Published on Web 11/23/2007
Reversible Gas Uptake by a Nonporous Crystalline Solid Involving Multiple Changes in Covalent Bonding Guillermo Mı´nguez Espallargas,† Michael Hippler,† Alastair J. Florence,‡ Philippe Fernandes,‡ Jacco van de Streek,§ Michela Brunelli,| William I. F. David,⊥ Kenneth Shankland,⊥ and Lee Brammer*,† Contribution from the Department of Chemistry, UniVersity of Sheffield, Sheffield S3 7HF, United Kingdom, Strathclyde Institute of Pharmacy and Biomedical Sciences, UniVersity of Strathclyde, 27 Taylor Street, Glasgow G4 0NR, Scotland, Institute for Inorganic and Analytical Chemistry, Frankfurt UniVersity, 60438 Frankfurt am Main, Germany, European Synchrotron Radiation Facility, 38042 Grenoble, France, and ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom Received July 14, 2007; E-mail:
[email protected] Abstract: Hydrogen chloride gas (HCl) is absorbed (and reversibly released) by a nonporous crystalline solid, [CuCl2(3-Clpy)2] (3-Clpy ) 3-chloropyridine), under ambient conditions leading to conversion from the blue coordination compound to the yellow salt (3-ClpyH)2[CuCl4]. These reactions require substantial motions within the crystalline solid including a change in the copper coordination environment from square planar to tetrahedral. This process also involves cleavage of the covalent bond of the gaseous molecules (H-Cl) and of coordination bonds of the molecular solid compound (Cu-N) and formation of N-H and Cu-Cl bonds. These reactions are not a single-crystal-to-single-crystal transformation; thus, the crystal structure determinations have been performed using X-ray powder diffraction. Importantly, we demonstrate that these reactions proceed in the absence of solvent or water vapor, ruling out the possibility of a waterassisted (microscopic recrystallization) mechanism, which is remarkable given all the structural changes needed for the process to take place. Gas-phase FTIR spectroscopy has permitted us to establish that this process is actually a solid-gas equilibrium, and time-resolved X-ray powder diffraction (both in situ and ex situ) has been used for the study of possible intermediates as well as the kinetics of the reaction.
Introduction
Although chemical reactions in molecular crystals that proceed without destruction of crystallinity have been known for many years, their study has been largely confined to crystals of organic compounds. Such reactions are typically induced photochemically or thermally1-3 and require motions on a length scale of a few Ångstroms by neighboring molecules within the crystals either in order that covalent bonds can be formed or subsequent to bond breaking during the reaction. However, many such reactions are irreversible. An illustrative example is carbon-carbon bond formation in cycloaddition reactions between alkenes.1,2,4,5 Examples of metal-organic compounds that permit irreversible reactions such as polymerizations in the solid state have been known for some time.6 Reactions of organometallic compounds as solids (surfaces, amorphous, and crystalline) have also been reviewed.7 †
University of Sheffield. University of Strathclyde. Frankfurt University. | European Synchrotron Radiation Facility. ⊥ ISIS Facility. ‡ §
(1) (2) (3) (4) (5) (6)
Schmidt, G. M. J. Pure Appl. Chem. 1971, 27, 647. Tanaka, K.; Toda, F. Chem. ReV. 2000, 100, 1025. MacGillivray, L. R. CrystEngComm 2002, 4, 37. Mustafa, A. Chem. ReV. 1952, 51, 1. Friscic, T.; MacGillivray, L. R. Z. Krist. 2005, 220, 351. Georgiev, I. G.; MacGillivray, L. R. Chem. Soc. ReV. 2007, 36, 1239.
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Of particular relevance to the present study are solid-gas reactions involving crystalline metal-organic compounds.8 Reactions of this type, defined rather broadly, can be divided into three general classes: (i) sorption of gases by crystalline porous materials where the gas molecules are incorporated in the interior of the pores; (ii) reactions between nonporous crystals and aqueous vapors of volatile acids and bases leading to the incorporation of these molecules into hydrogen-bonded networks; and (iii) absorption of gas molecules by nonporous molecular crystals with formation of covalent bonds to the substrate, where retention of crystallinity is unexpected and accordingly extremely rare. The sorption of gases by crystalline porous materials such as metal-organic frameworks is well established9,10 and of widespread interest for applications including gas storage, (7) Coville, N. J.; Cheng, L. J. Organomet. Chem. 1998, 571, 149. (8) Meijer, M. D.; Klein Gebbink, R. J. M.; van Koten, G. In PerspectiVes in Supramolecular Chemistry: Crystal Design: Structure and Function; Desiraju, G., Ed.; Wiley: Chichester, U.K., 2003; Vol. 7, Chapter 9. (9) Kitagawa, S.; Kitaura, R.; Noro, S.-i. Angew. Chem., Int. Ed. 2004, 43, 2334. (10) (a) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Science 2002, 295, 469. (b) Zhao, X.; Xiao, B.; Fletcher, A. J.; Thomas, K. M.; Bradshaw, D.; Rosseinsky, M. J. Science 2004, 306, 1012. (c) Forster, P. M.; Eckert, J.; Chang, J.-S.; Park, S.-E.; Fe´rey, G.; Cheetham, A. K. J. Am. Chem. Soc. 2003, 125, 1309. (d) Lin, X.; Blake, A. J.; Wilson, C.; Sun, X. Z.; Champness, N. R.; George, M. W.; Hubberstey, P.; Mokaya, R.; Schro¨der, M. J. Am. Chem. Soc. 2006, 128, 10745. 10.1021/ja075265t CCC: $37.00 © 2007 American Chemical Society
Reversible Gas Uptake
chemical separations, and molecular sensing.9,11-13 Typically physisorption results in gas molecules that are rather weakly bound to the interior surfaces of the pores,14 but although crystallinity of the solid is retained in some cases after sorption or desorption,15 often this is not the case.16 Recent developments have also shown that binding of gas molecules is feasible through specific interactions, for example, hydrogen bonding interactions17 or coordination bond formation,18,19 within pores. Reactions between crystalline powders of the organometallic zwitterion [Co(η5-C5H4CO2H)(η5-C5H4CO2)] and aqueous vapors of volatile acids and bases has been reported by Braga, Grepioni, and co-workers.20-22 These reactions lead to the formation of salts [Co(η5-C5H4CO2H)(η5-C5H4CO2H)]X‚nH2O (X ) Cl-, BF4-,21 CF3COO-,21 CHF2COO-,22 CH2ClCOO-22) if exposed to acids or [Co(η5-C5H4CO2)2](HY)‚nH2O (Y ) NH3,20 NH2Me,20 NMe320) if exposed to bases (n g 0). Formation and cleavage of hydrogen bonds as well as protonation/deprotonation of the carboxylate/carboxyl groups is required to accommodate the gas molecules in the solid.23 In some cases, water molecules are also incorporated in the products upon acid or base uptake (i.e., n > 0). These reactions are all reversible upon thermal treatment of the resultant salts. The third class of solid-gas reactions involves not only absorption of gas molecules by nonporous molecular crystals but also the resultant formation of metal-ligand covalent bonds. Such reactions converting crystalline reactant into crystalline product are rare. An early example reported by van Koten and co-workers involves the reaction an organoplatinum complex with SO2 gas.24 In this reversible reaction, the coordination geometry at the platinum center is converted from square planar to square pyramidal but nevertheless requires the formation of only an axial Pt-S bond enabling SO2 to be bound upon its uptake by these crystals. In two very recent publications, reactions involving methanol coordination25 and pyridine coordination26 have also been identified. In parallel with the present paper, we have also reported reversible ethanol insertion into and elimination from the Ag-O bond of a nonporous crystalline coordination polymer.27 (11) Kesanli, B.; Lin, W. Coord. Chem. ReV. 2003, 246, 305. (12) James, S. L. Chem. Soc. ReV. 2003, 32, 276. (13) Halder, G. J.; Kepert, C. J.; Moubraki, B.; Murray, K. S.; Cashion, J. D. Science 2002, 298, 1762. (14) Rowsell, J. L. C.; Spencer, E. C.; Eckert, J.; Howard, J. A. K.; Yaghi, O. M. Science 2005, 309, 1350. (15) (a) Serre, C.; Millange, F.; Thouvenot, C.; Nogue´s, M.; Marsolier, G.; Louer, D. Fere´y, G. J. Am. Chem. Soc. 2002, 124, 13519. (b) Kitaura, R.; Seki, K.; Akiyama, G.; Kitagawa, S. Angew. Chem., Int. Ed. 2003, 42, 428. (16) (a) Rosi, N.; Eddaoudi, M.; Kim, J.; O’Keefe, M.; Yaghi, O. M. Angew. Chem., Int. Ed. 2002, 41, 284. (b) Sun, J.; Weng, L.; Zhou, Y.; Chen, J.; Chen, Z.; Liu, Z.; Zhao, D. Angew. Chem., Int. Ed. 2002, 41, 4471. (17) Matsuda, R.; Kitaura, R.; Kitagawa, S.; Kubota, Y.; Belosludov, R. V.; Kobayashi, T. C.; Sakamoto, H.; Chiba, T.; Takata, M.; Kawazoe, Y.; Mita, Y. Nature 2005, 436, 238. (18) Beauvais, L. G.; Shores, M. P.; Long, J. R. J. Am. Chem. Soc. 2000, 122, 2763. (19) Bradshaw, D.; Warren, J. E.; Rosseinsky, M. J. Science 2007, 315, 977. (20) Braga, D.; Cojazzi, G.; Emiliani, D.; Maini, L.; Grepioni, F. Chem. Commun. 2001, 2272. (21) Braga, D.; Cojazzi, G.; Emiliani, D.; Maini, L.; Grepioni, F. Organometallics 2002, 21, 1315. (22) Braga, D.; Maini, L.; Mazzotti, M.; Rubini, K.; Grepioni, F. CrystEngComm 2003, 5, 154. (23) Related gas-solid acid base reactions are also established for organic compounds, see: Paul, I. C; Curtin, D. Y. Acc. Chem. Res. 1973, 6, 217. (24) Albrecht, M.; Lutz, M.; Spek, A. L.; van Koten, G. Nature 2000, 406, 970. (25) Supriya, S.; Das, S. K. J. Am. Chem. Soc. 2007, 129, 3464. (26) Lennartson, A.; Håkansson, M.; Jagner, S. New J. Chem. 2007, 31, 344. (27) Libri, S.; Mahler, M.; Mı´nguez Espallargas, G.; Singh, D. C. N. G.; Soleimannejad, J.; Adams, H.; Burgard, M. D.; Rath, N. P.; Brunelli, M.; Brammer, L. Angew. Chem., Int. Ed. 2007, 46, in press.
ARTICLES
Very recent reports by us28 and by Orpen and co-workers29 have shown that microcrystalline samples of coordination complexes with pyridine-derived ligands can undergo reaction with hydrated vapors of HCl leading to formation of crystalline hydrogen-bonded salts. These reactions require cleavage of the M-N (M ) Cu,28 Co,29 Zn,29) and H-Cl bonds and formation of N-H and M-Cl bonds, thereby inserting HCl into the M-N coordination bond. However, although water molecules are not included in the crystals of the product salts, given the presence of excess water vapor in the reactions, a highly plausible mechanism for these reactions has been thought to involve a microscopic recrystallization front that migrates across the crystals, analogous to that demonstrated for some anion exchange reactions involving crystalline solids.30 In this study, we substantially extend our earlier report and are able to demonstrate that the molecular coordination compound trans-[CuCl2(3-Clpy)2] 1 (3-Clpy ) 3-chloropyridine) prepared as a microcrystalline powder can react directly with gaseous HCl in the absence of water yielding the crystalline salt (3-ClpyH)2[CuCl4] 2. This definitively rules out the possibility of a water-assisted (microscopic recrystallization) mechanism and requires instead a quite remarkable process that involves transport of HCl through nonporous crystals,31 coupled with reaction within these crystals that involves multiple changes in covalent bonding and a major change in coordination geometry at the metal center. This reaction has been examined in detail using X-ray powder diffraction and gas-phase IR spectroscopy, including establishing the operation of a solidgas equilibrium process and investigating the kinetics of the reverse (HCl elimination) reaction. Experimental Section General. All reagents were purchased from Aldrich, Lancaster, or Avocado and used as received. HCl gas was purchased from BOC (grade N2.6, 99.6% HCl; H2O content
