CRYSTAL GROWTH & DESIGN
Lattice Inclusion Complexes Prepared from 1,3,5-Tris(3-nitrobenzoyl)benzene
2006 VOL. 6, NO. 1 193-196
V. S. Senthil Kumar, F. Christopher Pigge,* and Nigam P. Rath Department of Chemistry & Biochemistry, UniVersity of MissourisSt. Louis, One UniVersity BouleVard, St. Louis, Missouri 63121-4499 ReceiVed June 15, 2005
ABSTRACT: The title triaroylbenzene derivative forms isostructural lattice inclusion adducts with benzene, toluene, nitrobenzene, and DMSO. The host molecules self-assemble via dimeric C-H‚‚‚O hydrogen bonds to form 2D tapes with guest molecules occupying interlayer cavities. In contrast, a guest-free form of the inclusion host features a centrosymmetric four-point hydrogen-bonding recognition pattern that results in a square grid packing motif. Introduction The study of crystalline organic inclusion complexes has provided a wealth of insight into factors governing the formation of solid-state composite materials. In addition, inclusion complexes and clathrates have numerous potential practical applications in diverse areas of solid-state chemistry.1 For example, porous materials hold promise as selective small-molecule sequestration and/or storage devices.2 Certain inclusion hosts provide a matrix for solid-state reactions between appropriately oriented guest molecules.3 Inclusion complexes may also play an important role in the design of functional materials that exhibit desirable optical, magnetic, and/or electrical properties.4 A common design approach frequently implemented for the construction of inclusion hosts is to embed hydrogen-bonding functional groups (OH, CO2H, CONH2, etc.) within a relatively large and rigid organic framework.5 The presence of a rotational axis of symmetry has also been identified as a structural characteristic contributing to inclusion host ability.6 Taken together, these architectural features act in concert to prevent efficient molecular close packing in the condensed phase. Consequently, such materials show a pronounced tendency to crystallize as inclusion complexes with small-molecule solvates of suitable size and shape. The hydrogen-bonding functional groups provide additional sites for intermolecular host-guest interactions beyond weaker van der Waals attractions. In contrast, it has proven more difficult to prepare inclusion complexes from conformationally flexible molecules that do not possess functional groups capable of engaging in conventional hydrogen-bonding interactions. Indeed, most organic molecules tend not to crystallize with included solvates.7 As a class, however, 1,3,5-triaroylbenzenes (TABs) constitute an exception to this general trend. For example, the cyano-substituted TAB 1 was found to form isostructural inclusion complexes (pseudopolymorphs) with numerous solvent guests.8 In lieu of strong hydrogen bonding, these complexes were mediated by various weak solid-state C-H‚‚‚X (X ) O/N) interactions.9 In addition, two solvent-free polymorphic modifications of 1 have been structurally characterized as well.8,10 The 3-methoxy-TAB 2 also forms isostructural inclusion complexes with select guest species. In these instances, the molecular symmetry adopted by both the TAB host and included guests was mirrored in the overall crystal symmetry.11 The 4-nitro-TAB derivative 3 has * To whom correspondence should be addressed. Current address: Department of Chemistry, 305 Chemistry Building, University of Iowa, Iowa City, IA 52242-1294. E-mail:
[email protected].
also proven to be a viable inclusion host capable of adopting at least two distinct crystalline host-guest network topologies.12
Previously, the inclusion complex between 3-nitro-TAB 4 and benzene (stoichiometry 4‚0.5C6H6) was prepared and structurally characterized.12 In keeping with the behavior of related TAB derivatives 1-3, it was anticipated that 4 would display inclusion host capabilities beyond a single benzene clathrate. This has proven to be the case, and the structural features of three new inclusion complexes between 4 and toluene, nitrobenzene, and DMSO are reported herein. In addition, the crystal structure of solvate-free 4 has been obtained as well. This study further demonstrates the general clathrating ability of triaroylbenzenes while also illustrating the interplay between conformational flexibility and weak C-H‚‚‚O/N hydrogen bonding in influencing crystalline network formation. Results and Discussion The triaroylbenzene derivative 4 was prepared from 3-nitrobenzaldehyde as described previously.12 As also reported earlier, crystallization of 4 from benzene produced a 2:1 hostguest inclusion complex. Crystallographic data are shown in Table 1. As part of ongoing studies investigating the solid-state properties of triaroylbenzenes, single crystals of 4 obtained from other solvents were examined by X-ray diffraction. For crystals obtained from toluene and nitrobenzene solutions, inclusion complexes 4‚0.5(toluene) and 4‚0.5(nitrobenzene) were obtained. These two complexes, along with the benzene adduct, are isostructural. Furthermore, crystallization of 4 from a mixture of acetone and DMSO afforded a fourth isostructural inclusion complex of stoichiometry 4‚0.5(DMSO).
10.1021/cg050270z CCC: $33.50 © 2006 American Chemical Society Published on Web 09/17/2005
194 Crystal Growth & Design, Vol. 6, No. 1, 2006
Kumar et al.
Table 1. Crystallographic Data for Clathrates of 4 as Well as a Solvate-Free Form
cryst syst space group a/Å b/Å c/Å R/deg β/deg γ/deg V/Å3 Z Dcalcd m T/K no. of reflns no. of unique reflns no. of reflns with I > 2σ(I) no. of params R1 [I > 2σ(Ι)]a wR2
4‚0.5(benzene)
4‚0.5(toluene)
4‚0.5(nitrobenzene)
triclinic P1h 10.3402(9) 10.4427(9) 13.4887(11) 87.854(6) 80.536(5) 64.230(5) 1292.85(19) 2 1.450 0.109 218 12255 4542 2571 379 0.0840 0.2201
triclinic P1h 10.1724(2) 10.4722(2) 13.8239(3) 87.577(1) 80.213(1) 63.244(1) 1294.83(5) 2 1.466 0.110 143 20918 4550 2569 410 0.0844 0.2343
triclinic P1h 10.1533(2) 10.4483(2) 13.7561(3) 88.7710(10) 81.7330(10) 64.5780(10) 1302.99(5) 2 1.496 0.115 146 24478 5677 4056 443 0.0746 0.2323
These composite materials are best described as lattice inclusion complexes as the solvent molecules occupy cavities within the triaroylbenzene host network. With the exception of benzene, guest solvates are disordered and appear to be held in place by van der Waals attractions. Included benzene molecules, however, act as C-H hydrogen bond donors toward carbonyl and nitro group acceptors, as has been previously discussed.12 Given the isostructural nature of these complexes, the solidstate networks generated via self-assembly of 4 are obviously similar across the series. An interesting feature of these structures is that the TAB framework itself is also disordered, resulting from rotation of one of the nitroarene rings. Thus, the TAB molecules adopt one of two distinct conformations as shown in Figure 1. These conformations exhibit comparable occupancy factors.13 A network of TAB molecules is established through various weak hydrogen-bonding interactions summarized in synthons I-III (Scheme 1).14 Nitrobenzoyl rings from inversion-related host molecules self-assemble via centrosymmetric C-H‚‚‚O hydrogen bonding to generate TAB dimers as depicted in synthon I (d(H‚‚‚O) ) 2.60-2.65 Å, θ(C-H‚‚‚O) ) 168.6172.6°). The dimers are further linked by secondary C-H‚‚‚O
Figure 1. Two distinct conformations (a and b) adopted by 4 in the inclusion complexes with toluene, nitrobenzene, and DMSO. In the benzene clathrate, only conformation a is observed.
Scheme 1.
4‚0.5(DMSO) triclinic P1h 9.9282(2) 10.6462(3) 13.6124(4) 89.671(2) 81.8300(10) 62.8080(10) 1263.93(6) 2 1.483 0.153 150 19522 5493 3261 416 0.0785 0.2382
4 (guest-free) triclinic P1h 6.5650(2) 12.9681(3) 13.3554(3) 89.030(1) 87.706(1) 86.816(1) 1134.23(5) 2 1.538 0.118 150 17856 5407 3911 352 0.0455 0.1029
Hydrogen Bond Patterns Observed in the Solid-State Structures of 4
hydrogen-bonding interactions of the type shown in synthon II (2.47-2.56 Å, 124.9-128.9°). In this intermolecular arrangement, the central trisubstituted arene rings and four of the nitroarene arms define a rectangle. The remaining two nitrobenzoyl groups are engaged in centrosymmetric H-bonding (synthon I) through the center of this rectangle (Figure 2). Individual dimers are connected to inversion-related neighbors via additional C-H‚‚‚O hydrogen bonds of the type illustrated by synthon III (2.58-2.70 Å, 118.7-139.3°) and through inversionrelated nitro groups. Included solvate molecules reside in roughly cubic shaped cavities and are shielded from neighboring guests by the TAB network. A 2D view of the extended packing in the nitrobenzene clathrate is provided in Figure 3.
Figure 2. View of the dimeric arrangement of TAB derivatives observed in the inclusion complexes of 4. C-H‚‚‚O hydrogen bonds are shown in yellow.
Lattice Inclusion Complexes Prepared from a TAB
Figure 3. Extended packing observed in 4‚0.5(nitrobenzene). Other inclusion complexes of 4 are isostructural. Nitrobenzene solvates (violet) are disordered. Note the inversion-related NO2 dimers present between vertically stacked solvate molecules.
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The propensity of 4 to form crystalline inclusion complexes in the presence of appropriate guest solvates despite the ability to achieve close packing in the absence of guest incorporation illustrates the solid-state structural diversity possible in conformationally flexible systems. Moreover, the lack of strong conventional hydrogen bond donors/acceptors permits hydrogenbonding patterns to be adjusted, presumably to generate the most favorable array of intermolecular interactions as a function of the crystallization conditions (solvent in this case). While attempts to remove included guests from 4 resulted in loss of crystallinity (behavior consistent with a true clathrate), one can envision that the proper TAB-guest combination may afford flexible organic composites in which nondestructive guest removal, exchange, and/or modification may be possible. In turn, such TAB-based “soft” supramolecular materials would have potential applications as separation/storage devices and chemical catalysts.15 The synthetic accessibility of functionalized triaroylbenzenes should greatly facilitate realization of this goal. In addition, structural studies involving even relatively simple TABs should continue to provide insight into various factors affecting the formation of organic solid-state networks. Experimental Section
Figure 4. View of the 2D square grid network in the extended packing of 4 (no guest) (down a). The four-point hydrogen-bonding pattern (synthon IV) is indicated in yellow. Square grids are filled with nitrobenzoyl groups shown in green.
Attempts to crystallize 4 from other solvents such as chloroform, ethanol, methanol, 2-propanol, and DMF were unsuccessful. A guest-free modification of 4, however, was obtained upon crystallization from either nitromethane or nitroethane. In this structure, the TAB building blocks are arranged in a topologically distinct manner when compared to the inclusion complexes discussed above. In the solvate-free form, TAB dimers are generated through a centrosymmetric four-point recognition pattern involving two unique hydrogenbonding interactions (2.54 and 2.64 Å, 133.1° and 155.0°s synthon IV in Scheme 1). Lateral C-H‚‚‚O hydrogen bonds also appear to contribute to generation of a 2D square grid network (Figure 4). The square internal voids are then filled with nitrobenzoyl rings from two opposing 3-nitro-TAB building blocks. A similar four-point hydrogen-bonding pattern was encountered in a guest-free polymorph of the 4-cyano-TAB derivative 1.8,10 In this latter structure, self-assembly of the TAB framework results in a honeycomb packing motif with internal voids filled by cyanobenzoyl arms enamating from TABs located on opposite sides of the hexagonal openings. Thus, the structures of 4 and 1 have much in common beyond the hydrogen-bonding pattern depicted in synthon IV. Presumably, the variation in packing morphology (honeycomb in 1, square grid in 4) is a reflection of the different substitution patterns on the TAB core. It will be interesting to see if other TAB derivatives will also display this general solid-state network motif.
Triaroylbenzene 4 was prepared as described previously. X-rayquality single crystals were obtained by slow evaporation of neat solutions at ambient temperature. Crystals of 4‚0.5(DMSO) were obtained from a mixture of acetone and DMSO, while crystals of 4 (no guest) were obtained from nitromethane or nitroethane. Preliminary crystal examination and data collection were performed using a Bruker SMART CCD area detector system single-crystal X-ray diffractometer. The SHELXTL-PLUS software package was used for structure solution and refinement.16 Hydrogens were fixed at idealized geometries and treated isotropically as riding groups. Crystal data are given in Table 1. The structure 4‚0.5(benzene) was previously deposited with the CCDC (refcode LOVXID). CCDC reference numbers for the remaining structures: 269485-269488.
Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research (ACS PRF No. 37468-AC4). Supporting Information Available: X-ray data with details of the refinement procedure (CIF). This material is available free of charge via the Internet at http://pubs.acs.org.
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196 Crystal Growth & Design, Vol. 6, No. 1, 2006 (6) MacNicol, D. D.; Downing, G. A. In ComprehensiVe Supramolecular Chemistry; MacNicol, D. D., Toda, F., Bishop, R., Eds.; Pergamon: Oxford, 1996; Vol. 6, pp 421-464. (7) Nangia, A.; Desiraju, G. R. Chem. Commun. 1999, 605. (8) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. Cryst. Growth Des. 2004, 4, 1217. (9) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond in Structural Chemistry and Biology; Oxford University Press: Oxford, 1999. (10) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. New J. Chem. 2003, 27, 1554. (11) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. CrystEngComm 2004, 6, 531. (12) Pigge, F. C.; Ghasedi, F.; Zheng, Z.; Rath, N. P.; Nichols, G.; Chickos, J. S. J. Chem. Soc., Perkin Trans. 2 2000, 2458.
Kumar et al. (13) Disorder in the TAB framework incorporated into a crystalline metalorganic coordination polymer has also been observed: Pigge, F. C.; Burgard, M. D.; Rath, N. P. Cryst. Growth Des. 2003, 3, 331. (14) For examples of related hydrogen bonding synthons, see: Thaimattam, R.; Xue, F.; Sarma, J. A. R. P.; Mak, T. C. W.; Desiraju, G. R. J. Am. Chem. Soc. 2001, 123, 4432. (15) Soldatov, D. V. J. Inclusion Phenom. Macrocyclic Chem. 2004, 48, 3. (b) Holman, K. T.; Pivovar, A. M.; Swift, J. A.; Ward, M. D. Acc. Chem. Res. 2001, 34, 107. (16) Sheldrick, G. M., Bruker Analytical X-Ray Division, Madison, WI, 1999.
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