Design and Synthesis of Novel Aza-Aromatic Host-Guest Complexes: Crystal Structures of 1,7-Phenanthroline with Thiodipropionic and Thiodiglycolic Acids V. R. Pedireddi†
CRYSTAL GROWTH & DESIGN 2001 VOL. 1, NO. 5 383-385
Division of Organic Chemistry, National Chemical Laboratory, Pune 411 008, India Received March 15, 2001
ABSTRACT: Aza-aromatic compounds such as 1,10-phenanthroline and 1,7-phenanthroline constitute a new class of hosts involving hydrogen bonds as well as hydrophobic interactions. Crystal structures of 1,7-phenanthroline with thiodipropionic and thiodiglycolic acids are discussed, showing the incorporation of the thiodipropionic acid as a guest molecule in channels of 1,7-phenanthroline and the thiodiglycolic acid as being sandwiched between layers of the aza molecules. The design and synthesis of novel host-guest systems is a significant area of research in both molecular and supramolecular chemistry.1-4 While crown ethers, cryptands, etc.5 represent hosts synthesized via covalent methods, recent developments in noncovalent synthesis6 have led to the evolution of hosts such as trimesic acid,7 trithiocyanuric acid,3b,8 and various derivatives of dinitrobenzoic acid,9 for example, serving as representative examples for both guest-specific as well as rigid noncovalent hosts. In the majority of instances, the noncovalent hosts are generally designed and synthesized by employing appropriate functional groups at required symmetry positions to form cyclic networks through hydrogen bonds. However, the reported synthesis of host structures by Toda10 and Desiraju11 using bulky functional moieties such as tert-butyl, triphenyl, etc. highlights the influence of the irregular shape of the molecules in the formation of the new type of hosts, accommodating various guest molecules in the cavities/voids created by the “loose packing” of host molecules. A close look at this kind of host, however, reveals that hydrophobic interactions (in the form of an excess C-H moiety on the periphery of the host molecules) also play a crucial role in addition to the size and shape of the molecules in the formation of the observed host networks. Indeed, such an effect can be seen vividly even in a simple molecular adduct12a of 1,10-phenanthroline (1) and water as shown in Figure 1. In this adduct, while
water molecules interact with molecules of 1 through O-H‚‚‚N hydrogen bonding, the neighboring molecules of 1 form a cyclic network surrounding the water molecules through hydrophobic interactions. In fact, 1 could be considered as a host, specific only for dimensionally similar species, i.e., water-like, as it forms different type of structures such as herringbone or layered types in other molecular complexes.12b †
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Figure 1. Host network of 1,10-phenanthroline in its water adduct.
Chart 1. Representation of a Supermolecule of 1,7-Phenanthroline through C-H‚‚‚N Hydrogen Bonds
Therefore, to incorporate larger molecules in the cavities created by the hosts such as 1, the formation of larger cavities is a prerequisite. This can be achieved by increasing the dimension of the host molecule. Such an exercise, of course, could be performed very easily following noncovalent routes as described by Desiraju.11 Hence, 1,7-phenanthroline13 (2) has been considered for further study, as it has the capacity to form a supermolecule through the formation of C-H‚‚‚N hydrogen bonds as shown in Chart 1, thereby increasing the host dimension, with the requisite C-H moiety to yield a hydrophobic environment, without involving any complicated synthetic procedures. Indeed, a host lattice network is noted in the cocrystals 2a,14,15 obtained upon crystallization of 2 with
10.1021/cg015511r CCC: $20.00 © 2001 American Chemical Society Published on Web 07/10/2001
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Crystal Growth & Design, Vol. 1, No. 5, 2001
Pedireddi
Figure 3. Channels along the [010] direction in the crystal structure of 2a. Guest molecules (thiodipropionic acid) are not shown for a clear visualization of the channels. Figure 2. Two-dimensional arrangement of 1,7-phenanthroline and thiodipropionic acid molecules in the complex 2a. Dashed lines represent hydrogen bonds, and the unique distances are shown. Note the captivity of acid molecules by the phenanthroline molecules. Table 1. Characteristics of Hydrogen Bonds in the Crystal Structures of 2aa and 2bb H bond
H‚‚‚acceptor (X)/Å
X‚‚‚donor (Y)/Å
X- H‚‚‚Y/deg
O-H‚‚‚N
1.65 1.84 1.90
2.62 2.65 2.69
173 176 162
C-H‚‚‚O
2.57 2.54 2.84 2.56 2.53
3.46 3.23 3.34 3.39 3.39
165 132 127 144 155
C-H‚‚‚N
2.57
3.45
149
a
b
In Roman type. In boldface type.
thiodipropionic acid16 from CH3OH. A two-dimensional arrangement of the molecules in the cocrystals is shown in Figure 2. In these cocrystals, the carboxylic group of the acid interacts with the host by forming acyclic O-H‚‚‚N (H‚‚‚N ) 1.65 Å) and C-H‚‚‚O (H‚‚‚O ) 2.57 Å, see Table 1) hydrogen bonds rather than a pairwise cyclic hydrogen bond coupling, generally noted in the cocrystals of acids with aza-aromatic compounds as shown schematically.17
It is further evident from Figure 2 that, as expected, adjacent molecules of 2 interact with each other, forming centrosymmetric C-H‚‚‚N hydrogen bond couplings (H‚‚‚N ) 2.57 Å, Table 1) to yield a supermolecule. These supermolecules organize to yield a two-dimensional sheet structure comprised of cavities that are being filled by thiodipropionic acid molecules. An important feature of the cocrystal is the arrangement in three dimensions wherein the sheets align along the [010] direction, yielding channels stabilized by π-π interactions between the molecules of 2. The channel
structure is shown in Figure 3. It is important to note these kinds of channels are facilitated by the formation of C-H‚‚‚N hydrogen bonds between the adjacent molecules of 2; otherwise, a different type of host-guest type complex would have resulted, as noted in cocrystallization (from CH3OH) of 2 with thiodiglycolic acid, which yields the pillared type host-guest complex18 2b in contrast to the channel type host-guest complex noted in 2a. It appears that the unusual hairpin conformation of the thiodiglycolic acid molecule led to incompatibility between the dimension of the guest and cavity size and, as a result, complex formation proceeds through strong hydrogen bonds between host-guest molecules. In fact, this kind of bent conformation for the thiodiglycolic acid was also observed in its molecular complex with 4,4′-bipyridine.17b A crystal structure determination of 2b reveals that molecules of 2 and the acid interact to yield molecular tapes, as shown in the two-dimensional arrangement in Figure 4a. These molecular tapes arrange in three dimensions, as shown in Figure 4b. Unlike in the complex 2a, the acid molecules in 2b form regular strong19 pairwise O-H‚‚‚N/C-H‚‚‚O hydrogen bond couplings, with the corresponding H‚‚‚N and H‚‚‚O distances being 1.84, 1.90 and 2.54, 2.84 Å, respectively (see Figure 4a). Other characteristics of these hydrogen bonds are listed in Table 1. It is, further, interesting to note that C-H‚‚‚N hydrogen bonds observed between the molecules of 2 in the complex 2a are absent in the complex 2b, supporting the importance of these particular bonds in forming the channel type structure. Instead, the adjacent acid molecules couple together through the formation of a centrosymmetric dimer via the C-H‚‚‚O (H‚‚‚O, 2.56 Å) hydrogen bond (see Figure 4a). This arrangement packs in three dimensions, yielding a pillared layer type structure wherein molecules of 2 and acid are arranged alternately (Figure 4b). In conclusion, this study provides two novel crystal structures which may open new directions toward the synthesis of different host-guest complexes, taking into account various features such as shape, hydrophobic interactions, and hydrogen bonding. It is also possible
Aza-Aromatic Host-Guest Complexes
Figure 4. (a) Two-dimensional arrangement showing interaction between the molecules of 2 and thiodiglycolic acid forming molecular tapes in the complex, 2b. Note the bent configuration of the acid molecules unlike thiodipropionic acid in Figure 2. Dashed lines represent hydrogen bonds. (b) Three-dimensional arrangement of molecules of 1,7-phenanthroline and thiodiglycolic acid molecules in 2b, forming a pillared type structure.
to extend the study in the creation of combinatorial libraries of intermolecular interactions for the exploration of formation of various types of host-guest systems, and experiments are in progress in this direction. Acknowledgment. I thank Dr. Paul Ratnasamy and Dr. K. N. Ganesh, respectively, Director and Head of the Division of Organic Chemistry, National Chemical Laboratory, Pune, India, for their support and financial assistance. Also, I thank the reviewers for their valuable comments and suggestions for the improvement of style of presentation as well as for additional insights into the structural features. Supporting Information Available: X-ray crystallographic information files (CIF) for compounds 2a and 2b. This material is available free of charge via the Internet at http:// pubs.acs.org.
References (1) (a) Atwood, J. L.; Davies, J. E. D.; MacNicol, D. D. Inclusion Compounds; Academic Press: London, 1984; Vol. 1-3. (b) Vogtle, F. Supramolecular Chemistry; Wiley: Chichester, U.K., 1971.
Crystal Growth & Design, Vol. 1, No. 5, 2001 385 (2) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311. (3) (a) Pedireddi, V. R.; Jones, W.; Chorlton, A. P.; Docherty, R. Tetrahedron Lett. 1998, 39, 5409. (b) Pedireddi, V. R.; Chatterjee, S.; Ranganathan, A.; Rao, C. N. R. J. Am. Chem. Soc. 1997, 119, 10867. (4) (a) Hollingsworth, M. D.; Harris, K. D. M.; Jones, W.; Thomas, J. J. J. Inclusion Phenom. 1987, 5, 273. (b) MacGillirvray, L. R.; Atwood, J. L. J. Am. Chem. Soc. 1997, 119, 6931. (5) (a) Lehn, J.-M. Science 1986, 225, 849. (b) Lehn, J.-M. In Supramolecular Chemistry: Concepts and Perspectives; VCH Verlag: Weinheim, Germany, 1995. (c) Cram, D. J. Science 1983, 219, 1. (6) (a) Whitesides, G. M.; Simanek, E. E.; Mathias, J. P.; Seto, C. T.; Chin, D. N.; Mammen, M.; Gordon, D. M. Acc. Chem. Res. 1995, 28, 37. (b) MacDonald, J. C.; Whitesides, G. M. Chem. Rev. 1994, 94, 2383. (c) Russel, V. A.; Evans, C. C.; Li, W.; Ward, M. D. Science 1997, 276, 54. (7) (a) Kolotuchin, S. V.; Fenlon, E. E.; Wilson, S. R.; Loweth, C. J.; Zimmerman, S. C. Angew. Chem., Int. Ed. Engl. 1995, 34, 2654. (b) Melendez, R. E.; Sharma, C. V. K.; Zaworotko, M. J.; Bauer, C.; Rogers, R. D. Angew. Chem., Int. Ed. Engl. 1996, 35, 2213. (c) Sharma, C. V. K.; Zaworotko, M. J. Chem. Commun. 1996, 2665. (d) Zimmerman, S. C. Science 1997, 276, 543. (8) Ranganathan, A.; Pedireddi, V. R.; Chatterjee, S.; Rao, C. N. R. J. Mater. Chem. 1999, 9, 2407. (9) Pedireddi, V. R.; Jones, W.; Chorlton, A. P.; Docherty, R. Chem. Commun. 1996, 987. (10) Toda, F.; Akagi, K. Tetrahedron Lett. 1968, 9, 3695. (11) Jetti, R. K. R.; Kuduva, S. S.; Reddy, D. S.; Xue, F.; Mak, T. C. W.; Nangia, A.; Desiraju, G. R. Tetrahedron Lett. 1998, 39, 913. (12) (a) Tian, Y.-P.; Duan, C.-Y.; Xu, X.-X.; You, X.-Z. Acta Crystallogr. 1995, C51, 2309. (b) Allen, F. H.; Kennard, O. Chem. Des. Automation News 1993, 8, 31. (13) A three-dimensional crystal structure of 1,7-phenanthroline is not known from the literature. The crystallization of it is in progress to obtain suitable crystals for X-ray diffraction studies. (14) Crystal data for complex 2a: 2(C12H8N2):(C6H10O4S), monoclinic, space group C2/c, a ) 27.128(3) Å, b ) 4.793(1) Å, c ) 22.658(2) Å, β ) 114.76(1)°, V ) 2675.3(7) Å3, Z ) 4, Dc ) 1.337 Mg m-3, µ(Mo KR) ) 0.165 mm-1, F(000) ) 1128, λ ) 0.710 73 Å, 1 < θ < 24° (-29 e h e 29, -5 e k e 5, -18 e l e 25), 4793 total reflections, 1910 independent reflections which were used in the refinement. H atoms were obtained from Fourier difference maps. The structure was solved to R1 ) 0.041 and wR2 ) 0.089. (15) (a) Siemens SMART System; Siemens Analytical X-ray Instruments Inc., Madison, WI, 1995. (b) Sheldrick, G. M. SHELXTL Users Manual; Siemens Analytical X-ray Instruments Inc.: Madison, WI, 1993. (16) The choice of the acid compound lies with the fact that the carboxylic group interacts with the hetero nitrogen atom readily, forming O-H‚‚‚N and C-H‚‚‚O hydrogen bonds. (17) (a) Pedireddi, V. R.; Jones, W.; Chorlton, A. P.; Docherty, R. Chem. Commun. 1996, 997. (b) Pedireddi, V. R.; Chatterjee, S.; Ranganathan, A. Rao, C. N. R. Tetrahedron 1998, 54, 9457. (c) Garcia-Tellado, F.; Goswami, S.; Chang, S. K.; Geib, S.; Hamilton, A. D. J. Am. Chem. Soc. 1990, 112, 7393. (18) Crystal data for 2b: (C12H8N2):(C4H6O4S), monoclinic, space group C2/c, a ) 22.317(6) Å, b ) 6.846(2) Å, c ) 20.946(9) Å, β ) 108.82(5)°, V ) 3028.8(2) Å3, Z ) 8, Dc ) 1.449 Mg m-3, µ(Mo KR) ) 0.236 mm-1, F(000) ) 1376, λ ) 0.710 73 Å, 1 < θ < 24° (-21 e h e 14, -6 e k e 7, -23 e l e 18), 2598 total reflections, 1802 independent reflections of which were used in the refinement. The structure was solved to R1 ) 0.051 and wR2 ) 0.105. H atoms were placed in calculated positions. (19) Although the O-H‚‚‚N hydrogen bond in 2b appears to be weaker than in 2a, this would not be the case from the topological considerations, as it is a part of a cyclic hydrogen bond pattern unlike in 2a.
CG015511R
