Designer HostâGuest Complexes - American Chemical Society

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Designer Host−Guest Complexes: Co-Crystals of 1,3Adamantanedicarboxylic Acid and 4,7-Phenanthroline with Some Guests Yogesh Manjare,*,† V. Nagarajan,*,†,‡ and Venkateswara Rao Pedireddi† †

School of Basic Sciences, Indian Institute of Technology Bhubaneswar, Toshali Bhavan, Bhubaneswar 751 007, India Department of Colloids and Materials Chemistry, CSIR-Institute of Minerals and Materials Technology, Bhubaneswar 751 013, India

‡

S Supporting Information *

ABSTRACT: Multicomponent host−guest complexes consisting of 1,3-adamantanedicarboxylic acid (1) and 4,7-phenanthroline (phen) as the host moiety with different guests are prepared through co-crystallization. Detailed structural analysis of the obtained complexes, characterized by the single-crystal X-ray diffraction method, has been reported. In all the complexes, molecules of 1 and phen constitute a unique four-membered cyclic host network into a two-dimensional arrangement. Further stacking of such networks resulted in a channel structure directed by the guest species through O−H···O hydrogen bonds.

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INTRODUCTION The design of molecular solids through noncovalent interactions is one of the frontier areas of research under supramolecular chemistry as it provides tailor-made molecular materials for various purposes.1 Among several types of assemblies, multicomponent molecular host−guest complexes have drawn a great deal of attention as complementary functional groups from each component establish noncovalent interactions to yield host molecular assemblies.2 Several functional groups like -COOH, -CONH2, etc., are wellknown to form robust intermolecular interactions not only for host−guest complexes but also for supramolecular assemblies of various exotic architectures.3 It has been observed from the literature that some of the host−guest complexes of multicomponent systems possess hydrocarbons or solvent molecules as guest species.4 Among them, in a considerable number of assemblies, guest species are found to be dynamic within the cavities, which makes it difficult to understand the intermolecular interactions between the host and guest moieties.4a−f To circumvent such problems, robust host−guest assemblies could be prepared by considering guests that (i) have an appropriate dimension with respect to cavity size, (ii) exist preferably as solids under ambient conditions, (iii) form robust intermolecular interactions with the hosts, etc. In our recent co-crystallization experiments, the preparation of host−guest assemblies assisted by various hydrogen bonding patterns has been reported.5 To continue, we attempted to prepare host−guest complexes of 1,3-adamantanedicarboxylic acid (1) and 4,7-phenanthroline (phen) with different guest © XXXX American Chemical Society

species. The rigid phen molecules could be directed to form either tape or cyclic structure depending upon the topology of the carboxylic acid moieties of the coformers. For instance, 1,3,5-cyclohexanetricarboxylic acid with a V-shaped topology of the carboxylic acid groups forms a four-membered cyclic structure; however, oxalic acid and terephthalic acid with a linear topology form a tape structure in two-dimension as shown in Figure 1.6 In this study, 1 with V-shaped topological carboxylic acid groups could preferably form a cyclic fourmembered structure with phen through O−H···N/C−H···O hydrogen bonds as schematically represented in Figure 2. However, in the three-dimensional arrangement, such a cyclic structure could form host−guest complexes (in the presence of suitable guest species), the self-filled layer structure or interpenetrated assemblies. Herein, we obtained a host−guest complex when the coformers were crystallized from a MeOH/ H2O solution, wherein the host moiety is constituted by 1 and phen and the guest species are water molecules. However, the exact position of water molecules was found to be difficult to identify because of the high level of thermal motion of water within the channels; as a result, the intermolecular interaction between the water and the host moieties could not be established. Thus, to understand the intermolecular interactions in detail, different guest species, as shown in Chart 1, are Received: October 26, 2013 Revised: December 9, 2013

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dx.doi.org/10.1021/cg401596s | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

Article

Figure 1. Two-dimensional arrangement in the co-crystals of 4,7-phenanthroline with (a) 1,3,5-cyclohexanetricarboxylic acid, (b) oxalic acid, and (c) terephthalic acid.

Table 2. Thus, a void space with dimension of ∼7 Å × 8 Å is realized in the two-dimensional geometry. Such an arrangement is shown in Figure 3a. Further, such host networks are found to be stacked along a crystallographic axis through the π···π interaction established between the molecules of phen of consecutive host networks to form a channel that is occupied by molecules of water (Figure 3b). The water molecules in the channels are disordered because of their high level of thermal motion, which made it difficult to determine the exact number of water molecules in the asymmetric unit. Nevertheless, thermogravimetric analysis of a freshly prepared sample indicates the presence of one molecule of water in the asymmetric unit (see the Supporting Information). However, the exact position of the water molecule and its interaction with the host could not be established properly because of the diffused distribution of electron density. However, the arrangement of water molecules and their interactions is instituted as shown in Figure 3c based on the host−guest complexes obtained with different guest species that are discussed below. Herein, we conceived the points discussed in the Introduction that helped to resolve such problems that mainly arose because of the high level of thermal motion. Thus, we have conducted co-crystallization of 1 and phen in the presence of phenol as a guest species because a phenol molecule is larger than a water molecule and phenol also has the same hydrogen bonding group as water.

Figure 2. Expected cyclic structure of the co-crystal of 1 and phen.

chosen for the preparation of host−guest complexes of 1 and phen that are discussed herein.

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RESULTS AND DISCUSSION Structure of Host−Guest Complex of 1, phen, and Water. Co-crystallization of 1 and phen from a MeOH/H2O solution gave good quality crystals, which have been characterized by the single-crystal X-ray diffraction method (see Table 1). The crystals are labeled as 1a for discussion. The analysis reveals that the crystals contain a 1:1 (1:phen) ratio along with water molecule(s).7 Coformers 1 and phen interact each other to form a quartet molecular host through pairwise hydrogen bonding patterns, comprised of O−H···N/C−H···O hydrogen bonds. Characteristics of hydrogen bonds are listed in Chart 1

B


formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (g/cm3) μ (mm−1) 2θ range (deg) T (K) F(000) λ (Å) Δρmin.max (e/Å3) total no. of reflections no. of unique reflections no. of reflections used no. of parameters R1, I > 2σ(I) wR2, I > 2σ(I) CCDC no.

1b C12H16O4:C12H8N2:0.5(C6H4O) 450.50 triclinic P1̅ 6.603(5) 11.176(3) 15.867(4) 107.52(3) 97.80(4) 95.45(4) 1094.8(4) 2 1.367 0.094 50.58 120 476 0.71073 −0.466, 0.804 10729 3970 3553 315 0.0440 0.1156 933564

1a

C12H16O4:C12H8N2:H2O 451.44 monoclinic P21/c 6.899(1) 30.620(5) 12.598(2) 90 119.82(6) 90 2309.2(6) 4 1.160 0.080 50.06 120 852 0.71073 −0.287, 0.314 16563 4071 1438 290 0.0962 0.2203 933563

1c C12H16O4:C12H8N2:0.5(C6H6O2) 459.51 triclinic P1̅ 6.632(3) 11.162(6) 15.860(8) 107.18(7) 97.52(7) 95.98(7) 1099.4(1) 2 1.388 0.096 50.58 120 486 0.71073 −0.287, 0.393 10695 3974 3553 323 0.0401 0.1088 933565

Table 1. Crystallographic Data and Structure Refinement Parameters for Complexes 1a−1e C12H16O4:C12H8N2:C6H6O2 919.01 triclinic P1̅ 6.682(2) 16.442(6) 22.078(8) 68.80(5) 87.00(6) 78.68(5) 2216.8(1) 2 1.377 0.095 50.46 120 972 0.71073 −0.334, 0.845 21308 7953 6544 629 0.0615 0.1724 933567

1d

C12H16O4:C12H8N2:C6H6O2 919.01 monoclinic P21/c 11.081(5) 29.945(1) 13.34(5) 90 95.50(7) 90 4406.2(3) 4 1.385 0.096 50.70 120 1944 0.71073 −0.395, 0.400 22282 7985 6873 613 0.0751 0.2008 933566

1e

Crystal Growth & Design Article

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Table 2. Characteristics of Hydrogen Bond Parameters (distances in angstroms and angles in degrees) Observed for Complexes 1a−1e O−H···N

C−H···O

O−H···O

complex

H···N

O···N

O−Ĥ ···N

H···O

C···O

C−Ĥ ···O

1a 1b

1.96 1.72 1.74 1.72 1.76 1.73 1.77 1.79 1.82 1.65 1.71 1.73 1.77

2.77 2.66 2.68 2.67 2.66 2.66 2.66 2.66 2.68 2.62 2.67 2.66 2.67

173 175 168 175 167 168 176 169 176 165 179 166 177

2.74 2.39 2.69 2.40 2.69 2.39 2.46

3.40 3.25 3.28 3.26 3.30 3.25 3.30

120 155 124 153 125 154 150

1.87

2.69

178

1.86 1.92

2.68 2.74

179 178

2.35 2.41

3.23 3.28

160 156

1.89 1.95

2.70 2.72

180 157

1c 1d

1e

H···O

O···O

O−Ĥ ···O

2.67

Figure 4. Channels noted in the crystals of 1b, formed by 1 and phen, which are occupied by molecules of phenol with a disordered -OH group.

Figure 3. (a) Host network obtained by the aggregation of two molecules each of 1 and phen through pairwise hydrogen bonding patterns, in the crystals of 1a. (b) Channel structure observed in the structure of 1a. (c) Lateral view of the channel structure of 1a with the interaction of the water molecule with the host moieties.

Structure of Host−Guest Complex of 1, phen, and Phenol. Crystallization of 1, phen, and phenol from a dimethyl sulfoxide (DMSO) solution gave crystals with constituents in a ratio of 1:1:0.5 in the asymmetric unit (see Table 1). The complex is labeled as 1b for discussion. Packing analysis of 1b shows the same molecular arrangement, as observed in 1a, yielding channels formed by the alignment of host networks of 1 and phen, except that channels are occupied by phenol molecules that are embedded between the consecutive host networks as shown in Figure 4. However, the phenol molecule possesses special position disorder that results in the molecular arrangement shown in Figure 5a, and such a molecular arrangement is chemically incorrect. The correct structure could be that shown in either panel b or panel c of Figure 5. This disordered phenol molecule that mimics hydroquinone, in

Figure 5. (a) Lateral view of stacking of host networks in 1b, separated by phenol (in the disordered orientation). (b and c) Representations of phenol in disordered orientations.

fact, led to further co-crystallization of 1 and phen in the presence of hydroquinone, which is also the same size as phenol with an extra hydrogen bonding donor group. D



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Structure of Host−Guest Complex of 1, phen, and Hydroquinone. Co-crystallization of 1, phen, and hydroquinone from DMSO gave good quality crystals of 1c suitable for single-crystal X-ray diffraction method. The structural analysis of 1c reveals that the molecular components are in a 1:1:0.5 ratio in the asymmetric unit (Table 1). A typical representation of the arrangement of molecules in 1c is shown in Figure 6. Thus, in 1c, the molecules of 1 and phen also

Figure 7. (a) Aggregation of molecules of 1 and phen in complex 1d along with resorcinol, which is bound to the molecules in the host network, by O−H···O hydrogen bonds. (b) Lateral view of channels in the structure of 1d with molecules of resorcinol inserted between the cyclic host structures.

Figure 6. (a) Host−guest structure of 1c, with channels filled by molecules of hydroquinone. (b) Side view of channels observed in 1c with hydroquinone embedded between layers of host ensembles, through O−H···O hydrogen bonds.

formed a host network through O−H···N/C−H···O pairwise hydrogen bonding patterns (Table 2). In contrast to the disordered nature of guest molecules observed in 1a and 1b, the structure of molecules of hydroquinone is fully ordered, including its functional moieties. Such an environment facilitated the unequivocal establishment of intermolecular interactions between the host and guest species. The cyclic host networks composed of 1 and phen are connected by the molecules of hydroquinone through O−H···O hydrogen bonds that are embedded between the consecutive cyclic networks (Figure 6b). Such a molecular arrangement observed in 1c demonstrates the importance of guest species in the formation of robust host−guest complexes. This observation drove us to conduct further co-crystallization experiments using the corresponding isomers of hydroquinone such as resorcinol and catechol. Structures of Host−Guest Complexes of 1, phen, and Resorcinol or Catechol. Crystals obtained from the DMSO solution of 1, phen, and either resorcinol or catechol were characterized by single-crystal X-ray diffraction method. The crystals were found to be composed of molecules of 1 and phen along with either resorcinol or catechol in a 1:1:1 ratio (Table 1). The assemblies of 1 and phen with resorcinol and catechol are denoted as 1d and 1e, respectively, for the purpose of discussion. Both complexes result in a host network and a packing arrangement similar to those of complexes 1a−1c, except for a notable difference in 1e in which the successive layers along the stacking direction are related by inversion symmetry while, in all other assemblies, the same was found to occur through translational symmetry. Typical host networks along with guest species observed in 1d and 1e are shown in Figures 7 and 8, respectively. Further analysis of these structures shows that the adjacent host networks, viewed along the channels, are connected through the guest molecules, either resorcinol or catechol, as the case may be, as noted in complex 1c, by O−H···O hydrogen bonds, as shown in Figures 7b and 8b.

Figure 8. (a) Arrangement of catechol in the channels constituted by the host network of 1 and phen, in the crystal structure of 1e. (b) Side view of the channels noted in 1e.

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CONCLUSIONS In conclusion, the preparation, structure elucidation, and analyses of host−guest molecular complexes with a multicomponent host network constituted by 1 and phen, with the incorporation of different guest species, are described here. 1 and phen form a unique four-membered cyclic structure in two dimension constituted by O−H···N/C−H···O pairwise hydrogen bonds. In three dimensions, such cyclic networks are stacked to yield a channel structure in the presence of guest species with hydrogen bond donor sites. It is quite clear from structures 1a−1e that guest species establish merely O−H···O hydrogen bonding interactions with host networks, which thus plays a major role in driving the channel structure. This study highlights the effective encapsulation of various guests with unique packing patterns in a three-dimensional arrangement. The study can be extended with the encapsulation of various other guest molecules with different functionalities to evaluate the strength of the obtained host network and channels toward different guest molecules.

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EXPERIMENTAL SECTION

Preparation of Host−Guest Complexes 1a−1e. The complexes were prepared by slow evaporation of a solution of 1 and phen, which were dissolved in a 1:1 ratio along with the appropriate guest components. While a MeOH/H2O mixture was used as the solvent of crystallization for 1a, in all other cases (1b−1e) DMSO was used for crystallization. Good quality crystals of the complexes were obtained over a period of 24 h. Determination of Structures by X-ray Diffraction. Good quality single crystals of 1a−1e were carefully selected using a Leica microscope and glued to a glass fiber using an adhesive. In all cases, the crystals were smeared in the adhesive solution to prevent the decay of E



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crystals. The intensity data were collected on a Bruker single-crystal Xray diffractometer, equipped with an APEX detector. Subsequently, the data were processed using the Bruker suite of programs (SAINT), and the convergence was found to be satisfactory with good Rint parameters. The details of the data collection and crystallographic information are given in Table 1. Absorption corrections were applied using SADABS.8 The determination of structures by direct methods and refinements by least-squares methods on F2 were performed using SHELXTL-PLUS. The processes were smooth without any complications. All non-hydrogen atoms were refined anisotropically, while hydrogen atoms were treated isotropically. All the intermolecular interactions were computed using PLATON.9 All packing diagrams were generated using Diamond.10

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ASSOCIATED CONTENT

S Supporting Information *

X-ray data in CIF format, experimental descriptions for the synthesis of complexes, and experimental details of crystallizations. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Telephone: +91 674 2576060. Fax: +91 2306 203. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge DST and UGC for financial support. DEDICATION We dedicate this paper to Prof. C. N. R. Rao, FRS, on the occasion of his 80th birthday and also for his Bharat Ratna award, the highest civilian award of India.

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