DOI: 10.1021/cg900134f
Structural Versatility of Eight Zinc(II) Coordination Polymers Constructed with a Long Flexible Ligand 1,4-Bis(1,2,4-triazol-1-yl)butane
2009, Vol. 9 3997–4005
Xun-Gao Liu, Li-Yan Wang, Xia Zhu, Bao-Long Li,* and Yong Zhang Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry and Chemical Engineering and Material Science, Soochow University, Suzhou 215123, P. R. China Received February 5, 2009; Revised Manuscript Received July 7, 2009
ABSTRACT: The reaction of 1,4-bis(1,2,4-triazol-1-yl)butane (btb) with Zn(II) salts yields four coordination polymers from a one-dimensional (1D) zigzag chain [Zn(btb)(H2O)3(SO4)]n (1), undulated two-dimensional (2D) (4,4) network {[Zn(btb)2(H2O)2](NO3)2 3 2H2O}n (2), to a 3-fold interpenetrating three-dimensional (3D) R-polonium cubic network {[Zn(btb)3](BF4)2}n (3) and {[Zn(btb)3](ClO4)2}n (4). 1 further constructs a novel 3-fold interpenetrating 3D hydrogen bonding network. Four coordination polymers {[Zn(btb)(bdc)] 3 5H2O}n (5), {[Zn(btb)(H2O)4][Zn(btb)(btc)]2 3 4H2O}n (6), {[Zn2(btb)(btec)(H2O)2] 3 2H2O}n (7), and {[Zn(btb)2(H2O)2](H4btec) 3 (H2btec) 3 2H2O}n (8) were obtained with btb and 1,4-benzenedicarboxylate (bdc), 1,3,5-benzenetricarboxylate (btc), and 1,2,4,5-benzenetetracarboxylate (btec). 5 is a 2D (6,3) network with six Zn(II) atoms at six corners and four bdc and two double btb at six edges. In 6, btb and btc link two kinds of Zn(II) atoms to form an undulated 2D network. Each 2D network polycatenates two other identical networks, thus giving a rare (2D f 3D) parallel polycatenation network. 7 is a (3,4)-connected pillared-layer 3D porous network where [Zn2(btec)]n 2D layers are interlinked by btb pillars. 8 is comprised of [Zn(btb)2(H2O)2]n2nþ cationic chains, H2btec2- anions, neutral H4btec, and lattice water molecules. A novel 3D hydrogen bonding network of 8 is further constructed. The btb ligands adopt three conformations, namely, the completely anti (anti-anti-anti) conformation in 1 and 4, the anti-anti-gauche conformation in 2, 5, 6, and 8, and the gauche-anti-gauche conformation in 3, 4, and 7. Furthermore, thermal stability and luminescent properties were investigated.
Introduction Open metal-organic frameworks (MOFs) have gained wide attention not only because of their variety of architectures and topologies, but also their potential application in magnetism, electric conductivity, molecular adsorption, molecular recognition, and catalysis.1 Design of effective ligands and the proper choice of metal centers are the keys to design and construct novel metal-organic frameworks. However, predicting the final supramolecular framework is difficult. Many factors such as the coordination geometry of the central atom, the structural characteristics of the ligand molecule, the solvent system, and the counterions can play the key role in the construction of the coordination networks. In contrast to rigid ligands that have little or no conformational changes when they interact with the metal ions, the flexible ligands have more possible coordination modes than the rigid ones because the flexible ligands can adopt different conformations according to the geometric needs of the different metal ions.2 The anions serve more than merely balancing the charges of a cationic complex and influence the structure of a supramolecular system through coordination to the metal.3 Dunbar and coworkers reported that the reaction of 3,6-di(2-pyridyl)-1,2,4,5tetrazine with first-row transition metals could yield a molecular square and a pentagon with one anion accommodated in the cavities of the polygons. In this case, anions function as templates through anion-π interactions.4 Moreover, metalorganic coordination polymers constructed from aromatic polycarboxylate ligands, such as 1,4-benzenedicarboxylate *Corresponding author. E-mail:
[email protected]. r 2009 American Chemical Society
(bdc),5-7 1,3,5-benzenetricarboxylate (btc),8,9 and 1,2,4,5-benzenetetracarboxylate (btec),10,11 have been extensively studied because of their diversity coordination modes and sensitivity to pH values of the carboxylate groups. On the other hand, a large number of mononuclear, oligonuclear, and polynuclear transition metal complexes of 1- and 4substituted 1,2,4-triazole derivatives have been synthesized and characterized due to their magnetic properties and novel topologies.12 The combination of 1- or 4-substituted 1,2,4-triazole derivatives and aromatic polycarboxylate ligands can result in novel topologies, magnetic and luminescence properties.13 In our previous attempt to investigate the design and control of coordination networks, we synthesized a number of novel coordination polymers with flexible triazole ligands such as 1,2-bis(1,2,4-triazol-1-yl)ethane (bte)14 and 1,4-bis(1,2,4-triazol-1-methyl)benzene (bbtz).15 1,4-Bis(1,2,4-triazol-1-yl)butane (btb)13c,13d,16 (Chart 1) is a longer and more flexible ligand compared to bte and bbtz. In order to investigate the influence of the inorganic anions on the structures of coordination polymers with long flexible ligand btb and design novel topologies with the long flexible ligand btb and aromatic polycarboxylate ligands, 1,4-benzenedicarboxylate (bdc), 1,3,5-benzenetricarboxylate (btc), and 1,2,4,5-benzenetetracarboxylate (btec) (Chart 2), eight zinc(II) coordination polymers [Zn(btb)(H2O)3(SO4)]n (1), {[Zn(btb)2(H2O)2](NO3)2 3 2H2O}n (2), {[Zn(btb)3](BF4)2}n (3), {[Zn(btb)3](ClO4)2}n (4), {[Zn(btb)(bdc)] 3 5H2O}n (5), {[Zn(btb)(H2O)4][Zn(btb)(btc)]2 3 4H2O}n (6), {[Zn2(btb)(btec)(H2O)2] 3 2H2O}n (7), and {[Zn(btb)2(H2O)2](H4btec) 3 (H2btec) 3 2H2O}n (8) were synthesized. The crystal structures are presented and discussed. Furthermore, the thermal stability and the luminescent properties of these compounds have been investigated. Published on Web 07/27/2009
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Chart 1. Three Conformations of btb Ligand
calc. for C24H36Cl2N18O8Zn: C, 34.28; H, 4.31; N, 29.99. Found: C, 34.21; H, 4.34; N, 29.89%. IR data (cm-1): 3141m, 2971w, 1751m, 1520s, 1450m, 1373m, 1281s, 1095s, 1026w, 1003s, 787m, 748m, 679s, 625s, 463w. Synthesis of {[Zn(btb)(bdc)] 3 5H2O}n (5). A solution of H2bdc (0.033 g, 0.2 mmol) in 10 mL of H2O was adjusted to approximately pH 6 with dilute NaOH solution. Then btb (0.039 g, 0.2 mmol) in 10 mL of CH3OH was added. This mixture was added to one side of the “H-shaped” tube, and Zn(NO3)2 3 6H2O (0.060 g, 0.2 mmol) in 20 mL of water was added to the other side of the “H-shaped” tube. Colorless crystals 5 were obtained in 76% yield (0.078 g) after one month. Anal. calcd. for C16H26N6O9Zn: C, 37.55; H, 5.12; N, 16.42%. Found: C, 37.42; H, 5.01; N, 16.29. IR data (cm-1): 3448m, 3111m, 2952w, 1561s, 1406s, 1282m, 1131m, 1001m, 894w, 828m, 747m, 509w, 447w. Synthesis of {[Zn(btb)(H2O)4][Zn(btb)(btc)]2 3 4H2O}n (6). A solution of H3btc (0.084 g, 0.4 mmol) in 10 mL of H2O was adjusted to approximately pH 5 with dilute Et3N solution and btb (0.116 g, 0.6 mmol) in 10 mL of CH3OH was added. Then Zn(NO3)2 3 6H2O (0.180 g, 0.6 mmol) in 10 mL water was added with continuous stirring. The mixture were filtered and the filtrate was allowing to stand for about one week. Colorless crystals of 6 were obtained in 26% yield (0.070 g). Anal. calcd. for C42H58N18O20Zn3: C, 37.90; H, 4.39; N, 18.94%. Found: C, 37.76; H, 4.25; N, 18.83. IR data (cm-1): 3380m, 1628vs, 1567s, 1536m, 1405m, 1335s, 1289m, 1204m, 1135m, 1057w, 996w, 903w, 772m, 733m, 641m, 594w, 455w. Synthesis of {[Zn2(btb)(btec)(H2O)2] 3 2H2O}n (7). A solution of H4btec (0.051 g, 0.2 mmol) in 10 mL of H2O was adjusted to approximately pH 5 with dilute Et3N solution and Zn(NO3)2 3 6H2O (0.120 g, 0.4 mmol) in 10 mL of water was added with continuous stirring. The mixture was filtered and the filtrate was added to a tube. Then btb (0.038 g, 0.2 mmol) in 10 mL of CH3OH was carefully added above the filtrate in the tube. Colorless crystals of 7 were obtained after three weeks in 79% yield (0.102 g). Anal. calcd. for C18H22N6O12Zn2: C, 33.51; H, 3.44; N, 13.02%. Found: C, 33.63; H, 3.53; N, 13.00. IR data (cm-1): 3350m, 1605vs, 1537s, 1497s, 1428s, 1382vs, 1328s, 1281m, 1142m, 996m, 926w, 895w, 818m, 764m, 679m, 619m, 533w. Synthesis of {[Zn(btb)2(H2O)2](H4btec) 3 (H2btec) 3 2H2O}n (8). A solution of H4btec (0.076 g, 0.3 mmol) in 10 mL of H2O was adjusted to approximately pH 3 with dilute Et3N solution and btb (0.058 g, 0.3 mmol) in 10 mL of CH3OH was added. Then Zn(NO3)2 3 6H2O (0.060 g, 0.2 mmol) in 10 mL of water was added with continuous stirring. The mixture was filtered and the filtrate was allow to stand for about two weeks. Colorless crystals of 8 were obtained in 37% yield based on btb and H4btec (0.057 g). Anal. calcd. for C36H42N12O20Zn: C, 42.05; H, 4.12; N, 16.35%. Found: C, 41.94; H, 4.05; N, 16.29. IR data (cm-1): 3519m, 3450m, 1737s, 1698s, 1559vs, 1497m, 1366m, 1289m, 1258w, 1135m, 1111m, 1057w, 996w, 888w, 841w, 764m, 710m, 641w, 602w, 432w. X-ray Crystallography. Suitable single crystals of compounds 18 were carefully selected under an optical microscope and glued to thin glass fibers. The diffraction data were collected on a Rigaku Mercury CCD diffractometer with graphite monochromated MoKR radiation (λ = 0.71073 A˚). Intensities were collected by the ω scan technique. The structures were solved by direct methods and refined with full-matrix least-squares technique (SHELXTL-97).18 The location occupancy factors of oxygen atoms O(5), O(6), O(7), O(8), O(9), and O(10) of disordered NO3- anions of compound 2 are assigned 0.70. The location occupancy factors of oxygen atoms O(11), O(12), O(13), O(14), O(15), and O(16) of disordered NO3anions are assigned 0.30. The location occupancy factors of oxygen atoms O(1), O(2), O(3), O(4), O(3B), and O(4B) of disordered ClO4anions of compound 4 are assigned as 1.0, 1.0, 0.80, 0.80, 0.20, and 0.20. The positions of hydrogen atoms of btb were determined with theoretical calculation. The parameters of the crystal data collection and refinement of 1-8 are given in Tables 1 and 2. Selected bond lengths and bond angles are listed in Table S1, Supporting Information.
Chart 2. The Polycarboxylate Ligands in 5-8
Experimental Section Materials and General Methods. All reagents were of analytical grade and used without further purification. 1,4-Bis(1,2,4-triazol-1yl)butane (btb) was synthesized according to a literature method.17 Elemental analyses for C, H, and N were performed on a PerkinElmer 240C analyzer. IR spectra were obtained for KBr pellets on a Nicolet 170SX FT-IR spectrophotometer in the 4000-400 cm-1 region. Thermogravimetric analysis (TGA) was measured on a Thermal Analyst 2100 TA Instrument and SDT 2960 Simutaneous TGA-DTA Instrument in flowing dinitrogen at a heating rate 10 °C/min. The luminescence measurements were carried out in the solid state at room temperature, and the spectra were collected with a PerkinElmer LS50B spectrofluorimeter. Synthesis of [Zn(btb)(H2O)3(SO4)]n (1). A methanolic solution (15 mL) of btb (0.192 g, 1.0 mmol) was added to an aqueous solution (15 mL) of Zn(SO4) 3 7H2O (0.290 g, 1.0 mmol) with stirring. The colorless single crystals 1 were obtained after the mixture was allowed to stand at room temperature for two weeks in 78% yield (0.317 g). Anal. calc. for C8H18N6O7SZn: C, 23.57; H, 4.45; N, 20.62. Found: C, 23.55; H, 4.53; N, 20.48%. IR data (cm-1): 3414m, 3128m, 2959w, 1628w, 1535m, 1388m, 1288m, 1126s, 1087s, 1003m, 879m, 784w, 679w, 652m, 459w. Synthesis of {[Zn(btb)2(H2O)2](NO3)2 3 2H2O}n (2). A methanolic solution (15 mL) of btb (0.192 g, 1.0 mmol) was added to an aqueous solution (15 mL) of Zn(NO3)2 3 6H2O (0.150 g, 0.5 mmol) with stirring. The colorless single crystals 2 were obtained after the mixture was allowed to stand at room temperature for two weeks in 61% yield (0.197 g). Anal. calc. for C16H32N14O10Zn: C, 29.75; H, 4.99; N, 30.37. Found: C, 29.57; H, 5.03; N, 30.62%. IR data (cm-1): 3457m, 2878w, 1528m, 1381s, 1211w, 1134s, 1011s, 903w, 648m, 463w. Synthesis of {[Zn(btb)3](BF4)2}n (3). A 10 mL aqueous solution of Zn(BF4)2 3 6H2O (0.175 g, 0.5 mmol) was added to a tube, and then a 10 mL CH3OH solution of btb (0.192 g, 1.0 mmol) was slowly added to the tube above the aqueous solution. Colorless crystals 3 were obtained after two weeks in 74% yield based on btb (0.203 g). Anal. calc. for C24H36B2F8N18Zn: C, 35.34; H, 4.45; N, 30.92. Found: C, 35.27; H, 4.48; N, 31.01%. IR data (cm-1): 3444m, 3135w, 2955w, 1531m, 1280m, 1209w, 1126s, 1083s, 1002w, 740m, 642w, 482w. Synthesis of {[Zn(btb)3](ClO4)2}n (4). A 10 mL aqueous solution of Zn(ClO4)2 3 6H2O (0.132 g, 0.5 mmol) was added to a tube, and then a 10 mL CH3OH solution of btb (1.0 mmol) was slowly added to the tube above the aqueous solution. Colorless crystals 4 were obtained after two weeks in 71% yield based on btb (0.196 g). Anal.
Results and Discussion Description of the Crystal Structures. [Zn(btb)(H2O)3(SO4)]n (1). The structure of 1 is a one-dimensional (1D)
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Table 1. Crystallographic Data for 1-4 formula fw crystal system space group temp (K) a (A˚) b (A˚) c (A˚) R (o) β (o) γ (o) V (A˚3) Z Fcalc (g/cm3) μ (mm-1) F(000) reflections collected unique reflections parameters goodness of fit R1 [I > 2σ(I)] wR2 (all data)
1
2
3
4
C8H18N6O7SZn 407.71 orthorhombic Pnma 153(2) 8.5223(9) 17.1570(19) 10.5244(11) 90 90 90 1538.8(3) 4 1.760 1.778 840 13942 1460 [R(int) = 0.0310] 127 1.083 0.0285 0.0767
C16H32N14O10Zn 645.93 monoclinic P21/n 193(2) 10.9909(17) 16.420(2) 15.714(2) 90 105.064(4) 90 2738.5(7) 4 1.567 0.973 1344 26612 4999 [R(int) = 0.0230] 456 1.052 0.0323 0.0949
C24H36B2F8N18Zn 815.70 trigonal P3 153(2) 10.894(2) 10.894(2) 8.4503(16) 90 90 120 868.5(3) 1 1.560 0.799 418 8616 1079 [R(int) = 0.0370] 82 1.083 0.0421 0.1032
C24H36Cl2N18O8Zn 840.98 trigonal R3 h 153(2) 18.9230(17) 18.9230(17) 25.307(2) 90 90 120 7847.9(12) 9 1.601 0.932 3906 25963 3210 [R(int) = 0.0456] 258 1.095 0.0524 0.1592
Table 2. Crystallographic Data for 5-8 formula fw crystal system space group temp (K) a (A˚) b (A˚) c (A˚) R (o) β (o) γ (o) V (A˚3) Z Fcalc (g/cm3) μ (mm-1) F(000) reflections collected unique reflections parameters goodness of fit R1 [I > 2σ(I)] wR2 (all data)
5
6
7
8
C16H26N6O9Zn 511.80 triclinic P1 193(2) 9.3644(19) 10.929(3) 12.025(3) 105.566(3) 94.993(3) 107.268(3) 1113.5(4) 2 1.527 1.162 532 11057 4054 [R(int) = 0.0189] 298 1.080 0.0463 0.1257
C42H58N18O20Zn3 1331.17 triclinic P1 298(2) 9.5864(18 10.2309(18) 14.952(3) 97.849(3) 106.200(4) 101.286(3) 1352.2(4) 1 1.635 1.413 686 13259 4919 [R(int) = 0.0434] 408 1.091 0.0610 0.1481
C18H22N6O12Zn2 645.16 monoclinic P21/n 173(2) 8.6296(18) 9.608(2) 14.497(3) 90 93.097(5) 90 1200.3(4) 2 1.785 2.074 656 11297 2197 [R(int) = 0.0503] 188 1.124 0.0549 0.1363
C36H42N12O20Zn 1028.19 triclinic P1 153(2) 8.0067(17) 9.8939(19) 14.203(3) 76.760(8) 83.927(9) 79.662(9) 1075.0(4) 1 1.588 0.668 532 10498 3896 [R(int) = 0.0205] 342 1.024 0.0294 0.0755
zigzag chain (Figure 1a). Zn1, O1, O3, O4, and S1 atoms are located at the symmetry plane of 1. Each Zn(II) atom displays a distorted octahedral coordination geometry {ZnN2O4}, coordinated by four oxygen atoms from three waters and one sulfate ion, and two triazole nitrogen atoms in cis-positions. Each btb ligand exhibits completely anti (anti-anti-anti) conformation. The btb ligands link the Zn(II) atoms to form a 1D zigzag chain with a Zn 3 3 3 Zn distance of 14.4269(11) A˚. There are intra- and interchain hydrogen bonding interactions between the coordinaton water molecules and the oxygen atoms of sulfate ions of adjacent chains (Table S2, Supporting Information). Each Zn(II) connects four other Zn(II) atoms from four other chains through the Zn-OSO3...H2O-Zn and Zn-H2O...O3SO-Zn hydrogen bonding interactions with the Zn...Zn distances of 8.522 A˚ (along the a direction) and 6.459 A˚, respectively (Figure 1b). Each Zn(II) center is 2connected through coordination bonding and 4-connected through hydrogen bonding. The overall Zn(II) is 6-connected. The overall topology of 1 is a novel three-dimensional (3D) hydrogen bonding network with the channel
dimensions of 14.43 17.97 A˚ (Figure 1c). Because of the porous nature of the single network, three equivalent 3D networks mutually interpenetrate each other to generate a 3-fold interpenetrating 3D network (Figure 1d). As to the best of our knowledge, such hydrogen bonding network is not reported until now.19 {[Zn(btb)2(H2O)2](NO3)2 3 2H2O}n (2). 2 is an undulated two-dimensional (2D) (4,4) network (Figure 2). Each Zn(II) atom is coordinated with four triazole nitrogen atoms, and two water molecules, in a distorted octahedral geometry {ZnN4O2}. All btb ligands show the anti-anti-gauche conformation. Each Zn(II) atom is square four-connected and extend to an undulated 2D (4,4) network. The Zn 3 3 3 Zn distances separation via btb are 9.8712(10) and 9.8884(10) A˚. There are hydrogen bonding interactions between the coordination water, lattice water molecules and the disordered nitrate anions (Table S3, Supporting Information). In the superposition structure, the 2D networks are stacked in an offset fashion so that the convex of one network can project into the concave of the other network (Figure S1, Supporting Information).
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Figure 1. (a) The 1D zigzag chain of 1, showing the coordination environment of Zn(II). (b) Showing the hydrogen bonding interactions of 1. (c) The 3D hydrogen bonding network of 1. The long sticks represent the btb ligands and the dotted lines represent the hydrogen bonds. (d) The novel 3-fold interpenetrating 3D hydrogen bonding network of 1. The long sticks represent the btb ligands and the dotted lines represent the hydrogen bonds.
Figure 2. The undulated 2D (4,4) network of 2.
{[Zn(btb)3](BF4)2}n (3) and {[Zn(btb)3](ClO4)2}n (4). The structures of 3 and 4 exhibit a similar 3-fold interpenetrating 3D R-polonium cubic network (Figure 3), the same as those of {[Cd(btb)3](ClO4)2}n and {[Cd(btb)3](PF6)2}n.16b However, {[Cd(btb)2(H2O)2](BF4)2}n shows a 3-fold interpenetrated diamondoid network.16b There is one kind of btb and Zn(II) atom in 3 (Figure S2, Supporting Information), but
there are two kinds of btb and Zn(II) atoms in 4 (Figure S3, Supporting Information). One kind of btb in 4 exhibits the gauche-anti-gauche conformation. The other kind of btb in 4 and btb in 3 show completely anti conformation. The Zn 3 3 3 Zn separations are 13.7872(19) A˚ in 3, 13.8029(10) and 13.8029(7) A˚ in 4. Each Zn(II) atom is an octahedral sixconnected and extends to form a 3D R-polonium cubic network. Because of the porous nature of the single network, three equivalent 3D networks mutually interpenetrate each other to generate a 3-fold interpenetrating 3D R-polonium cubic network. Though 3-fold interpenetrating networks exist, the microporous channels are still found, which are accommodated by the BF4- anions in 3 and the disordered ClO4- anions in 4. There are weak CH 3 3 3 F hydrogen bonding interactions in 3 (Table S4, Supporting Information) and CH 3 3 3 O hydrogen bonds interactions in 4 (Table S5, Supporting Information). These hydrogen bonding interactions further stabilize the crystal. {[Zn(btb)(bdc)] 3 5H2O}n (5). Compound 5 was briefly communicated on previously.13c Each Zn(II) atom displays a distorted tetrahedral coordination geometry {ZnN2O2}, coordinated by two oxygen atoms from two bdc, and two triazole nitrogen atoms. The bdc ligand exhibits the bismonodentate coordination mode and bridges two Zn(II) atoms (Chart 3a). The distances of Zn(1) 3 3 3 Zn(1B) and Zn(1) 3 3 3 Zn(1C) separation by bdc are 11.0467(21) and 10.9518(14) A˚ (Figure S4a, Supporting Information).
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Figure 3. (a) Schematic diagram of the R-polonium cubic network and (b) 3-fold interpenetrated R-polonium cubic network of 3 and 4.
Chart 3. Coordination Modes of bdc in 5 (a), btc in 6 (b), and btec in 7 (c)
The btb ligand shows the anti-anti-gauche conformation. Two btb ligands doubly bridge two Zn(II) atoms to form Zn2(btb)2 rings with a Zn(1) 3 3 3 Zn(1A) distance of 9.1663(15) A˚. If doubly bridging btb ligands are considered as a node, the Zn(II) center is a triagonal three-connected. The whole network is a special 2D (6,3) network, with six Zn(II) atoms at six corners and four bdc and two double btb at six edges (Figure 4, Figure S4b, Supporting Information). The disordered lattice water molecules fill the cavities. Wang and co-workers13b synthesized a coordination polymer [Zn2(bdc)2(btb)2](H2O)2 with a 3-fold interpenetrated diamondoid network, which has the same Zn/bdc/btb ratio as that of 5, and is a supramolecular isomer of 5. {[Zn(btb)(H2O)4][Zn(btb)(btc)]2 3 4H2O}n (6). 6 has an undulated 2D network (Figure 5a,b). There are two kinds of Zn(II) atoms and btb ligands (Figure S5a, Supporting Information). Zn1 is coordinated by four oxygen atoms from two chelating carboxylate groups and two triazole nitrogen atoms from two btb in the cis-positions in a distorted octahedral geometry {ZnN2O4}. Zn2 is coordinated by four oxygen atoms from four water and two triazole nitrogen atoms from two btb in the trans-positions in a distorted octahedral geometry {ZnN2O4}. Zn1 is four-connected but Zn2 is two-connected. One btb (C1-C8/N1-N6) exhibits the anti-anti-gauche conformation and connects Zn1 and Zn2 atoms (Zn1 3 3 3 Zn2 10.8253(16) A˚). The other btb (C9C12/N7-N9) shows the gauche-anti-gauche conformation
Figure 4. 2D (6,3) network of 5.
and links two Zn1 atoms (Zn1 3 3 3 Zn1D 12.6162(21) A˚) (Figure 5). The btc has three carboxylate groups, but it acts as bis(chelating) rod ligand to connect two Zn1 atoms (Zn1 3 3 3 Zn1A 10.2309(18) A˚) (Chart 3b). The remaining carboxylate group is not engaged in coordination but balances the charge of the structure. The btc and btb rods link the Zn(II) atoms and generate a 2D undulated network (Figure 5b and Figure S5b, Supporting Information). Quite remarkable is that there are two distinct rings (Figure 5a). One {Zn4(btc)2(btb)2} ring contains four Zn1 atoms, two btc molecules, and two gauche-anti-gauche btb ligands with dimensions of 10.23 12.62 A˚. The other {Zn6(btc)2(btb)4} ring contains four Zn1 and two Zn2 atoms, two btc molecules, two gauche-anti-gauche, and two antianti-gauche btb ligands with dimensions of 10.23 21.65 A˚. The 2D layers are strongly undulated with a total thickness of 23.1 A˚ (from the upper uncoordination COO group to the lower uncoordination COO groups) and effective thickness of 12.6 A˚ (from Zn(II) atoms to Zn (II) atoms bridged by btb) (Figure 5b and Figure S5b, Supporting Information). To minimize the big void cavities and stabilize the framework,
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Figure 5. (a) The undulated 2D network of 6, showing two kinds of distinct rings. (b) Viewing the undulated 2D network of 6 along the b direction. (c) Schematic diagram of the parallel polycatenation of three undulated 2D networks of 6.
the potential voids formed by a single 2D network show incorporation of other two identical networks, thus giving a 3-fold parallel interpenetrating network (Figure 5c). Each {Zn4(btc)2(btb)2} ring of one 2D layer is catenated two distinct {Zn6(btc)2(btb)4} rings of two other 2D layers (Figure S5c, Supporting Information). Each {Zn6(btc)2(btb)4} ring of one 2D layer is catenated two distinct {Zn4(btc)2(btb)2} rings of two other 2D layers (Figure S5d, Supporting Information). Compound 6 exhibits a rare polycatenated (2D f 3D) network, although catenated simple layers are relatively less common. To the best of our knowledge, only a few examples of (2D f 3D) entangled structures have been observed for polycatenating systems in parallel fashion. However, most of the studies have focused on the 3-connected (6,3) net and (4,4) nets due to their large voids.20 There are hydrogen bonding interactions between the COO groups of btc and the coordination water (O1 3 3 3 O7, O4 3 3 3 O8, O5 3 3 3 O7) inter-2D networks, the lattice water (O5 3 3 3 O10, O6 3 3 3 O9, O6 3 3 3 O10), between the coordination water and lattice water (O8 3 3 3 O9), and between the lattice water and triazole N atom (O9 3 3 3 N5) (Table S6, Supporting Information). These hydrogen bonding interactions further stabilize the 3D network. {[Zn2(btb)(btec)(H2O)2] 3 2H2O}n (7). Compound 7 possesses a novel (3,4) connected (Each Zn(II) center links two btec and one btb and each btec connects four Zn(II) atoms) three-dimensional network. Each Zn(II) center is coordinated by three oxygen atoms from two carboxylate groups and one water molecule, and one triazole nitrogen atom, in a distorted tetrahedral geometry (Figure S6a, Supporting Information). Four COO groups of a btec ligand all show the monodentate coordination mode. Each btec ligand connects four Zn(II) atoms through its four carboxylate groups (Chart 3c), resulting in a 2D [Zn2(btec)]n network (Figure 6a
and Figure S6b, Supporting Information) with Zn 3 3 3 Zn distances of 5.5164(9) and 9.5038(14) A˚. Each btb ligand exhibits the gauche-anti-gauche conformation. Each Zn(II) atom links a Zn(II) atom through one btb molecule with a Zn 3 3 3 Zn distance of 12.5087(19) A˚. The btb ligands pillar the 2D [Zn2(btec)]n networks generating a novel 3D network (Figure 6b). There are hydrogen bonding interactions between the coordination and lattice water molecules, between the coordination/lattice water molecules and carboxylate oxygen atoms of btec, and between the lattice water molecules and triazole nitrogen atoms (Table S7, Supporting Information). {[Zn(btb)2(H2O)2](H4btec) 3 (H2btec) 3 2H2O}n (8). 8 is comprised of the [Zn(btb)2(H2O)2]n2nþ cationic chains, H2btec2anions, neutral H4btec, and lattice water molecules (Figure S7, Supporting Information). In the cationic chain, each Zn(II) is coordinated by four triazole nitrogen atoms and two water molecules. Each btb ligand shows the anti-antigauche conformation and short building block with a Zn 3 3 3 Zn distance of 9.8939(19) A˚. Two btb ligands are wrapped around each other and are held together by Zn(II) atoms forming a 1D double stranded chain along the b direction with a rhombic window dimensions of 5.69 A˚ 8.64 A˚, and with the Zn 3 3 3 Zn distance of 9.8939(19) A˚, corresponding to the b axis translation. The 1D chains are parallel stacked along the a direction with the adjacent Zn 3 3 3 Zn distance of 8.0067(17) A˚, corresponding to the a axis translation, and extend along the c direction with the shortest Zn 3 3 3 Zn distance of 14.2035(28) A˚, corresponding to the c axis translation (Figure 7a). Because of the porous nature of the network, the part deprotonated H2btec2- anions are located at the rhombic windows which balance the charge of 1D cationic chains (Figure 7b). The neutral H4btec molecules are located at the interchains voids along the c axis. It is very interesting that
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Figure 7. (a) The packed diagram of 1D [Zn(btb)2(H2O)2]n2nþ cationic chains of 8. (b) The 3D hydrogen bonding network of 8. The dotted lines represent the hydrogen bonds. Figure 6. (a) A 2D [Zn2(btec)]n network of 7. (b) The pillared-layer 3D porous network of 7. The btec is simplified by showing only the carboxylate carbon atoms.
there are versatile hydrogen bonding interactions (Table S8, Supporting Information). There are versatile hydrogen bonding interactions between the H2btec2- anions and coordination water molecules (O2 3 3 3 O1, O5 3 3 3 O1), and the lattice water molecules (O3 3 3 3 O10), and neutral H4btec molecules (O2 3 3 3 O8), intra-H2btec anions (O3 3 3 3 O4). There are also hydrogen bonding interactions between the neutral H4btec molecules and lattice water molecules (O6 3 3 3 O10, O7 3 3 3 O10). Through these versatile hydrogen bonding interactions, a novel 3D hydrogen bonding network is constructed (Figure 7b). Such versatile hydrogen bonding network is unusual.19 To the best of our knowledge, no complexes that capture neutral H4btec molecules is reported, although a large number of btec complexes were synthesized.10,11 Thermal Stability. All compounds are stable and can retain crystallinity at room temperature for at least several weeks. TGA experiments were carried out to explore their thermal stability (Figure S8 and S9, Supporting Information). In the TGA curve of compound 1, the coordination water molecules were lost from 30 to 100 °C (observed: 12.31%; calculated 13.24%). The remaining substance is thermally stable upon heating to 300 °C. Then two main weight losses happened from 300 to 360 °C (observed: 17.26%) and from 360 to 448 °C (observed: 21.48%). The residue substance is 47.44% weight upon heating to 500 °C. No reasonable fragments can be assigned corresponding to the weight loss processes of 1.
The TGA curve of compound 2 shows the lattice water and coordination water molecules were lost from 60 to 110 °C (observed: 11.42%; calculated 11.15%). The remaining substance is thermally stable upon heating to 220 °C. 2 displays an explosive decomposition in the range of 220-285 °C (observed 70.77%). The residue substance may be ZnO upon heating to 500 °C (observed: 11.47%, calculated 12.60%). Compounds 3 and 4 were stable upon 260 and 274 °C, separatively. 3 displays a rapid decomposition in the range of 263-368 °C (observed 60.87%). The residue substance of 3 is 29.47% weight upon heating to 466 °C. 4 displays a rapid decomposition in the range of 276-350 °C (observed 52.71%). The residue substance of 4 is 40.39% weight upon heating to 493 °C. The lattice water molecules of compound 5 were lost from 30 to 80 °C. The framework of 5 maintains stability at 216 °C, followed by three main weight losses from 218 to 286 °C (observed: 10.02%), from 355 to 396 °C (observed: 19.61%), and from 396 to 500 °C (observed: 30.48%). The lattice water and coordination water molecules of compound 6 were lost from 50 to 130 °C. The framework of 6 maintains stablity at 197 °C. Then a series of weight losses occurred, which did not end until 500 °C. The lattice water and coordination water molecules of compound 7 were lost from 60 to 170 °C. The framework of 7 maintains stablity at 280 °C. Then continuous weight loss occurred, which did not end until 500 °C. The lattice water and coordination water molecules of compound 8 were lost from 50 to 135 °C. Then the continuous weight loss occurred, which did not end until 480 °C.
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The btb ligands adopt three different types of conformations, namely, the completely anti (anti-anti-anti) conformation in 1 and 4, the anti-anti-gauche conformation in 2, 5, 6, and 8, and the gauche-anti-gauche conformation in 3, 4, and 7. Furthermore, the thermal stability and luminescent properties were investigated. Acknowledgment. This work was supported by the Natural Science Foundation of China (No. 20671066), the Jiangsu Province (No. BK2006049), and the Funds of Key Laboratory of Organic Synthesis of Jiangsu Province.
Figure 8. The luminescent emission spectra of 1-4 in solid state.
Supporting Information Available: Selected bond lengths and angles, hydrogen bondings, additional figures for crystal structures, TGA, X-ray crystallographic file in CIF format. This material is available free of charge via Internet at http://pubs.acs.org.
References
Figure 9. The luminescent emission spectra of 5-8 in solid state.
Luminescent Properties. The solid state luminescent sepectra of 1-8 at room temperature were studied. Compounds 1, 2, 3 and 4 reveal the emission maxima at approximately 436, 434, 424, and 419 nm, respectively, upon excitation at 350 nm (Figure 8). The emissions of 1-4 can be attributed to the emission of ligand-to-metal charge-transfer (LMCT).16b,21 Compounds 5, 6, 7, and 8 reveal the emission maxima at approximately 420 and 439 nm, 403 and 410 nm, 475 nm, 432 and 458 nm, respectively, upon excitation at 350, 330, 320, and 340 nm, respectively (Figure 9). The emissions of 5-8 can be attributed to the mixed ligands (btb and bdc for 5, btb and btc for 6, btec for 7, btb and btec for 8) ligand-to-metal charge-transfer (LMCT).21 Conclusion Eight coordination polymers with the flexible ligand 1,4bis(1,2,4-triazol-1-yl)butane (btb) and Zn(II) salts (four inorganic anions: SO42-, NO3-, BF4-, and ClO4-) or aromatic polycarboxylate ligands, 1,4-benzenedicarboxylate (bdc), 1,3,5-benzenetricarboxylate (btc) and 1,2,4,5-benzenetetracarboxylate (btec) have been synthesized and structurally characterized. The results demonstrate that the nature of counteranions or/and aromatic polycarboxylate ligands have a remarkable influence on the self-assembly of the flexible ligand with metal atoms and result in coordination architectures with different structures. However, the same structures can be obtained when other Zn(II) salts (such as SO42-, ClO4-, BF4-) instead of Zn(NO3)2 3 6H2O are used in the synthesis of polycarboxylate compounds 5-8. The polycarboxylate ligands affect the structures. The ligand btb can adjust its configuration comfortably to meet the geometric requirement of the central metal atoms, which results in a variety of fascinating coordination polymers.
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