25565
2006, 110, 25565-25567 Published on Web 12/06/2006
Coordination Symmetry-Dependent Structure Restoration Function of One-Dimensional MOFs by Molecular Respiration Atsushi Kondo,† Hiroshi Noguchi,† Hiroshi Kajiro,*,‡ Lucia Carlucci,§ Pierluigi Mercandelli,§ Davide M. Proserpio,§ Hideki Tanaka,† Katsumi Kaneko,† and Hirofumi Kanoh*,† Graduate School of Science and Technology, Chiba UniVersity, Yayoi, Inage, Chiba 263-8522, Japan, Nippon Steel Corporation, Shintomi, Futtsu, Chiba 293-8511, Japan, and Dipartimento di Chimica Strutturale e Stereochimica Inorganica, UniVersita` di Milano, Milano, Italy ReceiVed: August 23, 2006; In Final Form: October 23, 2006
One-dimensional metal-organic compounds with cis, trans symmetry-controlled counter anions were synthesized (cis compound {[Cu(azpy)(H2O)2(OTs)2]‚2H2O‚(acetone)} (1) and trans compound {[Cu(H2O)4Cu(azpy)2(OTs)2(H2O)2]‚2(OTs)‚2H2O‚2EtOH} (2)). Only 2, having trans conformation, exhibited a complete structure-restoration effect with a mechanism involving layering of molecular “bricks” of water and solvent molecules.
1. Introduction In the field of metal-organic frameworks (MOFs), many researchers have realized control of the dimensionality of compounds and their framework structures.1 In the next stage of MOF chemistry, it has become important to control the local symmetry structures, including specific functions for catalysis, sensing, host-guest chemistry, optics, and magnetics through the development of their selective synthesis. It is known that counter anions and solvents have strong effects on the structure of MOFs.2 Relevant counter anions bear structures with different morphology3 and often each solvent prefers to produce an inherent dimensional framework.4 However, there are few systematic reports on the interaction between counter anions and solvents controlling the local symmetry in the MOFs, although careful studies on the interaction between counter anions and solvents themselves may show a key to the fine control of MOFs. In the meantime, there are many examples of structural destruction-construction by guest exclusion-inclusion.5 It shows the character of the softness of MOFs clearly. However, few papers are reported standing on the view point that aims to restore the framework structure partially and selectively in the process of restoration by guest molecules. In this work, we selected the p-toluensulfonate anion (OTs) as a counteranion, two kinds of solvents (acetone and ethanol) and trans-4,4′-azobispyridine (azpy) as a ligand. Because p-toluenesulfonate can interact with metal cations through ionic bonding and with aromatic ligand through π-π interaction, OTs * Corresponding authors. Hirofumi Kanoh: tel: (+81) 43-290-2770; fax: (+81) 43-290-2788; e-mail:
[email protected]. Hiroshi Kajiro: tel: (+81) 439-80-2709; fax: (+81) 439-80-2746; e-mail: hkajiro@ re.nsc.co.jp. † Graduate School of Science and Technology, Chiba University. ‡ Nippon Steel Corporation. § Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Universita` di Milano.
10.1021/jp065438l CCC: $33.50
acts as a bifunctional chelate and is expected to play an important role in the structural formation of MOFs. In addition, the strong interaction between the electron-deficient OTs ring and electron-rich azpy ring can be expected to form a fine structure. In this paper, we demonstrate the cis- and transsymmetry control with solvent molecules of OTs in onedimensional (1D) chain compounds and symmetry-selective structural self-restoration by exposure to vapors. 2. Experimental Section We synthesized 1D chain coordination polymers; the compound {[Cu(azpy)(H2O)2(OTs)2]‚2H2O‚(acetone)} (1) was grown in water-acetone, and {[Cu(H2O)4Cu(azpy)2(OTs)2(H2O)2]‚ 2(OTs)‚2H2O‚2EtOH} (2) was grown in water-ethanol.6 The single-crystal structures of the compounds were solved by direct method and full-matrix least-squares analysis (SHELXTL-97)7 using the WinGX program package8 and examined by elemental analysis.6,9 Thermal gravimetric analysis was performed from room temperature to 500 °C under N2 gas flow (200 mL/min). Structure restorations by molecular respiration were examined by in situ X-ray diffraction measurements on improved Bruker MXP3 system with graphite-monochromated Cu KR radiation (λ ) 1.5406 Å) operated at 1000 W power (40 kV, 25 mA). 3. Results and Discussion 3.1. Crystal Structure of 1 and 2. In 1, the Cu(II) ion is in a distorted octahedral geometry, coordinated by two oxygen atoms from water, two nitrogen atoms from azpy, and two oxygen atoms from OTs (Figure 1). The OTs anions interact with an azpy through π-π stacking (the distances between the ring of the azpy ligands and the ring of OTs anion; 3.36 and 3.37 Å) and turn in the same direction (cis conformation). Alternatively, in 2, the Cu(II) atoms have two atomically separate environments. One Cu ion is in an environment similar to that of the Cu(II) ion in 1, coordinated by two oxygen atoms © 2006 American Chemical Society
25566 J. Phys. Chem. B, Vol. 110, No. 51, 2006
Letters
Figure 1. Local structures of Cu on 1 (left) and 2 (right) with 50% thermal ellipsoid. Hydrogen atoms are omitted for clarity. Figure 3. XRPD patterns of 2; (a) simulation pattern from the structure obtained by single-crystal structure determination, (b) heating up to 100 °C, (c) water vapor exposure, and (d) water and ethanol vapor exposure.
Figure 2. Schematic (left) and space-filling (right) representation of solvent position in 1 (a) and 2 (b).
from water, two nitrogen atoms from azpy, and two oxygen atoms from OTs, and the other Cu(II) ion is surrounded by four oxygen atoms from water and two nitrogen atoms from azpy. The two Cu(II) ions are bridged by an azpy ligand and aligned one after the other. It is noteworthy that the metal ion in a 1D polymer including an OTs anion is in two different coordination environments. There are also two kinds of OTs anions; one interacts with one Cu ion directly, whereas the other coordinates with the other Cu ion via water molecules by hydrogen bondings. Both OTs anions are stabilized by π-π stacking and the distances between the rings of azpy ligands and the rings of OTs are longer than that in 1. This means that OTs molecules in 2 are bound weakly and have a higher degree of freedom than that in 1. Two oxygen atoms of one OTs connect to two water molecules that coordinate to the Cu atom. Moreover, the two kinds of OTs anions of coordination and hydrogen bondings have mutual trans conformations. In both compounds, included guest molecules are stabilized by hydrogen bondings between the guest molecules and OTs (Figure 2). In 1, an oxygen atom of the acetone molecule bonds to the β hydrogen of the OTs aromatic ring (bonding distance: 2.618 Å), and hydrogen atoms of acetone molecules bond to oxygen atoms of the two other OTs (bonding distances: 2.959 and 3.313 Å, respectively). In 2, a hydrogen atom on C2 of an ethanol molecule bonds to the oxygen atom of OTs that coordinates to the Cu(II) atom via a water molecule (bonding distance: 1.812 Å) and a hydrogen atom of the hydroxyl group bonds to an oxygen atom of another OTs (bonding distance: 3.125 Å). Interestingly, ethanol molecules connect to only one Cu(II) atom via a water molecule and bind 1D chains running in the opposite direction. 3.2. Thermal Stability and Structure Restoration. Thermal gravimetric analysis showed that the weight loss up to 100 °C from 1 corresponded to the loss of guest molecules (observed, 12.2%; calcd, 13.1%), whereas that from 2 corresponded to the
loss of guests and all water molecules (observed, 13.2%; calcd; 13.9%). In situ XRPD measurements showed a decline in crystallinity of both compounds by heating up to 100 °C, and even by a vacuum only at room temperature. This reveals that these compounds are very soft materials and guest molecules support the crystal structures. We succeeded in controlling the coordination symmetry with the aid of OTs to provide polymorphism exhibiting a completely different response to vapor exposure, as shown below. The effect of vapor exposure on crystallinity was examined after vacuum treatment at 100 °C, as shown in Figure 3 (see also the Supporting Information). We exposed the compounds to a mixed vapor of water and a polar organic compound (methanol, ethanol, 1-propanol, 2-propanol, or acetone). Compound 1 did not have its crystal structure restored by exposure of any of the vapor mixtures. Compound 2 recovered its structure by exposure to water vapor. Exposure to the waterethanol vapor mixture led to even better restoration of the crystal structure. The water/methanol vapor mixture showed a similar restorative effect on 2. None of the other coexisting solvents restored the crystal structure of 2. From these results, restoration of the crystalline structure of trans conformation compound 2 was strongly dominated by the alcohol hydroxyl group and 2 also exhibited size selectivity. It is noteworthy that only trans conformation compound 2 exhibits an explicit structure-memory function facilitated with the assistance of an optimum vapor. That is to say, 2 with a definite local symmetry can recognize specific molecules capable of its crystalline structure according to the memory of its “mother structure,” even after losing its crystalline structure by vacuum treatment. It is quite significant that guest molecules can contribute to the restoration process even in the gas phase: these molecules are most likely adsorbed on the residual crystallite nuclei of the collapsed compound, after which the mother structure is rebuilt step-by-step through the insertion of guest molecules in the collapsed frames. This indicates a layering mechanism of molecular “bricks,” which requires an optimum local symmetry. In summary, we have synthesized and characterized new 1D metal-organic compounds and controlled the symmetry of the counteranion through interaction between ion/π bidentate anions, an electron-rich ligand, and guest molecules, which should have associated electron donor and acceptor properties. Furthermore, we succeeded in inducing the local symmetry-dependent structural restoration by vapor exposure. Acknowledgment. This work was supported by a Grantin-Aid for Scientific Research (Chemistry of Coordination Space) (no. 18033008) by the Japan Society for the Promotion
Letters qof Science. A.K. is partially supported by the 21 COE program: Frontiers of Super-Functionality of Organic Devices. Supporting Information Available: Materials relating to synthetic procedures, experimental details, characterized data, and X-ray crystallographic file (CIF) for 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) (a) Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1990, 112, 15461554. (b) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 14601494. (c) Khlobstov, A. N.; Blake, A. J.; Champness, N. R.; Lemenovskii, D. A.; Majouga, A. G.; Zyk, N. V.; Schro¨der, M. Coord. Chem. ReV. 2001, 222, 155-192. (d) Carlucci, L.; Ciani, G.; Proserpio, D. M. New J. Chem. 1998, 1319-1321. (e) Carlucci, L.; Ciani, G.; Proserpio, D. M. J. Chem. Soc., Dalton Trans. 1999, 1799-1804. (f) Kondo, M.; Shimamura, M.; Noro, S.; Minakoshi, S.; Asami, A.; Seki, K.; Kitagawa, S. Chem. Mater. 2000, 12, 1288-1299. (g) Barnett, S. A.; Champness, N. R. Coord. Chem. ReV. 2003, 246, 145-168. (h) Cussen, E. J.; Claridge, J. B.; Rosseinsky, M. J.; Kepert, C. J. J. Am. Chem. Soc. 2002, 124, 9574. (i) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334-2375. (j) Serre, C.; Millange, F.; Surble´, S.; Fe´rey, G. Angew. Chem., Int. Ed. 2004, 43, 6285-6289. (k) Bourrelly, S.; Llewellyn, P. L.; Serre, C.; Millange, F.; Loiseau, T.; Fe´rey, G. J. Am. Chem. Soc. 2005, 127, 13519-13521. (2) (a) Withersby, M. A.; Blake, A. J.; Champness, N. R.; Cooke, P. A.; Hubberstey, P.; Li, W. S.; Schro¨der, M. J. Cryst. Eng. 1999, 2, 123136. (b) Noro, S.; Kitaura, R.; Kondo, M.; Kitagawa, S.; Ishii, T.; Matsuzaka, H.; Yamashita, M. J. Am. Chem. Soc. 2002, 124, 2568-2583. (3) (a) Jung, O. S.; Kim, Y. J.; Lee, Y. A.; Park, K. M.; Lee, S. S. Inorg. Chem. 2003, 42, 844-850. (b) Reger, D. L.; Semeniuc, R. F.; Rassolov, V.; Smith, M. D. Inorg. Chem. 2004, 43, 537-554. (4) (a) Yaghi, O. M.; Davis, C. E.; Li, G.; Li, H. J. Am. Chem. Soc. 1997, 119, 2861-2868. (b) Carlucci, L.; Ciani, G.; Moret, M.; Proserpio, D. M.; Rizzato, S. Chem. Mater. 2002, 14, 12-14. (c) Khlobystov, A. N.; Brett, M. T.; Blake, A. J.; Champness, N. R.; Gill, P. M. W.; O’Neill, D. P.; Teat, S. J.; Wilson, C.; Schro¨der, M. J. Am. Chem. Soc. 2003, 125, 6753-6761. (d) Zeng, M. H.; Feng, X. L.; Chen, X. M. Dalton Trans. 2004, 2217-2223.
J. Phys. Chem. B, Vol. 110, No. 51, 2006 25567 (5) (a) Kepert, C. J.; Prior, T. J.; Rosseinsky, M. J. J. Am. Chem. Soc. 2000, 122, 5158-5168. (b) Carlucci, L.; Ciani, G.; Moret, M.; Proserpio, D. M.; Rizzato, S. Angew. Chem., Int. Ed. 2000, 39, 1506-1510. (c) Rosi, N. L.; Eddaoudi, M.; Kim, J.; O’Keeffe, M.; Yaghi, O. M. Angew. Chem., Int. Ed. 2002, 41, 284-287. (d) Uemura, K.; Kitagawa, S.; Kondo, M.; Fukui, K.; Kitaura, R.; Chang, H-C.; Mizutani, T. Chem.sEur. J. 2002, 8, 3586-3600. (e) Wu, C-D.; Lin. W. Angew. Chem., Int. Ed. 2005, 44, 1958-1961. (f) Braga, D.; Grepioni, F. Chem. Commun. 2005, 36353645. (6) The synthesis of compounds 1 and 2 are carried out in a similar fashion. A solution of azpy (0.184 g, 1.0 mmol) in 12.5 mL of solvent (acetone for 1, ethanol for 2) was layered on to a solution of Cu(OTs)2 (0.203 g, 0.50 mmol) in 6.25 mL of water. Dark-green single crystals suitable for X-ray structure analysis were grown for a few days at room temperature. Anal. calcd for 1: C, 44.75; H, 4.36; N, 8.70. Found: C, 44.57; H, 4.64: N, 8.92. Anal. calcd For 2: C, 43.82; H, 4.83; N, 8.18. Found: C, 43.34; H, 4.93; N, 7.79. (7) Sheldrick, G. M. SHELXTL-97, Program for Structure Refinement, University of Go¨ttingen, Go¨ttingen, Germany, 1998. (8) Farrugia, L. J. J. Appl. Cryst. 1999, 32, 837-838. (9) All crystallographic measurements were made on Bruker SMART APEX CCD area detectors with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å for 1 and 2) operated at 1500 W power (50 kV, 30 mA). Both structures were solved by direct method and fullmatrix least-squares analysis (SHELXTL-97). Anisotropic thermal factors were assigned to all the non-hydrogen atoms. Crystal data for 1: C27H36CuN4O11S2, monoclinic, space group P21 (No. 4), a ) 7.890(50), b ) 15.945(50), c ) 13.063(50) Å, β ) 94.588(5)°, V ) 1638.1(13) Å3, Z ) 2, Mw ) 720.26, Dc ) 1.46 g cm-3. The final R1 and wR2 are 0.0690 and 0.1841 for 401 parameters and 7832 independent reflections. For 2: C52H72Cu2N8O22S4, monoclinic, space group P21/c (No. 14), a ) 24.3572(8), b ) 7.9688(2), c ) 17.4501(6) Å, β ) 105.1720(1)°, V ) 3268.97(18) Å3, Z ) 2, Mw ) 1416.50, Dc ) 1.439 g cm-3. The final R1 and wR2 are 0.0468 and 0.1272 for 435 parameters and 6214 independent reflections. The data collection was performed at 140 K (1) and 295 K (2) on Bruker Smart CCD. Data collection for 1 was also performed at 295 K and the framework structure was almost the same as that at 140 K. The lattice constants along the a and b axis are a little longer, and along the c axis a little shorter than that at 140 K. The unit cell volume of 1 at 295 K is 1.018 times that at 140 K.
