benzoic Acids: Novel Supramolecular Tectons - American Chemical

Hydrogen-Bonded Dimers of 3,5-Bis(hydroxymethyl)benzoic Acids: Novel Supramolecular Tectons Shigeo Kohmoto,*,† Yu Kuroda,† Yasunobu Someya,† Keiki Kishikawa,† Hyuma Masu,‡ Kentaro Yamaguchi,‡ and Isao Azumaya‡

CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 8 3457–3462

Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba UniVersity, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan, and Faculty of Pharmaceutical Science at Kagawa Campus, Tokushima Bunri UniVersity, 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan ReceiVed January 13, 2009; ReVised Manuscript ReceiVed June 12, 2009

ABSTRACT: As a new supramolecular tecton based on hydrogen bonding for crystal engineering, benzoic acid derivatives possessing two hydroxymethyl groups were developed and their crystal structures were investigated by single crystal X-ray analysis. The hydrogen-bonded dimer of the acid which possesses four hydrogen-bonding sites creates two types of networks, a zigzag and a straight hydrogen-bonded network. Zigzag hydrogen-bonded networks were created with methoxy (1) and benzyloxy (2) derivatives. It was found that the ladder structure was created via a straight hydrogen-bonded network when 2 included either methanol or ethanol in its cavity. The introduction of a long alkoxy group (hexyloxy) (3) resulted in the formation of an alternate hydrogenbonded network. Ethyl benzoate derivative (4) also formed a hydrogen-bonded network in a zigzag manner. Introduction Considerable effort has been devoted over decades to design organic crystals using hydrogen-bonding motifs.1-3 It is challenging to develop a new tecton4,5 based on hydrogen bonding for crystal engineering. The aggregation of smaller supramolecular units into larger arrays represents an actual approach to complicated organic assemblies and can lead to a new generation of solids with promising properties. By the choice of tectons, either tetrahedral or trigonal ones, three-dimensional or twodimensional self-assembled networks could be created, respectively.6,7 The former provided large chambers in their networks. The hydroxyl group is the most common and simplest functional group for hydrogen bonding. Yet, various modes of assemblies are known even for monoalcohols.8 An appropriate design of tectons in which the directions of hydrogen bondings are welldefined is highly desirable. The molecules with two hydroxyl groups as hydrogen-bonding sites, such as diols9-12 and bisphenols,13 were intensively studied as potential host compounds. Several benzene derivatives with two hydroxymethyl groups are used to investigate the diversity of hydrogen-bonding networks.14-20 Out of them, interesting approaches to the hydrogen-bonded ladder structures were reported by Bishop et al.19 and Foces-Foces et al.20 On the basis of their results, we considered that rectangular-shaped molecules with four hydroxyl groups with two of them located on the same side and the others on the opposite side of the molecule can be potential tectons for hydrogen-bonded networks. For our study, we have employed benzoic acid derivatives with two hydrogen-bonding sites, 4-alkoxy-3,5-bis(hydroxymethyl)benzoic acids, whose hydrogen-bonded dimers provide the above-mentioned rectangular-shaped tectons. The dimeric forms of carboxylic acids are well studied as reliable hydrogen-bonding motifs. Trimesic acid provides stacked chicken-wire networks and channels containing disordered guests.21-23 Investigation was also carried out on hydrogen-bonded networks of dicarboxylic acids.24,25 A hydrogen-bonded network of 4-alkoxy-3,5-bis(hydroxymethyl)benzoic acids in a zigzag manner gives a sheet structure * To whom correspondence should be addressed. E-mail: kohmoto@ faculty.chiba-u.jp. † Chiba University. ‡ Tokushima Bunri University.

(the upper structure in Figure 1) and a straight hydrogen bonding affords a ladder structure (the bottom structure in Figure 1). In the ladder structure, the rectangular-shaped cavities are connected laterally via hydrogen bonding. These cavities can be utilized for guest inclusion. Previously, hydrogen-bonded networks of the compounds with four hydroxy groups have been reported by Aoyama et al.26,27 and recently by Hamada et al.,28 with tetrakis(hydroxyphenyl)29 as a hydrogen-bonding motif. Experimental Section Materials and Methods. All the reagents and solvents employed were commercially available and used as received without further purification. 1H and 13C NMR spectra were recorded for samples in CDCl3 with Me4Si as an internal standard. Syntheses. Carboxylic acids 1-3 were prepared from ethyl 4-hydroxy-3,5-bis(hydroxymethyl)benzoate30 in two steps. The O-alkylation of the 4-hydroxyl group of ethyl 4-hydroxy-3,5-bis(hydroxymethyl)benzoate followed by the hydrolysis of the resulting ethyl 4-alkoxybenzoate afforded the corresponding acids. Ethyl 4-hexoxy-3,5-bis(hydroxymethyl)benzoate (4). Ethyl 4-hydroxy-3,5-bis(hydroxymethyl)-benzoate (0.401 g, 1.77 mmol), potassium carbonate (0.361 g, 2.61 mmol), and potassium iodide (0.273 g, 1.64 mmol) were dissolved in acetone (100 mL) and stirred for 30 min. Then, 1-bromohexane (0.506 g, 3.07 mmol) was added to the solution and the resulting mixture was stirred under reflux for 2 days. After the precipitate formed was filtered off, the filtrate was evaporated. The residue was purified with column chromatography on silica gel (hexane/ethyl acetate ) 2: 1) to afford 4 as crystals (0.383 g, 70%). mp 79-80 °C (ethyl acetate/hexane): 1H NMR (400 MHz, CDCl3) δ 0.92 (t, J ) 7.1, 3H), 1.33-1.41 (m, 7H), 1.49 (quintet, J ) 7.6, 2H), 1.83 (quintet, J ) 7.2, 2H), 3.94 (t, J ) 6.8, 2H), 4.36 (q, J ) 7.2, 2H), 4.75 (s, 4H), 8.04 (s, 2H): 13C NMR (100 MHz, CDCl3) δ 14.1, 14.4, 22.6, 25.7, 30.4, 31.7, 60.8, 61.1, 75.4, 126.6, 130.3, 134.3, 159.1, 166.1: MS (FAB) m/z 311 [MH]+, 333 [M + Na]+: IR (KBr) ν 1715 cm-1 (CdO): Anal. Calcd for C17H26O5: C, 65.78; H, 8.44. Found: C, 65.78; H, 8.31. 4-Hexyloxy-3,5-bis(hydroxymethyl)benzoic acid (3). To an ethanol (20 mL) solution of 4 (0.275 g, 0.886 mmol), an aqueous solution of potassium hydroxide (15%, 2 mL) was added and stirred for 2 h at 70 °C. After being cooled to room temperature, the reaction mixture was neutralized with 1 M HCl aqueous solution. The white powder that precipitated was washed with H2O. The crude product was reprecipitated with THF/hexane to afford 3 as a white powder (0.189 g, 76%). mp 155-159 °C (ethyl acetate): 1H NMR (400 MHz, DMSO-d6) δ 0.88 (t, J ) 6.8, 3H), 1.31 (m, 4H), 1.42 (m, 2H), 1.69 (quintet, J ) 6.9,

10.1021/cg9000347 CCC: $40.75  2009 American Chemical Society Published on Web 06/24/2009

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Kohmoto et al. Chart 1. 4-Alkoxy-3,5-bis(hydroxymethyl)benzoic Acids Examined

(FAB) m/z 212 [MH]+: IR (KBr) ν 1685 cm-1 (CdO): Anal. Calcd for C10H12O5: C, 56.60; H, 5.70. Found: C, 56.71; H, 5.74. 4-Benzyloxy-3,5-bis(hydroxymethyl)benzoic Acid (2). In a manner similar to the preparation of 3, 2 was obained in 73% from the corresponding ester. mp 175-178 °C (ethyl acetate): 1H NMR (400 MHz, DMSO-d6) δ 4.58 (s, 4H), 4.91 (s, 2H), 7.42 (m, 7H): 13C NMR (125.6 MHz, DMSO-d6) δ 57.8, 75.4, 126.2, 128.0, 128.1, 128.3, 128.4, 135.5, 137.1, 156.7,1672: MS (FAB) m/z 289 [MH]+: IR(KBr) ν 1690 cm-1 (CdO): Anal. Calcd for C16H16O5: C, 66.66; H, 5.59. Found: C, 66.44; H, 5.50. X-ray Crystallography. X-ray diffraction data for the crystals were measured on CCD diffractometers. Data collections were carried out at low temperature [200 K for 4, 150 K for 1, 120 K for the ethanol inclusion complex of 2 (2 · EtOH), 90 K for 3, and 15 K for 2 and the methanol inclusion complex of 2 (2 · MeOH)] by using liquid nitrogen or liquid helium. All structures were solved by direct methods SHELXS97,31 and the non-hydrogen atoms were refined anisotropically against F2, with full-matrix least-squares methods SHELXL-97.31 All hydrogen atoms were positioned geometrically and refined as riding. Crystal data for 1-4 and the methanol or ethanol inclusion complexes of 2 are attached as Table 1 and Supporting Information.

Results and Discussion

Figure 1. Schematic representation of two types of hydrogen-bonded networks created by the dimeric form of carboxylic acids as tectons possessing tetrakis(hydroxymethyl) groups. Zigzag and straight type hydrogen-bonded networks are created to afford sheet and ladder structures, respectively. 2H), 3.79 (t, J ) 6.4, 2H), 4.54 (s, 4H), 7.95 (s, 2H): 13C NMR (100 MHz, DMSO-d6) δ 14.0, 22.1, 25.1, 29.8, 31.1, 57.6, 73.8, 125.9, 128.2, 135.3, 156.9, 167.3: MS (FAB) m/z 283 [MH]+, 305 [M + Na]+: IR (KBr) ν 1685 cm-1 (CdO): Anal. Calcd for C15H22O5: C, 63.81; H, 7.85. Found: C, 63.74; H, 7.72. 4-Methoxy-3,5-bis(hydroxymethyl)benzoic Acid (1). In a manner similar to the preparation of 3, 1 was obained in 46% from the corresponding ester. mp 221-225 °C (ethanol): 1H NMR (500 MHz, DMSO-d6) δ 3.72 (s, 3H), 4.55 (s, 4H), 7.95 (s, 2H): 13C NMR (125.6 MHz, DMSO-d6) δ 57.6, 61.3, 126.0, 128.3, 135.2, 157.9, 167.3: MS

3,5-Bis(hydroxymethyl)benzoic acid derivatives 1-4 (Chart 1) were prepared by alkylation of 3,5-bis(hydroxymethyl)-4hydroxybenzoic acid ethyl ester (for 4) followed by hydrolysis (for 1, 2, and 3). All of them gave single crystals suitable for single crystal X-ray analysis upon recrystallization. Compound 2 afforded solvated crystals, 2 · MeOH or 2 · EtOH, when it recrystallized from methanol or ethanol, respectively. Their crystal data are summarized in Table 1. In its crystal structure, compound 1 adopts a dimeric form by hydrogen bonding with a neighboring molecule with the O(carbonyl)-O(hydroxy) distance of 2.60 Å (Figure 2a). A zigzag-type network in a direction of the c axis is created by the hydrogen bonding between two neighboring hydroxyl groups with the O-O distance of 2.70 Å. Each one-dimensional array is connected to another array by the hydrogen bonding between the two neighboring carboxyl groups. They construct a 2-D sheet

Table 1. Crystallographic Data for 3,5-Bis(hydroxymethyl)benzoic Acid Derivatives 1-4 compound

1

2

2 · MeOH

2 · EtOH

3

4

formula crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Dc (Mg m-3) Z T (K) R1, [I > 2σ(I)] wR2 [I > 2σ(I)]

C10H12O5 monoclinic P21/c 4.3526(4) 16.547(2) 13.448(1) 90 93.818(1) 90 966.4(2) 1.458 4 150 0.0422 0.1246


2 · 0.6(CH3OH) triclinic P1j 9.341(1) 11.811(1) 21.760(3) 87.034(2) 81.170(2) 69.384 (2) 2220.4(5) 1.380 6 15 0.0416 0.1124

2 · 0.33(C2H5OH) triclinic P1j 9.355(3) 11.981(4) 21.803(8) 86.705(4) 80.899(4) 68.099(4) 2239(1) 1.351 6 120 0.0674 0.2082

C15H22O5 monoclinic P21/c 10.37(1) 8.326(8) 18.23(2) 90 94.74(1) 90 1568(3) 1.196 4 90 0.0627 0.1763


Dimers of 3,5-Bis(hydroxymethyl)benzoic Acids

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Figure 2. Packing diagram of 1 showing a sheet structure. A view along the a axis (a) and a side-view along the b axis (b). Hydrogen bonds are indicated with black dotted lines.

Figure 3. Packing diagram of 2 showing a waved-sheet structure. A view along the a axis (a) and a side-view along the c axis (b).

Figure 4. Packing diagram of 2 · MeOH. A ladder structure is constructed by hydrogen bonding (a). Disordered methanol molecules are colored green (major part) or light green (minor part). The π-π and CH/π interactions between two neighboring molecules in the ladder structure in which distances are indicated in Å (b). A side-view along the a axis (c) in which methanol molecules are indicated by spacefilling models. The dimers corresponding to the lid parts of the cavity are colored magenta.

structure on the bc plane. Moreover, a hydrogen-bonded network in the direction of the a axis is also created with the O-O distance of 2.68 Å between the two overlapping hydroxyl groups. The hydrogen bonding among the sheets created the 3-D hydrogen-bonded network (Figure 2b).

A crystal structure of benzyloxy derivative 2 which was recrystallized from ethyl acetates afforded a pattern of hydrogenbonded network similar to that of methoxy derivative 1 (Figure 3). However, it formulated a waved-sheet structure instead of a plain sheet. Since a benzyloxy group is fairly larger than a methoxy group, it is difficult to locate in a packing manner

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Figure 7. DSC diagrams of crystals of 2 (a), 2 · MeOH (b), and 2 · EtOH (c) on heating (5 °C/min).

Figure 5. Packing diagram of the ladder structure of 2 · EtOH. Hydrogen bonds are indicated with black dotted lines. The terminal methyl group of the ethanol molecule is disordered (light green part).

Figure 6. TGA diagrams of crystals of 2 · MeOH (a) and 2 · EtOH (b).

similar to the methoxy derivative. In order to create enough space for the benzyloxy group, the sheet waves. Hydrogenbonded network along the b axis is formed in a zigzag manner with a O-O distance of 2.65 Å. The waved sheets are stacked along the a axis by hydrogen bonding with a O-O distance of 2.70 Å. In contrast, solvates of 2 were obtained by recrystallization from methanol or ethanol. Methanol solvated crystals 2 · MeOH showed a crystal structure different from that of 2 (Figure 4). The single crystal X-ray analysis of 2 · MeOH showed that a ladder structure was fabricated via hydrogen bonding between adjacent hydroxymethyls of the hydrogen-bonded dimers which were aligned in a straight manner (Figure 4a). Stacking of the two units of the ladder via π-π interaction between the phenyl rings of the benzoic acid part and CH/π (T-shape) interaction in the benzyloxy moieties afforded a cavity capable of including guest molecules (Figure 4b). In particular, this CH/π interaction is important for the stacking between the hydrogen-bonded dimers since other derivatives did not give a ladder structure.

Figure 8. XRD patterns of crystal of 2 (a), 2 · MeOH (b), 2 · MeOH after heating for 10 min at 120 °C (c), 2 · EtOH (d), and 2 · EtOH after heating for 10 min at 120 °C (e), respectively.

The cavity includes methanol molecules. From the single crystal X-ray analysis at 15 K, the methanol molecules are disordered in three parts (Supporting Information). The total number of the methanol molecules in a cavity was calculated to be 3.6. The molar ratio of compound 2 and methanol in the crystal is 3:1.8. The reason why the ratio is not an integer might be due to the incomplete solvation of the cavities. Four molecules of methanol are included in some cavities, while three molecules are included in other cavities. In the crystal of 2 · MeOH, the cavities are covered with two sets of the hydrogenbonded dimers on both upper and bottom sides (Figure 4c). Therefore, these hydrogen-bonded dimers play a role as lids to keep the guest molecules inside the cavity. This is an example of three-deck hydrogen-bonded layers with hydrophilic groups inside the layer and hydrophobic outside. In these lamellar-type crystals,32 the cavities exist as compartments in the crystal. In contrast to the large number of examples of cavities as channels33-36 in crystalline materials, examples of this kind of compartment-type cavities are rare. Almost the same dimension of cavities is created in the ethanol solvated crystals 2 · EtOH (Figure 5). Two molecules of ethanol are included in the cavity. The disorder of ethanol

Dimers of 3,5-Bis(hydroxymethyl)benzoic Acids

Crystal Growth & Design, Vol. 9, No. 8, 2009 3461

Figure 9. Packing diagrams of 3. Dimers of equivalent positions are indicated with the same color. A top-view along the b axis (a) and a side-view along the c axis (b, upper), and schematic representation of the hydrogen-bonded network (b, bottom). Overlapping of the network-layers (cyanmagenta and blue-red) (c).

molecules was observed. Lattice parameters of 2 · EtOH measured at 120 K are almost the same as those of 2 · MeOH measured at 15 K (Table 1). These results also indicate the rigidity of the host framework. In 2 · EtOH two molecules of ethanol were included in the cavity because of its larger molecular volume compared to that of methanol. The terminal methyl group of the ethanol molecule is disordered. In order to verify the amount of included methanol and ethanol determined by single crystal X-ray analysis, thermogravimetric analysis (TGA) of inclusion crystals was carried out. Figure 6a,b shows the TGA diagrams of 2 · MeOH and 2 · EtOH, respectively. The ratios of solvated methanol and ethanol (2:alcohol) were determined to be ca. 3:1.7 and 3:1.0, respectively, by TGA analysis. The ratios were almost the same to those obtained by single crystal X-ray analysis. Moreover, 1 H NMR analysis of 2 · EtOH in DMSO-d6 attested that the ratio of ethanol solvated was 3(2):1(ethanol). Because of the insolubility of 2 · MeOH in deuterated solvents, the amount of methanol solvated could not be determined by 1H NMR analysis. Differential scanning calorimetry (DSC) measurements of 2 · MeOH and 2 · EtOH have also been carried out and compared with that of 2. A single endothermic peak was observed at 184.7 °C for 2 corresponding to its melting (Figure 7a). The solvated crystals, 2 · MeOH and 2 · EtOH, showed one additional endothermic peak at 84.2 and 98.5 °C, respectively, in addition to their melting peaks at 184.5 °C. These peaks correspond to the liberation of solvated methanol and ethanol molecules, which appear at a higher temperature than those of their boiling points (Figure 7b,c). The results indicate that the solvated crystals are reasonably stable. This could be caused by the tight packing of solvent molecules in the covered cavities. Powder XRD analysis of 2 and the solvated crystals, 2 · MeOH and 2 · EtOH, were carried out to examine whether the release of methanol and ethanol molecules by heating from the crystals could result in the phase transition leading to the crystal structure of 2. Figure 8a-c shows the XRD patterns of 2, 2 · MeOH, and 2 · MeOH after heating at 120 °C for 10 min, respectively. The XRD patterns of 2 · EtOH before and after heating at 120 °C for 10 min are shown in Figure 8, panels d and e, respectively. They clearly show that heating induces elimination of methanol

and ethanol to generate new crystalline phases which are different from that of 2. Elimination of methanol and ethanol could result in the destruction of the packing structures of 2 · MeOH and 2 · EtOH, respectively. However, even after the destruction, they have good crystallinity since their XRD patterns (Figure 8c,e) appear in sharp reflection peaks. They showed almost the same XRD patterns, which indicated that the same crystalline structure was obtained by elimination of solvent molecules from both solvated crystals. The crystalline structure of 2 is stable upon heating. Control experiments show that no change in its XRD pattern was observed after heating for 10 min at 120 °C. In contrast to the zigzag-type hydrogen-bonded network observed in 1 and 2, a straight-type hydrogen-bonded network was observed in the crystal structure of 3 due to the alternate arrangement of dimers (Figure 9a). Hydrogen-bonded network between the hydroxymethyl groups of neighboring dimers was observed in the direction of the c axis with O-O distances of 2.72 Å. However, the network does not form a sheet structure. The neighboring dimers along the c axis are tilted alternately with the tilt angle of ca. 46° in the direction of the b axis (Figure 9b). The hydroxyl groups at both ends of the dimer connect with discrete dimers each other. Thus, this 3-D hydrogen-bonded network is not a ladder. Furthermore, two network-layers sliding along the a axis are stacked with two hydrogen bonds between the overlapping hydroxyl groups with the O-O distances of 2.76 Å (Figure 9c). Because of this hydrogen-bonded network, no cavity can be generated in the crystals. In order to examine effectiveness of this hydrogen-bonded network created by hydroxymethyl groups, we investigated the crystal structure of ester derivative 4. The crystal structure of 4 resembles those of 1 and 2 rather than that of 3 (Figure 10a). Even the absence of the rigid hydrogen-bonded dimeric form of carboxylic acid, the zigzag-type hydrogen-bonded network similar to those of 1 and 2 was observed. The hexyloxy and ethyl ester moieties are sandwiched between two hydrogenbonded layers creating a hydrophobic layer. Since the volume of hexyloxy moiety and that of the twice of ethyl ester moiety are roughly the same, they can well fill in the space between

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Kohmoto et al. ethanol solvated crystals, 2 · MeOH and 2 · EtOH, are available free of charge via the Internet at http://pubs.acs.org.

References (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23)

Figure 10. Hydrogen-bonded networks of 4. Intermolecular hydrogenbonded network created in an alternate way along the c axis (a), and a side-view showing the hydrogen-bonded network among the sheets along the a axis (b). Hydrogen bonds are indicated with black dotted lines. Certain molecules are colored magenta for clarity.

(24) (25) (26)

the hydrogen-bonded layers generating a curved sheet structure (Figure 10b).

(28)

(27)

(29) (30)

Conclusion (31)

We have demonstrated that the hydrogen-bonded dimer of 3,5-bis(hydroxymethyl)benzoic acid derivatives can be useful supramolecular tectons for crystal engineering. By utilizing four hydrogen-bonding sites three-dimensionally hydrogen-bonded network can be created. Two ways of hydrogen bonding, zigzag and straight types, are available. A unique ladder network was fabricated by choosing proper substituents and solvents for crystallization. Supporting Information Available: The crystallographic information files (CIF) and crystal data of compounds 1-4, and methanol and

(32) (33) (34) (35) (36)

Etter, M. C. Acc. Chem. Res. 1990, 23, 120–126. Desiraju, G. R. Acc. Chem. Res. 1996, 29, 441–449. Desiraju, G. R. Acc. Chem. Res. 2002, 35, 565–573. Simard, M.; Su, D.; Wuest, D. J. Am. Chem. Soc. 1991, 4696–4698. Wuest, J. D. Chem. Commun. 2005, 5830–5837. Fournier, J.-H.; Maris, T.; Wuest, J. D.; Guo, W.; Galoppini, E. J. Am. Chem. Soc. 2003, 125, 1002–1006. Malek, N.; Maris, T.; Perron, M.-E`.; Wuest, J. D. Angew. Chem., Int. Ed. 2005, 44, 4021–4025. Brock, C. P.; Duncan, L. L. Chem. Mater. 1994, 6, 1307–1312. Jacobs, a.; Masuku, N. L. Z.; Nassimbeni, L. R.; Taljaard, J. H. CrystEngComm 2008, 10, 322–326. Roex, T. le; Nassimbeni, L. R.; Weber, E. Chem. Commun. 2007, 1124–1126. Sanyal, N.; Lahti, P. M. Cryst. Growth Des. 2006, 6, 1253–1255. Caira, M. R.; Jacobs, A.; Nassimbeni, L. R.; Toda, F. J. Chem. Crystallogr. 2006, 36, 43–443. Sarma, R. J.; Baruah, J. B. Cryst. Growth Des. 2007, 7, 989–1000. Masci, B.; Thuery, P. Acta Crystallogr. 2002, C68, o575-o579. Perrin, R.; Lamartine, R.; Vicens, J.; Perrin, M.; Thozet, A.; Hanton, D.; Fugier, R. New J. Chem. 1986, 10, 179–190. Oehler, D.; Thozet, A.; Perrin, M. Acta Crystallogr. 1985, C41, 1766– 1768. Perrin, M.; Cherared, M. Acta Crystallogr. 1986, C42, 1623–1625. Chu, Z.-L.; Huang, W.; Gou, S.-H. Acta Crystallogr. 2005, E61, o1624-o1626. Nguyen, V. T.; Ahn, P. D.; Bishop, R.; Scudder, M. L.; Craig, D. C. Eur. J. Org. Chem. 2001, 4489–4499. Rodrı´guez, M. L.; Febles, M.; Pe´rez, C.; Pe´rez-Herna´ndez, N.; Martin, J. D.; Foces-Foces, C. Acta Crystallogr. 2005, C61, o138-o142. Neudo¨rfl, J.; Ermer, O. HelV. Chim. Acta 2001, 84, 1268–1312. Liu, R.; Mok, K.-F.; Valiyaveettil, S. New J. Chem. 2001, 25, 890– 892. Paz, F. A. A.; Bond, A. D.; Khmyak, Y. Z.; Klinowski, J. New J. Chem. 2002, 26, 381–383. Moorthy, J. N.; Natarajan, P. Cryst. Growth Des. 2008, 3360–3367. Moorthy, J. N.; Natarajan, P. J. Mol. Struct. 2008, 885, 139–148. Kobayashi, K.; Endo, K.; Aoyama, Y.; Masuda, H. Tetrahedron Lett. 1993, 34, 7929–7932. Endo, K.; Sawaki, T.; Koyanagi, M.; Kobayashi, K.; Masuda, H.; Aoyama, Y. J. Am. Chem. Soc. 1995, 117, 8341–8352. Akimoto, K.; Suzuki, H.; Kondo, Y.; Endo, K.; Akiba, U.; Aoyama, Y.; Hamada, F. Tetrahedron 2007, 63, 6887–6894. Sarma, R. J.; Baruah, J. B. Cryst. Growth Des. 2007, 5, 989–1000. Zinke, A.; Ott, R.; Leggeewie, E.; Hassanein, A.; Zankl, G. Monatsh. Chem. 1956, 87, 552. Chem. Abstr. 1957, 51, 2845c. A short history of SHELX . Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122. Sarma, R. J.; Baruah, J. B. CrystEngComm 2005, 7, 706–710. Sisson, A. L.; Sanchez, V. D. A.; Magro, G.; Griffin, A. M. E.; Shah, S.; Charmant, J. P. H.; Davis, A. P. Angew. Chem., Int. Ed. 2005, 44, 6878–6881. Pantos, G. D.; Pengo, P.; Sanders, J. K. M. Angew. Chem., Int. Ed. 2007, 46, 194–197. Ranganathan, A.; Heisen, B. C.; Dix, I.; Meyer, F. Chem. Commun. 2007, 3637–3639. Chen, Z.-F.; Zhang, Z.-L.; Tan, Y,-H.; Tang, Y.-Z.; Fun, H.-K.; Zhou, Z.-Y.; Abrahams, B. F.; Liang, H. CrystEngComm 2008, 10, 217–231.

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benzoic Acids: Novel Supramolecular Tectons - American Chemical

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