Syntheses, Structures, and Luminescent Properties of Six New Zinc(II

May 28, 2013 - Six new Zn(II) coordination polymers have been constructed by employing a flexible ..... Journal of Coordination Chemistry 2015 68, 173...
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Syntheses, Structures, and Luminescent Properties of Six New Zinc(II) Coordination Polymers Constructed by Flexible Tetracarboxylate and Various Pyridine Ligands Xin Zhang, Lei Hou,* Bo Liu, Lin Cui, Yao-Yu Wang, and Biao Wu* Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, College of Chemistry and Materials Science, Northwest University, Xi’an 710069, P. R. China S Supporting Information *

ABSTRACT: Under solvothermal conditions, six new Zn(II) coordination polymers, [(CH3)2NH2]2[Zn(L)]·2H2O (1), [Zn2(L)(py)2] (2), [Zn2(L)(bpe)2]·bpe·6H2O (3), [Zn2(L)(bpe)(DMA)(H2O)]·5H2O (4), [Zn2(L)(bpy)0.5(H2O)2]·2.5H2O (5), and [Zn2(L)(bpe)(H2O)]·3H2O (6) [H4L = 5,5′-(p-xylylenediamino)-1,1′,3,3′-(benzenetetra-carboxylic acid), py = pyridine, bpy = 4,4′-dipyridine and bpe = 1,2-bis(4pyridyl)ethane], have been synthesized by employing a flexible tetracarboxylic acid H4L and different auxiliary pyridine-based ligands. In 1−6, all L4− ligands are 4-connected nodes; however, the diverse configurations of the two terminal isophthalate units of L4− around the central −NHCH2PhCH2NH− spacer lead to various topological nets. 1 shows a three-dimensional (3D) 2-fold interpenetrated 4-connected dia network resulting from the vertical configuration of the two isophthalate units of L4−. 2 displays a 3D (4,4)-connected pts net in which the two isophthalate units of L4− adopt a parallel configuration. The two isophthalate units of L4− in 3 are also almost parallel, resulting in an intriguing 3D 2-fold interpenetrated network with the (4,4)-connected bbf net. 4 is a two-dimensional bilayer structure, extending into a 3D supramolecular framework through interlayer hydrogen-bonding interactions. 5 and 6 disclose similar 3D structural architectures, in which the two isophthalate units of L4− are almost vertical and exhibit tetrahedral topological nodes, inducing a rare (4,5)-connected xww net and an unprecedented (4,6)-connected network, respectively. The thermal stabilities and luminescent properties of 1−6 have also been studied in detail. The complexes exhibit intense solid-state fluorescent emissions at room temperature.

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in coordination polymers.6 It has been reported only in a few coordination polymers, in which the aliphatic amine carboxylate ligands link the d-block transition metal centers with different coordination geometries and flexibility, generating various frameworks from two-dimensional (2D) layers to threedimensional (3D) architectures, 3D polycatenation/polythreading/polyrotaxane/polycatenane frameworks6b,c and 3D porous frameworks.6a,d These findings indicate that the aliphatic amine benzene-carboxylic ligands as flexible bridging ligands7 are promising candidates for constructing coordination polymers with diverse structures and properties. In consideration of this point, an aliphatic amine tetracarboxylate ligand, 5,5′-(pxylylenediamino)-1,1′,3,3′-(benzenetetracarboxylic acid) (H4L), has been designed and synthesized to build coordination polymers with various architectures. H4L has two terminal isophthalic acid units and two aliphatic amine groups between the central phenylene fragment. The carboxylate groups possess diverse coordination modes and can adapt to the coordination geometries of metal centers. Moreover, the two flexible −CH2NH− spacers in H4L can twist and rotate freely to

INTRODUCTION As a result of the structural richness and promising applications as adsorption, catalysis, guest exchange, magnetism, and optics materials, coordination polymers1 have attracted great interest for chemists.2 The assembly of coordination polymers can be influenced by several key factors, such as temperature, solvent, reactant concentration, and pH value, etc., as well as some internal factors, such as coordination geometries of the central metals, configurations, and flexibility of the organic ligands.3 Therefore, in order to obtain the target frameworks with specific structures and functions, it is important to regulate the synthesis conditions and/or design the organic ligands. To realize the infinite extension of structure, organic ligands with two or more coordination atoms, such as N, O, and S atoms, are often employed.4 The multicarboxylic acids are the most widely used linkers for the assembly of various coordination polymers.5 They can adopt a variety of coordination modes to conform to the requirements of the coordination geometries of metal centers and, thus, result in diverse multidimensional architectures. Notably, although multicarboxylate ligands have been intensively investigated in a large number of known coordination polymers, the aliphatic amine benzene-carboxylic acids, which possess the carboxyl groups and flexible −CH2NH− spacers, are much less common © 2013 American Chemical Society

Received: April 17, 2013 Revised: May 20, 2013 Published: May 28, 2013 3177

dx.doi.org/10.1021/cg400579w | Cryst. Growth Des. 2013, 13, 3177−3187

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Scheme 1. (a) Structures of H4L and Pyridine-Based Coligands. (b) Various Topological Structures of Complexes 1−6

NH-isophthalate-H4,6), 7.66 (s, 2H, NH-isophthalate-H2) (Figure S2 of the Supporting Information). 13C NMR [100 MHz, (CD3)2SO]: δ 169.4 (CO), 149.6 (NH-isophthalate-C5), 139.2 (phenylene-C), 134.8 (NH-isophthalate-C1,3), 128.2 (phenylene-CH), 119.1 (NH-isophthalate-C2), 117.0 (NH-isophthalate-C4,6), 47.3 (CH2) (Figure S3 of the Supporting Information). ESI-MS (methanol): m/z 487.11 (44%), [L + Na]+. Synthesis of [(CH3)2NH2]2[Zn(L)]·2H2O (1). A mixture of ZnSO4·7H2O (0.043 g, 0.15 mmol), H4L (0.069 g, 0.15 mmol), H2O (2 mL), N,N′-dimethylformamide (DMF) (2 mL), and two drops of py were stirred for 2 h in air. The solution was placed in the Teflon-lined stainless steel vessel (25 mL), sealed, and heated to 120 °C for 24 h. Cooling the vessel to room temperature gave purple sheet crystals (0.064 g). Yield: 65% (based on Zn). Anal. Calc. (%) for C28H36N4O10Zn (Mr = 654.02): C, 51.42; H, 5.54; N, 8.56. Found: C, 51.38; H, 5.52; N, 8.59. IR (KBr, cm−1): 3744(w), 3441(m), 3324(s), 3059(m), 2781(m), 2493(s), 1624(w), 1575(s), 1466(w), 1426(w), 1351(s), 1287(w), 1134(w), 1104(w), 1019(m), 884(m), 816(w), 781(s), 726(s), 611(w), 514(w), 436(w). Synthesis of [Zn2(L)(py)2] (2). The preparation of 2 was similar to that of 1, except N,N′-dimethylacetamide (DMA) (2 mL) was used instead of DMF. Red crystals of 2 were collected (0.034 g) in 60% yield (based on Zn). Anal. Calc. (%) for C34H26N4O8Zn2 (Mr = 749.41): C, 54.49; H, 3.50; N, 7.48. Found: C, 54.30; H, 3.48; N, 7.50. IR (KBr, cm−1): 3069(w), 2927(w), 1624(s), 1513(m), 1422(s), 1365(s), 1286(w), 1226(w), 1140(w), 1109(w), 1076(w), 1021(w), 922(m), 879(m), 830(w), 782(s), 725(s), 691(w), 627(w), 536(w), 445(m). Synthesis of [Zn2(L)(bpe)2]·bpe·6H2O (3). 3 was synthesized through the same synthetic procedure as that for 1 except that bpe (0.014 g, 0.075 mmol) was used instead of py and ZnSO4·7H2O was replaced by ZnCl2 (0.020 g, 0.15 mmol). Yield: 0.033 g, 35% (based on Zn). Anal. Calc. (%) for C60H58N8O14Zn2 (Mr = 1245.97): C, 57.84; H, 4.69; N, 8.99. Found: C, 57.64; H, 4.67; N, 9.01. IR (KBr, cm−1): 3746(w), 3447(m), 3325(m), 3064(w), 2797(w), 2492(w), 1613(s), 1573(s), 1503(w), 1422(w), 1350(s), 1213(w), 1138(w), 1096(w), 1073(w), 1022(m), 988(w), 885(m), 835(m), 776(s), 727(s), 677(w), 551(s). Synthesis of [Zn 2(L)(bpe)(DMA)(H2O)]·5H2O (4). 4 was synthesized through the same synthetic procedure as that for 2, except that bpe (0.014 g, 0.075 mmol) was used instead of py. Yield: 0.026 g, 40% (based on Zn). IR (KBr, cm−1): 3751(w), 3433(s), 3377(s), 2927(w), 2846(w), 1784(w), 1609(s), 1360(s), 1142(w), 1102(w), 1074(w), 1024(m), 985(m), 929(w), 893(w), 836(w), 810(w), 776(m), 733(m), 603(w), 547(m), 430(w). Synthesis of [Zn2(L)(bpy)0.5(H2O)2]·2.5H2O (5). 5 was synthesized following the same synthetic procedure as that of 2, except that bpy (0.012 g, 0.075 mmol) was used instead of py. Yield: 0.020 g, 38% (based on Zn). IR (KBr, cm−1): 3751(w), 3433(s), 3065(m), 2933(m), 1959(w), 1915(w), 1578(s), 1428(m), 1359(s), 1278(m),

make it serve as the topological nodes with different geometrical configurations, such as the 4-connected tetrahedron or square plane. Indeed, HnL(4‑n)-containing (n = 0−4) complexes were only documented in one one-dimensional (1D) polymer, [Ag 2 (L1) 2 ]2 (L)·7H 2 O [L1 = 1,1′-(1,4butanediyl)bis(2-methylbenzimidazole)], in which L4− was only a counteranion.8 Meanwhile, the mixed-ligands strategy,7a,d,9 incorporating pyridine-based colinkers with different lengths and rigidness/ flexibility, has proven successful in the creation of various coordination polymers.10 In order to further study the effect of pyridine-based coligands in the self-assembly process of coordination polymers, we have herein taken H4L and different lengthed pyridine ligands (Scheme 1) and yielded six new polymers under solvothermal conditions, [(CH3)2NH2]2[Zn(L)]·2H2O (1), [Zn2(L)(py)2] (2), [Zn2(L)(bpe)2]·bpe·6H2O (3), [Zn 2 (L)(bpe)(DMA)(H 2 O)]·5H 2 O (4), [Zn 2 (L)(bpy)0.5(H2O)2]·2.5H2O (5), and [Zn2(L)(bpe)(H2O)]·3H2O (6) [py = pyridine, bpy = 4,4′-dipyridine, and bpe = 1,2-bis(4pyridyl)ethane]. The structures, thermal stabilities, and luminescent properties of 1−6 have been studied in detail.

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EXPERIMENTAL SECTION

Materials and Measurements. All reagents and solvents for the synthesis were purchased from commercial sources and used as received without further purification. The ligand H4L was synthesized by a modified method.6d Infrared spectra were obtained in KBr pellets on a Nicolet Avatar 360 Fourier-transform infrared (FT-IR) spectrometer in the 4000−400 cm−1 region. Proton nuclear magnetic resonance (1H NMR) spectra and 13C NMR were recorded at 25 °C on a Varian 400 and 100 MHz, respectively. Elemental analyses of C, H, and N were determined with a Perkin-Elmer 2400C elemental analyzer. Thermogravimetric analyses (TGA) were carried out in a nitrogen stream using a Seiko Extar 6000TG/DTA equipment with a heating rate of 5 °C min−1. Powder X-ray diffraction (PXRD) data were recorded on a Bruker D8 ADVANCE X-ray powder diffractometer (Cu Kα, 1.5418 Å). Luminescence spectra were investigated with a Hitachi F-4500 fluorescence spectrophotometer. Synthesis of H4L. Triethylamine (2.8 mL, 20 mmol) was added to a stirred mixture of 5-aminoisophthalic acid (0.90 g, 5.0 mmol), terephthalaldehyde (0.35 g, 2.6 mmol), and dry methanol (50 mL). After 1 h, the mixture became limpid, and an excess of NaBH4 was slowly added at 4 °C. After 2 h, the solvent was concentrated in vacuo. The residue was dissolved in water (50 mL) and acidified with AcOH to a pH 5−6. After filtration, the product was obtained as a yellowish solid (0.85 g, 73%). IR (KBr, cm−1): 3429(s), 1686(s), 1605(s), 1512(m), 1430(s), 1276(s), 927(s), 871(s) (Figure S1 of the Supporting Information). 1H NMR [400 MHz, (CD3)2SO]: δ 4.30 (d, J = 4.8 Hz, 4H, CH2), 7.32 (s, 4H, phenylene-CH), 7.33 (s, 4H, 3178

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Table 1. Crystal Data and Structure Refinements for Complexes 1−6

a

complex

1

2

3

4

5

6

empirical formula M crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z dc (g cm−3) μ (mm−1) F(000) θ range (deg) reflections data/parameters R(int) GOF on F2 R1,a wR2b [I > 2σ(I)] R1,a wR2b (all data) Δρmax /Δρmin (eA−3)

C28H36ZnN4O10 653.98 monoclinic C2/c 16.317(7) 13.020(6) 13.591(6) 90 100.303(4) 90 2841(2) 4 1.529 0.930 1368 2.01−25.10 7812/2410 2410/197 0.0199 0.957 0.0400, 0.1271 0.0429, 0.1299 0.517/−0.717

C34H26Zn2N4O8 749.33 monoclinic C2/c 21.639(2) 9.2791(11) 17.132(2) 90 111.495(2) 90 3200.6(6) 4 1.555 1.558 1528 2.02−26.00 8381/3128 3128/217 0.0220 1.113 0.0624, 0.1967 0.0765, 0.2291 2.167/−0.914

C60H58Zn2N8O14 1245.88 monoclinic P21/n 9.0531(19) 19.218(4) 16.342(3) 90 92.804(4) 90 2839.8(10) 2 1.457 0.920 1292 2.12−26.00 15091/5527 5527/379 0.0500 1.057 0.0547, 0.1560 0.0993, 0.2009 0.548/−0.510

C40H37Zn2N5O10 878.49 monoclinic C2/c 22.953(5) 28.260(5) 16.064(3) 90 125.983(5) 90 8432(3) 8 1.384 1.198 3616 1.31−25.10 21173/7502 7502/517 0.0862 0.975 0.0635, 0.1641 0.1176, 0.1980 0.685/−0.906

C29H24Zn2N3O10 705.25 monoclinic P21/c 20.504(4) 9.5776(17) 19.444(4) 90 103.735(3) 90 3709.2(12) 4 1.263 1.343 1436 2.04 −25.99 19306/7250 7250/398 0.0586 1.000 0.0716, 0.2058 0.1043, 0.2325 0.755/−0.601

C36H34Zn2N4O12 845.37 monoclinic P21/c 19.67(3) 9.540(12) 18.23(2) 90 101.71(3) 90 3350(8) 4 1.658 1.507 1700 2.28−26.00 17515/6513 6513/471 0.0866 1.117 0.0724, 0.1573 0.1285, 0.1841 1.071/−0.990

R1 = ∑∥Fo| − |Fc∥/∑|Fo|. bwR2 = [∑w(Fo2 − Fc2)2 /∑w(Fo2)2]1/2.

Figure 1. (a) The coordination environment of the Zn(II) atom in 1. Symmetry codes include #1: 1 − x, y, 1.5 − z; #2: 0.5 + x, −0.5 + y, z; #3: 0.5 − x, −0.5 + y, 0.5 − z; #4: 1 − x, y, 0.5 − z. (b) Tetrahedral node of L4−. (c) View of the 2-fold interpenetrated dia net (Zn, orange balls; L4−, blue balls) in 1. (d) 3D structure of 1 showing the 1D channels along the [110] direction. C36H34N4O12Zn2 (Mr = 845.49): C, 51.14; H, 4.05; N, 6.63. Found: C, 51.01; H, 4.03; N, 6.65. IR (KBr, cm−1): 3745(w), 3445(m), 3325(s), 3058(m), 2923(w), 2788(m), 2490(m), 1616(w), 1577(s), 1464(m), 1424(m), 1351(s), 1291(w), 1138(w), 1095(w), 1020(s), 991(w), 886(m), 817(w), 776(s), 727(s), 679(w), 611(w), 553(m), 517(w), 429(m).

1228(w), 1146(m), 1101(w), 1074(w), 1015(m), 905(m), 882(w), 818(w), 778(s), 727(s), 681(w), 637(m), 588(w), 559(w), 472(m). Synthesis of [Zn2(L)(bpe)(H2O)]·3H2O (6). The preparation of 6 was similar to that of 3, except that ZnCl2 was replaced by Zn(NO3)2·6H2O (0.045 g, 0.15 mmol). Yellow crystals of 6 were collected (0.019 g) in 30% yield (based on Zn). Anal. Calc. (%) for 3179

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Figure 2. (a) The coordination environment of the Zn(II) atom in 2. Symmetry codes are #1: 0.5 − x, 2.5 − y, −z; #2: x, 2 − y, −0.5 + z; #3: 1 − x, y, 0.5 − z. (b) Zn2(O2CR)4 cluster in 2. (c) Schematic view of the dinuclear Zn2(O2CR)4 cluster and L4− as tetrahedral and square-planar nodes, respectively. (d) pts net of 2 (clusters, yellow balls; L4−, blue balls).

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Crystallographic Data Collection and Refinement. Suitable crystals of 1−6 were mounted on a glass fiber with nail polish. Singlecrystal X-ray diffraction data 1−6 were collected on a Bruker-AXS SMART CCD diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at room temperature. The data integration and reduction were processed with APEX II. The structures were solved by the direct method using SHELXTL and embarked on a fullmatrix least-squares refinement on F2 with SHELXL-97.11 The solvent molecules in 4 and 5 were highly distorted, and their contributions were removed from the diffraction data through using the SQUEEZE routine of PLATON.12 All nonhydrogen atoms were anisotropically refined. All hydrogen atoms of water were located in successive different Fourier maps and the other hydrogen atoms were treated as riding. The hydrogen atoms for the crystallization water molecules in 6 could not be located from their difference Fourier maps because of the high degree of hydration and thermal motion. Crystallographic data, selected bond lengths, and angles of 1−6 are shown in Table 1 and Table S1 of the Supporting Information.

RESULTS AND DISCUSSION

Crystal Structure of [(CH3)2NH2]2[Zn(L)]·2H2O (1). Complex 1 crystallizes in the monoclinic space group C2/c and exhibits a 2-fold interpenetrated dia framework. The asymmetric unit contains one Zn(II) atom and one L4−, which are located at the 2-fold axis with 50% occupancy. The Zn(II) atom is surrounded by four oxygen atoms from four different carboxylate groups of four L4− [Zn−O = 1.9749(19) and 1.994(2) Å], generating a distorted tetrahedral coordination geometry (Figure 1a). Four carboxylate groups of one L4− display the same monodentate coordination modes. Each L4− is fully deprotonated and links four Zn(II) atoms, and each Zn(II) atom connects four L4− to form an anionic framework. Notably, the two isophthalate units of L4− are almost vertical and form a tetrahedral topological node (Figure 1b). As a result, the whole framework forms a classical uninodal dia 66 net.13 In the crystal stacks, two identical networks interweave to 3180

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give a 2-fold interpenetrated framework (Figure 1c). Interestingly, two different types of channels with 31.3% volume are formed along the 110 direction (Figure 1d),14 which are occupied by [(CH3)2NH2]+ counterions and solvent water molecules, respectively. Crystal Structure of [Zn2(L)(py)2] (2). 2 is a 3D framework with the monoclinic space group of C2/c. The asymmetric unit contains one Zn(II) atom, a half L4− [Zn−O = 1.940(3)−2.011(4) Å], and one coordinated py [Zn−N = 1.995(5) Å] (Figure 2a). The Zn(II) atom is trigonalbipyramidally (τ = 0.971)15 coordinated to one chelating and two bridging carboxylate groups of three L4− and one py ligand. Two Zn(II) atoms are combined by two carboxylate bridges from two different L4− to form a dinuclear Zn2(O2CR)4 cluster (Figure 2b). Each cluster as a distorted 4-connected tetrahedral node is linked by four L4− to form a 3D framework (Figure 2c). As for L4−, the carboxylate groups show bis(bridging-bidentate) and bis(chelating-bidentate) coordination fashions. Each L4− connects four adjacent clusters and can be simplified as a 4connected node. However, different from 1, the two isophthalate units of L4− in 2 are almost parallel, featuring a square-planar topological node (Figure 2c). Thus, the whole net of 2 can be rationalized as a binodal (4,4)-connected pts net with the same point symbols of 4284 (Figure 2d),16 but disclosing the different long vertex symbols of 4.4.82.82.88.88 and 4.4.87.87.87.87 for L4− and dinuclear clusters, respectively. The coordinated py results in nonaccessible solvent voids in 2. Crystal structure of [Zn2(L)(bpe)2]·bpe·6H2O (3). 3 displays a 3D architecture with the monoclinic space group P21/n. As shown in Figure 3a, the asymmetric unit contains one Zn(II) atom, one L4−, one bpe ligand, and one bpe and three water guest molecules, where the L4− and free bpe molecule have 50% occupancy. The Zn(II) atom is tetrahedrally coordinated by two carboxylate monodentate oxygen atoms from two L4− [Zn−O = 1.959(3) and 1.969(3) Å] and two nitrogen atoms from two bpe ligands [Zn−N = 2.051(4) and 2.088(4) Å]. L4− show a ‘‘Z-shaped’’ conformation with the dihedral angles of 86.652(9)° between the central and terminal phenyl rings. Each L4− connects four Zn(II) atoms to form a 2D jagged layer with the intralayer Zn(II)···Zn(II) separations across L4− of 15.392 and 9.475 Å (Figure 3b). The interlinkages between bpe and Zn(II) atoms generate a zigzag chain. The combination of chains and layers along the a axis produces a 3D framework (Figure 3c). Similar with the situation of L4− in 2, the two isophthalate units of L4− in 3 are almost parallel, exhibiting a square-planar topological node. Therefore, there are two kinds of 4-connected nodes in 3, namely tetrahedral Zn(II) centers and square-planar L4− with the ratio of 2:1. The framework of 3 can be designated as a binodal (4,4)-connected bbf net with the point symbol of (6482)(66)2 (Figure S4 of the Supporting Information) and the long vertex symbols of 62.62.62.62.84.84 and 6.6.6.6.62.62, respectively.17 In 3, two independent nets are interpenetrated through an overlapping stack along the c axis to generate tetragonal channels with an opening of ca. 4.6 × 7.0 Å2 (excluding van der Waals radii of the atoms) (Figure 3, panels d and e), which have 33.9% volume filled by free bpe and water molecules.14 In comparison to the 3D dia network with the uninodal tetrahedral node in 1, the pts net of 2 and the bbf net of 3 contain tetrahedral and square-planar nodes. For pts net in 2, two different nodes have the same point symbols with a 1:1 ratio; however, the ratio in 3 is 2:1 [Zn(II)/L4−], as well as the different point symbols. So far, the large majority of 3D

Figure 3. (a) The coordination environment of the Zn(II) atom in 3. Symmetry codes of #1: 2 − x, 2 − y, 1 − z; #2: −0.5 + x, 1.5 − y, −0.5 + z; #3: −0.5 − x, 0.5 + y, 0.5 − z. (b) The 2D jagged layer in 3 viewed along the different directions. (c) The 3D structure of 3 interconnected by chains (green) and layers. (d) The 3D structure of 3 showing channels along the c axis. (e) The 2-fold interpenetrated bbf net of 3.

coordination polymers have been reported, which usually possess low-connected structural topologies dominated especially by the 4-connected nodes. The most common 4connected nets are those which are easily constructed through tetrahedral and/or square-planar nodes, such as lonsidaleite (lon), SrAl2 (sra), quartz (qtz), sodalite (sod), NbO (nbo), CdSO4 (cds), and square (sql) net.2a,18 From both the zeolite chemistry and crystal engineering points of view, the frameworks possessing 4-connected nodes can usually create larger cavities and bigger channels than those based on higher connected nodes, although in some cases the higher (e.g., 6connected) node-based MOFs may have very large surface area and high porosity.19 Accordingly, the use of 4-connected tetrahedral and/or square-planar centers as basic structural units for constructing open-framework materials has become a hot research topic. However, the cavities in 1, 2, and 3 are decreased because of the interpenetration and/or the filling of [(CH3)2NH2]+ cations, coordinated py, and free bpe molecules, respectively. Crystal structure of [Zn2(L)(bpe)(DMA)(H2O)]·5H2O (4). Complex 4 is a 2D layer structure crystallizing in the monoclinic space group C2/c. The asymmetric unit contains two independent Zn(II) atoms, one bpe, two distinct L4− with 50% occupancy, one aqua ligand, and one coordinated DMA molecule (Figure 4a). Zn1 atom is five-coordinated by three carboxylate oxygen atoms from two L4−, one bpe nitrogen atom, and one terminal aqua ligand, forming a distorted 3181

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Figure 4. (a) The coordination environments of the Zn(II) atoms in 4. Symmetry codes of #1: 1 − x, y, 0.5 − z; #2: 2 − x, −y, 2 − z; #3: 1 − x, y, −0.5 − z; #4: 2 − x, y, 1.5 − z. (b) View of the 2D jagged layer in 4 along the different directions in 4. (c) 2D bilayer structure formed by two jagged layers in an alternate fashion with bpe linkers (orange). (d) Topological structure of the 2D bilayer.

trigonal-bipyramidal geometry (τ = 0.988).15 Zn2 atom is sixcoordinated by one bpe nitrogen atom, four carboxylate oxygen atoms from two L4−, and one DMA ligand. The Zn−O and Zn−N distances fall within the ranges of 1.911(4)−2.408(4) and 2.049(5)−2.068(5) Å, respectively. The structure of 4 is more intricate than 3, due to two different types of coordination fashions of L4− in 4. In the first one, four carboxylate groups all show chelating-bidentate modes, whereas they adopt bis(chelating-bidentate) and bis(monodentate) modes in the second one. Two Zn1 atoms and two Zn2 atoms are connected by four isophthalate units from four L4−, forming an isolated {Zn4[(O2C)8R4]} metallacycle with the dimensions of ca. 10.9 × 10.3 Å2.20 One metallacycle is extended by four −NHCH2PhCH2NH− spacers of four L4− to give a 2D jagged layer (Figure 4b). Interestingly, two layers in an alternate fashion are connected by bpe linkers to generate a new 2D bilayer (Figure 4, panels c and d). The adjacent bilayers are held together by the interlayer N−H···O#1 (symmetry code of #1: 3/2 − x, 1/2 − y, 1 − z; N···O = 3.028(9) Å, ∠N−H···O = 148°) hydrogen-bonding interactions to form a 3D supramolecular architecture.21 Crystal Structure of [Zn2(L)(bpy)0.5(H2O)2]·2.5H2O (5). 5 is a 3D framework with the monoclinic space group P21/c. The asymmetric unit contains two independent Zn(II) atoms, one L4−, a half bpy ligand, and two coordinated water molecules. As shown in Figure 5a, Zn1 atom is five-coordinated by one bpy nitrogen atom, three carboxylate oxygen atoms from three L4−,

and one water molecule, giving a distorted trigonal-bipyramidal geometry (τ = 0.995).15 The Zn2 atom is octahedrally coordinated by six oxygen atoms from one chelating and three bridging carboxylate groups of four L4−, and one terminal aqua ligand. Two Zn(II) atoms are combined by three bridging carboxylates of three L4− to form a dinuclear Zn2(O2CR)4 cluster. Each L4− links four clusters through four carboxylate groups with two bridging bidentate, one chelating-bidentate, and one monatomic bridge coordination modes, generating a 2D layer paralleling to the bc plane (Figure 5b). In the layer, 1D channels are formed along the b axis with the sizes of ca. 6.1 × 6.1 Å2 (Figure 5c).20 The adjacent layers arrange in an eclipsed fashion and are further extended by bpy linkers along the a axis to form a 3D framework (Figure S5 of the Supporting Information). PLATON14 calculation indicates 30.7% accessible free voids after the removal of guest molecules. Topologically, each dinuclear cluster binds four L4− and one bpy ligand and, thus, is treated as a 5-connected distorted trigonal-bipyramidal node (τ = 0.992)15 (Figure S6 of the Supporting Information). L4− can be viewed as a distorted 4-connected tetrahedral node, in which the two isophthalate units adopt a parallel configuration. Thereby, the framework of 5 can be designated as a rare binodal (4,5)-connected xww net with the point symbol of (44·62)(44·64·82) (Figure 5d). Until now, only one La(III) coordination polymer with xww topology was reported in known complexes.22 3182

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Figure 5. (a) The coordination environments of the Zn(II) atoms in 5. Symmetry codes are #1: −x, 1 − y, 2 − z; #2: −x, 2 − y, 2 − z; #3: x, 1.5 − y, 0.5 + z. (b) 2D layer in 5 viewed along the a and b axes, respectively. (c) View of the 1D channels in the layer of 5. (d) xww Net of 5 (the azure and blue spheres represent the dinuclear clusters and L4−, respectively; the purple rods represent bpy ligands).

cluster can be viewed as a 6-connected node, and each L4− acts as a 4-connected tetrahedral node due to the two almost vertical isophthalate units of L4−. Thus, 6 can be rationalized as a (4,6)-connected 3D net with the point symbol of (44·5·6)(44·53·64·74) (Figure 6b). To the best our knowledge, this topology has been unobserved before this work. Coordination Modes and Configurations of L 4− Ligand. The above results indicate that L4− can adopt various coordination modes and configurations in the self-assembly process of coordination polymers, as shown in Figure 7. In 1 and 3, four carboxylate groups of one L4− all adopt monodentate coordination modes to link four Zn(II) atoms (mode I). In 2, one L4− connects six Zn(II) atoms through bis(bridging-bidentate) and bis(chelating-bidentate) coordination modes (model II). However, the two isophthalate units of L4− in 1 are almost vertical compared to the nearly parallel

Crystal Structure of [Zn2(L)(bpe)(H2O)]·3H2O (6). 6 shows the similar structural architectures with 5 due to their approximate cell parameters (Table 1). The main difference is the different coordination environment around Zn2 atom, as shown in Figure 6a. In 6, the dinuclear cluster also exists, in which the Zn2 atom is five-coordinated by one chelating and two bridging carboxylate groups of three L4− and one bpe ligand, forming a trigonal-bipyramidal geometry (τ = 0.920).15 The carboxylate group with the monatomic η2-bridged mode in 5 does not appear in 6, which instead links Zn1 atom with the monodentate η1-coordinated mode, inducing the decrease of the coordination number around the Zn2 atom in 6. In addition, the terminal aqua ligand around the Zn2 atom in 5 is replaced by the bpe ligand. As a result, the 1D channels as shown in the 2D layers of 5 do not exist in 6 because of the occupation of bpe ligands. Topologically, each dinuclear Zn(II) 3183

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Figure 6. (a) The coordination environments of the Zn(II) atoms in 6. Symmetry codes are #1: −x, −y, −z; #2: −x, 1−y, −z; #3: x, 0.5 − y, −0.5 + z. (b) Topological structure of 6 (the azure and blue spheres represent the dinuclear clusters and L4−, respectively; the purple and green rods represent bpe ligands).

Figure 7. Coordination modes of L4− in complexes 1−6.

configurations in 2 and 3, which leads to the tetrahedral node of L4− in 1 rather than the square-planar nodes in 2 and 3. In 4, two independent L4− show the different coordination modes: one bridges four Zn(II) atoms through four carboxylate groups with chelating-bidentate and monodentate modes (mode III), while the other connects four Zn(II) atoms with chelatingbidentate modes (mode IV). In 6, four carboxylate groups of one L4− bridge six Zn(II) atoms by three different coordination modes, including two bridging-bidentate, one chelatingbidentate, and one monodentate modes (mode V). The coordination fashion of L4− in 5 is similar to 6, except that the monodentate carboxylate group in 6 becomes the monatomic bridge mode (mode VI) in 5. In addition, the two isophthalate units of L4− are almost vertical in 1, 5, and 6, which form 4-connected tetrahedral nodes, whereas the two isophthalate units of L4− in 2 and 3 are almost parallel, leading to 4-connected square-planar nodes. The different coordination modes and configurations of L4− impose a remarkable effect on the various structures of 1−6. Effects of the Pyridine-Based Coligands on the Structures. Complexes 2−6 show the effects of the pyridine-based coligands on their frameworks, which can relate to the lengths of pyridine ligands. The coordination of py in 2 increases the coordination number of the Zn(II) center. In 3, bpe acts as a linear linker, and the framework of 3 is simplified

as a distorted 4-connected bbf net. Additionally, in 2 and 3, there exist cavities, which are occupied by the coordinated pyridine molecules and the free bpe guests, respectively. In 4, two types of L4− ligands bridge four Zn(II) centers to form a 2D jagged layer, which is extended by bpe linkers to form a 2D bilayer. When bpy in 5 was displaced by bpe in 6, the (4,5)connected net of 5 is increased to (4,6)-connected net of 6, due to the coordination of more bpe. Meanwhile, the incorporations of bpy and bpe linkers in 5 and 6 render that the 2D layers based on L4− connecting dinuclear Zn(II) clusters are further extended into 3D frameworks. These results indicate that the lengths of pyridine-based coligands improve the dimensions and complexities of the frameworks. TGA and Luminescent Properties. The PXRD patterns from the experimental samples of complexes 1−6 are in agreement with the simulated ones from their respective singlecrystal structures (Figure S7 of the Supporting Information), confirming the phase purity of the complexes. In order to characterize the thermal stability of 1−6, TGA were carried out under a nitrogen atmosphere (Figure S8 of the Supporting Information). TGA curve of 1 exhibits an initial weight loss (19.1%) from 30 to 305 °C, corresponding to the releases of [(CH3)2NH2]+ cations and lattice water molecules (calcd 19.5%). The further heating leads to the loss of L4−. 2 has no weight loss before 357 °C, and then began to release py 3184

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Figure 8. Solid-state emission spectra of H4L and complexes 1−6 at room temperature.

and L4− ligands with a significant weight loss in 357−590 °C. For 3, an initial weight loss of 23.0% from 30 to 335 °C is assigned to the losses of six water molecules and one free bpe molecule (calcd 23.3%), followed by the structural collapse due to the removal of L4−. 4 shows a first weight loss of 20.7% from 30 to 364 °C, corresponding to the removals of one DMA and six water molecules (calcd 20.1%), in which the sharp weight loss of 9.4% before 120 °C results from the release of the free water molecules (calcd 9.3%). The second weight loss step from 364 to 670 °C is attributed to the decompositions of L4− and bpe ligands. For 5, a weight loss of 10.7% below 135 °C is due to the releases of 2.5 free water and two-coordinated water molecules (obsd 10.7%, calcd 10.8%), and the framework starts to decompose at above 185 °C. 6 shows the first weight loss in the range of 55−360 °C, corresponding to the removals of one bpe and four water molecules (obsd 29.6%, calcd 30.0%), and then the framework decomposes. To further evaluate the structural stability of the networks, complexes 1−6 were heated at different temperatures (1, 220 °C; 2, 250 °C; 3 and 4, 200 °C; 5, 150 °C; and 6, 200 °C) under vacuum (∼1 Pa) for 5 h to remove the solvents (Figure S9 of the Supporting Information). The PXRD patterns of the desolvated samples of 1, 3 (the uncoordinated bpe molecule remains in the framework at this temperature), 4 and 6 display sharp and intense peaks with almost neglectable peak shifts, thus indicating the structural stability of these four complexes after desolvation. However, the PXRD pattern of the desolvated 5 shows weakening and disappearance of some diffraction peaks, implying partial structural collapse or distortion after desolvation. In 2, there are no solvent molecules, and the PXRD pattern obtained after heating the complex at 250 °C under vacuum confirms that the structure is stable at this temperature. Luminescent complexes have received remarkable attention in view of various potential applications, such as in chemical sensors, photochemistry, electroluminescent display, and so on.7b,d,9b,23−26 The solid-state luminescent emission properties of H4L, bpy, bpe, and complexes 1−6 at room temperature were investigated (Figure 8 and Table 2). The main emission peaks of H4L, bpy, and bpe are at 492 nm (λex = 321 nm), 350 nm (λex = 300 nm), and 370 nm (λex = 300 nm), respectively, which can be assigned to the π* → n or π* → π transitions.6c,24 Upon photoexcitation, 1−6 display the maximum emission peaks at 409 nm (λex = 281 nm), 421 nm (λex = 300 nm), 413 nm (λex = 300 nm), 430 nm (λex = 300 nm), 432 nm (λex = 300 nm), and 408 nm (λex = 300 nm), respectively. Comparing with the emissions of H4L, bpy and bpe ligands, the emission bands of 1−6 indicate significant blue/red shifts, which can be

Table 2. Wavelengths of the Emission Maxima and Excitation (nm) complex

1

2

3

4

5

6

λem λex ligand λem λex

409 281 H4L 492 321

421 300

413 300 bpy 350 300

430 300

432 300 bpe 370 300

408 300

attributed to the charge transfer of L4− and/or pyridine-based ligands to Zn(II) centers (LMCT).24c,25 The emission shoulder peak at 518 nm of 5 is similar to that of the free H4L, which is ascribed to the intraligand π* → π charge transfer.6c,23b,24a,25b The different emission energies of 1−6 are probably attributable to the different coordination configurations of ligand L4− and the coordination environments around the Zn(II) centers, which induce different HOMO−LUMO energy gaps. Complexes 1 (λem = 409 nm) and 6 (λem = 408 nm) show blue shifts of emission bands in comparison with those of 2 (λem = 421 nm) and 3 (λem = 413 nm), which can be ascribed to the tetrahedral coordination configurations of L4− in 1 and 6 rather than the square-planar configurations in 2 and 3. Notably, although L4− also features tetrahedral coordination configurations in 4 (λem = 430 nm) and 5 (λem = 432 nm), their luminescence displays obvious red shifts compared to those of 1 and 6, which should arise from the coexistence of the higher 5- and 6-coordinated environments of Zn(II) centers in 4 and 5, while only 4- or 5-coordinated Zn(II) centers exist in 1 and 6. The differences in emission spectra associated with the different local environment around metal ions were also observed in other Zn(II)-based complexes.24a,c,26

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CONCLUSION In summary, six new Zn(II) coordination polymers have been successfully constructed by employing a flexible aliphatic amine carboxylate ligand 5,5′-(p-xylylenediamino)-1,1′,3,3′-(benzenetetracarboxylate) (L4−) with different lengthed pyridine-based coligands, which show diverse structures from 2D bilyers to 3D 4-, (4,4)-, (4,5)-, and (4,6)-connected frameworks. The diversity of the coordination modes and configurations of L4−, the lengths of pyridine-based ligands affect cooperatively the structures of coordination polymers with interesting and varying motifs. H4L has a flexible −NHCH2PhCH2NH− spacer between the two isophthalate units, which provides a changeable bridging orientation. When the two isophthalate units of L4− are vertical or parallel as a 4-connected tetrahedral or square-planar node, 1−3 exhibit 4-connected dia, pts, and 3185

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(7) (a) Aakeröy, C. B.; Champness, N. R.; Janiak, C. CrystEngComm 2010, 12, 22. (b) Habib, H. A.; Hoffmann, A.; Höppe, H. A.; Steinfeld, G.; Janiak, C. Inorg. Chem. 2009, 48, 2166. (c) Henninger, S. K.; Habib, H. A.; Janiak, C. J. Am. Chem. Soc. 2009, 131, 2776. (d) Habib, H. A.; Hoffmann, A.; Höppe, H. A.; Janiak, C. Dalton Trans. 2009, 1742. (e) Wisser, B.; Chamayou, A. C.; Miller, R.; Scherer, W.; Janiak, C. CrystEngComm 2008, 10, 461. (8) Zhang, L. H.; Yang, J. Z. Kristallogr. 2010, 225, 407. (9) (a) Habib, H. A.; Sanchiz, J.; Janiak, C. Inorg. Chim. Acta 2009, 362, 2452. (b) Habib, H. A.; Sanchiz, J.; Janiak, C. Dalton Trans. 2008, 1734. (c) Wisser, B.; Lu, Y.; Janiak, C. Z. Anorg. Allg. Chem. 2007, 633, 1189. (10) (a) Kieltyka, R.; Englebienne, P.; Fakhoury, J.; Autexier, C.; Moitessier, N.; Sleiman, H. F. J. Am. Chem. Soc. 2008, 130, 10040. (b) Kong, D.; Zon, J.; McBee, J.; Clearfield, A. Inorg. Chem. 2006, 45, 977. (c) Maji, T.; Mostafa, K. G.; Matsuda, R.; Kitagawa, S. J. Am. Chem. Soc. 2005, 127, 17152. (d) Marinho, M. V.; Yoshida, M. I.; Guedes, K. J.; Krambrock, K.; Bortoluzzi, A. J.; Hörner, M.; Machado, F. C.; Teles, W. M. Inorg. Chem. 2004, 43, 1539. (e) Jin, K.; Huang, X.; Pang, L.; Li, J.; Appel, A.; Wherland, S. Chem. Commun. (Cambridge, U.K.) 2002, 2872. (11) (a) Sheldrick, G. M. SHELXS-97, Program for Solution of Crystal Structures; University of Göttingen: Germany, 1997. (b) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; University of Göttingen: Germany, 1997. (c) Madison, W. Bruker APEX2 Software, version 2.0-1, Bruker AXS Inc.: Fitchburg, WI, 2005. (12) Delgado-Friedrichs, O.; O’Keeffe, M. Acta Crystallogr., Sect. A 2005, 61, 358. (13) (a) Wang, Z. L.; Fang, W. H.; Yang, G. Y. Chem. Commun. (Cambridge, U.K.) 2010, 46, 8216. (b) Park, J. H.; Lee, W. R.; Ryu, D. W.; Lim, K. S.; Jeong, E. A.; Phang, W. J.; Koh, E. K.; Hong, C. S. Cryst. Growth Des. 2012, 12, 2691. (c) He, J.; Chen, H.; Xiao, D.; Sun, D.; Zhang, G.; Yan, S.; Xin, G.; Yuan, R.; Wang, E. CrystEngComm 2011, 13, 4841. (d) Sharma, M. K.; Lama, P.; Bharadwaj, P. K. Cryst. Growth Des. 2011, 11, 1411. (14) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7. (15) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349. (16) (a) Chen, B. L.; Ockwig, N. W.; Fronczek, F. R.; Contreras, D. S.; Yaghi, O. M. Inorg. Chem. 2005, 44, 181. (b) Delgado Friedrichs, O.; O’Keeffe, M.; Yaghi, O. M. Solid State Sci. 2003, 5, 73. (c) Lu, Y. B.; Wang, M. S.; Zhou, W. W.; Xu, G.; Guo, G. C.; Huang, J. S. Inorg. Chem. 2008, 47, 8935. (17) (a) Hu, J. S.; Shang, Y. J.; Yao, X. Q.; Qin, L.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G.; Xue, Z. L. Cryst. Growth Des. 2010, 10, 2676. (b) Kostakis, G. E.; Hewitt, I. J.; Ako, A. M.; Mereacre, V.; Powell, A. K. Philos. Trans. R. Soc., A 2010, 368, 1509. (18) (a) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319. (b) Eddaoudi, M.; Li, H.; Yaghi, O. M. J. Am. Chem. Soc. 2000, 122, 1391. (19) (a) Furukawa, H.; Koh, N.; Go, Y. B.; Aratani, N.; Choi, S. B.; Choi, E.; Yazaydin, A. Ö .; Snurr, R. Q.; O’Keeffe, M.; Kim, J.; Yaghi, O. M. Science 2010, 329, 424. (b) Koh, K.; Van Oosterhout, J. D.; Roy, S.; Wong-Foy, A. G.; Matzger, A. J. Chem. Sci. 2012, 3, 2429. (c) Koh, K.; Wong-Foy, A. G.; Matzger, A. J. J. Am. Chem. Soc. 2010, 132, 15005. (d) Koh, K.; Wong-Foy, A. G.; Matzger, A. J. J. Am. Chem. Soc. 2009, 131, 4184. (e) Oisaki, K.; Li, Q.; Furukawa, H.; Czaja, A. U.; Yaghi, O. M. J. Am. Chem. Soc. 2010, 132, 9262. (f) Li, H.; Eddaoudi, M.; Yaghi, O. M. Nature 1999, 402, 276. (g) Rosi, N. L.; Kim, J.; Eddaoudi, M.; Chen, B.; O’Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2005, 127, 1504. (20) Mercury 1.4.2; Cambridge Crystallographic Data Centre: Cambridge, U.K., 2001−2005. (21) (a) Xu, X. B.; Lan, F. F.; Yang, S. Y.; Li, M.; Huang, R. B.; Zheng, L. S. J. Chem. Crystallogr. 2010, 40, 551. (b) Munakata, M.; Wu, L. P.; Yamamoto, M.; Kuroda-Sowa, T.; Maekawa, M. J. Am. Chem. Soc. 1996, 118, 3117. (c) Taylor, R.; Kennard, O.; Versichel, W. Acta Crystallogr., Sect. B 1984, 40, 280.

bbf nets, respectively. 5 and 6 show similar 3D structural patterns and feature a rare (4,5)-connected xww net and an unprecedented (4,6)-connected framework, respectively. 1−6 display strong luminescence with different energies, which may potentially be used in the development of the luminescent materials.

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ASSOCIATED CONTENT

S Supporting Information *

1

H NMR, 13C NMR, and IR spectra of H4L, additional structural figures of complexes 3 and 5, PXRD patterns and TGA curves of complexes 1−6, and selected bond lengths and angles. CCDC reference numbers are 933120−933125. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*(L.H.) E-mail: [email protected]. (B.W.) E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 21271149 and 21001088) and the Scientific Research Projects of Shaanxi Education (Grant 2010JK872).

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REFERENCES

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