ARTICLE pubs.acs.org/crystal
Two-Component Supramolecular Organic Hosts as Colorimetric Indicators for Aromatic Guests: Visual Molecular Recognition via Cationπ Interactions Sandipan Roy and Kumar Biradha* Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India
bS Supporting Information ABSTRACT:
Supramolecular two-component organic host systems composed of 2,20 ,6,60 -tetracarboxybiphenyl (H41)/4,40 -bipyridylethylene (bpe) and (H41)/4,40 -bipyridine (bpy) were shown to recognize various aromatic guest molecules. The inclusion of the guest molecules in the host systems is evident from the remarkable exhibition of different colors in their corresponding inclusion complexes. The host networks are formed by the self-assembly of two (H31) anions and dication (H2bpe or H2bpy) via OH 3 3 3 O and NH 3 3 3 O hydrogen bonding. The pyridinium ions have exhibited greater tendency to interact with aromatic guest molecules via strong cationπ interactions. The host system (H31)2(H2bpe) was found to recognize anthracene, phenanthrene, and pyrene, while (H31)2(H2bpy) was found to recognize several aromatic guests such as phenanthrene, pyrene, phenol, o-cresol, m-cresol, p-cresol, and chlorobenzene. The crystal structures of all these materials were determined and analyzed in terms of hydrogen bonding between the two host components and hostguest interactions. The extent of cationπ interactions is reflected in the color of these complexes. Solid-state diffusion reflectance spectral (DRS) studies have been carried out for all these different colored complexes.
’ INTRODUCTION The design of supramolecular host systems has been one of the primary focuses in the burgeoning field of crystal engineering1 and molecular recognition2 due to their several applicative aspects such as catalysis,3 chemical separation,4 gas-storage devices,5 and targeted drug delivery.6 In the context of analytical chemistry, the development of host systems for colorimetric analysis is of primary focus for a supramolecular chemist because it is a simple technique for the identification of molecules with the naked eye.7 To date, most of the visual molecular recognition systems that have been explored are for the recognition of metal ions8 and anions,9 and very few examples are reported for the recognition of organic guest molecules.7,10 For such a purpose, the prerequisite is to design organic host systems that are capable of forming crystalline inclusion complexes with specific colors upon inclusion of guest molecules. Organic ionic hosts formed by two components are expected to fulfill such a requirement due to their ability to exert charge transfer cationπ interactions11 with guest molecules. The mixing of colorless proton donor with colorless proton acceptor in the presence of aromatic guests is expected to result in different colored crystals due to the formation of a three-component charge transfer (CT) complex that exhibits a large absorption band in the visible region. Recently, the supramolecular synthons II and III were shown to form two-component host architectures for a variety of aromatic guest molecules.12 Previously we have reported that H41 with 4, r 2011 American Chemical Society
40 -bipyridylethylene (bpe) forms cocrystals of [H41][bpe]2 from concentrated MeOH solution, while crystals of an ionic complex were obtained from dilute MeOH solution.13 The cocrystals were found to exhibit an 8-fold interpenetrated diamondoid network via synthon-III, and the ionic complex exhibited layered networks via synthons-I and -II. However, the use of 4,40 -bipyridine (bpy) in place of bpe resulted in crystals of three types of ionic architectures depending on the solvent of crystallization. One of the interesting aspects in the structures of salts is that the bpe/bpy is typically enough to deprotonate only one of the four COOH groups of H41. Among the other three COOH groups, one is involved in an intramolecular OH 3 3 3 O with the deprotonated COO, while the other two COOH groups assemble the H31 units in one or two dimensions via OH 3 3 3 O hydrogen bonds.
Received: June 1, 2011 Revised: July 14, 2011 Published: July 18, 2011 4120
dx.doi.org/10.1021/cg200690c | Cryst. Growth Des. 2011, 11, 4120–4128
0.1455
1.432
0.0635
Interaction
2
NH 3 3 3 O
0.1747
1.381
0.0697
3
0.1665
1.430
0.1435
1.448
0.0467
1
1081.4(9)
106.631(14)
96.29(2)
12.498(5) 112.704(19)
12.474(8)
8.103(3)
P1
triclinic
293(2)
942.83
8 C49H38N2O18
4
0.1519 0.1672
7
8
0.1676
1.425
0.0441 0.0758
1.432 1.426
0.0546
1 2 2
1082.2(2) 2363.4(8) 2317.7(4)
96.264(3)
106.516(2)
90.402(6) 90.121(3)
90.00
20.873(4) 90.00 21.3350(19) 90.00
90.00
12.4229(11) 8.2058(16) 7.9936(7)
12.5539(17) 113.319(3)
8.1441(7) 13.799(3)
P1 P21/n
13.5901(12)
triclinic monoclinic monoclinic
P21/n
293(2) 293(2) 293(2)
928.80 1018.93 994.90
6
OH 3 3 3 Oa CH 3 3 3 O NH 3 3 3 O OH 3 3 3 O OH 3 3 3 Oa CH 3 3 3 O NH 3 3 3 O OH 3 3 3 O OH 3 3 3 Oa CH 3 3 3 O NH 3 3 3 O OH 3 3 3 O OH 3 3 3 Oa CH 3 3 3 O NH 3 3 3 O OH 3 3 3 O OH 3 3 3 Oa NH 3 3 3 O
D3 3 3A (Å)
D-H 3 3 3 A (deg)
2.05 2.48 1.93 1.83 1.69 2.08(4) 1.84(4) 1.63(4) 1.57(4) 1.98(5) 1.82(4) 1.88(3) 1.62(4) 1.78(4) 1.67(4) 2.31 1.77(2) 1.81(3) 1.71(2) 1.71(2) 2.23 1.91(4) 1.75(5) 1.74(5) 1.60(4) 2.54 2.40(4) 1.77(2) 1.460(18) 2.42 2.51(2) 1.66 1.59(3) 1.89 1.95(6)
2.863(6) 2.985(6) 2.716(5) 2.637(5) 2.509(6) 2.834(5) 2.791(5) 2.650(4) 2.619(4) 2.763(5) 2.548(4) 2.808(4) 2.612(3) 2.604(4) 2.572(4) 3.004(5) 2.706(3) 2.644(2) 2.628(3) 2.578(2) 3.087(3) 2.671(6) 2.661(5) 2.593(6) 2.569(5) 3.242(6) 2.976(3) 2.706(2) 2.522(2) 3.204(3) 3.019(4) 2.631(3) 2.526(3) 2.744(5) 2.781(5) 2.661(6) 2.649(4) 2.613(5) 2.624(6) 2.547(4) 2.525(4) 3.068(7) 2.776(4) 2.736(4) 2.601(4) 2.624(3) 2.641(3) 2.655(4) 2.523(4) 2.556(3) 3.279(5) 3.141(5) 2.763(5) 3.003(6) 2.532(3)
158 118 162 168 174 152(4) 161(4) 170(4) 170(3) 168(5) 172(5) 163(3) 169(2) 171(3) 171(2) 132 160(2) 171(3) 161(2) 172(2) 152 154(4) 169(4) 167(4) 172(4) 133 109(2) 172(2) 176.1(18) 141 112.3(19) 168 179(3) 170 153(6)
OH 3 3 3 O
0.1458
1.396
0.0568
1
OH 3 3 3 Oa NH 3 3 3 O OH 3 3 3 O
H3 3 3A (Å)
0.2014
1.417
0.0801
2
OH 3 3 3 Oa
10
CH 3 3 3 O NH 3 3 3 O
2.30
0.1395 wR2 (on F2, all data)
1.413
0.0710 R1 (I > 2σ(I))
Dcalc (Mg/m3)
1
OH 3 3 3 O
Z
1243.4(3) 2465.4(16) 1236.0(11) vol (Å3)
100.823(4)
98.386(4) 73.624(12)
87.688(12) 105.456(15)
98.199(15) γ (deg)
β (deg)
14.0636(19) 114.499(4) 22.904(9) 82.541(11) 13.746(7 110.023(14) c (Å) R (deg)
12.7391(18) 13.877(5) 12.611(6) b (Å)
8.0203(11)
P1 P1
8.154(3) 8.150(4)
P1 space group
a (Å)
triclinic triclinic triclinic system
293(2) 293(2)
1052.98 1052.98
293(2) T (K)
1046.98
9
MW
compound formula
2 C59H44N2O17
3 C59H44N2O17
4 C60H40N2O16
5 C56H38N2O16
6 C58H38N2O16
7 C48H36N2O18
5
Table 1. Crystallographic Parameters for the Crystal Structures of 211
OH 3 3 3 Oa NH 3 3 3 O OH 3 3 3 O
0.0693
1077.5(3)
1 2
106.722(4)
96.338(5)
Complexes
OH 3 3 3 O
2
2202.6(12) 2189.5(3)
110.169(7)
96.909(10) 96.957(2)
109.554(2)
12.587(2) 113.496(5) 14.895(6) 115.035(10)
8.0922(10)
Table 2. Hydrogen Bonding Parameters in the Crystal Structures of 2-11
14.8308(12) 116.417(2)
14.222(4)
12.4611(15)
ARTICLE
14.4399(12)
P1 P1
12.872(3) 12.7869(10)
P1
293(2)
triclinic triclinic triclinic
929.23 942.83
293(2) 293(2)
942.83
9 C49H38N2O18
10 C49H38N2O18
11 C48H33ClN2O16
Crystal Growth & Design
OH 3 3 3 Oa CH 3 3 3 O 11
a
4121
Intramolecular.
NH 3 3 3 O OH 3 3 3 Oa
2.44 2.36 1.92(4) 2.55(4) 1.51(3)
139
151 142 163(3) 114(3) 175(3)
dx.doi.org/10.1021/cg200690c |Cryst. Growth Des. 2011, 11, 4120–4128
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Figure 1. Illustrations for the crystal structures of 2 and 3: (a) one-dimensional chain (chain B) of H31 units through OH 3 3 3 O hydrogen bonds; (b) corrugated layer formed by chains via CH 3 3 3 O and aromatic interactions; (c) joining of anionic layers by H2bpe units via synthon-II to form 3D-network, guests colored orange; (d,e) cationπ interactions between (d) H2bpe and anthracene and (e) H2bpe and phenanthrene.
These studies encouraged us to explore the visual guest recognition nature of H41bpe/bpy host systems. Here it is worth mentioning the studies of Stoddart’s group in which the CT interactions between electron-deficient bpe cations and electronrich aromatics have been extensively used to build mechanically interlocked molecular machines such as rotaxanes and catenanes.14 Further, Imai et al.7a have developed a two-component supramolecular host system that consists of 1,10 -bis-2napthol and p-benzoquinone for the selective visual recognition of aromatic guest molecules via charge transfer π 3 3 3 π interactions. In their studies, it was efficiently demonstrated that inclusion adducts can be obtained not only by conventional crystallization but also by simple solid-state dry grinding without use of any solvents. Here we intend to utilize the aromatic guest recognition ability of H2bpy or H2bpe cations in their complexes with H41 via cationπ CT interactions. These host systems have shown the capability of including several aromatic guest molecules such as phenol, o-cresol, m-cresol, p-cresol, chlorobenzene, anthracene, phenanthrene, and pyrene.
’ RESULTS AND DISCUSSION The compound H41 was prepared by catalytic oxidation of pyrene.15 In order to explore the guest inclusion behavior of
complexes of H41 with bpe/bpy, the reactions of H41 with bpe or bpy have been carried out in the presence of excess aromatic guest molecules (solid or liquid form) in MeOH or CH3CN. In the case of bpe, single crystals suitable for X-ray diffraction studies were obtained for the complexes [H31]2[H2bpe] 3 anthracene 3 MeOH (2), [H31]2[H2bpe] 3 phenanthrene 3 MeOH (3), and [H31]2[H2bpe] 3 pyrene (4). In the case of bpy, single crystals are obtained for the complexes [H31]2[H2bpy] 3 phenanthrene (5), [H31]2[H2bpy] 3 pyrene (6), [H31]2[H2bpy] 3 phenol 3 H2O (7), [H31]2[H2bpy] 3 o-cresol 3 H2O (8), [H31]2[H2bpy] 3 m-cresol 3 H2O (9), [H31]2[H2bpy] 3 p-cresol 3 H2O (10), and [H31]2[H2bpy] 3 Cl-benzene (11). Except the crystals of 11, all the crystals exhibited different colors depending on the type of guest molecule present. It is interesting to note here that the [H31]2[H2bpe] host exhibits the capability to include only solid guest molecules, while the [H31]2[H2bpy] host system has shown more versatility for the inclusion of both solid and liquid guest molecules. All the crystal structures have been characterized and analyzed for understanding the aggregations of ions and inclusion of guest molecules. The charge transfer (CT) properties of these materials were further examined by solid-state diffuse reflectance spectra (DRS). The crystallographic parameters for all the crystal structures are given 4122
dx.doi.org/10.1021/cg200690c |Cryst. Growth Des. 2011, 11, 4120–4128
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Figure 2. Illustrations for the crystal structure of 4: (a) one-dimensional chain (chain A) of H31 units through OH 3 3 3 O hydrogen bonds and synthon-I; (b) corrugated layer formed by the chains via CH 3 3 3 O hydrogen bonds and aromatic interactions; (c) joining of anionic layers into a threedimensional network by H2bpe units via synthon-II, guests colored green; (d) cationπ interaction of pyrene with H2bpe.
in Table 1, and hydrogen-bonding parameters are given in Table 2. H41 and bpe Hosts. All three complexes (24) exhibited similar composition of H41, bpe, and guest. The geometry of the H31 moiety is also similar in all three cases because it forms intramolecular hydrogen bonds between the COO and COOH groups. However, the crystal structures are not isostructural because some important differences exist between them. The crystal structures of 2 and 3 also contain a molecule of MeOH in addition to one aromatic guest per host, while 4 contains exclusively pyrene. However, the structures of 2 and 3 also differ from each other in terms of asymmetric unit contents: 3 contains two times the components of 2. As a result, the anthracene and bpe sit on an inversion center in the case of 2. In all three cases, the monoanions assemble into one-dimensional hydrogen bonding chains (A and B), but the hydrogen bonding pattern of 4 differs from that of 2 and 3. In 4, the anions exhibit three connections to form a one-dimensional chain (chain A): one synthon-I and two charge-assisted OH 3 3 3 O hydrogen bonds, COOH 3 3 3 OOC (Figure 2a). The anions in 2 and 3 assemble via four OH 3 3 3 O hydrogen bonds and do not exhibit synthon-I to form chain B (Figure 1a). In both cases, the chains have zigzag geometry and further assemble into highly corrugated two-dimensional layers via CH 3 3 3 O and aromatic interactions (Figures 1b and 2b). These layers are connected into
Figure 3. DRS for 2 (green line), 3 (red line), and 4 (black line).
three-dimensional networks by H2bpe units via synthon-II and other hydrogen-bonding interactions (Figures 1c and 2c). The H2bpe units can best be described as pillars between the layers. The aromatic guests are sandwiched via cationπ interactions between the pillars along the a-axis in all three cases (Figures 1d,e and 2d). Therefore, half of the length of the a-axis represents the plane to plane distance between H2bpe and aromatic guests (8.154 Å in 2 and 3 and 8.020 Å in 4). The distances between the centroids of aromatic rings and N+ pyridinium are much shorter than the distances between the planes of guest and pyridinium ions: 3.574, 3.452, and 3.281 Å in 2, 3, and 4 respectively. The crystals of complexes 2, 3, and 4 exhibit dark-red, orange, and 4123
dx.doi.org/10.1021/cg200690c |Cryst. Growth Des. 2011, 11, 4120–4128
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Figure 4. Illustrations for the crystal structures of 5 and 6: (a) assembling of anions (H31) to form a corrugated layer via synthon-I and other OH 3 3 3 O hydrogen bonds; (b) side view of the layer; (c) three-dimensional network via joining of anionic layers by H2bpy using charge-assisted NH 3 3 3 O hydrogen bonds (synthon-II); (d,e) cationπ interactions (guests colored violet) between (d) H2bpy and phenanthrene (disordered) and (e) H2bpy and pyrene.
Figure 5. DRS for 5 (red line) and 6 (black line).
bright red colors, respectively. The solid-state diffuse reflectance spectra (DRS) for the samples 24 indicate different absorption edges justifying the different colors observed (Figure 3). The absorption edges of 2, 3, and 4 are located at around 506, 400, and 487 nm, respectively. H41 and bpy Hosts. Previously, we have reported that the reactions of H41 with bpy in MeOH, t-butanol, and 2-propanol result in single crystals of salts [H31][Hbpy] 3 MeOH, [H31][Hbipy] 3 2H2O, and [H31]4[Hbpy]2[H2bpy] 3 4H2O, respectively.13 All three structures exhibited different compositions of the components and solvents. Change of concentration or
component ratios was found to have no effect on the formation of these crystals. These results and above-described results with bpe encouraged us to study these complexation reactions further in the presence of different aromatic guest molecules. Unlike the above-described [H31]2[H2bpe] hosts, the [H31]2[H2bpy] hosts were found to include both solid and liquid guest molecules to yield crystals of complexes 511. Solid Guest Molecules. Although several reactions were tried in the presence of different solid guest molecules, single crystals suitable for X-ray diffraction studies were obtained only in case of phenanthrene (5) and pyrene (6). It was found that in both cases, one of the four COOH groups was deprotonated similar to the one observed in 24. The crystal structures of 5 and 6 are isostructural, but they differ from those of complexes 24. The anions assemble into a corrugated 2D-layer via synthon-I and other OH 3 3 3 O hydrogen bonds (Figure 4a). In the 2D-layer, each anion exhibits three-connectivity, one through synthon-I and two through COO 3 3 3 HOOC charge-assisted hydrogen bonds. These layers are connected by H2bpy units via synthon-II (Figure 4c). Similar to the complexes 24, the phenanthrene and pyrene guest molecules are sandwiched between H2bpy units along the b-axis (Figure 4d,e). The plane to plane distances of guest molecules and H2bpy units are 3.997 and 4.103 Å in 5 and 6, respectively. The crystals that include phenanthrene (5) exhibit a yellowish green color, which is different from the color of crystal 3, which also contains phenanthrene. The crystals including pyrene (6) exhibit dark red color similar to those of 2, which contains anthracene. The distances between the cationic N-atom 4124
dx.doi.org/10.1021/cg200690c |Cryst. Growth Des. 2011, 11, 4120–4128
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Figure 6. Illustrations for the crystal structure of 7 and 8: (a) one-dimensional chain (chain B) of H31 units through OH 3 3 3 O hydrogen bonds; (b) corrugated two-dimensional layers via CH 3 3 3 O and aromatic interactions; (c) the two-dimensional anionic layers are connected into a threedimensional network by H2bpy units via synthon-II, guest colored pink; (d,e) cationπ interactions between (d) H2bpy and o-cresol (disordered) and (e) H2bpy and phenol (disordered).
of H2bpy and the centroid of the closest C6-ring of the aromatic guest molecules are 3.401 and 3.327 Å in 5 and 6, respectively. The solid-state DRS spectra indicate that the absorption edges for 5 and 6 are located at around 400 and 487 nm, respectively (Figure 5). Liquids (Phenols and Isomeric Cresols) as Guest Molecules. The host system of [H31]2[H2bpy] included phenol, o-cresol, m-cresol, and p-cresol to yield single crystals of complexes 7, 8, 9, and 10, respectively. Interestingly all were found to include one each of guest and H2O molecules per host. However, the crystal structures differ significantly. The hydrogen bonding patterns of host components in 7 and 8 (Figure 6) are similar to those observed in [H31]2[H2bpe] host with anthracene (2) or phenanthrene (3) guest molecules. It is interesting to note here that 2 and 3 also contain one molecule of MeOH each in addition to the aromatic guest molecule. The smaller size of bpy compared with bpe accounts for the accommodation of smaller aromatics such as phenol and o-cresol in 7 and 8 although they have similar hydrogen bonding patterns to 2 and 3 (chain B) (Figure 6a). The guest molecules in 7 and 8 are heavily disordered. The crystal structures of complexes 9 and 10 are isostructural with that of 4. Both 9 and 10 contain a one-dimensional chain A similar to the one observed in 4 (Figure 7a). The p-cresol in 10 exhibits disorder, while m-cresol in 9 exhibits perfect order. All four structures form anionic layers, which are pillared by H2bpy units via NH 3 3 3 O and CH 3 3 3 O hydrogen bonds (Figures 6c and 7c). The phenolic guests are sandwiched via cationπ interactions between the pillars along the a-axis in 7 and 8 and along the c-axis in 9 and 10 (Figures 6d,e and 7d,e). Therefore, half of the length of the a-axis represents the plane to plane distance between H2bpe and aromatic guests in 7 (8.144 Å) and
8 (8.103 Å), while that distance is one fourth of the c-axis in 9 (14.831 Å) and 10 (14.895 Å). The crystals of complexes 7 and 8 exhibit a similar yellow color, while those of 9 and 10 exhibit dark yellow and dark red colors, respectively. The solid-state diffuse reflectance spectra (DRS) for samples 710 show absorption edges of 375, 395, 405, and 415 nm, respectively (Figure 8). It is interesting to note here that the [H31]2[H2bpy] host also includes a chlorobenzene guest molecule to form crystals of 11. The crystal structure of 11 was found to be isostructural with those of 9 and 10, but the crystals were found to be colorless; this could be due to the presence of a highly electronegative atom such as Cl, which makes the ring electrondeficient thereby reducing the cationπ charge transfer interactions. Accordingly, the DRS spectrum of 11 shows no absorption edge in the visible region (Figure 8). The chlorbenzene molecule in 11 exhibits disorder, which has been successfully modeled. Importance of H41 in Obtaining Cationπ Interactions in Solid-State Complexes. In order to establish the role of organic anion, similar reactions have been carried out by taking HCl in place of H41. All such reactions initially resulted in colored solutions that have the similar shades to the corresponding solids that are observed with H41 reactions. However, all these reactions were found to produce colorless crystals that correspond to HCl salts of bpe/bpy or guest molecules. These reactions clearly indicate the importance of H41 for the inclusion of guest molecules in the solid state and therefore retaining cationπ interactions in the solid state. Mechanochemical Grinding and Precipitation Reactions. In recent days, mechanochemical dry or wet grinding has been frequently used to prepare cocrystals or organic salts.16 However in the present study, the dry grinding of the H41, bpe/bpy, and 4125
dx.doi.org/10.1021/cg200690c |Cryst. Growth Des. 2011, 11, 4120–4128
Crystal Growth & Design
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Figure 7. Illustrations for the crystal structures of 9 and 10: (a) one-dimensional chain (chain A) of H31 units through OH 3 3 3 O hydrogen bond and synthon-I; (b) corrugated two-dimensional layer formed by the chains via CH 3 3 3 O and aromatic interactions; (c) joining of anionic layers by H2bpy units via synthon-II to form a 3D-network, guests colored pink; (d,e) cationπ interactions between (d) H2bpy and p-cresol (disordered) and (e) H2bpy and m-cresol.
Scheme 1. Model of Disorder for Phenathrene in 5 and Chlorobenzene in 11
Figure 8. DRS for 7 (black line), 8 (green line), 9 (blue line), 10 (red line), and 11 (pink line).
aromatic guest molecule was found to be ineffective in producing any colored materials. Similarly, solvent drop assisted grinding was also found to be ineffective in producing similar colored materials as the conventional crystallization reactions. Further, repetition of the reactions in the concentrated solutions was found to produce similar colored materials as precipitates within a short period.
Through this type of precipitation reaction, we have explored some more guest molecules such as naphthalene, biphenyl, Rnaphthol, β-naphthol, 9-anthryl alcohol, 9-anthraldehyde, perylene, resorcinol, phloroglucinol, and hydroquinone. The information about these reactions and colors of these materials are given in the Supporting Information.
’ CONCLUSIONS Two new supramolecular two-component organic host systems, [H31]2[H2bpe] and [H31]2[H2bpy], with the capability to include aromatic guest molecules have been developed. The mixing of three colorless components was found to generate 4126
dx.doi.org/10.1021/cg200690c |Cryst. Growth Des. 2011, 11, 4120–4128
Crystal Growth & Design various colored crystals due to the formation cationπ interactions between the pyridinium ions and aromatic guest molecules. Crystal structure analyses revealed that [H31] can self-assemble in three ways via strong hydrogen bonding: two types of zigzag chains and one two-dimensional layer. The geometry of the anion was found to be similar in all the structures analyzed. The synthons I and II were found to play an important role in the aggregation besides charge-assisted OH 3 3 3 O hydrogen bonds. The N+ to centroid of the guest molecules varies from 3.281 to 3.854 Å, while the absorption edge varies from 375 to 506 nm. Further, the [H31]2[H2bpe] host system was found to include only solid aromatic guest molecules, while the [H31]2[H2bpy] host system was found to include both solid and liquid aromatic guests, in particular those containing phenolic moieties. The different colors observed in these complexes indicate that these hosts may serve as colorimetric indicators for various aromatic moieties in the solid state.
’ EXPERIMENTAL SECTION FTIR spectra were recorded with a Perkin-Elmer instrument, Spectrum Rx, serial no. 73713. Powder XRD data were recorded with a PHILIPS Holland PW-171 defractometer. The diffuse reflectance spectra (DRS) of the inclusion crystals were recorded with a Cary model 5000 UVvisibleNIR spectrophotometer. Melting point measurements were carried out using Fisher Scientific instrument Cat. No. 12-144-1. Preparation of Crystals of Materials 211. [H31]2[H2bpe] 3 Anthracene 3 MeOH, 2. H41 (0.01 g, 0.030 mmol), bpe (0.011 g, 0.060 mmol), and 3 equiv of anthracene (0.016 g) were dissolved in methanol (8 mL) with warming. The resultant solution was allowed to evaporate slowly at room temperature; deep red block-like single crystals suitable for X-ray diffraction were obtained in about 6570% yield within 2 days. The crystals were separated from the mother liquor by filtration, washed with hexane, and dried under vacuum, Mp > 300 °C. Elemental analysis (%) calcd for C59H44N2O17: C, 67.30; H, 4.21; N, 2.66. Found: C, 66.96; H, 3.89; N, 2.50. Similar procedure was employed for the preparation of crystals 36 by taking the corresponding components. [H31]2[H2bpe] 3 Phenanthrene 3 MeOH, 3. Yield 6065%, Mp > 300 °C. Elemental analysis (%) calcd for C59H44N2O17: C, 67.30; H, 4.21; N, 2.66. Found: C, 66.96; H, 4.06; N, 2.78. [H31]2[H2bpe] 3 Pyrene, 4. Yield 6570%, Mp > 300 °C. Elemental analysis (%) calcd for C60H40N2O16: C, 68.96; H, 3.86; N, 2.68. Found: C, 68.75; H, 3.77; N, 2.84. [H31]2[H2bpy] 3 phenanthrene, 5. Yield 6570%, Mp > 300 °C. Elemental analysis (%) calcd for C56H38N2O16: C, 67.60; H, 3.85; N, 2.82. Found: C, 67.24; H, 3.69; N, 2.84. [H31]2[H2bpy] 3 Pyrene, 6. Yield 6570%, Mp > 300 °C. Elemental analysis (%) calcd for C58H38N2O16: C, 68.37; H, 3.76; N, 2.75. Found: C, 67.56; H, 3.28; N, 2.89. [H31]2[H2bpy] 3 Phenol 3 H2O, 7. H41 (0.01 g, 0.030 mmol) and bpy (0.0094 g, 0.060 mmol) were dissolved in acetonitrile/methanol (3:1, 4 mL) with warming, then phenol (1 mL) was added and mixed well. The resultant solution was allowed to evaporate slowly at room temperature, light green prismatic like single crystals were formed overnight in about 5560%, and the crystals were filtered, washed with a little hexane, and dried under vacuum. Mp > 300 °C. Elemental analysis (%) calcd for C48H36N2O18: C, 62.07; H, 3.91; N, 3.02. Found: C, 61.29; H, 3.45; N, 2.84. A similar procedure was employed for the preparation of crystals 811 by taking the corresponding components. [H31]2[H2bpy] 3 o-Cresol 3 H2O, 8. Yield 5560% Mp > 300 °C. Elemental analysis (%) calcd for C49H38N2O18: C, 62.42; H, 4.06; N, 2.97. Found: C, 61.84; H, 3.71; N, 3.15.
ARTICLE
[H31]2[H2bpy] 3 m-Cresol 3 H2O, 9. Yield 4550%, Mp > 300 °C. Elemental analysis (%) calcd for C49H38N2O18: C, 62.42; H, 4.06; N, 2.97. Found: C, 61.84; H, 3.71; N, 3.15. [H31]2[H2bpy] 3 p-Cresol 3 H2O, 10. Yield 4550%, Mp > 300 °C. Elemental analysis (%) calcd for C49H38N2O18: C, 62.42; H, 4.06; N, 2.97. Found: C, 61.84; H, 3.71; N, 3.15. [H31]2[H2bpy] 3 Cl-benzene, 11. Yield 4550%, Mp > 300 °C. Elemental analysis (%) calcd for C48H33ClN2O16: C, 62.04; H, 3.58; N, 3.01. Found: C, 61.56; H, 2.99; N, 2.85. Crystal Structure Determination. All of the single-crystal data was collected on a Bruker-APEX-II CCD X-ray diffractometer that uses graphite monochromated Mo KR radiation (μ = 0.71073 Å) at room temperature (293 K) by the hemisphere method. The structures were solved by direct methods and refined by least-squares methods on F2 using SHELX-97.17 Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were fixed at calculated positions and refined using a riding model. The H-atoms attached to O- or N-atoms are located wherever possible and refined using the ridging model. Pertinent crystallographic details are given in Table 1, and hydrogen bonding parameters are given in Table 2. The MeOH molecules in 2 and 3 could not be located, and aromatic guests as well as water molecules in 7, 8, and 10 could not be modeled and refined. Therefore Platon squeeze option was used in the final refinement of these structures.18 The guest-occupied volumes in the crystal structures of 211 are 30.5%, 30.3%, 28.2%, 26.1%, 27.6%, 22.2%, 22%, 20.9%, 21.2%, and 21.3%, respectively, of the crystal volumes. The disorder of phenanthrene guest in 5 and disorder of chlorobenzene in 11 were modeled as shown in Scheme 1.
’ ASSOCIATED CONTENT
bS
Supporting Information. IR-spectra, X-ray powder patterns, information on colored solutions obtained with HCl without H41, information for the formation of colored complexes with other guest molecules via precipitation reactions, and crystallographic information for complexes 211 (CIF). This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. Fax:+91-3222-282252. Tel: +91-3222-283346.
’ ACKNOWLEDGMENT We gratefully acknowledge financial support from DST and DST-FIST for the single-crystal X-ray facility. S.R. thanks IITKGP for a research fellowship. ’ REFERENCES (1) (a) Desiraju, G. R. Angew. Chem. 1995, 107, 2541. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311. (b) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101, 1629. (c) Nangia, A. CrystEngComm 2002, 4, 93. (d) Desiraju, G. R. J. Mol. Struct. 2003, 656, 5. (e) Braga, D.; Brammer, L.; Champness, N. R. CrystEngComm 2005, 7, 1. (f) Biradha, K. CrystEngComm 2003, 5, 374. (g) Desiraju, G. R. Crystal Engineering The Design of Organic Solids; Elsevier: New York, 1989. (h) Biradha, K.; Su, C.-Y.; Vittal, J. J. Cryst. Growth Des. 2011, 11, 875. (2) (a) Lehn, J. M. Angew. Chem., Int. Ed. Engl. 1990, 29, 1304. (b) Etter, M. C.; Lipkowska, Z. U.; Ebrahimi, M. Z.; Panunto, T. W. J. Am. Chem. Soc. 1990, 112, 8415. (c) Fan, E.; Vicent, C.; Geib, S. J.; Hamilton, A. D. Chem. Mater. 1994, 6, 1113. (d) Tellado, F. G.; Geib, S. J.; Goswami, S.; Hamilton, A. D. J. Am. Chem. Soc. 1991, 113, 9265. (e) Pedireddi, V. R.; Jones, W.; Chorlton, A. P.; Docherty, R. 4127
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