Phenylenediacrylate Modulated by Bis(pyridyl) Ligands - American

Article pubs.acs.org/crystal

Entangled Metal−Organic Frameworks of m-Phenylenediacrylate Modulated by Bis(pyridyl) Ligands Qian Sun, Yan-Qin Wang, Ai-Ling Cheng, Kun Wang, and En-Qing Gao* Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, Shanghai 200062, China S Supporting Information *

ABSTRACT: Solvothermal reactions of m-phenylenediacrylic acid (H2mpda) and zinc(II) salts in the presence of different bis(pyridyl) ancillary ligands afforded a series of supramolecular interpenetrated coordination architectures with formula [Zn(mpda)(bpee)]n (1), [Zn(mpda)(bpea)]n (2), and [Zn(mpda)(bpp)]n·2.5H2O (3) (bpee = 1,2bis(4-pyridyl)ethylene, bpea = 1,2-bis(4-pyridyl)ethane, bpp = 1,3-bis(4pyridyl)propane). X-ray analyses revealed that all of the compounds feature tetrahedral-based coordination geometry around Zn(II), twodimensional (2D) 44 coordination networks with different linkers, and parallel 2D→2D interpenetration, which is stabilized by interlayer hydrogen-bonding interactions. The arc-shaped mpda ligand collaborates with quasi-linear bpee or bpea to generate 2D achiral networks with chairshape windows in 1 and 2, but with two different arc-shaped ligands (mpda and bpp); the single network in 3 is homochiral and has boat-shaped windows. The different shapes of the networks result in different interpenetration modes. Both networks of 1 and 2 exhibit 3-fold parallel interpenetration and give trilayers. Differently, two layers of the same handedness in 3 interpenetrate to give a homochiral bilayer featuring double helical motifs, and the alternating stacking of oppositely handed bilayers renders the compound racemic. The interpenetration mode and the formation of the double helices in 3 benefit not only from the arc shape of the two bridging ligands but also from the match of the two ligands in length.

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INTRODUCTION Crystal engineering, aiming at predicting and controlling the packing of molecular building units in crystals, has attracted much attention over the past three decades due to its potential exploitation for the synthesis of technologically important materials.1 The current interest in the crystal engineering of metal−organic frameworks (MOFs) stems from their potential applications as zeolite-like materials for molecular selection, ion exchange, and catalysis, as well as from the intriguing variety of architectures and topologies.2−4 Under the direction of crystal engineering, the structure topology of MOFs can be controlled to some degree by the careful selection of metal ions with specific coordination preference, spacer ligands with different geometrical characters, the counteranions, and the reaction conditions. Nevertheless, precise prediction or modulation of the structure of a molecular solid is still a daunting task because the structures are often governed by many weak noncovalent intermolecular forces such as hydrogen bonding and π−π stackings.5 Besides, the structural diversity can occur as a result of supramolecular isomerism and supramolecular entanglement, which challenges our knowledge of crystal engineering.6−11 Interpenetration, as an important subgroup of entangled systems, has attracted a great deal of attention. An increasing number of interpenetrating nets have been reported, and some excellent reviews have been devoted to the © 2012 American Chemical Society

classification and elucidation of the interpenetrating topologies.12,13 Interpenetration is an approach of the nature to avoid the voids or open space in a single network. The interpenetrating topology is dependent not only upon the metal-linker coordination geometry and the shape of the linkers, but also upon the subtle supramolecular interactions between the interpenetrating nets. In cases with mixed bridging ligands, the design of the frameworks is still more challenging and the occurrence of interpenetration sometimes requires that the different bridging ligands match each other in shape and also in length.14 Going further with our previous work with m-phenylenediacrylate (mpdc, Chart 1), which can serve as a long and bent bridging ligands,15 we initiated a study to explore the assembly with mixed mpdc and bis(pyridyl) ligands. Three bis(pyridyl) ligands (Chart 1), 1,2-bis(4-pyridyl)ethylene (bpee), 1,2-bis(4-pyridyl)ethane (bpea), and 1,3-bis(4-pyridyl)propane (bpp), have been chosen for the following considerations: (i) these relatively long linkers in combination with the bent mpdc linker may lead to new interpenetrating networks; and (ii) bpee is usually flat due to the conjugating tether, while bpea and bpp are rather flexible and may adopt Received: October 29, 2011 Revised: March 29, 2012 Published: March 30, 2012 2234

dx.doi.org/10.1021/cg201432w | Cryst. Growth Des. 2012, 12, 2234−2241

Crystal Growth & Design

Article

(KBr, ν/cm−1):3430 br, 2925 m, 1640 s, 1611 s, 1425 vs, 1380 m, 1266 s, 1067 m, 1025 s, 968 s, 848 s, 785 m, 748 s, 550 s. [Zn(mpdc)(bpea)]n (2). Zn(NO3)2·6H2O (0.1 mmol, 0.030 g), H2mpda (0.1 mmol, 0.022 g), and bpea (0.1 mmol, 0.0185 g) were dissolved in the mixture solvent of DMSO/DMF/H2O (3/2/1 v/v) and transferred to a 25 mL stainless steel reactor with Teflon linear. After being stirred in air for 30 min, the mixture was heated to 110 °C and kept at that temperature for 4 days. Upon cooling to room temperature, colorless rod-shaped crystals of 2 were obtained. The crystals were separated by filtrate and washed with water and ethanol, and then dried. Yield: 58% (0.027 g) based on Zn. Anal. Calcd for C24H20N2O4Zn: C, 61.88; H, 4.33; N, 6.01. Found: C, 61.94; H, 4.26; N, 6.03. IR (KBr, ν/cm−1): 2920 m, 1645 m, 1620 s, 1585 s, 1510 w, 1485 w, 1430 s, 1360 vs, 1225 s, 1030 s, 962 s, 843 s, 670 m, 548 s. [Zn(mpdc)(bpp)]·2.5H2O (3). A mixture of Zn(NO3)2·6H2O (0.1 mmol, 0.030 g), H2mpda (0.1 mmol, 0.022 g), and bpp (0.1 mmol, 0.02 g) was dissolved in DMF (4 mL) and water (2 mL), was stirred in air for 30 min, and then heated in a 23 mL Teflon-lined autoclave at 110 °C for 4 days. After being cooled to room temperature, yellow block crystals of 3 were obtained. The crystals were filtrated and washed with water and ethanol, and then dried, yielding (0.033 g) 64% based on Zn. Anal. Calcd for C25H29N2O6.5Zn: C, 56.99; H, 5.55; N, 5.32. Found: C, 57.39; H, 5.83; N, 5.23. IR (KBr, ν/cm−1): 3380 br, 2940 m, 1650 s, 1615 s, 1570 vs, 1500 m, 1484 w, 1433 v, 1370 vs, 1260 m, 1225 s, 1060 m, 1027 s, 991 s, 873 m, 822 s, 796 s, 725 s, 681 m. X-ray Crystallographic Measurements. Diffraction data for 1−3 were collected at 293 K on a Bruker Apex II CCD area detector equipped with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Empirical absorption corrections were applied using the SADABS program.17 The structures were solved by the direct method and refined by the full-matrix least-squares method on F2, with all nonhydrogen atoms refined with anisotropic thermal parameters.18 All of the hydrogen atoms attached to carbon atoms were placed in calculated positions and refined using the riding model, and the water hydrogen atoms were located from the difference maps. All calculations were carried out with the SHELXTL crystallographic software. A summary of the crystallographic data and refinement parameters ais provided in Table 1, with selected distances and angles of the structures listed in Table 2.

Chart 1

different shapes associated with the trans or gauche conformation of the tethers. With these ligands, we could test the effects of the different rigidity or shape on the final frameworks formed, and, in particular, we could reveal how these ligands behave to match the arc-shaped mpdc linker to generate different interpenetration topologies. Here, we report three 2D Zn(II) metal−organic frameworks exhibiting different 2D-to-2D interpenetrating topologies. In [Zn(mpda)(bpee)]n (1) and [Zn(mpda)(bpea)]n (2), bpee and bpea (in trans conformation) serve as quasi-linear linkers, and they collaborate with arc-shaped mpdc linkers and tetrahedral Zn(II) ions to generate highly corrugated layers with chairlike windows, which feature 3-fold parallel interpenetration. In [Zn(mpda)(bpp)]n·2.5H2O (3), bpp adopts the arc-shaped trans−gauche conformation, and the two sets of arcshaped ligands (mpdc and bpp) combined with tetrahedral Zn(II) ions produce 2D layers with boat-like windows, and two layers of the same handedness interpenetrate to give a homochiral bilayer featuring double helical motifs, but the alternating stacking of oppositely handed bilayers renders the compound racemic. The thermal properties of the compounds are also reported.

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Table 1. Crystal Data and Structure Refinement for Compounds 1−3 compounds formula fw T/K crystal system Sspace group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z Dc (g cm−3) μ (mm−1) unique reflns Rint R1 (I > 2σ(I)) wR2 (all data)

EXPERIMENTAL SECTION

Materials and General Methods. All of the solvents and reagents for synthesis were commercially available. m-Phenylenedicarboxylic acid (H2mpda) was prepared according to the literature report.16 Elemental analyses were determined on an Elementar Vario ELIII analyzer. The FT-IR spectra were recorded in the range 500−4000 cm−1 using KBr pellets on a Nicolet NEXUS 670 spectrophotometer. Thermogravimetric analyses (TGA) were performed on a Mettler Toledo TGA/SDTA851 instrument under flowing air at a heating rate of 10 °C min−1. Powder X-ray diffraction (PXRD) data were collected on a Bruker D8-ADVANCE diffractometer equipped with Cu Kα at a scan speed of 1° min−1. Synthesis of Compounds 1−3. [Zn(mpdc)(bpee)]n (1). A mixture of Zn(NO3)2·6H2O (0.1 mmol, 0.03 g), H2mpda (0.1 mmol, 0.022 g), and bpee 0.018 g (0.1 mmol) in DMF (2 mL) and water (2 mL) was heated in a 23 mL Teflon-lined autoclave at 110 °C for 4 days. After being cooled to room temperature, colorless blocks of crystals of 1 were isolated in yield 45% (based on Zn). Anal. Calcd for C24H18N2O4Zn: C, 62.15; H, 3.91; N, 6.04. Found: C, 61.88; H, 3.94; N, 6.27. IR 2235

1

2

3

C24H18ZnN2O4 463.77 296(2) monoclinic P21/c 8.5502(2) 20.0981(4) 12.8744(3) 90 99.4030(10) 90 2182.65(8) 4 1.411 1.158 5323 0.0320 0.0308 0.0822

C24H20ZnN2O4 465.79 293(2) triclinic P1̅ 8.605(11) 11.526(14) 12.862(16) 113.698(17) 99.844(17) 101.204(17) 1101(2) 2 1.405 1.148 3786 0.0259 0.0513 0.1517

C25H29N2O6.5Zn 526.87 296(2) monoclinic C2/c 18.8968(7) 16.8266(6) 16.1483(6) 90 108.3490(10) 90 4873.6(3) 8 1.436 1.053 5640 0.0233 0.0565 0.1681



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corresponding crystallographic data (see the Supporting Information). Descriptions of Crystal Structures. X-ray analysis revealed that the structures of the three compounds all consist of interpenetrated infinite 2D (4,4) networks. The asymmetric unit contains a Zn(II) ion, a mpdc dianionic ligand, and a bis(pyridyl) ligand (two halves in 2), with two and a half water molecules in 3. Crystallizing in different crystal systems and possessing different bis(pyridyl) ligands, 1 and 2 exhibit very similar structures. The structure of 3 is quite different. The structures are described and compared as follows in a bottomup way. Coordination Sphere. As shown in Figure 1, the Zn(II) ions in all of the compounds are coordinated by two carboxylate groups from two mpdc ligands and two nitrogen atoms (N1, N2) from three bis(pyridyl) ligands. The coordination geometry is primarily tetrahedral with strong coordination bonds. The Zn−N distances range from 2.02 to 2.09 Å, and the Zn−O distances are somewhat shorter (from 1.95 to 1.97 Å) except for Zn1−O3 (2.083 Å) in 3 (Table 2). As shown in Figure 1, each carboxylate group has an oxygen atom (O1 or O4) hanging over a tetrahedral face, with a long Zn−O distance between 2.75 and 2.80 Å, except for the relatively short Zn1−O4 (2.49 Å) in 3. Taking into account the weak coordination, the carboxylate group adopts a highly asymmetric bidentate mode, and the coordination geometry around Zn(II) becomes a bicapped tetrahedron (highly distorted octahedron). The weak coordinated oxygens in 1 and 2 cap the two [N2O] faces of the tetrahedron, but those in 3 cap the two [NO2] faces (the Zn1---O4 line is close to the O2---O3 edge of the tetrahedron). The weak coordination capping is concomitant with the distortion of the [ZnN2O2] tetrahedral geometry. The unique capping mode in 3 leads to a significant expansion in the O2−Zn1−O3 angle (145°) and some reduction in some O−Zn−N angles (from 95° to 100°) as compared to the ideal tetrahedral angle. By contrast, the largest angle for the tetrahedral geometry is N−Zn−O for 1 and N−Zn−N for 2, with the O2−Zn1−O3 angles being slightly smaller than the ideal tetrahedral angle (Table 2). The different capping modes lead to a more marked difference in the O1−Zn1−O4 angle, which is 70° in 3 but 148° and 151° in 1 and 2, respectively. As will be shown, the capping mode plays an important role in determining the coordination network.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for Compounds 1−3a compound 1 Zn1−O3A Zn1−O2 Zn1−O1 O3A−Zn1−O2 O3A−Zn1−O4A O2−Zn1−N2B O2−Zn1−N1

1.962(1) Zn1−N1 1.971(6) Zn1−N2B 2.752(0) Zn1−O4A 106.01(5) O3A−Zn1−N2B 52.29(7) O1−Zn1−O2 122.29(5) O3A−Zn1−N1 100.74(6) N2B−Zn1−N1 compound 2

2.094(4) 2.027(2) 2.773(8) 115.33(6) 52.80(6) 103.65(6) 106.29(6)

Zn1−O2 Zn1−O3A Zn1−O1 O2−Zn1−O3A O3A−Zn1−O4A O3A−Zn1−N2 O3A−Zn1−N1

1.958(3) Zn1−N1 1.972(3) Zn1−N2 2.756(1) Zn1−O4A 104.41(2) O2−Zn1−N1 52.20(9) O1−Zn1−O2 107.99(2) O2−Zn1−N2 109.87(2) N2−Zn1−N1 compound 3

2.032(4) 2.032(4) 2.795(1) 107.08(2) 52.36(8) 112.12(2) 114.87(2)

Zn1−O2 Zn1−O3B Zn1−O1 O2−Zn1−N1 N1−Zn1−N2A N1−Zn1−O3B O2−Zn1−O4B N2A−Zn1−O4B

1.942(3) 2.083(4) 2.763(1) 97.41(1) 109.25(1) 100.20(1) 88.06(2) 134.40(2)

Zn1−N1 Zn1−N2A Zn1−O4B O2−Zn1−N2A O2−Zn1−O3B N2A−Zn1−O3B N1−Zn1−O4B O3B−Zn1−O4B

2.055(3) 2.062(3) 2.485(8) 106.73(1) 144.96(2) 95.68(2) 111.23(1) 57.34(2)

a Symmetry code for 1: A, x − 1, y, z − 1; B, x − 1, −y + 3/2, z + 1/2. 2: A, x − 1, y, z − 1. 3: A, x − 1/2, y + 1/2, z; B, x − 1/2, y − 1/2, z.

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RESULTS AND DISCUSSION Syntheses and General Characterization. Compounds 1−3 were synthesized with H2mpda and Zn(II) metal ions under proper hydrothermal conditions. All of the FT-IR spectra (see the Supporting Information) show no absorption bands around 1700 cm−1, consistent with the complete deprotonation of the carboxylic groups of the mpda ligand in the compounds. The strong absorption in the range of 1640−1645 cm−1 may be assigned to the υas(COO) vibration, and the strong bands at about 1390 cm−1 to υs(COO). The results are well consistent with the structures. The PXRD patterns of these compounds are in good agreement with those calculated from the

Figure 1. Views of the coordination environments of the metal ions in 1 (a), 2 (b), and 3 (c). The bicapped tetrahedral geometry is highlighted. 2236



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Coordination Networks. Compounds 1−3 are all comprised of 2D corrugated 44 layer motifs with mpdc and bis(pyridyl) ligands (bpee, bpea, or bpp) as linkers between metal ions (Figures 2 and 3). In these compounds, the bent

In a different direction, the bis(pyridyl) ligands also link Zn(II) ions into chains. In compounds 1 and 2, the combination of the tetrahedral metal ions and the quasi-linear bpea and bpee linkers leads to zigzag chains along the [201̅] direction with the turn angles (defined by three adjacent metal ions) of 118° and 123°, respectively (Figure 2). The Zn···Zn distance is about 13 Å. Differently, the bpp ligands in 3 adopt an arcshaped trans−gauche conformation and serve as arc bridges to link metal ions into wavelike chains (Figure 3), which resemble the [Zn(mpdc)]n chain but in a different direction. The Zn···Zn distance separated by bpp is identical to that by mpdc. In 1 and 2, the [Zn(mpdc)]n and [Zn(bpee)]n (or [Zn(bpea)]n) chains in different directions ([101] and [201̅], respectively) intersect at the metal sites to result in a highly corrugated layer along the (010) plane. The window of the layer is a large 42-membered loop composed of four metal ions, two bpee/bpea linkers, and two mpdc linkers. The corrugation of the layer results from the parallel alignment of the [Zn(bpee)]n (or [Zn(bpea)]n) zigzag chains, with the metal ions in the layer being located in two parallel planes. The mpdc arc bridges between the zigzag chains bulge outward from the layer ridges, affording a chairlike shape for the tetrametallic window. In 3, two different sets of wavelike chains ([Zn(mpdc)]n and [Zn(bpp)]n) along different directions ([110] and [110̅ ]) intersect at the metal centers to produce a layer parallel to (001). All of the metal centers in the layer are coplanar and arranged in a rhombic lattice. The two different arc bridges bulge up and down, respectively, from the plane defined by metal ions, and the tetrametallic window of the layer has a boat-like shape. The layer is homochiral and features helical chains along the a direction with alternating mpdc and bpp bridges. The helical chains in each layer have the same handedness and share metal ions. Supramolecular Entanglement and Packing. Generally, longer ligands will give rise to larger voids, and to occupy the voids, it is more likely to obtain interpenetrated networks.19 For interpenetration of identical 2D nets, two general types have been recognized: parallel interpenetration and inclined interpenetration. The latter always generates a 3D entangled assembly, while the former may be 2D-to-3D when the interpenetration propagates “infinitely” in the direction perpendicular to the layer or 2D-to-2D when a finite number

Figure 2. (a) The 2D network bridged by mpdc and bpee ligands in compound 1. (b) A side view of the 2D network.

mpdc ligands serve as “arc bridges” to link collinear Zn(II) ions into a chain. All of the arc bridges along the chain bulge toward the same side of the straight line defined by metal ions, affording a wavelike chain shape with the metal ions and the benzene rings furnishing the alternating crests and troughs. The Zn···Zn distances separated by mpdc in 1 and 2 are 14.2 Å approximately, while in 3 the distance is decreased to 12.65 Å. The smaller repeat length in 3 is consistent with a smaller turn angle of the wave chain: Zn···Ctip···Zn = Ctip···Zn···Ctip = 94.5° (Ctip is the 5-C atom of the 1,3-substituted benzene ring). For 1 and 2, the angles are about 115.2°. The differences are clearly related to coordination geometry: the capping mode in 3 pulls the two carboxylate groups closer than that in 1 and 2 (Figure 1).

Figure 3. (a) The 2D network bridged by mpdc and bpp ligands in compound 3 (the purple rods serve to highlight the helical arrangement along the a direction), and (b,c) two side views of the 2D layer. 2237



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Figure 4. The 3-folded entanglement of the layers in 1 and 2. (a) A schematic view; and (b,c) the weak interactions between the entangling layers in 1 and 2, respectively.

of 2D nets are involved.12,13 For parallel interpenetration to occur, the layer should have an ingredient of undulation or open space in the direction perpendicular to the mean plane of the layer. In 1−3, the tetrahedral coordination of Zn(II) and the arc shape of the linkers (mpdc and bpp) provide the undulating ingredients, and 2D-to-2D parallel interpenetration occurs. For 1 and 2, the interpenetration occurs between three layer motifs that are related by the translation along the [010] direction and share the same mean plane, with each window of one layer threaded by two linear linkers (bpee or bpea) from other two layers (Figure 4a). The 3-fold interpenetration in 1 and 2 is reinforced by weak C−H···O hydrogen bonds between the layers (Figure 4b and c). Each weakly coordinated carboxylate oxygen atom (O1 or O4) from one layer forms hydrogen bonds with two or three C−H groups of a bis(pyridyl) ligand from another layer, with H···O distances in the range of 2.3−2.8 Å and C−H···O angles in the range of 140−155°. Furthermore, in both compounds, the entangled trilayers are stacked along the crystallographic b axis with deep interdigitation between the mpdc ligands and with interlayer C−H···O interactions (see the Supporting Information). The hydrogen bonds involve the pyridyl C24−H groups from one trilayer and the carboxylate O3 atoms from another trilayer, with C24···O3 = 3.05 Å, C24−H···O3 = 116.4° for 1 and C24···O3 = 3.24 Å, C24−H···O3 = 143.9° for 2. A topologically different mode of parallel interpenetration is found in compound 3 (Figure 5). The interpenetration occurs between two layers related by the C2 crystallographic axis along the b direction. Because of the C2 relation, each bilayer resulting from the 2-fold interpenetration is homochiral, and the [Zn(mpdc)]n chain from one layer is parallel to the [Zn(bpp)]n chain from the other layer. In other words, the [Zn(mpdc)]n and [Zn(bpp)]n chains from one layer are perpendicular to, respectively, their equivalents from the other layer. The entangled bilayer features double helices along the

Figure 5. (a−c) Schematic views of the 2-fold entanglement in 3 (different colors are used for mpdc and bpp). (d) A double-stranded helice along the a direction (different colors are used for the two strands). The gray rods in (c) and (d) serve to highlight the helical features.

a direction, which consists of two C2-related strands from the two entangling layers. The unusual interpenetration of 2238



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the layers can be regarded as resulting from the sharing of metal ions between adjacent double helices. As shown in Figure 5b, the double helices define chiral channels along the a direction. The arc shape of the two bridging ligands is obviously important to the interpenetration mode and the formation of the double helices in 3, but also important is the match of the two bridging ligands in length. As was already mentioned above, the Zn···Zn distance separated by bpp is identical to that by mpdc. This indicates that the two chain motifs from different ligands ([Zn(mpdc)]n and [Zn(bpp)]n) have identical period length. Therefore, the different motifs from two layers can be aligned in parallel to allow the observed interpenetration mode and the formation of double helices. Just like compounds 1 and 2, compound 3 has weak hydrogen bonds to reinforce the double helice and layer entanglement (Figures 5d and 6). The weak interactions involve the

Figure 7. The interdigitating packing of the bilayers in 3.

Figure 8. Thermogravimetric analyses (TGA) in compounds 1−3.

molecules per formula (calc. 8.5%), and the rapid weight loss above 240 °C indicates decomposition of the organic ligands TGA measurements were also performed for a desolvated sample 3′, which was obtained by heating 3 at 150 °C under vacuum for 3 h. No weight loss was observed upon heating from room temperature to about 200 °C (see the Supporting Information), suggesting the absence of guest molecules in 3′. To study the stability of the framework upon desolvation, powder X-ray diffraction (PXRD) of 3′ was measured and compared to that of 3 (Figure 9). 3′ shows less peaks and

Figure 6. The interactions between the entangling layers in compound 3.

pyridyl C15−H and C14−H groups from one layer and the carboxylate O4 and O2 atoms from the other layer. The relevant parameters are 165° and 3.5 Å for C15−H···O4, and 141° and 3.3 Å for C14−H···O2. The C15−H···O4 contact is operative between the two strands of the double helices (Figure 5d). The entangled bilayers in 3 are shaped like double-edged saws, and they are stacked in a complementary and interdigitating fashion to minimize interlayer voids (Figure 7). Neighboring bilayers are related by inversion centers and hence oppositely handed, rendering the crystal racemic. The chiral channels related to the double helices are occupied by free water molecules. PLATON calculations suggested that the solvent-accessible voids in the structure comprise 11% of the crystal volume (539.3 Å3 per unit cell). Thermal Study and Guest Inclusion. To study the thermal stability of the compounds, thermogravimetric analysis (TGA) was performed on compounds 1−3 in nitrogen atmosphere (Figure 8). The TGA curves of 1 and 2 are similar. Consistent with the absence of any solvent molecules in the structures, the two compounds show no significant loss up to about 320 °C. The sharp weight-loss step observed around 350 °C is attributed to decomposition of the organic components of the compounds. Compound 3 exhibits a weight loss of 8.3% upon heating to 190 °C, corresponding to the loss of 5/2 water

Figure 9. PXRD patterns of 3 from the single-crystal data (a), for the as-synthesized sample (b), for the evacuated sample (c), and for the resolvated sample (d). 2239



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weaker intensities than 3, suggesting some degree of framework collapse. In addition, after the evacuated solid 3′ was exposed in water at room temperature for 24 h, the PXRD positions are almost coincident with those for 3, suggesting the recovery of the framework. The differences in relative intensity may be due to preferential orientations.

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CONCLUSIONS In summary, we have described three 2D metal−organic networks of zinc(II) that combine mpdc and different bis(pyridyl) ligands. All of the compounds exhibit the 44 net topology, and the arc-shaped mpdc ligand plays similar roles in the structures. The different bis(pyridyl) ligands make imprints not only on the layer shape but also on the interpenetration mode between layers. The quasi-linear ligands (bpee or bpea) lead to highly corrugated layers with chairlike windows, which exhibit 3-fold parallel interpenetration. The combination of two arc-shaped and length-matched ligands (mpdc and bpp) produces 2D layers with boat-like windows, and the layers are 2-fold interpenetrated to give homochiral bilayers featuring double helical motifs and chiral channels (note that alternating stacking of oppositely handed bilayers renders the compound racemic). This work represents a nice example of the manipulation of interpenetration, taking advantage of the shape of bridging ligands and of the match between different bridging ligands.

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ASSOCIATED CONTENT

* Supporting Information S

Supplementary structural characterization diagrams; crystallographic data in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Fax: (+86)-21-62233404. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China (No. 21173083) and the Fundamental Research Funds for the Central Universities.

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REFERENCES

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Phenylenediacrylate Modulated by Bis(pyridyl) Ligands - American

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