Unusual Anion-Anion Assembly inside a Macrocycle-Defined Channel in the Crystal Lattice Michał J. Chmielewski,† Łukasz Dobrzycki,‡ Janusz Jurczak,*,†,‡ and Krzysztof Woz´niak*,‡
CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 4 1339-1341
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland, and Department of Chemistry, Warsaw University, Pasteura 1, 02-093 Warszawa, Poland Received April 28, 2005
ABSTRACT: We describe the unprecedented formation of anion channels by an uncharged, amide-based macrocyclic receptor in the crystal structure of its benzoate complex. Head-to-tail aggregation of benzoate anions by means of CH‚‚‚O hydrogen bonds leads to an infinite anion chain threaded inside the macrocycle-defined channel. The supramolecular chemistry of anions is often perceived as a less developed area as compared to that of cation coordination chemistry. Nevertheless, the gap between these fields of research is being bridged quickly by the discovery of yet more examples of anion recognition phenomena analogous to those well established for cations. For example, the anion-template approach1 has been shown to give excellent results, in particular in the synthesis of rotaxanes2 and catenanes.3 The well-known stabilization of unusual oxidation states of cations by ligand coordination is paralleled by the stabilization of anion radicals4 and unusual valence tautomers of the croconate dianion5 by hydrogen bond donating receptors. Examples of anionic analogues of cation helicates have been demonstrated both in solution6 and in the solid state.7,8 Binuclear anion complexes have been obtained in the solid state by simultaneous encapsulation of two anions within cavities of macrocyclic9 or macrobicyclic10,11 receptors. In this communication we describe a new analogy between cation and anion chemistrysa crystal structure in which neutral macrocyclic anion receptors are aligned one above another to form channels filled with coordinated anionic guests. Although recognized for cations, such a phenomenon is, to the best of our knowledge, unprecedented in the field of anion coordination chemistry. Cation channels formed in crystals of some complexes of crown ethers with alkali-metal cations were studied as models of transmembrane cation conducting channels12,13 and also with the aim of constructing molecular iono-electronic devices.14 The tetraamide receptor 1 was designed to bind anions by four NHamide‚‚‚A- hydrogen bonds. The synthesis and
anion binding properties of receptor 1 and its smaller analogues were described earlier.15 Its structure consists of two rigid and planar 2,6-pyridinediamide moieties linked by flexible aliphatic chains. The 24-membered macro ring * To whom correspondence should be addressed.
[email protected] (J.J.);
[email protected] (K.W.). † Polish Academy of Sciences. ‡ Warsaw University.
E-mail:
Figure 1. X-ray crystal structure of 1×PhCOO-×TBA+×H2O (ORTEP; displacement ellipsoids scaled to the 60% probability level). The TBA cation is omitted for clarity. Dashed lines are indicative of hydrogen-bonding interactions.
Figure 2. (a) View along the channel formed by receptor moieties 1 with benzoate anions inside and (b) a perpendicular projection.
of the receptor was designed to accommodate two oxygen atoms of the carboxylate anion. To verify this design, a single crystal of the benzoate complex 1×PhCOO-×TBA+×H2O was obtained by slow evaporation of an ethanolic solution
10.1021/cg0501938 CCC: $30.25 © 2005 American Chemical Society Published on Web 06/11/2005
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Figure 4. Projection of the crystal lattice onto the XY plane. Hydrogens are omitted for clarity. Coloring scheme: benzoate anions, red; macrocyclic receptors, green; TBA cations, blue; water molecules, purple.
Figure 3. Dimeric crystal channels linked by water molecules: (a) view along the channel; (b) view in the perpendicular direction.
of the receptor and tetrabutylammonium (TBA) benzoate. X-ray analysis16 confirmed the expected binding mode but also revealed that the macro ring of 1 is slightly too large for its guest (Figure 1). The receptor adapts itself, twisting both pyridinediamide fragments relative one to the other, thus making use of the flexibility in the aliphatic linkers. The twist facilitates the formation of four strong NHamide‚‚‚Obenzoate hydrogen bonds (2.00-2.13 Å) which hold the benzoate anion in an almost perpendicular orientation to the mean plane of the macrocycle. The structure of the binary complex described above is repeated by vertical translation in such a way that the macrocycles form channels passing through the crystal lattice parallel to the Z axis (Figure 2). The size of the channel approximated by distances between the amide nitrogen atoms is ca. 5.8 Å (N1‚‚‚N19) × 4.5 Å (N1‚‚‚N7). The channel is occupied by benzoate anions aligned in a head-to-tail manner. Such an arrangement is stabilized by the bifurcated, charge-assisted CHaromatic‚‚‚A- hydrogen
bond formed between the hydrogen atom in the para position of the benzene ring and both carboxylate oxygen atoms of the neighboring anion (Figure 2b) (CH‚‚‚O distances 2.36 and 2.50 Å, donor-acceptor CH‚‚‚O distances 3.17 and 3.35 Å, respectively). As a result of these attractive forces, the hydrogen atom significantly deviates from the plane of the benzene ring (∼0.17 Å) toward the oxygens. CSD searches revealed no other examples of such mode of interaction in the salts of aromatic carboxylic acids.17 The dimerization of anions is, in principle, unfavorable due to electrostatic repulsion. In some cases however, multiple, strong hydrogen bonds are able to offset this repulsion, as demonstrated by the existence of water-glued Cl- dimers18 or by the simultaneous encapsulation of two Cl- inside one macrocyclic cavity.9 Even more spectacular face-to-face dimerization of pyrrole anions driven by the formation of four strong CONH‚‚‚N-pyr hydrogen bonds was reported by Gale and co-workers.19 In the present crystal structure anionic centers are far enough from each other that even weak CH‚‚‚O- hydrogen bonds can stabilize the structure. Thus, benzoate anions form an infinite one-dimensional polymeric core threaded inside stacked macrocycles in a way that resembles infinite [∞]pseudorotaxane. This anionic thread seems to act as a template for organizing the receptor molecules into channelsshydrogen bonds anchor the macro rings on the supramolecular polymer so far apart (7.85 Å) that they cannot interact directly (Figure 2). Interestingly, all the anionic polymers are oriented in the same direction, which is reflected in the crystal symmetry (polar space group Pna21). Neighboring stacks of receptors are joined in pairs by water molecules (Figure 3). Each water molecule forms two short (1.90 and 1.98 Å) hydrogen bonds with carbonyl oxygens of two macrocyclic tetraamides from parallel columns, thus forming a helical network of hydrogen bonds in the crystal lattice (Figure 3b). Tetrabutylammonium cations are also arranged in vertical columns. Four such columns surround the anionic channel (Figure 4). Analogously, each of these columns of cations is surrounded by four channels filled with anions. It is interesting to note here that each of the four anion channels adjacent to the central cation column is arranged in a different manner. As a result, an amazing mosaic-like projection onto the XY unit cell plane is seen (Figure 4). In conclusion, we have described the first crystal structure in which an infinite chain of anions fill the channel defined by molecules of uncharged, macrocyclic receptors. Aggregation of benzoate anions by means of CH‚‚‚Ohydrogen bonds to form an infinite head-to-tail supramolecular polymer in the solid state is probably responsible for the formation of this channel architecture. Accordingly,
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the present finding suggests a promising approach to the formation of similar structures using self-aggregating anions. Supporting Information Available: Crystallographic information file (CIF) giving crystal data for 1×PhCOO-×TBA+×H2O. This material is available free of charge via the Internet at http:// pubs.acs.org.
References (1) Vilar, R. Angew. Chem., Int. Ed. 2003, 42, 1460-1477. (2) Hu¨bner, G. M.; Glaser, J.; Seel, C.; Vo¨gtle, F. Angew. Chem., Int. Ed. 1999, 38, 383-386. (3) Sambrock, M. R.; Beer, P. D.; Wisner, J. A.; Paul, R. L.; Cowley, A. R. J. Am. Chem. Soc. 2004, 126, 15364-15365. (4) Carroll, J. B.; Gray, M.; Cooke, G.; Rotello, V. M. Chem. Commun. 2004, 442-443. (5) Lam, Ch.-K.; Cheng, M.-F.; Li, Ch-L.; Zhang, J.-P.; Chen, X.-M.; Li, W.-K.; Mak, T. C. W. Chem. Commun. 2004, 448449. (6) Sa´nchez-Quesada, J.; Seel, C.; Prados, P.; de Mendoza, J. J. Am. Chem. Soc. 1996, 118, 277-278. (7) Keegan, J.; Kruger, P. E.; Nhuyzen, M.; O’Brien, J.; Martin, N. Chem. Commun. 2001, 2192-2193. (8) Coles, S. J.; Frey, J. G.; Gale, P. A.; Hursthouse, M. B.; Light, M. E.; Navakhun, K.; Thomas, G. L. Chem. Commun. 2003, 568-569. (9) Szumna, A.; Jurczak, J. Helv. Chim. Acta 2001, 84, 37603765. (10) Hossain, Md. A.; Linares, J. M.; Mason, S.; Morehouse, P.; Powell, D.; Bowman-James, K. Angew. Chem., Int. Ed. 2002, 41, 2335-2338. (11) Yue, N. L. S.; Eisler, D. J.; Jennings, M. C.; Puddephat, R. J. Inorg. Chem. 2004, 43, 7671-7681. (12) Behr, J.-P.; Lehn, J.-M.; Dock, A.-C.; Moras, D. Nature 1982, 295, 526-527.
(13) Meadows, E. S.; Barbour, L. J.; Fronczek, F. R.; Evans, C. M.; Watkins, S. F.; Gokel, G. W. Inorg. Chim. Acta 2000, 300-302, 333-338. (14) Akutagawa, T.; Hasegawa, T.; Nakamura, T.; Takeda, S.; Inabe, T.; Sugiura, K.; Sakata, Y.; Underhill, A. E. Chem. Eur. J. 2001, 7, 4902-4912 and references therein. (15) (a) Chmielewski, M. J.; Jurczak, J. Tetrahedron Lett. 2004, 45, 6007-6010. (b) Chmielewski, M. J.; Jurczak, J. Chem. Eur. J., in press. (16) Crystal data for 1×PhCOO-×TBA+×H2O. C47H73N7O7, Mr ) 848.12, orthorhombic, a ) 36.4719(18) Å, b ) 16.3165(9) Å, c ) 7.8470(6) Å, U ) 4669.7(5) Å3, T ) 100(2) K, space group Pna21 (No. 33), Z ) 4, µ(Mo KR) ) 0.081 mm-1, 42 460 reflections collected, 6240 unique (Rint ) 0.087) which were used in all calculations. Final R indices (I > 2σ(I)): R1 ) 0.0509, wR2 ) 0.1088, R indices (all data): R1 ) 0.0767, wR2 ) 0.1295. (17) For other examples of remarkable CHaromatic-anion interactions see: (a) Chmielewski, M. J.; Szumna, A.; Jurczak, J. Tetrahedron Lett. 2004, 45, 8699-8703. (b) Kwon, J. Y.; Jang, Y. J.; Kim, S. K.; Lee, K.-H.; Kim, J. S.; Yoon, J. J. Org. Chem. 2004, 69, 5155-5157. (c) Lee, C.-H.; Na, H.-K.; Yoon, D.-W.; Won, D.-H.; Cho, W.-S.; Lynch, V. M.; Shevchuk, S. V.; Sessler, J. L. J. Am. Chem. Soc. 2003, 125, 7301-7306. (d) Jeong, K.-S.; Cho, Y. L. Tetrahedron Lett. 1997, 38, 3279-3282. (18) Gao, J.; Boudon, S.; Wipff, G. J. Am. Chem. Soc. 1991, 113, 9610-9614. (19) (a) Camiolo, S.; Gale, P. A.; Hursthouse, M. B.; Light, M. E.; Shi, A. J. Chem. Commun. 2002, 758-759. (b) Gale, P. A.; Navakhun, K.; Camiolo, S.; Light, M. E.; Hursthouse, M. B. J. Am. Chem. Soc. 2002, 124, 11228-11229.
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