Microporous Heptazine Functionalized (3,24)-Connected rht-Metal

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Heptazine functionalized (3,24)-Connected rht Metal-Organic Framework: Synthesis, Structure and Gas Sorption Properties. Mohamed Eddaoudi, Ryan Luebke, #ukasz weselinski, Zhijie Chen, Youssef Belmabkhout, and Lukasz Wojtas Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/cg401802s • Publication Date (Web): 14 Jan 2014 Downloaded from http://pubs.acs.org on January 16, 2014

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Crystal Growth & Design

A Microporous Heptazine functionalized (3,24)-Connected rht Metal-Organic Framework: Synthesis, Structure and Gas Sorption Analysis. Ryan Luebke, † Łukasz J. Weseliński, † Youssef Belmabkhout, † Zhijie Chen, † Łukasz Wojtas,‡ Mohamed Eddaoudi*,† †

Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, 4700 King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia ‡ Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, USA

Supporting Information Placeholder ABSTRACT: Here we synthesized the highly porous rht-MOF9 as the first example of an rht-MOF having a polycyclic central core. This material was synthesized from a pre-designed polyheterocyclic nitrogen-rich hexacarboxylate (tri-isophthalate) ligand, which serves as the 3-connected, trigonal molecular building block (MBB). When reacted under the proper conditions, this ligand, having three coplanar isophthalic acid moieties, codes for the in-situ formation of the targeted 24-connected copper based supermolecular building block (SBB) having rhombicuboctahedral geometry. This combination of a 24-connected building block linked through 3-connected nodes results in a novel material with the singular rht topology. The rht-MOF-9 compound exhibits promising H2 and CO2 adsorption properties in comparison to previously reported rht-MOFs.

Metal-organic frameworks (MOFs) are a unique class of materials which, due to their modular nature, present researchers with the ability to tune their physical and chemical properties for use in a wide diversity of applications.1 MOFs, due to their high degree and controlled porosity, are particularly suited for gas storage and separation applications. Targeted synthesis through use of several design methods2-7 has allowed tremendous advances in the ability to construct materials with desired topologies and functionality. Through judicious selection of ligands and careful control of reaction conditions, MOFs can be assembled from pre-determined building blocks. The supermolecular building block (SBB) approach offers potential to design functional MOF materials by targeting specific metal organic polyhedra (MOPs) which can act as highly connected nodes in the resulting structure, thus limiting the possible topological outcomes and improving predictability of structure. It has been shown by our group that a 24-connected copper paddlewheel based SBB having rhombicuboctahedral geometry linked through trigonal (3-connected) nodes results in a singular net (Figure 1) having rht topology (the naming of this topology is derived from the connectivity of the nodes i.e. rhombicuboctahedral and trigonal).6, 8 This design strategy has allowed for directed

synthesis of rht-MOFs based on extended and/or functionalized ligands, resulting in a diversity of highly porous MOFs.6, 8-12 MOFs are particularly well suited for use in applications including carbon capture or CO2 storage, where selective adsorption or storage of large amounts of CO2 is required.13-14 The high degree of porosity and moderate heats of adsorption (20-50 kJ mol1 14 ) have allowed the synthesis of MOFs which can reversible adsorb CO2 in amounts up to ~8 mmol g-1, at low pressure (1 bar at 298K)15 and greater than 50 mmol g-1, at high pressure (50 bar at 298K).16 Thus MOFs are positioned to be a strong competitor with liquid amine, zeolite, or activated carbon based sorbents in these processes. 13 One strategy successfully used in enhancing the energetics and resultant uptake of CO2 in MOF materials, is through introduction of nitrogen donor groups to the organic ligand. This has resulted in dramatic increases in isosteric heats of adsorption (Qst) at low loading. This is exemplified by MIL-53/Amino-MIL-53 where the amine functionalized analog exhibits low loading Qst enhancements (35 vs. 50 kJ mol-1).17 Furthermore, improvements of Qst (of ~5 kJ mol-1) at all reported loadings was shown in a mixed ligand Zn based material MTAF-3,18 an analog of MOF508,19 which was modified through incorporation of triazole functionality into one of the ligands. To exploit the tunability of the rht-MOF series for use as sorbents for CO2, we previously reported rht-MOF-7, synthesized from a nitrogen rich ligand having secondary amine and triazine functionality. As anticipated, rht-MOF-7 shows a particularly strong affinity for CO2 due to the exposed nitrogen donor groups in the cavities. To further enhance the CO2 uptake of this system, herein we report the synthesis of an rht-MOF (rht-MOF-9) synthesized from an analogous ligand having an s-heptazine (tri-striazine) core in place of the s-triazine core in the rht-MOF-7. To the best of our knowledge, rht-MOF-9 is the first example of an rht-MOF having a polycyclic central core. The organic ligand 2,5,8-tris(3,5-dicarboxyphenylamino)-1,3,4,6,7,9,9bheptaazaphenalene (TDCPAH) is composed of a nitrogen rich sheptazine center which is linked to three isophthalic acid moieties

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through secondary amines (Figure 1). The readily exposed amines and a polarized core (s-heptazine) are attractive features for H2 and CO2 adsorption studies and as a comparison to reported data from rht-MOF-1 and rht-MOF-7

Figure 1. Strategy for synthesis of rht-MOFs. (Top Left) The molecular building blocks: a trigonal tri-isophthalate ligand and a bimetal tetracarboxylate paddlewheel cluster and (Bottom Left) their corresponding geometries, represented as a green triangle and a red square. (Center) The combination of these building blocks results in a polyhedron having external functionality consisting of 24 trigonal nodes. (Right) When expanded to the 3periodic net, the resultant structure has rht-a topology represented as polyhedra linked through triangles. Indeed, the solvothermal reaction of Cu(NO3)2·2.5 H2O and TDCPAH in a solution of DMF, DMSO and HBF4 yielded blue octahedral crystals of rht-MOF-9. Single crystal diffraction reveals that the compound has a formula unit of Cu3(TDCPAH)(Solvent)x and that the compound crystallized in the tetragonal I4/m space group with unit cell edge lengths of a=b=27.934(2)Å and c=41.081(4)Å. Topological analysis confirms that the material has the expected rht-a net. In the crystal structure of rht-MOF-9, each central s-heptazine core is covalently linked at the 2, 5 and 8-positions through amine moieties to the 5-position of each isophthalate terminus. The 120˚ angle between the carboxylates of the isophthalate terminus allows formation, in situ, of the 24-connected rhombicuboctahedral20-21 (rco)22 SBB (Figure 2a). This SBB, is one of the three cages in this structure and is composed of 24 isophthalate ligands connected by 12 dimeric copper paddlewheels (shown as red squares in Figures 1, 2). The diameter of the cage, accounting for van der Walls radii is ~13Å. The packing of the rhombicuboctahedral SBBs results in the formation of two additional cages, a truncated cube (tcu)22 and an augmented rhombic dodecahedron (rdo-a).22 The tcu cage (Figure 2b) encloses a space that is tetrahedral in geometry and can accommodate a sphere of ~9Å in diameter (represented by a yellow sphere in Figure 2). This cage is delimited by four TDCPAH ligands; (represented as green triangles in the tiling representation in Figure 2). The isophthalate moieties are linked at the corners of the tetrahedral cage through 3 copper paddlewheels forming a 3membered ring. The rdo-a cage (Figure 2c) encloses space that is octahedral in geometry with a minimal diameter, which passes through the center of the cage, of ~17Å. The cage is delimited by 8 TDCPAH ligands which lie on the faces of the octahedral enclosed space. The isophthalate moieties are linked through copper

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paddlewheels at each vertex of the octahedra forming a 4membered ring.

Figure 2. Crystal structure fragments (left) showing the three cages in rht-MOF-9 and the corresponding tiling representations (right). (a) rco, (b) tcu, (c) rdo-a. Thermogravimetric analysis (TGA) experiments performed on the as synthesized rht-MOF-9 reveal an initial solvent loss of ~50% which occurred in the temperatures range of room temperature to 250˚C. The rate of loss decreases slightly between 250˚C and 350˚C at which point framework decomposition begins (see Supporting Information Figure S8). A methanol exchanged sample, was prepared by washing the crystalline product with DMF over a period of 3 days, refreshing the solution 3-4 times per day. This was followed by solvent exchange with methanol over the course of 3 days, again refreshing the solution 3-4 times per day. TGA of the methanol exchanged sample reveal a 15% loss of mass occurs around 100˚C which can be attributed to loss of coordinated solvent. The sample remains stable and does not lose an appreciable amount of mass until decomposition, which occurs at around 275˚C (see Supporting Information Figure S8). Low pressure gas sorption analysis was performed on an activated sample of rht-MOF-9. To activate the sample, through removal of guest solvent molecules, the methanol exchanged sample was placed under dynamic vacuum and subsequently heated at a rate of 1˚C per minute and held at 55˚C for 6 hours followed by additional heating at a rate of 1˚C per minute and held at 85˚C for 6 hours. Gas sorption studies confirmed the permanent porosity of this compound. The pore size distribution based on the argon isotherm (Figure 3) collected at 87 K reveals relatively narrow pore size distribution (see Supporting Information Figure S6) with three distinct pore size ranges of 8-11Å, 12-16Å and 17-21Å which are consistent with the crystallographic dimensions of the rco, tco and rdo-a cages respectively. The available free volume for rht-MOF-9 was determined experimentally from the N2 and Ar isotherms based on the uptake at 0.95 p/po (1.07 cc g-1 and 1.01 cc g-1 respectively) (Figures 3, S5), which is in good agreement with the free volume based on the crystal structure ( 0.943


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cc g-1). The apparent BET and Langmuir surface areas, based on the Ar isotherm, were estimated to be 2420 m2 g-1 and 3070 m2 g-1 respectively. These values are significantly higher than the surface areas for our previously reported rht-MOF-7 (Langmuir 2170 m2 g-1),9 synthesized from a slightly smaller (s-triazine based) trigonal MBB. The surface area of rht-MOF-9 is closely comparable to the prototypical parent rht-MOF-1 which has a slightly larger (tetrazole and Cu trimer based) trigonal inorganic MBB (BET 2847 m2 g-1, Langmuir 3223 m2 g-1).6

Figure 3. Low pressure fully reversible argon adsorption (solid squares) and desorption (open squares) isotherms at 87 K for the methanol exchanged rht-MOF-9. CO2 adsorption experiments showed that rht-MOF-9 exhibits only a slightly lower CO2 uptake than rht-MOF-7 at very low pressure below 0.05 bar (ca. 38 torr) and 298 K (Figure 4). Interestingly, at relatively low partial pressures (0.1 bar (76 torr) akin to post-combustion capture, the CO2 uptake for rht-MOF-9 showed higher volumetric and gravimetric uptake (95 cc/cc, 1.1 mmol g-1) than rht-MOF-1 (37 cc/cc, 0.32 mmol g-1) and rhtMOF-7 (68 cc/cc, 0.83 mmol g-1). At 1 bar, the total CO2 uptake was also drastically improved and rht-MOF-9 exhibits one of the highest gravimetric and volumetric uptakes reported for rhtMOFs. This observed enhancement in CO2 uptake, combined with a noticeable reduction in the Qst at low loading when compared to rht-MOF-7, can be translated into an enhancement in the energy/efficiency tradeoff for gas separation applications. However, it should be noted that reduced CO2 Qst (at low loading) compared to rht-MOF-7 (32 kJ mol-1 vs. 45 kJ mol-1) and the low degree of energy uniformity (see Supporting Information Figure S7) will not necessarily induce an improvement in the affinity and CO2 selectivity over other gases such as CH4 and N2. In this case, further studies are sought in our group to explore the CO2 separation properties of rht-MOF-9. It should be mentioned that the accuracy of the Qst determination for rht-MOF-9 was confirmed by the established linearity of CO2 isosters for the entire studied range of CO2 loadings. In light of the high surface area achieved when incorporating the polycyclic central core, we found it compelling to further explore the H2 adsorption properties of rht-MOF-9. Interestingly, at 77 K and 1 bar, rht-MOF-9 shows a relatively higher gravimetric uptake of ~2.72 wt% (Figure 5) Qst of 6.9 kJ mol-1 at low loading and 5.8 kJ mol-1 at higher loading (see Supporting Information Figure S4). This uptake is greater than the best reported rhtMOFs23 and is in excess of rht-MOF-7 (2.65 wt% @ 1bar and 77

K)24 and considerably higher uptake than rht-MOF-1 (2.4 wt% @ 1 bar and 77 K).6 The increase in uptake compared to rht-MOF-7 can be likely attributed to the increase in the specific surface area due to ligand extension and subsequent rdo-a cages expansion (see Supporting Information Table S2). Whereas, the increase in comparison to rht-MOF-1 can likely be attributed to enhanced interactions due to the effect of the localized charge density and highly confined pores/cages, in the tcu and rdo-a cages, resulting in more uniform MOF-sorbent interactions (see Supporting Information Figure S4a). The combination of high surface area and high mass density (this last in direct relationship with the charge density) may explain the enhancement in H2 adsorption as was pointed out in recent work.25

Figure 4. CO2 adsorption isotherms at 298 K on rht-MOF-9 in comparison to the corresponding data for rht-MOF-1 and rhtMOF-7

Figure 5. Low pressure fully reversible hydrogen isotherms for the methanol exchanged rht-MOF-9 at 77 K (red squares) and 87 K (blue squares). Solid squares and open squares represent adsorption and desorption respectively. Powder x-ray diffraction (PXRD) measurements were performed to confirm phase purity and confirm the stability of rhtMOF-9 after sorption and solvent exchange (see Supporting Information Figure S9). The experimental PXRDs are consistent with the PXRD pattern calculated based on the crystal structure using the Reflex module in Accelrys Materials Studio v6.1 (see Supporting Information Figure S9). Variable Temperature PXRD (VTPXRD) experiments, performed under vacuum on the methanol exchanged sample, are consistent with the TGA measurements



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and show a high degree of thermal stability, with significant reduction of crystallinity beginning near 250˚C (Figure 6). Unfortunately similar to many of the reported rht-MOFs, rht-MOF-9 loses crystallinity after prolonged exposure to air.

Figure 6. Variable temperature PXRD of methanol exchanged rht-MOF-9 while under vacuum. Crystallinity is retained up to 200˚C upon which there is a substantial loss of crystallinity as noted by the reduction in diffraction intensity. We have successfully used the rht-MOF platform to prepare a nitrogen rich functionalized rht-MOF-9 which exhibits a high specific surface area in combination with high charge density. By incorporating a ligand having a s-heptazine central core linked to three isophthalic acid moieties through secondary amines, rhtMOF-9 exhibits high CO2 uptake at both relatively low (0.1 bar) and atmospheric pressures. In addition H2 storage capacity at 1 bar and 77 K was found to be exceptionally high in comparison to other reported MOFs and is the highest reported low pressure uptake for rht-MOFs. Further adsorption studies are in progress to evaluate the performance of rht-MOF-9 for CO2 separation in the presence of N2, CH4 and H2 containing gas mixtures as well as hydrogen and methane storage at relatively high pressures.

ASSOCIATED CONTENT Supporting Information Experimental procedures, PXRD, TGA, crystallographic structural analysis, additional gas sorption plots and ligand synthesis and characterization. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *E-Mail: [email protected]

Author Contributions RL designed the experiments, synthesized and characterized the material, wrote the manuscript, and performed data interpretation; ŁJW synthesized and characterized the ligand; ZC collected low pressure sorption isotherms; YB analyzed CO2 sorption data; ŁW refined the crystal structure.

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT

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REFERENCES (1) MacGillivray, L. R., Metal-organic frameworks: design and application. Wiley. com: 2010. (2) Liu, Y.; Eubank, J. F.; Cairns, A. J.; Eckert, J.; Kravtsov, V. C.; Luebke, R.; Eddaoudi, M., Angew. Chem. Int. Ed. 2007, 46, 18, 3278. (3) Schoedel, A.; Wojtas, L.; Kelley, S. P.; Rogers, R. D.; Eddaoudi, M.; Zaworotko, M. J., Angew. Chem. Int. Ed. 2011, 50, 48, 11421. (4) Xue, D.-X.; Cairns, A. J.; Belmabkhout, Y.; Wojtas, L.; Liu, Y.; Alkordi, M. H.; Eddaoudi, M., J. Am. Chem. Soc. 2013, 135, 20, 7660. (5) Cairns, A. J.; Perman, J. A.; Wojtas, L.; Kravtsov, V. C.; Alkordi, M. H.; Eddaoudi, M.; Zaworotko, M. J., J. Am. Chem. Soc. 2008, 130, 5, 1560. (6) Nouar, F.; Eubank, J. F.; Bousquet, T.; Wojtas, L.; Zaworotko, M. J.; Eddaoudi, M., J. Am. Chem. Soc. 2008, 130, 6, 1833. (7) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O'Keeffe, M.; Yaghi, O. M., Science 2002, 295, 5554, 469. (8) Eubank, J. F.; Nouar, F.; Luebke, R.; Cairns, A. J.; Wojtas, L.; Alkordi, M.; Bousquet, T.; Hight, M. R.; Eckert, J.; Embs, J. P.; Georgiev, P. A.; Eddaoudi, M., Angew. Chem. Int. Ed. 2012, 51, 40, 10099. (9) Luebke, R.; Eubank, J. F.; Cairns, A. J.; Belmabkhout, Y.; Wojtas, L.; Eddaoudi, M., Chem. Commun. 2012, 48, 10, 1455. (10) Farha, O. K.; Eryazici, I.; Jeong, N. C.; Hauser, B. G.; Wilmer, C. E.; Sarjeant, A. A.; Snurr, R. Q.; Nguyen, S. T.; Yazaydın, A. Ö.; Hupp, J. T., J. Am. Chem. Soc. 2012, 134, 36, 15016. (11) Peng, Y.; Srinivas, G.; Wilmer, C. E.; Eryazici, I.; Snurr, R. Q.; Hupp, J. T.; Yildirim, T.; Farha, O. K., Chem. Commun. 2013, 49, 29, 2992. (12) Hong, S.; Oh, M.; Park, M.; Yoon, J. W.; Chang, J.-S.; Lah, M. S., Chem. Commun. 2009, 36, 5397. (13) Liu, Y.; Wang, Z. U.; Zhou, H.-C., Greenhouse Gases: Science and Technology 2012, 2, 4, 239. (14) Sabouni, R.; Kazemian, H.; Rohani, S., Environ Sci Pollut Res 2013, 1. (15) Caskey, S. R.; Wong-Foy, A. G.; Matzger, A. J., J. Am. Chem. Soc. 2008, 130, 33, 10870. (16) Furukawa, H.; Ko, N.; Go, Y. B.; Aratani, N.; Choi, S. B.; Choi, E.; Yazaydin, A. Ö.; Snurr, R. Q.; O’Keeffe, M.; Kim, J.; Yaghi, O. M., Science 2010, 329, 5990, 424. (17) Arstad, B.; Fjellvåg, H.; Kongshaug, K.; Swang, O.; Blom, R., Adsorption 2008, 14, 6, 755. (18) Gao, W.-Y.; Yan, W.; Cai, R.; Williams, K.; Salas, A.; Wojtas, L.; Shi, X.; Ma, S., Chem. Commun. 2012, 48, 71, 8898. (19) Chen, B.; Liang, C.; Yang, J.; Contreras, D. S.; Clancy, Y. L.; Lobkovsky, E. B.; Yaghi, O. M.; Dai, S., Angew. Chem. Int. Ed. 2006, 45, 9, 1390. (20) Eddaoudi, M.; Kim, J.; Wachter, J.; Chae, H.; O'keeffe, M.; Yaghi, O., J. Am. Chem. Soc. 2001, 123, 18, 4368. (21) Moulton, B.; Lu, J.; Mondal, A.; Zaworotko, M. J., Chem. Commun. 2001, 9, 863. (22) O’Keeffe, M.; Peskov, M. A.; Ramsden, S. J.; Yaghi, O. M., Acc. Chem. Res. 2008, 41, 12, 1782. (23) Wilmer, C. E.; Farha, O. K.; Yildirim, T.; Eryazici, I.; Krungleviciute, V.; Sarjeant, A. A.; Snurr, R. Q.; Hupp, J. T., Energy & Environmental Science 2013, 6, 4, 1158. (24) Li, B.; Zhang, Z.; Li, Y.; Yao, K.; Zhu, Y.; Deng, Z.; Yang, F.; Zhou, X.; Li, G.; Wu, H.; Nijem, N.; Chabal, Y. J.; Lai, Z.;

Authors gratefully acknowledge KAUST for funding.


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Han, Y.; Shi, Z.; Feng, S.; Li, J., Angew. Chem. Int. Ed. 2012, 51, 6, 1412. (25) Goldsmith, J.; Wong-Foy, A. G.; Cafarella, M. J.; Siegel, D. J., Chem. Mater. 2013, 25, 16, 3373.



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Microporous Heptazine Functionalized (3,24)-Connected rht-Metal

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