Self-Assembly of Sticky TABs: Inclusion ... - ACS Publications

Self-Assembly of Sticky TABs: Inclusion Complexes and Hydrates from 1,3,5-Tris(4-hydroxybenzoyl)benzene F. Christopher Pigge,*,† Mayuri K. Dighe,† and Nigam P. Rath‡

CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 12 2732-2738

Department of Chemistry, UniVersity of Iowa, Iowa City, Iowa 52242, and Department of Chemistry & Biochemistry, UniVersity of Missouri - St. Louis, One UniVersity BouleVard, St. Louis, Missouri 63121 ReceiVed July 5, 2006; ReVised Manuscript ReceiVed September 29, 2006

ABSTRACT: Six structures of crystalline materials obtained via the self-assembly of a 1,3,5-triaroylbenzene (TAB) derivative peripherally functionalized with phenol residues (“sticky” groups) have been determined. Two general structural types were observed: highly symmetrical assemblies mediated by direct ArOsH···OdC hydrogen bonding (space group R3c) and extensively hydrated structures in which water molecules occupy bridging positions between phenol and carbonyl groups (space group P21/n). The former architecture accommodates included solvate molecules (EtOAc or H2O) within an interpenetrated R-Po type TAB network. In the case of the hydrate, water molecules do not appear to be involved in any intermolecular interactions despite excellent hydrogenbonding ability. Structures of the latter type feature well-defined voids for guest enclathration (guest ) acetone, EtOH, MeOH). The observed supramolecular interactions are discussed in the context of potential applications in crystal engineering. Introduction The predictable and controlled self-assembly of solid-state molecular arrays constitutes the principal aim of crystal engineering. It is anticipated that such control will enable the design and synthesis of numerous functional organic materials imbued with preselected properties. A sampling of features deemed to be desirable in organic and metal-organic solids includes nonlinear optical activity, sorption/desorption capability, conductivity, and selective guest inclusion. Solids possessing one (or more) of these characteristics may be regarded as prototypes for molecule-based materials potentially suitable for incorporation into inter alia new optical, electronic, and chemical separation/storage devices.1 While research in this area is rapidly expanding, the lofty objectives implicit in the term “crystal engineering” remain largely unmet. The current state of affairs serves as a testament to the magnitude of the problem being confronted. Indeed, despite advances in computational methods and a better understanding of the noncovalent attractions that govern supramolecular aggregation, the ability to reliably predict crystal structures of even relatively simple organic compounds has not yet been achieved.2 Consequently, the empirical evaluation of organic crystals, cocrystals, and salts remains a valuable exercise for the identification of important supramolecular synthons.3 The harnessing of strong and directional intermolecular interactions coupled with judicious choice of organic building block (tecton approach) then provides an opportunity to rationally influence (control) microscopic aspects of solid-state structure.4 It remains difficult, however, to translate control over local intermolecular interactions into control of bulk solid-state properties that arise from macroscopic structural features. Hence, fundamental studies of organic crystals, particularly involving closely related compounds whose molecular attributes (e.g., functional groups, * To whom correspondence should be addressed. Ph: 319-335-3805; fax: 319-335-1270; e-mail: [email protected]. † University of Iowa. ‡ University of Missouri - St. Louis.

geometry, symmetry) can be systematically varied, remains a vitally important area of research within this branch of supramolecular chemistry. Various 1,3,5-triaroylbenzene (TAB) derivatives have been found to exhibit a range of solid-state features relevant to contemporary studies in crystal engineering. For example, the 4-cyano-substituted TAB 1 exists in two polymorphic modifications, while crystallization from certain solvents results in formation of isostructural inclusion complexes.5 Solid-state networks in each case are mediated by weak hydrogen-bonding interactions (CsH···O/N). Likewise, 3-nitro and 4-nitro TABs 2 and 3 also show a pronounced tendency to act as inclusion hosts for small molecule (solvent) guests.6,7 Presumably the relatively large and semirigid TAB framework contributes to this behavior. Indeed, such structural features have been advocated as important criteria in the design of effective enclathrating agents.8 In the case of 2 and 3, a number of hydrogen-bonding motifs were observed as well involving aromatic CsH groups as hydrogen-bond donors and carbonyl and nitro groups as hydrogen-bond acceptors. Highly symmetrical and selective inclusion complexes were also obtained from 4a when crystallized in the presence of guest species that could accommodate 3-fold symmetry.9 In contrast to the inclusion host capability of 1-4a, methyl-substituted TAB 5 crystallizes as a close-packed structure with two independent TAB molecules in the asymmetric unit.10 Each molecule is part of two distinct interpenetrating solid-state networks. Interestingly, one distinct network can be classified as a threedimensional R-Po type, while the other adopts a two-dimensional square grid topography. This constitutes, then, a rare example of a purely organic interpenetrated structure with non-identical networks of different dimensions. Finally, the solid-state features of halo-TABs 6 have been recently reported.11 Various types of halogen bonding appear to play significant roles in defining the structures of the chloro, bromo, and iodo congeners. The chloro and bromo analogues are isostructural and exhibit numerous X···OdC interactions, whereas the iodo derivative exhibits type II I···I halogen bonding.

10.1021/cg0604226 CCC: $33.50 © 2006 American Chemical Society Published on Web 11/18/2006

Self-Assembly of Sticky TABs

Crystal Growth & Design, Vol. 6, No. 12, 2006 2733 Scheme 1

The studies described above indicate that relatively simple TABs are potentially useful for probing a range of solid-state phenomena, including hydrogen and halogen bonding, network interpenetration, and inclusion complex formation. Triaroylbenzene-derived clathrates are particularly interesting from a materials standpoint as these complexes can be viewed as prototypes of soft supramolecular materials such as micro/ mesoporous solids and/or selective sorption agents. The inclusion complexes obtained from 1-4, however, all exhibited limited stability that thwarted attempts to remove or exchange guest species. Since the solid-state hydrogen-bonding interactions operative in these structures all involve weak aromatic CsH hydrogen-bond donors, it was reasoned that incorporation of functional groups capable of participating in stronger and more predictable hydrogen-bonding interactions (“sticky” groups) may result in more robust crystalline architectures while also providing a starting point for the design of functional organic cocrystals and salts. In this context, the TAB-based tris(phenol) 7 has been prepared and structurally characterized.

Phenols (especially polyphenols) continue to receive considerable attention from the crystal engineering community as such compounds ultimately may prove to be useful building blocks for the preparation of functional materials. Various polyphenols have been found to display inclusion host ability, while others exhibit intriguing hydrogen-bonding motifs.12 Unusual modes of network interpenetration also have been observed in certain bis(hydroxyphenyl)cyclohexanones studied by Desiraju and Nangia,13 and in a tetrakis(dihydroxyphenyl)silane investigated by Wuest.14 Additionally, phenolic residues readily participate in hydrogen-bonding interactions with basic amines and nitrogen heterocyclessa tendency that has been exploited to great effect in the design and synthesis of numerous organic cocrystals.15 Finally, although indirectly related to crystal engineering applications, cyclic arrays of polyphenols (e.g., resorcinarenes, calixarenes) are capable of engaging in solution-phase selfassembly processes to deliver remarkably stable and expansive multimolecular aggregates.16 Given the rich supramolecular chemistry exhibited by polyphenol-functionalized compounds, it was deemed worthwhile to examine the behavior of hydroxylsubstituted TABs, commencing with a study of the tris(4-

hydroxyphenyl) derivative 7. A total of six crystalline samples of 7 have been obtained from various solvents yielding structures that fall into two categories: highly symmetrical layer-type inclusion complexes and clathrated structures in which the crystalline host lattice is extensively hydrated. Results and Discussion The preparation of tris(phenol) 7 was accomplished in a straightforward manner as outlined in Scheme 1. The known enaminone17 8 was subjected to the cyclotrimerization conditions described by Elghamry to afford (4-methoxy)TAB 9 in excellent yield.18 Removal of the methyl groups with BBr3 then provided 7. Purification of 7 was achieved via silica gel flash column chromatography using EtOAc as the eluent. Single crystals of 7·1.5(EtOAc) were obtained directly from column fractions, and crystallographic data are provided in Table 1. The material exhibits threefold symmetry (R3c space group) with two independent TAB molecules in the asymmetric unit (Figure 1).19 The two molecules are nearly identical except for a slight difference in torsion angle about the carbonyl linkages (34.70° vs 37.41°). Each molecule is incorporated into similar octahedral or R-Po type hydrogen-bonded networks. The triaroylbenzene 7 possesses three conventional hydrogen-bond donors (the three phenolic residues) and up to six hydrogen-bond acceptors (phenols can act as hydrogen-bond acceptors12 in addition to the three carbonyl groups). In the structure of 7·1.5(EtOAc), however, each TAB is connected to six adjacent molecules via OsH···OdC hydrogen bonds (DOsO ) 2.678 - 2.690 Å); thus the phenol units only serve as hydrogen-bond donors. Six molecules surround a central TAB in an octahedral array as shown in Figure 2, thereby providing the basis for generation of the observed R-Po networks. Two such interpenetrated networks exist in 7·1.5(EtOAc) as illustrated in Figure 3.20 Ethyl acetate solvate molecules appear to be held in place by van der Waals attractions and occupy positions in layers sandwiched between carbonyl acceptors and phenol donors (vide infra). Amorphous samples of 7 obtained by solvent evaporation of column chromatography fractions followed by drying under vacuum were subjected to alternative crystallization conditions. Slow evaporation of an acetone solution deposited two types of single crystals visually distinguishable under a microscope. X-ray diffractometry revealed that one type of crystal was isostructural with the inclusion complex described above except for the presence of H2O molecules in place of EtOAc solvates. In this structure [stoichiometry 7·0.5(H2O)], there are again two independent TAB molecules in the asymmetric unit, each of which is incorporated into mutually interpenetrating R-Po type networks. Enclathrated water is present within the lattice as shown in Figure 4. Interestingly, water solvates appear to be isolated from each other as well as the TAB network. The closest

2734 Crystal Growth & Design, Vol. 6, No. 12, 2006

Pigge et al.

Table 1. Crystallographic Data

cryst syst space group a/Å b/Å c/Å R/deg β/deg γ/deg V/Å3 Z Dcalcd m T/K, instrument used no. of reflns no. of unique reflns no. of reflns with I > 2σ(I) no. of params R1 [I > 2σ(I)] wR2

7‚3(H2O) ‚0.5(MeOH)

7‚1.5(EtOAc)

7‚0.5(H2O)

rhombohedral R3c 17.6686(1) 17.66860(1) 32.0818(6) 90 90 120 8673.48(18) 18 1.311 0.096 170(2) SMART

rhombohedral R3c 17.1120(3) 17.1120(3) 33.4225(12) 90 90 120 8475.6(4) 12 1.052 0.076 100(2) APEXII

monoclinic P21/n 13.1901(3) 13.5784(3) 14.0338(4) 90 90.4950(10) 90 2513.37(11) 4 1.378 0.104 100(2) APEXII


monoclinic P21/n 13.0899(12) 13.4348(12) 14.1899(12) 90 91.572(2) 90 2494.5(4) 4 1.343 0.102 167(2) SMART


17786 3729

30818 2792

39692 7104

61990 4382

26796 4346

43062 4881

2456

2383

5461

2976

2480

4009

238 0.0787 0.2375

216 0.0454 0.1356

364 0.0593 0.1781

353 0.0725 0.2238

340 0.1126 0.2458

325 0.0522 0.1550

7‚3(H2O)‚0.5(acetone)

approach to an oxygen atom of water is by an aromatic hydrogen atom ∼3.2 Å away, while adjacent water molecules are >5.5 Å apart. Water has excellent hydrogen-bonding ability (as both donor and acceptor), and it is rare to observe an organic crystalline hydrate in which the water solvates are not participating in any intermolecular interactions.21 In contrast to the hydrate described above, other crystals isolated concomitantly with 7·0.5(H2O) incorporate water into an extensively hydrogen-bonded crystalline lattice. Disordered acetone solvate molecules are also present. The structure of 7·

Figure 1. Two unique TAB molecules in the asymmetric unit of 7· 1.5(EtOAc). EtOAc solvate omitted for clarity. The two molecules differ in the torsion angle about the aroyl linkages.

Figure 2. Octahedral array of 7 in 7·1.5(EtOAc). The central TAB (light blue) is connected to six adjacent TABs via OsH···OdC hydrogen bonding. “Axial” TABs are shown in green, and “equatorial” TABs are shown in magenta. Hydrogen bonds indicated by yellow lines.

7‚3(H2O)‚0.5(EtOH)

7‚3(H2O)

3(H2O)·0.5(acetone) was solved in the P21/n space group and possesses one TAB in the asymmetric unit. Unlike the previously discussed structures, adjacent TABs do not engage in direct hydrogen-bonding interactions; instead, water molecules serve as hydrogen-bonding bridges to produce a 2D gridlike network. Acetone solvates are present in well-defined voids as depicted in Figure 5. Close-packing is achieved via inclined interpenetration of a second identical network. This interpenetration effectively encloses the voids containing the included guest molecules to afford a true clathrate (vide infra). Triaroylbenzene 7 proved to be rather insoluble in common organic solvents, a property that hampered our ability to obtain X-ray quality crystals from a wide range of potential solvates. The tris(phenol) does dissolve in warm halogenated solvents (CH2Cl2, CHCl3), but only amorphous powders were recovered after cooling and slow evaporation. Likewise, crystals of 7 were unable to be obtained from toluene and acetonitrile solutions. Certain alcohols were found to be more suitable crystallization solvents, and crystals isostructural with 7·3(H2O)·0.5(acetone) were obtained by slow evaporation of ethanolic and methanolic solutions. As can be seen in Table 1, these monoclinic crystals have virtually identical unit cell dimensions. They each possess network architectures similar to that shown in Figure 5, differing only in the identity of the included solvate. Despite the presence of hydroxyl groups, the MeOH and EtOH solvates appear to

Figure 3. Interpenetration of independent R-Po networks in 7·1.5(EtOAc).


Crystal Growth & Design, Vol. 6, No. 12, 2006 2735

Figure 6. View of hydrogen-bonding interactions in the monoclinic crystalline hydrates 7·3(H2O)·0.5(X) where X ) acetone, EtOH, MeOH, or nothing. Hydrogen atoms have been omitted for clarity. Oxygen atoms of included H2O molecules are shown as red spheres. Each phenol ring is part of a separate TAB molecule. Hydrogen bonds are indicated by dashed lines.

Figure 4. View (down b) of the extended packing in 7·0.5(H2O). Independent triaroylbenzene networks are shown in blue and magenta. Isolated water molecules are shown in space filling representation. Complex is isostructural with 7·1.5(EtOAc).

Figure 5. Partial view of the extended packing (down c) of 7·3(H2O)· 0.5(acetone). For clarity, only a few water molecules (red) are shown. Disordered acetone solvates are depicted in green.

be functioning in a space-filling capacity and are not incorporated into the hydrated TAB hydrogen-bonding network (vide infra). Consistent with this notion, the dimensions of the alcohol solvate appear to be important for successful crystallization as attempts to incorporate larger alcohols into the TAB lattice (specifically isopropanol and tert-butanol) failed. Crystallization of 7 from nitrobenzene, however, afforded a crystalline hydrate in which the voids occupied by acetone (or MeOH or EtOH) solvates are present but empty. Presumably, these voids are not size/shape complementary with the dimensions of nitrobenzene. Despite the absence of included guest species, the integrity of the clathrate lattice is nonetheless maintained. A view of the TAB-H2O connectivity found in all the monoclinic crystals reported in this study is shown in Figure 6. A total of six water molecules (red spheres in Figure 6, hydrogens have been omitted

for clarity) form hydrogen-bonded bridges between six carbonyl groups from two separate molecules of 7 and six phenol residues originating from six different triaroylbenzenes (note that only the six phenol rings that are part of the hydrogen-bonded array are shown in Figure 6). Thus, parts of 14 different molecules are assembled to generate an irregular polyhedron with approximate dimensions of 9.0 × 8.2 × 7.5 Å. The water molecules donate hydrogen bonds to both carbonyl acceptors (DOsO ) 2.746-2.801 Å) and phenol oxygens (DOsO ) 2.8172.959 Å), while also serving as hydrogen-bond acceptors toward the six phenol donors (DOsO ) 2.566-2.653 Å). Consequently, each water molecule is surrounded by three hydrogen-bonding partnerssan environment that is frequently observed in organic crystalline hydrates.22 It is interesting, therefore, to note that TAB 7 is capable of forming two distinct crystalline hydrates that differ not only in stoichiometry [7·0.5(H2O) vs 7·3(H2O)] but also in supramolecular arrangement. Furthermore, the former hydrate features water molecules in their least commonly observed crystalline environment (no intermolecular interactions), while the latter features water molecules in their most commonly observed crystalline environment (three intermolecular interactions). Two attributes of triaroylbenzenes that can influence the crystalline packing (and by extension the solid-state properties) of these materials are the presence of substituents along the TAB periphery and the molecular conformation(s) encountered in individual derivatives. One objective of this work was the elucidation of strong and ideally predictable solid-state hydrogenbonding motifs originating from phenol moieties incorporated into the TAB framework. It is envisioned that engineering directional and energetically significant intermolecular interactions between individual TABs will allow for greater structural control over any resulting cocrystals or composites. The tris(phenol) 7, then, stands in contrast to previously characterized inclusion hosts 1-4 which are devoid of any strong hydrogenbond donors. From a crystal engineering perspective, the first two structures discussed above [7·1.5(EtOAc) and 7·0.5(H2O)] appear promising in that each phenol unit forms a single hydrogen bond to a carbonyl acceptor. Moreover, the C3

2736 Crystal Growth & Design, Vol. 6, No. 12, 2006

Figure 7. (a) Schematic representation of the C3 molecular conformation exhibited by TABs 3-5 and 7 in certain solid-state structures. The central 1,3,5-trisubstituted arene is drawn perpendicular to the plane of the paper (heavy horizontal line). (b) Dimerization of C3-symmetric TABs 4 and 5 into Piedfort units.

symmetry adopted by individual TAB molecules is reflected in the bulk structure, contributing to inefficient packing and hence solvent inclusion. As a measure of crystal porosity, the amount of solvent-accessible void space in the EtOAc inclusion complex was calculated to be ∼34% using the PLATON program.23 The combination of these features seemingly offers an opportunity for design of soft materials if a means can be found to enforce and elaborate upon this mode of packing. Notably (from a solid state design standpoint) this crystalline morphology and the corresponding hydrogen-bonding arrangement is not universally observed. Although only a limited number of structures have been determined, it appears that an alternative packing motif characterized by extensive hydration and decreased porosity [12% solvent-accessible space in 7·3(H2O)·0.5(acetone)] is more common. These results seem to reinforce earlier assertions made by Wuest concerning the limited utility of phenols in supramolecular design due to the numerous hydrogen-bonding motifs of comparable strength available to this functional group.12a Conformational flexibility of the TAB framework is an additional complicating factor in crystal design. However, despite the absence of uniform hydrogen-bonding interactions among the inclusion complexes and hydrates of 7, there is a degree of gross conformational homology across the series. Moreover, the molecular conformations adopted by 7 are similar to the predominant solid-state conformations exhibited by TABs 3-5.7,9,10 This conformation is depicted schematically in Figure 7a as if one were viewing the TAB with the central arene ring normal to the plane of the page. In structures of 3-5 and 7 the oxygen and aryl moieties are arrayed in C3 or nearly C3 propeller-like orientations (with respect to structures of 7, the triclinic crystals exhibit C3 molecular symmetry, while the monoclinic samples feature pseudo-C3 symmetric TABs due to slight differences in the three aroyl torsion angles). In crystalline samples of 4 and 5 individual TAB molecules effectively dimerize into Piedfort-type units via interdigitation of the aroyl groups (Figure 7b).24 This dimerization also results in favorable alignment of the carbonyl dipoles. The nitro derivative 3 behaves similarly except that the dimerization is slightly offset so that an aroyl ring of one molecule is positioned above the central arene of a second molecule. In contrast, the formation of Piedfort units from 7 has not been observed. Instead, phenol-to-carbonyl intermolecular hydrogen-bonding results in head-to-tail type stacking as can be seen in Figure 4, while network interpenetration and water of hydration preclude formation of Piedfort dimers in the monoclinic crystals. As compared to the 4-methoxy congener 4b, the hydroxyl groups in the periphery of 7 function as hydrogen-bond donors as well as more potent electron-releasing arene substituents. To what extent (if any) each of these features contributes to disruption of Piedfort dimerization is not yet known. It appears noteworthy, however, that aside from 7 all other TABs found to display propeller conformations (Figure 7a) are engaged in some type of Piedfort dimerization. The solid state conformations exhibited by other

Pigge et al.

structurally characterized TABs (i.e., 1, 2, and 6) differ considerably from each other as a function of TAB substituent and, for 1 and 2, included solvate.5,6,11 Significantly, none of these latter TABs was found to display the C3-like molecular structure found in 3-5 and 7. While the number of structures being compared is relatively small (∼35 total including all clathrates and polymorphs), a solid-state conformational bias may be emerging in favor of TABs possessing electron-rich peripheral substituents adopting C3 or pseudo-C3 molecular structures. If so, then this bias may have important consequences in the context of future studies in crystal engineering. Indeed, successful inclusion hosts frequently possess a rigidly enforced rotational axis of symmetry that leads to inefficient packing in the solid statesthus guest (solvate) inclusion.8,25 A further interesting feature observed in several crystalline networks containing C3-symmetric TABs is a correlation between molecular symmetry and crystal symmetry. For example, clathrates of TAB 4a exhibit trigonal/hexagonal packing (space group P3h), the interpenetrated structure of 5 crystallizes in the R3h space group, and two of the structures described in this work crystallize in R3c. In general, symmetry elements present at the molecular level are not reflected in the crystalline phase.26 The three TABs mentioned above are exceptions to this trend as their crystalline networks all possess elements of 3-fold symmetry. The possibility of controlling or influencing crystal symmetry (packing) through symmetry relationships at the molecular level is certainly intriguing and offers opportunities for designing aesthetically pleasing and potentially functional architectures (e.g., octupolar-based NLO materials).27 Finally, it was anticipated that preparing a TAB derivative capable of participating in conventional hydrogen-bonding interactions would provide more robust crystalline assemblies as compared to other TAB architectures mediated by weaker CsH···O/N interactions. In turn, increased crystalline stability would facilitate examination of solvate removal and/or exchange processes. Unfortunately, the various crystalline samples of 7 obtained in the course of this study proved to be exceedingly fragile. Removal of crystals from the corresponding mother liquor invariably resulted in rapid formation of opaque materials followed by disintegration into powders. Consequently, thermochemical characterization of these inclusion complexes was not pursued further. Conclusions The triaroylbenzene 7, like analogues 1-4, exhibits inclusion host behavior, and inclusion complexes with EtOAc, acetone, ethanol, methanol, and water were structurally characterized. Two structures were obtained in which TAB molecular symmetry was also reflected in the crystal symmetry. In combination with results obtained from crystallographic studies of 1-6, the tendency of TABs substituted with electron-donating groups (OH, OMe, Me) to adopt C3 (or pseudo-C3) conformations in the solid state has been noted. While opportunities for crystal engineering robust and functional (e.g., porous) materials from 7 alone appear limited, the presence of phenol groups should facilitate generation of organic cocrystals and metal-organic coordination polymers that may possess desirable properties while also displaying greater stability. Additionally, the incorporation of alternative hydrogen-bonding “sticky” groups (i.e., functional groups such as CO2H) grafted onto a more rigid TAB framework is expected to afford useful and versatile supramolecular building blocks (tectons) as well. Studies along these lines are underway.


Experimental Section 1,3,5-Tris(4-hydroxybenzoyl)benzene (7). Cyclotrimerization of enaminone17 8 was performed in a mixture of acetic acid/pyridine at elevated temperature according to the method of Elghamry18 to afford the known28 methoxy-substituted TAB 9. This material (0.20 g, 0.40 mmol) was dissolved in dry dichloromethane (∼5 mL) and cooled to -78 °C. Boron tribromide (1.5 mL) was added via syringe, and the reaction was maintained at -78 °C for 2 h, followed by warming to rt and then reflux overnight. After cooling of the sample, aqueous 5% NaOH was added, and the layers were separated. The aqueous phase was acidified by addition of aq. HCl. The resulting precipitate was collected by filtration and purified using silica gel flash column chromatography (EtOAc) to afford 7 as a buff-colored solid (0.14 g, 79%).29 mp 145-150 °C (dec). 1H-NMR (300 MHz, acetone-d ) δ 7.01 (d, J ) 4.8 Hz, 6H), 6 7.85 (d, J ) 4.8 Hz, 6H), 8.24 (s, 3H), 9.34 (s, 3H). 13C-NMR (75 MHz, acetone-d6) δ 116.3, 129.4, 133.5, 133.7, 139.7, 163.1, 193.9. HRMS (FAB+) calcd. for C27H19O6 439.1182 [M + H]+, found 439.1185. X-ray Crystallography. Single crystals of 7·1.5(EtOAc), 7· 3(H2O)·0.5(EtOH), and 7·3(H2O)·0.5(MeOH) were obtained by slow evaporation of solutions prepared from the indicated solvent. Slow evaporation of an acetone solution afforded 7· 0.5(H2O) and 7·3(H2O)·0.5(acetone) concomitantly. Crystals of 7·3(H2O) were obtained from nitrobenzene. Preliminary crystal examination and data collections were performed using a Bruker SMART 1K or APEXII CCD diffractometer equipped with graphite monochromated Mo KR radiation (λ ) 0.71073 Å). Crystals of appropriate dimensions were mounted on glass fibers in random orientations. Preliminary unit cell constants were determined with a set of narrow frame scans. Typical data sets consist of combinations of $ and φ scan frames with typical scan width of 0.5° and counting time of 10 to 30 s/frame at a crystal-to-detector distance of 4.0-5.0 cm. The collected frames were integrated using an orientation matrix determined from the narrow frame scans. SMART, ApexII, and SAINT software packages (Bruker Analytical X-ray, Madison, WI, 2005) were used for data collection and data integration. Analysis of the integrated data did not show any decay. Final cell constants were determined by global refinements of xyz centroids from the complete data set. Collected data were corrected for systematic errors using SADABS based on the Laue symmetry using equivalent reflections.30 Crystal data and intensity data collection parameters are listed in Table 1. Structure solution and refinement were carried out using the SHELXTL-PLUS software package (Sheldrick, G. M., Bruker Analytical X-ray Division, Madison, WI, 2005). Full matrix least-squares refinements were carried out by minimizing ∑w(Fo2 - Fc2).2 The non-hydrogen atoms were refined anisotropically to convergence. The hydrogen atoms were treated using appropriate riding models (AFIX m3). The final residual values and structure refinement parameters are listed in Table 1. The CCDC reference numbers for the deposited data are 613246, 613247, 613248, 613244, 613245, and 613249, respectively. Acknowledgment. We thank the University of Iowa for financial support, the National Science Foundation (CHE0420497) for funding the purchase of the APEXII diffractometer, and Dr. R. E. K. Winter (UM-St. Louis) for mass spectral data.

Crystal Growth & Design, Vol. 6, No. 12, 2006 2737 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.

References (1) (a) Braga, D.; Brammer, L.; Champness, N. R. CrystEngComm 2005, 7, 1. (b) Erk, P.; Hengelsberg, H.; Haddow, M. F.; van Gelder, R. CrystEngComm 2004, 6, 474. (c) Desiraju, G. R. J. Mol. Struct. 2003, 656, 5. d) Hollingsworth, M. D. Science 2002, 295, 2410. (2) Dunitz, J. D. Chem. Commun. 2003, 545. (3) Desiraju, G. R. Angew. Chem. Int. Ed. 1995, 34, 2311. (4) Wuest, J. D. Chem. Commun. 2005, 5830. (5) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. Cryst. Growth Des. 2004, 4, 1217. (6) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. Cryst. Growth Des. 2006, 6, 193. (7) Pigge, F. C.; Ghasedi, F.; Zheng, Z.; Rath, N. P.; Nichols, G.; Chickos, J. S. J. Chem. Soc. Perkin. Trans. 2000, 2, 2458. (8) Weber, E. In ComprehensiVe Supramolecular Chemistry; MacNicol, D. D.; Toda, F.; Bishop, R. Eds.; Pergamon: Oxford, 1996; Vol. 6, pp 535-592. (9) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. CrystEngComm 2004, 6, 531. (10) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. New J. Chem. 2004, 28, 1192. (11) Pigge, F. C.; Vangala, V. R.; Swenson, D. C. Chem. Commun. 2006, 2123. (12) Selected recent examples: (a) Fournier, J. H.; Maris, T.; Simard, M.; Wuest, J. D. Cryst. Growth Des. 2003, 3, 535. (b) Fournier, J. H.; Maris, T.; Wuest, J. D. J. Org. Chem. 2004, 69, 1763. (c) Thallapally, P. K.; Katz, A. K.; Carrell, H. L.; Desiraju, G. R. Chem. Commun. 2002, 344. (d) Aitipamula, S.; Thallapally, P. K.; Thaimattam, R.; Jasko´lski, M.; Desiraju, G. R. Org. Lett. 2002, 4, 921. (e) Aitipamula, S.; Nangia, A. Chem. Eur. J. 2005, 11, 6727. (f) Sarma, R. J.; Baruah, J. B. CrystEngComm 2005, 7, 706. (g) Moorthy, J. N.; Natarajan, R.; Venugopalan, P. J. Org. Chem. 2005, 70, 8568. (h) Venkataramanan, B.; James, W. L. G.; Vittal, J. J.; Suresh, V. Cryst. Growth Des. 2004, 4, 553. (i) Tanaka, T.; Tasaki, T.; Aoyama, Y. J. Am. Chem. Soc. 2002, 124, 12453. (j) Caira, M. R.; Horne, A.; Nassimbeni, L. R.; Toda, F. J. Mater. Chem. 1998, 8, 1481. (13) Aitipamula, S.; Desiraju, G. R.; Jasko´lski, M.; Nangia, A.; Thaimattam, R. CrystEngComm 2003, 5, 447. (14) Saied, O.; Maris, T.; Wang, X.; Simard, M.; Wuest, J. D. J. Am. Chem. Soc. 2005, 127, 10008. (15) Selected examples: (a) Sokolov, A. N.; Frisˇcˇic´, T.; MacGillivray, L. R. J. Am. Chem. Soc. 2006, 128, 2806. (b) Jayaraman, A.; Balasubramaniam, V.; Valiyaveettil, S. Cryst. Growth Des. 2006, 6, 636. (c) Jayaraman, A.; Balasubramaniam, V.; Valiyaveettil, S. Cryst. Growth Des. 2006, 6, 150. (d) Jayaraman, A.; Balasubramaniam, V.; Valiyaveettil, S. Cryst. Growth Des. 2005, 5, 1575. (e) Boldog, I.; Rusanov, E. B.; Sieler, J.; Domasevitch, K. V. New J. Chem. 2004, 28, 756. (f) Saha, B. K.; Nangia, A.; Nicoud, J. F. Cryst. Growth Des. 2006, 6, 1278. (g) Vishweshwar, P.; Nangia, A.; Lynch, V. M. CrystEngComm 2003, 5, 164. (h) Delen, Z.; Xie, C.; Hill, P. J.; Choi, J.; Lahti, P. M. Cryst. Growth Des. 2005, 5, 1867. (i) Glidewell, C.; Ferguson, G.; Gregson, R. M.; Campana, C. F. Acta. Crystallogr. 2000, B56, 68. (16) Rissanen, K. Angew. Chem. Int. Ed. 2005, 44, 3652. (17) Lin, Y.; Lang, S. A. J. Org. Chem. 1980, 45, 4857. (18) Elghamry, I. Synthesis 2003, 2301. (19) For a discussion of structures with multiple independent molecules in the asymmetric unit from a supramolecular perspective, see Steed, J. W. CrystEngComm 2003, 5, 169. (20) For a review of solid state interpenetration, see Batten, S. R.; Robson, R. Angew. Chem. Int. Ed. 1998, 37, 1460. (21) A recent CSD survey of organic hydrates found that the frequency of encountering water with zero or one intermolecular contact was less than 2%: Infantes, L.; Chisholm, J.; Motherwell, S. CrystEngComm 2003, 5, 480. (22) Based upon a recent CSD analysis: Gillon, A. L.; Feeder, N.; Davey, R. J.; Storey, R. Cryst. Growth Des. 2003, 3, 663.

2738 Crystal Growth & Design, Vol. 6, No. 12, 2006 (23) Spek, A. L. PLATON - A Multipurpose Crystallographic Tool, University of Utrecht, The Netherlands, 1999. (24) Jessiman, A. S.; MacNicol, D. D.; Mallinson, P. R.; Vallance, I. J. Chem. Soc. Chem. Commun. 1990, 1619. (25) 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. (26) (a) Pidcock, E.; Motherwell, W. D. S.; Cole, J. C. Acta. Crystallogr. 2003, B59, 634. (b) Brock, C. P.; Dunitz, J. D. Chem. Mater. 1994, 6, 1118.

Pigge et al. (27) Thalladi, V. R.; Brasselet, S.; Weiss, H. C.; Bla¨ser, D.; Katz, A. K.; Carrell, H. L.; Boese, R.; Zyss, J.; Nangia, A.; Desiraju, G. R. J. Am. Chem. Soc. 1998, 120, 2563. (28) Balasubramanian, K. K.; Selvaraj, S.; Venkataramani, P. S. Synthesis 1980, 29. (29) This material also has been prepared from fluoro-substituted TAB 6a: Colquhoun, H. M.; Arico, F.; Williams, D. J. Chem. Commun. 2001, 2574. (30) Blessing, R. H. Acta. Crystallogr. 1995, A51, 33.

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