 726(m), 630(m) and 491(m).

[Ag(2,4-DCPA)(bpp)](2): The synthesis of com- plex 2 was carried out in the same procedure as that of complex 1,except 4,4?-bipywas replaced by bpp. After reaction, colorless crystals were obtained in 41% yield(based on Ag). Analysis calculated for C21H19Cl2N2O2Ag (%): C, 49.44; H, 3.75; N, 5.49. Found (%): C, 49.60; H, 3.89; N, 5.60. IR(KBr pellet, cm-1): 3353(m), 1562(s), 1501(w), 1419(m), 1389(s), 1225(m), 1102(w), 1057(w), 911(w), 860(m), 801(m), 715(w), 663(w), 585(m) and 507(m).

{[Ag(4-DCPA)(bpp)]·(H2O)}(3): The synthe- sis of complex 3 was carried out in the same procedure as that of complex 1,except 2,4-DCPA and 4,4?-bipywere substituted by 4-DCPA and bpp, respectively. After reaction, colorless crystals were obtained in 47% yield(based on Ag).Analysis calculated for C21H22ClN2O3Ag (%): C, 51.09; H, 4.49; N, 5.67. Found (%): C, 51.34; H, 4.45; N, 5.64. IR (KBr pellet, cm-1): 3416(w), 2947(w), 2361(w), 1933(w), 1603(s), 1559(s), 1528(m), 1501(s), 1391(m), 1221(m), 1156(m), 1092(m), 1014(m), 858(m), 806(s), 677(m), 586(m), 509(s), 450(w).

2. 2 X-ray structure determination

Colorless single crystals of compounds 1～3 (0.26mm× 0.14mm× 0.12mm), (0.30mm× 0.20mm× 0.18mm) and (0.23mm× 0.18mm× 0.16mm) were mounted on glass fibers in a random orientation, respectively. The data were collected on a Bruker SMART APEXII CCD dif- fractometer at 296(2) K with Mo-radiation (= 0.71073 ?) by using anscan mode in the ranges of 1.71o＜＜25.00ofor 1, 2.33o＜＜24.99ofor 2 and 1.55o＜＜25.00ofor 3. Empirical absorption corrections were carried out by using the SADABS program[17]. The unit cell dimensions were deter- mined by direct methods using the SHELXS pro- gram of SHELXTL package and refined with SHELXL[18]. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were added theoretically, riding on the concerned atoms and refined with fixed thermal factors. For compound 1, the final= 0.0310 and= 0.0832 (= 1/[2(F2) + (0.0444)2+0.6526], where= (F2+ 2F2)/3).= 1.077, (Δ)max= 0.698, and (Δ)min= –0.903 e/?3; for 2, the final= 0.0315 and= 0.0680 (= 1/[2(F2) + (0.0324)2+ 0.7761], where= (F2+ 2F2)/3).= 1.015, (Δ)max= 0.522, and (Δ)min= –0.442 e/?3; for 3, the final= 0.0296 and= 0.0821 (= 1/[2(F2) + (0.0560)2+ 1.5435], where= (F2+ 2F2)/3).= 0.974, (Δ)max= 0.615, and (Δ)min= –0.745 e/?3. The selected bond lengths, bond angles and H-bonds for 1～3 are given in Tables 1 and 2, respectively.

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

Symmetry codes: i+1, –+1/2,+1/2; ii–1, –+1/2,–1/2 for 1. i –,+1/2, –+3/2; ii –, –, –+2; iii –,–1/2, –+3/2 for 2. i–1/2, –+1/2,+1/2; ii –+1, –+1, –+1; iii+1/2, –+1/2,–1/2 for 3

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

Symmetry codes: i+1, –+1/2,+1/2; ii–1, –+1/2,–1/2; iii, –+1/2,–1/2; iv –+1,+1/2, –+3/2; v –+1, –+1, –+1 for 1. ii –, –, –+2; iv, ––1/2,–1/2 for 2. iv –+1/2,+1/2, –+1/2 for 3

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. 1a and the selected bond distances and bond angles are listed in Table 2. Single-crystal X-ray diffraction analysis reveals that the asymmetric unit of1 contains two Ag(I) cations, three coordinated 2,4-DCPA anions, two coordinated nitrate anions, two 4,4?-bipy ligands and one free water molecule. The silver ions (Ag(1)) are five-coordinated by two different bipy N atoms, two O atoms of nitrates and one carboxylate O atom from 2,4-DCPAligands, and the local coordination sphere around the Ag(1) ion can be described as a distorted square pyramid with a AgO3N2chromophore. Atoms O(2), O(5), N(3) and N(4)idefine the equatorial plane, while nitrateO(4) atom occupies the apical site (O(2)–Ag(1)– O(5) = 170.58(8)oand N(3)–Ag(1)–N(4)i= 166.61(1)o).The Ag(1)–O and Ag(1)–N distances are in the range of 2.167(3)～2.914(1) ?. Moreover, the Ag(2) ions coordinate to two oxygen atoms from the 2,4-DCPA ligands and two nitrogen atoms from different bipy ligands,and the local coordination sphere around the Ag(2) ions can be described as a similar “” shapedwith a AgO2N2chro- mophore (O(1)–Ag(2)–O(2) = 49.51(7)oand N(2)ii– Ag(2)–N(1) = 166.18(10)o). The Ag(2)–N and Ag(2)–O distances fall in the range of 2.154(3)～2.638(2) ?. The 2,4-DCPA ligand is connected to twoAg(I) ions through deprotonated carboxylate groups with3:2coordination modes (chelating/bri- dging bidentate fashion).The dihedral angle between two pyridine ring planes of bipy ligand is 31.00(1)o(N(1) and N(2) atoms of pyridine ring) and 31.86(1)o(N(3) and N(4) atoms of pyridine ring). One free water molecule (OW) forms an intramo- lecular hydrogen bond with the coordinated 2,4- DCPAligand O(1) atom, with the OW– H(1OW)···O(1) bond length of 1.870(2) ? and the bond angle of 169.0(3)o(Table 2).

Fig. 1. (a) Molecular structure of complex 1 (Symmetry codes:i+1, –+1/2,+1/2;ii–1, –+1/2,–1/2);(b) 2-structure of complex 1; (c) 3-structure of complex 1

All the Ag(I) ions are surrounded by two nitrogen atoms from two bipy ligands form an infinite chain. The adjacent Ag-bipy chains produce “” of a ladder by Ag(1)···Ag(2) interactions (distances 3.2743(5) ?), much shorter than the van der Waals radii of two silver ions (3.440 ?)[19](Fig. 1b).The adjacent Ag···Ag distances of a ladder are 11.378 ? (Ag1···Ag1a) and 11.322 ? (Ag2···Ag2a). The two- dimensional layer structure of the compound is formed by intermolecular interactions including intermolecular hydrogen bonds and···stackings. There is one kind of intermolecular hydrogen bond types: OW–H(2OW)···O(5)iii= 2.380(2) ? (symme- try code:iii, –+1/2,–1/2). In addition, the 2-layer structure in complex 1 is further linked through···interaction (Cg1···Cg2 = 3.656 ?, the centroids Cg1 are made up of atoms N(1), C(14), C(15), C(16), C(17) and C(18). Moreover, the centroids Cg2 are composed of atoms N(3), C(19), C(20), C(21), C(22) and C(23)). With the help of C–H···(C(15)–H(15)···Cg = 2.732 ?, the centroids Cg are built by atoms C(3), C(4), C(5), C(6), C(7) and C(8)), adjacent polymeric sheets are assembled to form a supramolecular 3-network structure (Fig. 1c).

3. 1. 2 Crystallographic analysis of complex 2

The X-ray crystal structure of 2 contains silver atom, bpp and 2,4-DCPA anions in the asymmetric unit. Each silver atom is coordinated to two N atoms from two different bpp ligands and two oxygen atoms of one 2,4-DCPA anion. The local coor- dination sphere around the Ag(1) ion can be described as a similar “” shaped configuration (O(1)–Ag(1)–O(2) = 49.65(8)oand N(2)i–Ag(2)– N(1) = 150.97(9)o). The 2,4-DCPA ligand shows a bidentate chelating mode (Ag(1)–O: 2.570(2) and 2.671(1) ?), and the bpp ligand has adopted two end pyridyl N atoms that link two Ag atoms (Ag(1)–N: 2.191(3) and 2.209(2) ?). The interactions (Ag···Ag) also exist in 2 with the Ag(1)···Ag(1)iidistance of 2.999(7) ? (Fig. 2a).

All the Ag(I) ions are surrounded by two nitrogen atoms from two bpp ligands, forming an infinite chain. The Ag-bpp chains are linked into interesting two-dimensional layers (-sheet like) by Ag···Ag contact. The Ag1a···Ag1b distance separated by the bpp ligand is 13.0357 ?, and the bpp ligand has aconformation (the dihedral angle between two pyridine ring planes of the bpp ligands is 73.563(2)o) (Fig. 2(b))[20]. The 2,4-DCPA ligand is arranged at both sides of the two-dimensional layers with similar “Ω” model. With the help of C–H···(C(12)– H(12)···Cg = 3.513 ?, the centroids Cgare made up of atoms C(3), C(4), C(5), C(6), C(7) and C(8)), adjacent polymeric sheets are assembled to form a supramolecular 3-network structure (Fig. 2 c and d).

Fig. 2. (a) Molecular structure of complex 2 (Symmetry codes:i–,+1/2, –+3/2;ii–, –, –+2);(b)-sheet like layers structure of complex 2; (c) 2,4-DCPA ligand in layers on “Ω” model;(d) 3-structure of complex 2

3. 1. 3 Crystallographic analysis of complex 3

In complex 3, there are silver atoms, one bpp ligand, one 4-DCPA anion and one uncoordinated water molecule in the asymmetric unit. Each silver atom is coordinated by two nitrogen atoms from two bpp ligands and an oxygen atom of the 4-DCPA anions in the T-shaped three-coordinate configura- tion geometry[21]. The 4-DCPA ligand has adopt a monodentate coordination mode (Ag(1)–O(1) = 2.506(3) ?), and the bpp ligand shows two end pyridyl N atoms that connect two Ag atoms (Ag(1)–N: 2.170(3) and 2.182(3) ?). The Ag(1)···Ag(1)iiseparation is 3.0012(7) ?. The uncoordinated water molecule OW forms an intramolecular hydrogen bond with the coordinated 4-DCPAligands O(2), with the OW···O(2) bond length of 2.844(5)and the OW–H(1W)···O(2) bond angle of 140(7)o(Fig. 3(a) and Table 2).

Compared to complex 2, a similar-sheet like layer structure in complex 3 is also found. The Ag1···Ag1a distance separated by bpp ligand is 13.400 ?, and the bpp ligand has aconformation (the dihedral angle between two pyridine ring planes of the bpp ligands is 71.839(2)o) (Fig. 3b). The 4-DCPA ligands are arranged at both sides of the layer with similar “S” model. With the help of hydrogen-bonded interactions between adjacent 2sheets (OW–H(1W)···O(2) and OW–H(2W)···O(1)iv= 2.904(5) ?, symmetry codes:iv–+1/2,+1/2, –+1/2), a supramolecular 3-network structure (Fig. 3(c) and (d)) is found.

Fig. 3. (a) Molecular structure of complex 3 (Symmetry codes:i–1/2, –+1/2,+1/2;ii–+1, –+1, –+1);(b)-sheet like layer structure of complex 3; (c) 4-DCPA ligand in layers on “S” model;(d) 3-structure of complex 3

3. 2 IR spectrum

The asymmetric(COO–) and symmetrical(COO–) appear in 1601, 1477 and 1375 cm–1of complex 1. The two values of Δ(COO–) suggest the presence of two different coordinated modes of the carboxylate groups[22]. In complexes 2 and 3,the strong bands at 1562 and 1603 cm–1are assigned to the asymmetrical(COO–), while the shoulders at 1389 and 1391 cm-1correspond to the symmetrical(COO–), respectively. The separations (Δ) betweenv(COO–) andv(COO–) are 173 and 212 cm–1, indicating bidentate and monodentate coor- dinating modes in2 and 3, respectively. Meanwhile, the bands at 1527, 1501 and 1528 cm–1are assigned to the stretching vibration of -N=C- of pyridyl in 1, 2 and 3, respectively. In addition, the absorptions at 1225, 1068, 801 and 726 cm–1in1 belong to the absorption band of NO3–groups[23].

3. 3 Thermal analysis

In complexes 1 and 3, the first corresponding to the escape of one free water molecule is observed from 30 to 131 and 128 ℃(Obsd. 2.63 and 2.94%, Calcd. 2.22 and 2.65%, respectively). The second corresponding to the departure of nitrate anion, 2,4-DCPA and 4,4?-bipy ligand is observed from 132 to 668 ℃(Obsd. 72.46%, Calcd. 71.34%) in complex 1. In complexes 2 and 3, the weight loss step occurred from 142 to 558 ℃ and 128 to 305 ℃(Obsd. 77.74 and 64.29%, Calcd.78.83 and 63.28%) due to the decomposition of the framework structure of chloro-aromaticcarboxylic acids and bpp ligands, respectively. The final decomposition products by further heating complexes 1, 2 and 3 are all characterized to be metallic silver, with a total weight loss of 25.11, 22.26 and 20.52% (Calcd. 26.44%, 21.17 and 21.87%), respectively (Fig. 4)[24].

3. 4 X-ray powder diffraction

As shown in Fig. 5, the peak positions of the experimental patterns are in agreement with the simulated ones from single-crystal X-ray diffraction, which clearly demonstrates good purity of 1 and 2. There are a few unindexed diffraction differences between the measured and simulated patterns, which may be related to the different orientations of the crystals in the powdered samples.

Fig. 4. Thermogravimetric curves (TG) for complex

Fig. 5. PXRD patter for complexes 1 and 2 (black: simulation of single crystal; red: solid samples)

3. 5 Photoluminescent properties

In this study, fluorescent property of compound 3 has been investigated in the solid state. Two emission peaks at about 356 nm (ex= 297 nm)[25]and 455 nm (ex= 372 nm)[26]were observed for free 4-DCPA and bpp ligands, respectively. On complexation of these ligands with Ag(I) atoms, strong fluorescence with emission peak at about 485 nm (ex= 286 nm) for the compound is observed at room temperature (Fig. 6), while the emissions arising from the free ligands are not observed. The absence of ligand-based emission suggests energy transfer from the ligands to the Ag(I) atoms during photoluminescence. Therefore, the photolumine- scence can probably be assigned to the ligand-to- ligand charge-transfer transitions[27]. Fluorescence has hardly been ever observed in complexes 1 and 2, which may be attributed to heavy atom effects[28].

4 CONCLUSION

The complexes of {[Ag2(2,4-DCPA)(4,4?- bipy)2(NO3)]·(H2O)}(1), [Ag(2,4-DCPA)(bpp)](2) and {[Ag(4-DCPA)(bpp)]·(H2O)}(3) were syn- thesized and characterized.In complex 1, the Ag- bipy chains are linked into “” of a ladder by silver(I) ion contacts. In complexes 2 and 3, the two-dimensional-sheet like layersare observed by Ag···Ag interactions. Complex 3 emits the intense luminescence with the fluorescence of 485 nm in the solid state at room temperature.

Fig. 6. Solid-state photoluminescent spectrum for complex 3

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① This work was supported by the Guangdong Science and Technology Department(No. S2012020011054 and 2011B090400415)and the Zhanjiang Municipality(No. 2011C3108001) projects

② Corresponding authors.E-mail: gcsheng1968@126.com and swd60@163.com

10.14102/j.cnki.0254-5861.2011-0670

6 February 2015; accepted11 May 2015 (CCDC 1004210 for 1, 996494 for 2 and 995501 for 3)