ARTICLE pubs.acs.org/crystal
Porous Interpenetrating Metal-Organic Frameworks with Hierarchical Nodes Teppei Yamada,*,†,‡ Shoji Iwakiri,† Takafumi Hara,† Katsuhiko Kanaizuka,†,§ Mohamedally Kurmoo,|| and Hiroshi Kitagawa*,†,‡,^,# †
Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, Japan Division of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan § Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan Laboratoire DECOMET, CNRS-UMR7177, Universite de Strasbourg, 4 rue Blaise Pascal, CS90032, 67081 Strasbourg Cedex, France ^ JST CREST, Sanbancho 5, Chiyoda-ku, Tokyo 102-0075, Japan # Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
)
‡
bS Supporting Information ABSTRACT: We present the solvothermal syntheses, X-ray crystal structures, and gas sorption properties of a series of zinc-dicarboxylate-polypyridine where the dicarboxylate is 1,4-benzenedicarboxylate, 4,40 -biphenyldicarboxylate, or sulfone-4,40 -biphenyldicarboxylate and the polypyridine is bipyridine or 1,4-bis(4-pyridylethynyl)benzene. The structures consist of hierarchical two-, three-, and four-blade dimer or trimer nodes which generate the square or triangular topologies of the metal-carboxylate layers which are pillared by the bipyridine. Two- and 3-fold interpenetration of frameworks was observed depending on the length of both the carboxylate and the bipyridine. In all cases, the structure sustains a variable degree of space within the metal-organic frameworks where solvents are located. The solvents are easily lost and the structures display accessible voids where adsorption of other gases can be realized. The present set of compounds reveals a picture that does not conform to the current belief that interpenetration of lattices results in highly compact structures.
’ INTRODUCTION The chemistry of metal-organic frameworks (MOFs) is a fast growing subject1-3 having the potential of being a solution to the existing energy problems by providing hydrogen storage materials for transportation.4-7 Research in this area is therefore focused on the generation of porous materials, with particular emphasis devoted to the chemical control of the size as well as the surface of the pores.3,8-11 Thus, the choice of the metal center and the chemical and physical characteristics of the connecting ligands are the principal parameters. There are two ways in which the field is advancing: the first is where only one ligand makes the connection between the metals, usually a polycarboxylate,1,12,13 and the second is where two ligands are used, where the other is a polypyridine.11,14-16 In this field of MOF, there is a forced and constant reminder, which is becoming a belief, that noninterpenetrating networks can sustain porosity while interpenetration occurs as a natural consequence to avoid the presence of empty space.17,18 While this may be true in many cases, it cannot be generalized. Here, we present some cases where this belief is not r 2011 American Chemical Society
true. The present work aimed to introduce a highly rigid long bipyridine ligand with zinc carboxylate in order to understand the effect of interpenetration and pore generation. The modified bipyridine pillar chosen is 1,4-bis(4-pyridylethynyl)benzene (L1), which contains two peripheral pyridines symmetrically connected to a central benzene by two ethynes, giving the rigidity along the long axis, though rotation of the pyridine ring is possible. This work stems from the extension of previously used pillars, such as dabco, 4,40 -bpy, 4,40 -bipyridylethane, 4,40 -bipyridylethylene, and 4,40 -bipyridylethyne, with length increasing from 2.8 to 9.7 Å, and 1,4-bis(4-pyridylethynyl)benzene of 16.3 Å (Figure 1). We also vary the length of the dicarboxylate from 9 to 13 Å (Figure 1), constructing several coordination arrangements (Figure 2). Furthermore, the secondary aim was to introduce the presence of noncoordinating groups in the Received: December 29, 2010 Revised: February 13, 2011 Published: March 07, 2011 1798
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Crystal Growth & Design frameworks that can generate proton conductivity. Here, we use a sulfone containing dicarboxylate.
’ EXPERIMENTAL SECTION Synthesis of H2sbpdc. The sulfone-4,40 -biphenyldicarboxylic acid (H2sbpdc) was synthesized as reported previously (Figure 3).19 Briefly, fuming sulfuric acid was added to H2bpdc, and the mixture was heated. Synthesis of [Zn(bdc)(L1)]. The titled compound was synthesized using a solvothermal method. Zn(NO3)2 3 6H2O (119 mg, 0.40 mmol), H2bdc (66 mg, 0.40 mmol), and L1 (56 mg, 0.20 mmol) in DMF (15 mL) were stirred and sealed into a Teflon-lined autoclave and placed in a temperature-control oven. The temperature was slowly elevated to 120 C in 12 h and was kept at 120 C for 48 h. Yellow needle crystals were obtained as shown in Figure S1. Synthesis of [Zn3(bpdc)3(L1)]. The title compound was synthesized using a solvothermal method. Zn(NO3)2 3 6H2O (119 mg, 0.40 mmol), H2bpdc (97 mg, 0.40 mmol), and L1 (56 mg, 0.20 mmol) in DMF (15 mL) were stirred and sealed into a Teflon-lined tube that was then put into the temperature-control oven. The temperature was slowly
Figure 1. Various bridging ligands and their lengths.
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elevated to 120 C in 12 h and was kept at 120 C for 48 h. Yellow needle crystals were obtained as shown in Figure S2. Elemental analyses. Calculated (found) % for Zn3(bpdc)3(L1)(DMF)2.5(H2O): C 59.71 (59.94); H 4.00 (3.90); N 4.51 (4.45). Synthesis of [Zn2(sbpdc)2(L1)]. The title compound was synthesized using a solvothermal method. Zn(NO3)2 3 6H2O (119 mg, 0.40 mmol), H2sbpdc (129 mg, 0.40 mmol), and L1 (56 mg, 0.20 mmol) in DMF (15 mL) were stirred and sealed into a Teflon-lined tube that was then put into the temperature-control oven. The temperature was slowly elevated to 120 C in 12 h and was kept at 120 C for 48 h. Yellow needle crystals were obtained as shown in Figure S3. Elemental analyses. Calculated (found) % for Zn2(sbpdc)2(L1)(DMF)2(H2O): C 54.97 (54.66); H 3.42 (3.38); N 4.75 (4.95). Synthesis of [Zn2(sbpdc)2(bpy)] 3 4DMF. Zinc nitrate hexahydrate (119 mg, 0.40 mmol), H2sbpdc (129 mg, 0.40 mmol), and 4,40 bipyridine (bpy, 31 mg, 0.20 mmol) were added to 15 mL of DMF in a Teflon-lined autoclave and held at 120 C for 36 h. Yellow crystals of [Zn2(sbpdc)2(bpy)] 3 4DMF were obtained. Elemental analyses. Calculated (found) % for [Zn2(sbpdc)2(bpy)] 3 4DMF: C 51.05 (50.73); H 2.82 (3.02); N 4.36 (4.67). Single-Crystal X-ray Crystallography. For all compounds, some of the obtained crystals were quickly added to Paraton-N with minimum exposure to air and used for SCXRD analysis. Samples were mounted using a nylon cryoloop (Hampton Research) on a Bruker Smart Apex II CCD diffractometer equipped with a confocal Mo KR X-ray tube operated at 960 W (24 kV, 40 mA). The measurement was done in a cold nitrogen gas flow of 100(2) K. 1800 or 3600 frames were collected and were integrated with the SAINT software package. Adsorption collection was applied using SADABS. The structures were solved by a direct method (SHELX-9720 or SIR9721), and the subsequent difference was refined by the full matrix least-squares method (SHELX-S or SHELX-L20) using Yadokari-XG software packages.22 A summary of the crystal data is given in Table 1. As we were unable to locate the solvents due to severe disorder, the structure of the framework was finally solved after applying the SQUEEZE subroutine of PLATON.23
Figure 3. Synthetic scheme of H2sbpdc.19
Figure 2. Coordination arrangements of zinc dimers (a, c, and d) and trimer (b). 1799
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Table 1. Summary of Crystal Data of Obtained Compounds composition
Zn(bdc)(L1)
Zn3(bpdc)3(L1)
Zn2(sbpdc)2(L1)
[Zn2(sbpdc)2 (bpy)]
empirical formula
C28H16N2O4 Zn
C62H36N2O12 Zn3
C48H24N2S2O12 Zn2
C38H20O12N2 S2Zn2
formula weight
509.85
1197.04
1015.65
445.71
wavelength/Å (Mo KR) temperature/K
0.71073 100(2)
0.71073 100(2)
0.71073 100(2)
0.71073 100(2)
crystal system
triclinic
monoclinic
triclinic
monoclinic
space group
P1 (#2)
P21/c (#14)
P1 (#2)
P21/c (#14)
a/Å
10.049(2)
27.406(4)
17.830(2)
13.896(2)
b/Å
15.041(3)
14.461(2)
23.277(3)
23.221(3)
c/Å
20.708(4)
25.124(4)
24.071(3)
18.872(2)
R/deg
101.561(2)
β/deg γ/deg
93.894(3) 105.461(3)
94.255(2)
V/Å3
2931(1)
9929(3)
9721(1)
5931(1)
Z
4
8
8
4
crystal size/mm3
0.3 0.1 0.1
0.3 0.07 0.07
0.3 0.1 0.1
0.3 0.1 0.1
unique reflections
12416
19172
36116
14487
parameters
703
1069
1783
505
Dcalc, g cm-3
1.155
1.602
1.388
0.998
F(000) μ (Mo KR), mm-1
1040 0.868
4313 1.204
3984 0.613
1800 0.921
R1 [|I| > 2σ]
0.0879
0.0980
0.0501
0.0295
wR2 [all reflections]
0.2215
0.3092
0.1344
0.0773
goodness of fit
1.090
1.048
0.829
1.075
95.144(1) 90.322(1) 102.220(1)
103.102(1)
max. shift/error
0.002
0.013
0.000
0.003
max. peak, e Å-3
1.938
2.148
0.638
0.49
min peak, e Å-3
-1.741
-2.390
-0.777
-0.33
Gas Adsorption Measurement. Nitrogen gas adsorption measurement was carried out on all specimens at 77 K using BELSORP 18plus volumetric adsorption equipment (BEL Japan). Water, methanol, and ethanol adsorption measurements were performed for [Zn2(sbpdc)2(bpy)] 3 4DMF using the BELSORP 18-plus at 298 K. The samples were evacuated at 100 C for over 48 h prior to the adsorption measurements. Thermogravimetry. Thermogravimetry measurements were executed on [Zn(bdc)(L1)], [Zn3(bpdc)3(L1)], Zn2(sbpdc)2(L1), and [Zn2(sbpdc)2(bpy)] using Bruker TG/DTA 2000 SA (Bruker) with a heating rate of 5 C min-1 under 100 mL/min of nitrogen or helium gas flow. Estimation of Pore Size Distribution. Estimation of pore size distribution was made by the HK method24 from the result of the nitrogen gas adsorption isotherm of [Zn2(sbpdc)2(bpy)].
’ RESULTS AND DISCUSSION The general key feature of the four compounds is their pillared layered structures where the layers are formed of zinc atoms bridged by the dicarboxylate while the pillar is the polypyridine. They differ in the metallic nodes, where three different secondary building units (SBUs) were observed having a hierarchy going from two- to three- to four-bidentate carboxylate per pair of zinc atoms. These SBUs support divergent dicarboxylate either in four or six directions, which consequently generate the symmetry of the Zn-carboxylate layer network. The second key feature of the structures is the coexistence of interpenetration and porosity, where the former depends on the length of both the carboxylate and the polypyridine pillars. The porosity is created by the
mismatch of the length of the carboxylate and the pillars for efficiency packing of the individual frameworks. [Zn(bdc)(L1)]. The structure of [Zn(bdc)(L1)] is shown in Figure 4, and the summary of the bond distances and angles is given in Table S1. The SBU node consists of a zinc dimer in distorted octahedral geometry formed by two bidentate bridging carboxylates (Zn-O of 2.014 and 2.073 Å and O-Zn-O of 173.9) from two terephthalates diverging along the a-axis, two chelating (Zn-O of 2. 124 and 2.291 Å and O-Zn-O of 60.6) terephthalates propagating along the b-axis, and two pairs of bipyridine in trans-positions (Zn-N of 2.164 and 2.148 Å) pointing along the c-axis. The Zn 3 3 3 Zn distance is 4.322 Å. The bidentate bridging carboxylate adopts the synanti mode of coordination with Zn-O-C angles of 124 and 154, respectively. This SBU may be considered as a two-blade paddlewheel. Due to the different coordination modes of the carboxylate within the dimeric SBU, the 4 4 grid deviates from being square with sides of 10 and 15 Å and angle of 105. Two pillars at each metallic node connect the layers to generate one of the two identical 3D-frameworks. There are two interpenetrating 3D-frameworks in the structure. The two interpenetrating frameworks create a cavity between the criss-cross terephthalate belonging to each framework, which is approximately 7 7 7 Å3. It does not appear to be any window to access these cavities. Consequently, [Zn(bdc)(L1)] does not adsorb nitrogen gas. PLATON estimation gives 26.5% void. Given the modes of coordination around the zinc atoms and the double rigid pillars per node, one may regard the structure to have low flexibility. 1800
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Figure 4. (a) Perspective view of [Zn(bdc)(L1)] along the c axis. (b) Crystal structure view of the ab plane. Aqua, red, blue, and gray spheres represent zinc, oxygen, nitrogen, and carbon atoms, respectively. All hydrogen atoms and atoms of one branch were omitted for clarity. (c) Crystal structure and void (shown as blue spheres) in the frameworks.
[Zn3(bpdc)3(L1)]. The structure of [Zn3(bpdc)3(L1)] is shown in Figure 5, and selected bond lengths and angles are given in Table S2. The SBU consists of a linear trimeric node having an octahedral ZnO6 at the center and two tetrahedral ZnO3N at the ends. Each node has six bidentate carboxylate groups branching out almost symmetrically in a hexagonal fashion to form layers with a triangular network of Zn-carboxylate. This SBU may be regarded as a six-blade paddlewheel, where there are three per nearest Zn atoms. The triangle is almost isosceles with sides of 15.4 Å. There are two slightly different nodes: a symmetric one consisting of Zn2-Zn1-Zn2 and a nonsymmetric one with Zn4-Zn3-Zn5. There are two different modes of coordination of the carboxylate in each case: two of syn-syn and four of syn-anti. The triangular layers are pillared at each end of the trimeric SBU to generate the 3Dframework. There are three independent frameworks, which are interpenetrated by each other. It is worthwhile to note that one of them is unique and consists of Zn2-Zn1-Zn2 (yellow network in Figure 5) and the other two frameworks are identical and consist of Zn4-Zn3-Zn5 (blue and red networks in Figure 5); this accounts for the presence of five independent Zn for triangular networks of trimers. The packing efficiency of these frameworks is rather poor, and thus, there are void spaces occupied by solvent, which are disordered. Due to the disorder
of the solvents in these cavities, the structure was resolved only for the framework after using SQUEEZE. PLATON estimates 28.9% void in the structure. This space is not easily accessible and therefore the nitrogen uptake is low. [Zn2(sbpdc)2(L1)]. The structure of [Zn2(sbpdc)2(L1)] is shown in Figure 6, and selected bond distances and angles are given in Table S3. In contrast to the two compounds discussed above, [Zn2(sbpdc)2(L1)] contains the conventionally observed four-blade paddlewheel SBU. Thus, each Zn is five-coordinate with four oxygen atoms in the basal plane and an apical nitrogen atom of the pillared bipyridine. The carboxylate groups adopt the syn-syn mode. There are three independent dimers, Zn1-Zn2, Zn3-Zn4, and Zn5-Zn6 belonging to the three different interpenetrating frameworks. These paddlewheel dimeric units are bridged by the carboxylate to form distorted 4 4 grids which are pillared by the bipyridine. Two of the three frameworks (red and blue in Figure 6) are similar and have asymmetric dimers, Zn1-Zn2 and Zn3-Zn4, alternating within both frameworks. The third framework (green in Figure 6) contains symmetric dimers, Zn5-Zn5 and Zn6-Zn6, alternating within the framework. The carboxylate is asymmetric and polar, with the SO2 on one side. In the structure there are 50% pointing along the b-axis and the other 50% point in the opposite sense. As for Zn(bdc)(L1) and Zn3(bpdc)3(L1), the solvents are disordered 1801
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Figure 5. Crystal structure of [Zn3(bpdc)3(L1)] (a) along the b axis and (b) along the c axis. Aqua, red, blue, and gray spheres represent zinc, oxygen, nitrogen, and carbon atoms, respectively. All hydrogen atoms and atoms of two branches were omitted for clarity. (c) Arrangement of three branches.
and, therefore, the structures of only the frameworks were determined. The void space amounts to 44.4%. Given the long acid and the long bipyridine, there are three interpenetrated frameworks as for Zn3(bpdc)3(L1). In contrast to Zn3(bpdc)3(L1), where the structure is pseudotrigonal and each triangle can allow one framework to interpenetrate through, in the present compound the grid has double the area and thus all three frameworks are easily interpenetrated through the grids. Even though there are three frameworks, they do not fill all the available space; so the three frameworks are asymmetrically placed and leave some spaces where the solvents are located. However, the solvents are again disordered and only SQUEEZE refinements were performed. [Zn2(sbpdc)2(bpy)] 3 4DMF. The structure of [Zn2(sbpdc)2(bpy)] 3 4DMF is shown in Figure 7, and selected bond distances and angles are given in Table S4. The SBU is similar to that of Zn2(sbpdc)2(L1) but with less distortion of the paddlewheel. The 4 4 network of Zn carboxylate is also similar but with different angles. In contrast to Zn2(sbpdc)2(L1), for [Zn2(sbpdc)2(bpy)] 3 4DMF there are only two interpenetrating frameworks due to the presence of a shorter pillar bipyridine (bpy of ca. 7 Å) which is less than half of L1 (ca. 16 Å). The sbpdc ligand bends slightly (164), and the distortion derived from the bend is compensated by the ligand of another side, which directs in the opposite way, as shown in Figure 7. The structure of [Zn2(sbpdc)2(bpy)] 3 4DMF was isomorphic with conventional MOFs consisting of zinc, aryldicarboxylic acid, and pillar ligand such as bpy or 1,4-diazabicyclo[2.2.2]octane (dabco). Void volume was estimated to be 50.5% by PLATON.
Thermogravimetry. Thermogravimetry was executed for the sake of revealing the amounts of introduced solvents. Figure S4 indicates a single step weight loss of [Zn(bdc)(L1)] on heating the compound below 280 C. 18% of loss of weight corresponds to six DMF molecules for each unit cell. This CP consists of a void between the two branches; therefore, three DMF molecules are involved in each void. [Zn3(bpdc)3(L1)] showed 16% loss of weight until 270 C, which corresponds to one DMF molecule per each zinc ion (Figure S5). [Zn2(sbpdc)2(L1)] shows a gradual two step decrease of weight until 90 and 180 C, which corresponds to two DMF molecules (Figure S6). [Zn2(sbpdc)2(bpy)] shows the best weight loss until 170 C. Two step weight loss was observed, which corresponds to three and five DMF molecules, respectively (Figure S7). These data are summarized in Table 2. As shown in the table, void volume ranged between 26.5 and 50.5%. However, the volumes for each adsorbed DMF are similar to each other instead of any ligands and coordination geometry. The void volume of DMF in [Zn2(sbpdc)2(bpy)] is relatively high, and that is probably caused by the low packing of the DMF in the MOF, which has two kinds of voids, as shown in Figure 5b. Gas Sorption Property. We have already mentioned that Zn(bdc)(L1) and [Zn3(bpdc)3(L1)] do not show any nitrogen gas adsorption properties, even though they contain cavities. This is due to the lack of access to these cavities within the crystals. In contrast, both Zn2(sbpdc)2(L1) and [Zn2(sbpdc)2(bpy)] 3 4DMF exhibit gas-sorption properties, as there are channels with easy access. [Zn2(sbpdc)2(L1)] has a triply 1802
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Figure 6. (a) Perspective view of [Zn2(sbpdc)2(L1)] along the a axis. (b) Crystal structure of the ac plane. Aqua, yellow, red, blue, and gray spheres represent zinc, sulfur, oxygen, nitrogen, and carbon atoms, respectively. All hydrogen atoms and atoms of one branch were omitted for clarity. (c and d) Representations of the crystal structure and void space (blue ball) along the a (c) and the b (d) axes.
Table 2. Results of TG compound void volume ratio
a
a
Zn(bdc)(L1)
Zn3(bpdc)3(L1)
Zn2(sbpdc)2(L1)
[Zn2(sbpdc)2(bpy)]
26.5%
28.9%
44.4%
V/Å3
2931(1)
9929(3)
9721(1)
50.5% 5931(1)
Z
4
8
8
4
void volume in unit cell/Å3 weight loss
777 18%
2869 16%
4316 26%
2995 28%
adsorbed DMF/unit cell
6
24
40
20
void volume for each DMF/Å3
129
120
108
150
decomposition temp/K
290
395
345
405
Calculated by PLATON.
interpenetrated structure; however, it still has void volume (at a ratio of 50.5%). From the nitrogen adsorption isotherm measurement at 77 K (Figure 8), [Zn2(sbpdc)2(L1)] adsorbed a small amount of nitrogen due to its void volume. The Langmuir and BET surface area of [Zn2(sbpdc)2(L1)] were estimated to be ca. 57.32 (BET) and 67.59 (Langmuir) m2/g, respectively. The adsorption and desorption isotherms overlapped each other, and the adsorption behavior is reversible. [Zn2(sbpdc)2(bpy)] 3 4DMF formed a doubly interpenetrated structure, as is often the case with the MOFs consisting of 4,40 biphenyldicarboxylic acid.25 A one dimensional channel was observed along the c-axis, the dimension of which was estimated
to be ca. 11 8 Å. Four DMF molecules were observed in the channels in a highly disordered fashion. From elemental analyses and thermal analysis, DMF molecules can be eliminated by evacuation or at elevated temperature. Figure 9a shows the nitrogen adsorption isotherm of [Zn2(sbpdc)2(bpy)]. The adsorption and desorption behavior was reversible, the adsorption profile is classified to type I, and the specific surface area of [Zn2(sbpdc)2(bpy)] was estimated to be 301.14 (BET method) and 329.67 (Langmuir method) m2/g. Figure 9b shows the pore size distribution of [Zn2(sbpdc)2(bpy)] evaluated by the HK method.24 Steep peaks were observed in Figure 9b, showing that the compound has a uniform pore 1803
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Figure 7. Crystal structure of [Zn2(sbpdc)2(bpy)] 3 4DMF along the b axis (a) and along the a axis (b) and 1D arrangement of zinc dimer and sbpdc (c). Hydrogen atoms are omitted for clarity. Legends: Zn, pale blue; N, blue; O, red; C, gray; S, yellow. (d) Representation of crystal structure and void (blue and pink balls) in the framework.
Figure 8. Nitrogen gas adsorption isotherm of [Zn2(sbpdc)2(L1)] at 77 K.
consisting of the ordered frameworks. Two peaks in the figure indicate that the pore shape is rectangular, which is reasonable to its crystal structure. Adsorption isotherms of various solvents on [Zn2(sbpdc)2(bpy)] 3 4DMF were also measured as shown in Figure 10. Adsorption isotherms of these solvent molecules are almost same
in the low-pressure region. [Zn2(sbpdc)2(bpy)] 3 4DMF can uptake three more equivalents of water molecules above the humidity region. [Zn2(sbpdc)2(bpy)] 3 4DMF adsorbs two methanol molecules at high vapor pressure of methanol at each zinc dimer, and one ethanol can be uptaken into the [Zn2(sbpdc)2(bpy)] 3 4DMF. Comparison. The differences in the coordination could be due to various factors. The acidity of H2sbpdc is remarkably stronger than that of H2bpdc due to the electron-withdrawing effect of the sulfone group, as reported previously. Therefore, the shifted solution equilibrium favors the formation of the large and good crystals. The bpdc and bpy ligands often resulted in triangular grid MOFs, and the structure of [Zn3(bpdc)3(L1)] is thought to become triangular for the same reason as the previous reports.19 By using sbpdc, the triangular structure causes steric hindrance, and a paddlewheel type structure was obtained. As reported above, 4,40 bipyridyl and sbpdc affords a MOF of paddle-wheel coordination geometry. 1804
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Figure 9. (a) Nitrogen gas adsorption isotherm of [Zn2(sbpdc)2(bpy)] at 77 K. (b) Pore size distribution of [Zn2(sbpdc)2(bpy)] by the HK method.
interpenetrated, and it is suggested that the MOFs with large aperture will be realized if MOFs with L1 can be synthesized without interpenetrating.
’ ASSOCIATED CONTENT
bS
Supporting Information. Photographic views of crystals, selected bond lengths and bond angles of crystals and various bridging ligands, thermogravimetric curves, and crystallographic information files. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Figure 10. Adsorption isotherms [Zn2(sbpdc)2(bpy)] 3 4DMF at 298 K.
for
various
solvents
of
Unconventional Zn2(CO2)2 square-grids align in the ab plane of [Zn(bdc)(L1)]. [Zn2(bdc)2(bpy)], consisting of a paddlewheel structure, was reported in several papers;16,25,26 however, a Zn2(CO2)2 square-grid layer has not been reported in the case of bpy, dabco, or pyrazine, except for my previous study,8 which indicated that the uncommon coordination arrangement is due to the bulky side groups in the dicarboxylic ligands. In this study, [Zn(bdc)(L1)] contains a simple bdc ligand; therefore, this could result in the difference between the L1 and bpy. As L1 and bpy have the same pyridyl group available for coordination while the basicity and bulkiness are almost same, it could be derived from an arrangement of interpenetrating branches. [Zn2(bdc)2(bpy)]25 has a low void volume ratio (34.9%), which would become increased with subtracting bpy to L1. Therefore, the uncommon square-grid layer is constructed but with low void volume. In other words, it is indicated that ligands and metals have a tendency to be abstracted in the space made of metalorganic polyhedral cages.
’ SUMMARY Novel metal-organic frameworks having dicarboxylate and long and linear bridging ligand L1 (L1 = 1,4-bis(4-pyridylethynyl)benzene), [Zn(bdc)(L1)], [Zn2(sbpdc)2(L1)], and [Zn3(bpdc)3(L1)] were synthesized, and their structures were determined by single-crystal X-ray diffraction study. They have interpenetrated structures and showed low nitrogen uptakes. The coordination geometries of the SBU are different from each other, due to the structural difference of dicarboxylic ligands. From these results, MOFs consisting of L1 have a tendency to be
Corresponding Author
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