Concomitant Polymorphism in a Spirobicyclic Dione
2004 VOL. 4, NO. 6 1245-1247
V. S. Senthil Kumar,† K. C. Sheela,‡ Vijay Nair,‡ and Nigam P. Rath*,† Department of Chemistry & Biochemistry, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, Missouri 63121-4499, and Organic Chemistry Division, Regional Research Laboratory (CSIR), Trivandrum-695 019, India Received July 8, 2004;
CRYSTAL GROWTH & DESIGN
Revised Manuscript Received September 8, 2004
W This paper contains enhanced objects available on the Internet at http://pubs.acs.org/crystal. ABSTRACT: The title compound 3,5-bis(1,1-dimethylethyl)-5′-phenylspiro[bicyclo[3.1.0]hex-3-ene-6,7′-[6,8]dioxabicyclo[3.2.1]octane]-2,2′-dione, MF ) C25H30O4 (2) displays the phenomenon of concomitant polymorphism. The flexible nature of weak hydrogen bonding in the molecule seems to ease polymorph formation. Two distinct solid-state structures, a 1-D rodlike structure and a supramolecular polychaircyclohexane network, were obtained upon crystallization from hexane/EtOAc solution. Both the polymorphic structures are stabilized by weak C-H‚‚‚O hydrogen bonds. Introduction Polymorphism is the existence of the same chemical component in at least two distinct crystalline arrangement of molecules.1 Polymorphism has been a vital branch of solid-state supramolecular chemistry, and it has assumed special significance in the context of pigments and pharmaceuticals.2 Reproducibly getting the correct polymorph3 of a given compound is important in industries where the product specifications involve structurally reliant properties. Polymorphism in crystals implies that the total free energy difference between various forms of the same molecule is small.4 Since the variations in polymorphic forms arise from the different crystal packing and not because of the presence of different chemical species, polymorphs represent special situations for the study of structure-property relationships. Polymorphism occurs when slightly different and energetically similar intermolecular interactions are established during crystal growth. This can be a consequence of packing rigid molecules into different arrangements or of packing different low-energy conformations of the same molecules into different crystalline arrangements. In the latter case, the polymorphism is termed as conformational polymorphism.5 However, a recent report on polymorphism in hydrogen-bonded frameworks shows that even when the conformation and the localized connectivity between the molecules in two crystal structures remain the same, slight differences in intermolecular hydrogen bonds can lead to polymorphism.6 Indeed, conformationally flexible molecules have more degrees of freedom than rigid molecules and a greater scope for polymorphism might be expected in flexible molecules.7 The energies involved in rotating about single bonds and the energy differences between various polymorphic forms are comparable. Hence, it is not surprising that molecules that possess torsional degrees of freedom may exhibit conformational poly* To whom correspondence should be addressed. E-mail: nrath@ jinx.umsl.edu. † University of Missouri-St. Louis. ‡ Regional Research Laboratory (CSIR).
morphism.8 Herein, we report two low-temperature X-ray crystal structures of the spirobicyclic dione 3,5bis(1,1-dimethylethyl)-5′-phenylspiro[bicyclo[3.1.0]hex3-ene-6,7′-[6,8]dioxabicyclo[3.2.1]octane]-2,2′-dione (2), a substance that exhibits concomitant polymorphism.9
Experimental Section Synthesis. A solution of the cycloadduct 1 (λmax ) 387 nm, 0.050 g, 0.13 mmol) in dry acetonitrile (30 mL) was purged with argon for 15 min in a quartz vessel and irradiated for 12 min inside a Rayonet Photochemical reactor using a 350 nm lamp. The yellow reaction mixture becomes colorless. The solvent was evaporated off and the residue was purified by silica gel column chromatography using 8% ethyl acetate in hexane as the eluent to afford the compound 2 (0.047 g) in 94% yield. Chemical purity was confirmed by TLC and 1H NMR. The product was crystallized from a mixed solvent system hexanes/ethyl acetate (70:30). Both polymorphs were crystallized at room temperature and were separated under a microscope by visual inspection. Form A and Form B crystallize as rod and block shaped crystals, respectively. X-ray Crystallography. Preliminary examination and data collection were performed using a Bruker SMART CCD area detector system single-crystal X-ray diffractometer. The SMART and SAINT packages were used for data collection and data reduction, respectively.10 SHELXTL-PLUS software package was used for structure solution and refinement.10 Hydrogens were fixed at idealized geometries and treated isotropically using appropriate riding models. Projection view with 50% thermal ellipsoids for non-hydrogen atoms for Form A and Form B are presented in Figure 1, panels a and b, respectively.
Results and Discussion In the context of our efforts to gain insight into the cycloaddition chemistry of 1,2-quinones, we have explored the dipolar cycloaddition of carbonyl ylides to the latter.11 The cycloadducts such as 1 derived from this
10.1021/cg0497748 CCC: $27.50 © 2004 American Chemical Society Published on Web 10/08/2004
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Kumar et al.
Figure 2. (a) C-H‚‚‚O mediated infinite 1-D chain observed in the crystal structure of Form A. (b) The 1-D rodlike structure (along the b-axes) of Form A.
Scheme 1
Figure 1. Projection views with 50% thermal ellipsoids for non-hydrogen atoms for (a) Form A and (b) Form B. W 3D-rotatable images in PDB format for W (a) and W (b) are available.
reaction appeared to be excellent substrates for oxa-di-π methane rearrangement, and therefore we irradiated 1 at 296 nm. In the event, a very facile photo rearrangement12 occurred to afford 2 (Scheme 1). As a part of the structural investigation of 2, its solidstate structure was determined using X-ray crystallography. In its molecular periphery 2 has multiple hydrogen-bond donor and acceptor groups of comparable strength for weak hydrogen bonding.13 Initial recrystallization of 2 form EtOAc/hexane mixture yielded two concomitant polymorphs (Forms A and B) as characterized by low-temperature single-crystal X-ray diffraction.14 The two crystallographically distinct molecules observed in the two forms of 2 have similar conformations. Form A adopts a monoclinic crystal system in space group P21/c. In the crystal structure, each molecule of
2 is connected to its translation-related molecules via C-H‚‚‚O hydrogen bonding (2.32 Å, 137.1°) to form an infinite 1-D chain along [010] as shown in Figure 2a. The molecules in the 21 related chains are further connected by bifurcated C-H‚‚‚O hydrogen bonds (2.59 Å, 169.0°; 2.58 Å, 146.1°) to form a rodlike structure along the b-axes. Each molecule of Form A is thus connected to four molecules in the rods. Additional C-H‚‚‚O hydrogen bonds between the rods further
Concomitant Polymorphism in a Spirobicyclic Dione
Crystal Growth & Design, Vol. 4, No. 6, 2004 1247 parameters (cif files) are available free of charge via the Internet at http://pubs.acs.org.
References
Figure 3. The supramolecular polycyclohexane network in the crystal structure of Form B.
stabilize the structure. The rodlike structure is shown in Figure 2b. In Form B, 2 crystallizes in space group P21/n (Figure 3). The most prominent pattern observed in the crystal structure is centrosymmetric C-H‚‚‚O dimer. The molecules of 2 in Form B form a C-H‚‚‚O dimer with their inversion-related molecules (2.36 Å, 163.2°). Such dimers are connected by glide-plane-related molecules through additional C-H‚‚‚O hydrogen bonds (2.54 Å, 124.0°) to furnish a supramolecular polycyclohexane type network. Supramolecular chair cyclohexane network has also been assembled with C-H‚‚‚π interactions in the crystal structures of some terminal alkynes15 and in the crystal structure of a molecular complex of trihydroxybenzene with pyridyl derivative,16 with O-H‚‚‚O and C-H‚‚‚O hydrogen bonding in a molecular complex of 5-nitrosalicylic acid with dithianedioxide,17 and from a T-node scaffold in coordination polymers.18 Conclusions To summarize, two polymorphs of the cycloadduct 2 have been structurally characterized by low-temperature X-ray diffraction. The appearance of concomitant polymorphism suggests that subtle differences in intermolecular interactions involving weak C-H‚‚‚O interactions play a significant role. The presence of large number of potential hydrogen-bond donor and acceptor sites undeniably contribute significantly to the observed concomitant polymorphism in 2. In both crystalline forms, solid-state C-H‚‚‚O hydrogen bonds propagate two different networks (rodlike structure and polycyclohexane). The calculated densities (1.204 and 1.196 g cm-3) and packing coefficients (66.1 and 65.8%) of these two polymorphic forms are comparable. Even though the two compounds crystallize in two equivalent space groups, there is no compromise in crystal compactness of the two polymorphic modifications of 2. Further studies in search of new polymorphs are ongoing experiments with 2. Acknowledgment. Funding from the National Science Foundation for purchase of the X-ray diffractometer is acknowledged. Note Added after ASAP Posting An earlier version of this paper posted to the Web on October 8, 2004, had an incorrect structure for compound 1 on page 1. The structure is now correct in this new version posted October 20, 2004. Supporting Information Available: X-ray data with details of refinement, atomic coordinates, and geometrical
(1) (a) Desiraju, G. R. Science 1997, 278, 404-405. (b) Bernstein, J. Polymorphism in Molecular Crystals; Clarendon, Oxford, 2002, 151-187. (2) (a) Schmidt, M. U.; Englert, U. J. Chem. Soc., Dalton Trans. 1996, 2077-2082. (b) Hennigar, T. L.; MacQuarrie, D. C.; Losier, P.; Rogers, R. D.; Zaworotko, M. J. Angew. Chem., Int. Ed. Engl. 1997, 36, 972-973. (c) Lahav, M.; Leiserowitz, L. Angew. Chem., Int. Ed. 1999, 38, 2533-2536. (3) (a) Duntiz, J. D.; Bernstein, J. Acc. Chem. Res. 1995, 28, 193-200. (b) Henck, J.-O.; Bernstein, J.; Ellern, A.; Boese, R. J. Am. Chem. Soc. 2001, 123, 1834-1841. (4) (a) Threlfall, T. L. Analyst 1995, 120, 2435-2460. (b) Caira, M. R. Top. Curr. Chem. 1998, 198, 163-208. (5) Bernstein, J. Organic Solid State Chemistry; Ed. Desiraju, G. R.; Elsevier: Amsterdam, 1987; pp 471-518. (6) Barnett, S. A.; Blake, A. J.; Champness, N. R. CrystEngComm 2003, 5, 134-136. (7) Sarma, J. A. R. P.; Desiraju, G. R. Crystal Engineering; Seddon, K. R., Zaworotko, M., Eds.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1999; pp 325-356. (8) (a) Blagden, R.; Davey, R. J.; Lieberman, H. F.; Williams, L.; Payne, R.; Roberts, R.; Rowe, R.; Docherty, R. J. Chem. Soc., Faraday Trans. 1998, 94, 1035-1044. (b) Buttar, D.; Charlton, M. H.; Docherty, R.; Starbuck, J. J. Chem. Soc., Perkin Trans. 2 1998, 763-772. (c) Starbuck, J.; Docherty, R.; Charlton, M. H.; Buttar, D. J. Chem. Soc., Perkin Trans. 2 1999, 677-692. (d) Kumar, V. S. S.; Addlagatta, A.; Nangia, A.; Robinson, W. T.; Broder, C. K.; Mondal, R.; Evans, I. R.; Howard, J. A. K.; Allen, F. H. Angew. Chem., Int. Ed. 2002, 41, 3848-3851. (e) Jetti, R. K. R.; Boese, R.; Sarma, J. A. R. P.; Reddy, L. S.; Vishweshwar, P.; Desiraju, G. R. Angew. Chem., Int. Ed. 2003, 42, 1963-1967. (f) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. New J. Chem. 2003, 27, 1554-1556. (g) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. CrystEngComm 2004, 6, 102-105. (9) Bernstein, J.; Davey, R. J.; Henck, J.-O. Angew. Chem., Int. Ed. 1999, 38, 3441-3461. (10) (a) SMART and SAINT software package, Bruker Analytical X-ray Division, Madison, WI, 1999. (b) Sheldrick, G. M. Bruker Analytical X-ray Division, Madison, WI, 1999. (11) Nair, V.; Sheela, K. C.; Sethumadhavan, D.; Dhanya, R.; Rath, N. P., Tetrahedron, 2002, 58, 4171-4177. (12) Nair, V.; Sheela, K. C.; Rath, N. P., unpublished results. (13) Desiraju, G. R., Steiner, T. The Weak Hydrogen Bond in Structural Chemistry and Biology; OUP, Oxford, 1999. (14) Crystal data: MF ) C25H30O4. Form A: P21/c, a ) 10.8118(2), b ) 6.3556(1), c ) 32.0901(7) Å, β ) 99.259(2)°, V ) 2176.36(7) Å3, Z ) 4, Dc ) 1.204 g cm-3, T ) 223 K, F(000) ) 848, λ ) 0.71073 Å, µ ) 0.080, R1 ) 0.0496 for 3350 Fo > 2σ(Fo), wR(F2) ) 0.1137 for 4728 unique reflections and 268 parameters. Form B: P21/n, a ) 14.7437(2), b ) 9.6022(1), c ) 15.4922(2) Å, β ) 92.317(1)°, V ) 2191.47(5) Å3, Z ) 4, Dc ) 1.196 g cm-3, T ) 213 K, F(000) ) 848, λ ) 0.71073 Å, µ ) 0.080, R1 ) 0.0498 for 2916 Fo > 2σ(Fo), wR(F2) ) 0.1003 for 4482 unique reflections and 268 parameters. In both cases hydrogen atoms were treated using appropriate riding models and isotropic thermal parameters. Form B can also be solved in an equivalent cell in the space group P21/ c: a ) 14.7437(2), b ) 9.6022(1), c ) 20.9504(3) Å, β ) 132.365(1), V ) 2191.47(5) Å3, Z ) 4, Dc ) 1.196 g cm-3. As expected, this also exhibits the supramolecular polycyclohexane network in the crystal structure like in the P21/n space group. (15) Steiner, T.; Tamm, M.; Grzegorzewski, A.; Schulte, N.; Veldman, N.; Schreurs, A. M. M.; Kanters, J. A.; Kroon, J.; van der Maas, J.; Lutz, B. J. Chem. Soc., Perkin Trans. 2 1996, 2441-2446. (16) Biradha, K.; Zaworotko, M. J. J. Am. Chem. Soc. 1998, 120, 6431-6432. (17) Kumar, V. S. S.; Nangia, A.; Kirchner, M. T.; Boese, R. New. J. Chem. 2003, 27, 224-226. (18) Dong, Y.-B.; Smith, M. D.; Layland, R. C.; Loye, H.-C. Chem. Mater. 2000, 12, 1156-1161.
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