Solvothermal Synthesis and Structural Characterization of New Zn

Khlobystov, A. N.; Champness, N. R.; Roberts, C. J.; Tendler, S. J. B.; Thompson, C.; Schroder, M. CrystEngComm 2002, 426. [CAS]. (2) . Anion exchange...
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CRYSTAL GROWTH & DESIGN

Solvothermal Synthesis and Structural Characterization of New Zn-Triazole-Sulfoisophthalate Frameworks Hyunsoo

Park,†,‡

Gabriel

Krigsfeld,‡,#

and John B.

2007 VOL. 7, NO. 4 736-740

Parise*,†,‡,⊥

Department of Chemistry, Center for EnVironmental Molecular Science, and Department of Geosciences, State UniVersity of New York at Stony Brook, Stony Brook, New York 11794, and Department of Chemistry, Pace UniVersity, New York, New York 10038 ReceiVed October 23, 2006; ReVised Manuscript ReceiVed January 16, 2007

ABSTRACT: Two new Zn-based coordination polymers based polymers, namely, Zn7(TRZ)8(SIP)2‚7H2O (1) and Zn5Na2(DMA)4(TRZ)4(SIP)4‚5H2O (2) (TRZ ) 1,2,4-triazole, SIP ) sulfoisophthalate, and DMA ) dimethylamine), were synthesized under mild solvothermal conditions. Their crystal structures were characterized by single-crystal X-ray diffraction, and their thermal properties were examined by thermogravimetric analysis. Structure 1 crystallizes in monoclinic P21/n space group (a ) 14.050(3) Å, b ) 12.517(3) Å, c ) 15.377(3) Å, β ) 97.95(3)°, V ) 2678.3(9) Å3, Z ) 2), while structure 2 is described as triclinic P1h (a ) 9.701(2) Å, b ) 12.442(3) Å, c ) 17.218(3) Å, R ) 89.83(3)°, β ) 75.01(3)°, γ ) 73.33(3)°, V ) 1917.5(7) Å3, Z ) 1). Structure 1 contains 8- and 16-membered channels made of Zn polyhedra linked by TRZ, which are occupied by water molecules and SIP ligands. Structure 2 consists of one-dimensional chains of Zn-TRZ moieties that are linked to each other via SIP. It is a negatively charged open framework in which Na+ ions and protonated dimethylamine in the cavities serve as counterions. Introduction In recent years, substantial progress has been made in the field of metal-organic frameworks (MOFs). They have attracted considerable attention from various scientific communities because of their interesting framework topologies and potential applications in areas such as ion-exchange,1-5 catalysis,6-8 luminescence,9-11 and gas storage.12-16 Many MOFs have been prepared based on the connector and linker approach.12,17-19 Connectors are inorganic units, often clusters or chains of transition metal ions, that can yield different coordination geometries. Linkers are typically functionalized organic molecules such as carboxylate-type O-donors and amine- or pyridine-type N-donors. By combining connectors with linkers, extended structures are formed with well-defined pores or channels. Since there are a large number of choices available for both connectors and linkers, it is possible to create a vast range of new MOFs with interesting architectures and physical properties. One of the most common choices of linkers is aromatic polycarboxylates. They have been widely applied due to their structural rigidity and flexible coordination modes.12,17,18 Examples of these ligands include benzenedicarboxylate (BDC) and naphthalenedicarboxylate (NDC). However, the preparation of MOFs with aromatic sulfonates has been relatively unexplored.20-22 This can be attributed to the fact that sulfonates are generally thought of as weakly coordinating ligands.21 Nevertheless, a number of new coordination polymers have been recently reported using sulfoisophthalate (SIP) as a linker.23-27 This ligand, which consists of two carboxylate and one sulfonate groups, can manifest various coordination modes with metal centers, resulting in diverse topologies and multidimensional * To whom correspondence should be addressed. E-mail: jparise@ notes.cc.sunysb.edu. † Department of Chemistry, State University of New York at Stony Brook. ‡ Center for Environmental Molecular Science, State University of New York at Stony Brook. ⊥ Department of Geosciences, State University of New York at Stony Brook. # Pace University.

frameworks. Other commonly used ligands are polyaza heterocycles such as 1,2,4-triazole (TRZ) and its derivatives. These linkers can yield the formation of an MOF through multiple metal-N bonds. For instance, ZnF(AmTRZ), ZnF(Am2TRZ), and ZnF(TRZ) (Am2TRZ ) 3,5-amino-1,2,4-triazole and AmTRZ ) 3-amino-1,2,4-triazole), three-dimensional metal-organic architectures with nanotubular channels, have been recently reported.28,29 The efforts in our group have been geared toward the synthesis of MOFs by incorporating two different organic ligands, namely, triazolate and aromatic carboxylate. This approach has led to a number of new MOFs whose structures are built from two-dimensional, gridlike layers pillared by dicarboxylate linkers.30,31 We applied the same method with TRZ and SIP as linkers and successfully synthesized two new MOFs, Zn7(TRZ)8(SIP)2‚7H2O (1) and Zn5Na2(DMA)4(TRZ)4(SIP)4‚5H2O (2). This paper describes the details of their synthesis and structural characterization by single-crystal X-ray diffraction method. Experimental Section Synthesis. Both compounds were prepared under mild hydrothermal conditions using Teflon-lined 23-mL Parr stainless steel autoclaves. Starting materials include zinc nitrate hexahydrate (Zn(NO3)2‚6H2O, 99%, Sigma-Aldrich), 1,2,4-triazole (TRZ, 99%, Sigma-Aldrich), 5-sulfoisophthalic acid sodium salt (SIP, 98%, Sigma-Aldrich), N,N′dimethylformamide (DMF, 99%, Sigma-Aldrich), ethanol (99.9%, Sigma-Aldrich), and deionized water. The reactants were stirred for 1 h to ensure homogeneity before heating. After reaction, the products were filtered, washed with ethanol, and dried in air. Structure 1 was synthesized from a mixture of Zn(NO3)2‚6H2O (0.29 g, 100 mmol), TRZ (0.07 g, 100 mmol), and SIP (0.27 g, 100 mmol) with ethanol (2.56 g, 56 mmol) and deionized water (2.00 g, 111 mmol) as solvents. The reactants were heated at 170 °C for 3 days. Yellow, transparent block-shaped crystals were obtained as products. For structure 2, a mixture containing Zn(NO3)2‚6H2O (0.29 g, 100 mmol), TRZ (0.07 g, 100 mmol), SIP (0.16 g, 60 mmol), and DMF (7.00 g, 96 mmol) was heated at 170 °C for 1 day. The resulting products were aggregates of tiny, colorless needles. Crystal Structure Determination. The crystal structures of both compounds were determined by single-crystal X-ray diffraction. A suitable crystal from each compound was selected using a polarizing optical microscope and was glued to the tip of a glass fiber.

10.1021/cg060741x CCC: $37.00 © 2007 American Chemical Society Published on Web 03/07/2007

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Crystal Growth & Design, Vol. 7, No. 4, 2007 737

Table 1. Crystallographic Data and Refinement Details structure 1 empirical formula formula weight collection temp (K) wavelength (Å) space group unit cell dimensions (Å, °)

volume (Å3) Z, calc density (g/cm3) absorption coefficient(mm-1) F(000) crystal size (mm) θ range for data collection (°) index ranges total reflections independent reflections goodness-of-fit final R [I > 2σ(I)] R (all data) largest difference peak and hole (e Å-3)

C32H36N24O21S2Zn7 1614.69 293(2) 0.71073 P21/n a ) 14.050(3) b ) 12.517(3) c ) 15.377(3) β ) 97.95(3) 2678.3(9) 2, 1.976 3.260 1570 0.30 × 0.20 × 0.20 1.84 to 26.37 -17 e h e 16 -15 e k e 15 -18 e l e 19 4523 4261 [R(int) ) 0.039] 1.088 R1 ) 0.0401, wR2 ) 0.0931 R1 ) 0.0436, wR2 ) 0.0947 1.32 and -1.20

Data collection of 1 was performed on a Bruker P4 diffractometer equipped with a SMART 1K CCD detector using Mo KR radiation. Data were collected at room temperature with an exposure time of 30 s per frame with a detector distance of 5.02 cm. A total of 1650 frames were obtained with a step width of 0.30° in φ and ω, spanning a whole hemisphere of reciprocal space. Because of very small crystal dimensions, data collection of 2 was carried out at 15-ID ChemMatCARS beamline, Advanced Photon Source, Argonne National Laboratory, using a Bruker SMART 6000 CCD detector. Data were collected at 100 K with wavelength of 0.4959 Å with an exposure time of 1 s per frame and a detector distance of 5.0 cm. A randomly oriented region of reciprocal spaces was examined to a resolution of 0.75 Å. Two major sections of frames were collected with a step size of 0.30° in ω and φ. For both structures, the raw intensity data were collected and integrated with software packages SMART32 and SAINT,33 and an empirical absorption correction was applied using SADABS.34 The crystal structures were solved via direct method and refined by fullmatrix least-squares on F2 with SHEXLTL.35 All non-hydrogen atoms were refined anisotropically. Metal atoms were located first, and the remaining atoms (O, C, N) were found from subsequent Fourier difference map synthesis. The hydrogen atoms were added using geometrical constraints (HFIX command). The details of the crystal structures and refinements are given in Table 1. Other Characterizations. Phase purity and crystallinity were determined by powder X-ray diffraction using a Scintag PAD-X diffractometer with Cu KR radiation (step size of 0.02° and counting time of 1.2 s/step) in a 2θ range of 3.00-40.00°. The X-ray diffraction (XRD) patterns of both compounds are shown in Figure 1. These patterns are consistent with those of simulated based on the structure models derived from single-crystal X-ray diffraction data. In XRD of structure 1, the discrepancy in some peak intensities between calculated and observed is present. This is caused by the presence of a small amount of an unknown impurity in the sample. Thermogravimetric analysis (TGA) for each compound was performed using a Netzsch STA 449C instrument. Each sample was heated from room temperature to 800 °C in air with a heating rate of 5.0 °C/ min. The TGA plots of both compounds are shown in Figure 2.

Results and Discussion Structural Description. The crystal structure of Zn7(TRZ)8(SIP)2‚7H2O (1) is depicted in Figure 3. The asymmetric unit consists of four crystallographically independent Zn sites. The Zn(2) atom is in the octahedral coordination while Zn(3) and Zn(4) exhibit distorted trigonal bipyramidal geometries by

structure 2 C48H62N16Na2O33S4Zn5 1892.21 100(2) 0.4959 P1h a ) 9.701(2) b ) 12.442(3) c ) 17.218(3) R ) 89.83(3) β ) 75.01(3) γ ) 73.33(3) 1917.5(7) 1, 1.639 0.924 962 0.10 × 0.03 × 0.03 2.00 to 19.66 -13 e h e 12 -16 e k e 16 -22 e l e 23 8186 7865 [R(int) ) 0.042] 1.124 R1 ) 0.0476, wR2 ) 0.1274 R1 ) 0.0513, wR2 ) 0.1296 1.63 and -0.87

bonding to nitrogen atoms from TRZ molecules, oxygen atoms from dicarboxylate and water. The Zn(1), which is bonded to four N atoms, displays a distorted tetrahedral coordination. The Zn-O and Zn-N bond distances are in the ranges of 1.970(4)-2.204(4) Å and 1.986(4)-2.265(4) Å, respectively, which are comparable to the previously reported values.14,30 The bond valence sums around Zn atoms are consistent with the oxidation state of Zn2+,36 which indicates all the ligands to Zn are properly assigned. Structure 1 can be described as a dense three-dimensional framework that is built from alternating Zn polyhedra and TRZ molecules. The framework consists of 16-membered channels along the [010] direction, created by eight Zn polyhedra connected by eight TRZ molecules (Figure 3a). The size of the channel is approximately 13.45 × 5.97 Å,2 considering the van der Waals radii of Zn atoms.37 When viewed down the [100] and [001] directions, small eight-membered channels are also found (Figure 3b). The void dimensions are 3.01 × 3.41 and 3.01 × 3.53 Å2 along the a- and c-axes, respectively. However, the porosity of the framework is greatly reduced since free water molecules and SIP ligands are located inside the pores. The resulting solvent-accessible cavities were estimated to be only 9.6% of the unit cell volume.38 The SIP ligand adopts bridging monodentate connection modes for sulfonate and dicarboxylates as it is coordinated to three Zn centers across the 16-membered channel. The phenyl rings of SIP are aligned nearly face-toface with a separation distance of 4.11 Å along the [101] direction; therefore, moderate π-π interactions are expected.39 Strong hydrogen bonding interactions are also present between water and uncoordinated oxygens from carboxylates and sulfonates (Ow‚‚‚H‚‚‚O-C ) 2.55-2.87 Å). The structure of Zn5Na2(DMA)4(TRZ)4(SIP)4‚5H2O (2) is given in Figure 4. It contains three crystallographically unique Zn atoms. Zn(1), which lies at the origin, is coordinated to four nitrogen atoms from TRZ and two oxygen atoms from dicarboxylates to form an octahedron. Zn(2) and Zn(3) atoms are in tetrahedral coordination environments by bonding to two nitrogen atoms and two carboxyl oxygen atoms. The Zn-O and Zn-N bonds exhibit typical distances of 1.897(3)-2.135(2) Å

738 Crystal Growth & Design, Vol. 7, No. 4, 2007

Park et al.

Figure 1. Powder XRD results of structures 1 and 2. For each structure, observed (top) and calculated (bottom) are plotted.

Figure 3. Crystal structure of 1 viewed along the [010] (a) and [001] (b) directions. Zn polyhedra are light blue; sulfur, oxygen, carbon, and nitrogen atoms are depicted as yellow, red, gray, and blue circles, respectively. Water molecules are omitted for clarity.

Figure 2. TGA curves of structures 1 (above) and 2 (below).

and 1.982(3)-2.134(3) Å, respectively. The bond valence sums36 around all Zn atoms are close to the expected value of 2. Structure 2 consists of two infinite one-dimensional (1-D) chains made of alternating Zn tetrahedra and TRZ along the [100] direction. Two adjacent chains are subsequently linked to each other by Zn(1) octahedra, which are coordinated to two TRZ molecules from each chain (Figure 4a). As a result, eightmembered channels of 6.92 × 4.58 Å2 are created along the a-axis. These Zn-TRZ moieties are connected to each other by SIP ligands along the [010] and [001] directions (Figure 4b). The Zn-TRZ-SIP linkage results in a negatively charged (-6) open framework. The charges are compensated by Na+ ions and protonated dimethylamine (DMA) molecules in the pores. DMA, which was not a reactant, was probably produced by the hydrolysis of DMF under solvothermal conditions. Water molecules are also found inside the cavities. The Na+ ions display a distorted octahedral geometry by coordinating two oxygens from dicarboxylates, three oxygens from two sulfonates, and a water molecule. The Na-O bond lengths range from

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Crystal Growth & Design, Vol. 7, No. 4, 2007 739

Conclusion This work has presented the solvothermal synthesis and structure determination of two new MOFs using TRZ and SIP as organic ligands. Structure 1 is constructed from alternating Zn polyhedra and TRZ, which create 16-membered channels along the a-axis. The cavities are occupied by water and SIP ligands which coordinate to the Zn centers. Structure 2 is based on the 1-D chains of Zn-TRZ which are connected to each other by SIP, resulting in an open framework. The framework of 2 carries a net negative charge of -6, which is not commonly observed in MOFs. The charges are compensated by Na+ ions and protonated dimethylamine. Our future efforts will include the cation exchange studies of structure 2 with K+ and Cs+ ions. Acknowledgment. This work was supported by the National Science Foundation (DMR-0452444) and Center for Environmental Molecular Science (CHE-0221934). H.P. thanks Timothy Graber and Yu-Sheng Chen at ChemMatCARS, APS, for their assistance with single-crystal X-ray diffraction. ChemMatCARS Sector 15 is principally supported by the National Science Foundation/Department of Energy under Grant CHE-0087817. The Advanced Photon Source is supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Science, under Contract No. W-31-109-Eng-38.

Figure 4. Crystal structure of 2 viewed along the [010] (a) and [100] (b) directions. Zn polyhedra are shown in light blue; Na, O, C, N, S are displayed as purple, red, gray, blue, and yellow circles, respectively. In (a), water, DMA and Na+ ions are omitted for clarity.

2.295(4) to 2.529(3) Å, resulting in the bond valence sum of 1.20 around Na. The sulfonate groups are located near DMA molecules so that there are significant hydrogen bonding interactions between non-coordinating oxygen atoms and the protonated nitrogen from DMA (N-H‚‚‚O distance ) ∼2.80 Å). Water molecules also interact with carboxyl O atoms via hydrogen bonding (Ow-H‚‚‚O ) 2.77-2.83 Å). The aromatic groups of SIP are aligned offset along the a-axis with phenylphenyl distance of 3.9 Å, inducing π-π interactions. The potential solvent accessible volume38 in 2 was estimated to be 290 Å,3 which constitutes about 15% of the unit cell volume. Although 2 is moderately porous, its gas sorption properties were not investigated because of its low thermal stability. As discussed below, the framework starts to collapse quickly once the solvent molecules are removed. This structure represents a new anionic framework type, which is not often observed in MOFs. Therefore, it may be of interest to carry out ion-exchange experiments at room temperature to replace Na+ ions with other monovalent cations such as K+ or Cs+. Thermal Properties. Thermogravimetric analysis data for 1 and 2 are given in Figure 2. For structure 1, the event between RT and 340 °C is caused by the removal of water molecules (observed: 7.35%, calculated: 7.81%). There is a small region of plateau between 340 and 390 °C, then the framework starts to collapse as the organic ligands decompose. For structure 2, water molecules are lost between RT and 120 °C (observed: 5.06%, calculated: 4.76%). No stable region was observed in 2, implying its lack of thermal stability. The organic molecules are then removed progressively up to 680 °C. Both samples were recovered as grayish powders after heating, and X-ray analysis showed these to be amorphous.

Supporting Information Available: Crystallographic information files (CIF) for structures 1 and 2. These materials are free of charge via the Internet at http://pubs.acs.org.

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