CRYSTAL GROWTH & DESIGN
Contrasting Solid-State Structures of Trithiocyanuric Acid and Cyanuric Acid
2006 VOL. 6, NO. 4 846-848
Fang Guo,† Eugene Y. Cheung,† Kenneth D. M. Harris,*,† and V. R. Pedireddi‡ School of Chemistry, Cardiff UniVersity, Park Place, Cardiff CF10 3AT, Wales, UK, and DiVision of Organic Chemistry, National Chemical Laboratory, Pune 411 008, India ReceiVed February 28, 2006
ABSTRACT: Although trithiocyanuric acid (TTCA) has been investigated widely as an agent in the formation of molecular cocrystals, the crystal structure of pure TTCA has never been determined. Attempts to grow crystals of pure TTCA by crystallization from solution invariably lead to the formation of solvate cocrystals, and desolvation of these materials leads to polycrystalline powder samples. In this paper, we report the structure determination of pure TTCA directly from powder X-ray diffraction data, using the direct-space genetic algorithm technique for structure solution followed by Rietveld refinement. The structure presents interesting contrasts to that of the oxygen analogue, cyanuric acid, and alludes to the possibility that both compounds might be capable of exhibiting polymorphism. There is currently considerable interest in the development and exploitation of “crystal engineering” strategies1 for the design and construction of molecular crystals with premeditated structural properties. Within this field, much success has been achieved in the design of cocrystal structures, in part because additional versatility is introduced within the design strategy when two different molecular components are employed. Much of the classic work in this field involved the use of cyanuric acid (CA; Scheme 1) as one component in cocrystal structures,2 exploiting the fact that this molecule forms hydrogen bonded arrays with well-defined and predictable structural properties in two dimensions. Attention has also focused3 on studies of the sulfur analogue trithiocyanuric acid (TTCA; Scheme 1), which also forms a range of cocrystals constructed from well-defined hydrogen bonded arrays of TTCA molecules.3d To fully understand how to utilize such molecules in crystal engineering strategies, it is clearly imperative to understand the structural properties of the “pure” crystalline phases of each component. However, while the crystal structure of CA has been determined previously4 from single-crystal X-ray diffraction (XRD) data (to date, only one polymorph of CA has been reported), the crystal structure of TTCA has so far never been reported. In the course of our research on cocrystals of TTCA, we made extensive attempts to prepare single crystals of TTCA suitable for structure determination from single-crystal XRD data. However, TTCA has a strong propensity to form cocrystal (solvate) structures in crystallization experiments from the types of solvents in which it is readily soluble, and we have been unable to prepare pure TTCA by conventional crystallization. A sample of pure TTCA obtained commercially is crystalline (assessed from powder XRD (PXRD)) but does not contain crystals of suitable size for single-crystal XRD studies. In addition, we have shown (by powder XRD) that desolvation of the solvate cocrystals leads to pure TTCA, but in our experience, the line widths in the PXRD patterns of samples of pure TTCA obtained by desolvation of solvate cocrystals are significantly greater than the line widths for the commercial sample of pure TTCA. Under these circumstances, single-crystal XRD cannot be used for structure determination of the pure phase of TTCA, and alternative approaches for structural characterization are required. Fortunately, however, there have been significant advances in recent years in opportunities for carrying out complete structure determination of molecular solids directly from PXRD data,5 particularly through development of the “direct-space” strategy for structure solution.5a These techniques provide a viable route for structure determination of microcrystalline powder samples, and in this paper, * To whom correspondence should be addressed. E-mail: HarrisKDM@ cardiff.ac.uk. † Cardiff University. ‡ National Chemical Laboratory.
Scheme 1
we exploit this opportunity to establish the structural properties of the pure phase of TTCA. The polycrystalline sample of pure TTCA used in this work was obtained commercially. Structure determination was carried out directly from PXRD data6,7 using the direct-space genetic algorithm (GA) technique8 (in the program EAGER9) for structure solution,10 followed by Rietveld refinement11 using the program GSAS.12 The good agreement between calculated and experimental PXRD patterns in the final Rietveld refinement (Figure 1), together with the fact (see below) that the structure obtained is chemically and structurally sensible, vindicates the correctness of the structure. The crystal structure of TTCA comprises sheets of molecules (Figure 2a) parallel to the (12h0) plane.13 Within the sheet, there is extensive N-H‚‚‚S hydrogen bonding (pairs of molecules interact through two N-H‚‚‚S hydrogen bonds). Each N-H bond is a donor in one N-H‚‚‚S hydrogen bond, but the S atoms in the molecule differ in their behavior as hydrogen bond acceptors. Thus, one S atom accepts two N-H‚‚‚S hydrogen bonds, one S atom accepts one N-H‚‚‚S hydrogen bond, and the other S atom is not involved in any hydrogen bonding. In the hydrogen bonding network, groups of six molecules are arranged in a cyclic manner, at the center of which four S atoms (including two S atoms not involved in hydrogen bonding) are in van der Waals contact (S‚‚‚S, 3.37-3.52 Å). The hydrogen bonding network in the sheet can be considered as an intersection of two types of zigzag tapes: (a) one type, running horizontally in Figure 2a, is analogous to the tapes of Type 1 discussed (in the context of cocrystals of TTCA) previously;3d (b) the other type, running nearly vertically in Figure 2a, is analogous to the tapes of Type 3 discussed previously.3d The structural relationship between adjacent sheets (Figure 2b) is such that pairs of molecules (related across an inversion center) in adjacent sheets have an S atom of one molecule lying almost directly above the center of the ring of the other molecule, and vice versa.14 Each molecule interacts in this manner with a unique partner in one adjacent sheet but not in the other adjacent sheet. Adjacent sheets are offset such that there is no “overlap” between the π systems of the molecules in adjacent sheets. The crystal structure of TTCA shows important contrasts to the crystal structure of CA4 (Figure 3). Although both structures are based on hydrogen bonded sheets, there are significant differences in the details of the hydrogen bonding arrangement within the sheet. The CA structure can be described as an intersection of two types of hydrogen bonded tapes/chains: (a) a zigzag tape (horizontal in
10.1021/cg0601094 CCC: $33.50 © 2006 American Chemical Society Published on Web 03/22/2006
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Crystal Growth & Design, Vol. 6, No. 4, 2006 847 structure types are clearly merited. And experimental studies of the structural properties as a function of temperature and/or pressure may yield insights concerning possible phase transformations between the two structure types. Acknowledgment. We are grateful to EPSRC for general support (to K.D.M.H.) and to Cardiff University and Universities UK for a studentship (to F.G.). We thank Emma McCabe for her involvement at an early stage of this research, and V.R.P. is grateful to Dr K.N. Ganesh and Dr S. Sivaram for their support.
Figure 1. Experimental (+ marks), calculated (solid line), and difference (lower line) PXRD profiles for the final Rietveld refinement of TTCA.
Supporting Information Available: Structural data (in cif format) are available free of charge via the Internet at http://pubs.acs.org.
References
Figure 2. Crystal structure of TTCA showing (a) a single sheet viewed perpendicular to the plane of the sheet (dashed lines: N-H‚‚‚S hydrogen bonds; green: Type 1 tape; red: Type 3 tape) and (b) two adjacent sheets (in different colors) viewed perpendicular to the plane of the sheet.
Figure 3. Crystal structure of CA showing (a) a single sheet viewed perpendicular to the plane of the sheet (dashed lines: N-H‚‚‚O hydrogen bonds; green: Type 1 tape; red: linear chain) and (b) two adjacent sheets (in different colors) viewed perpendicular to the plane of the sheet.
Figure 3a) involving two N-H‚‚‚O hydrogen bonds between each pair of adjacent molecules and directly analogous to the zigzag tape of Type 1 in the TTCA structure; and (b) a linear chain (vertical in Figure 3a) involving a single N-H‚‚‚O hydrogen bond between adjacent molecules in the chain. In the CA structure, each N-H bond and each CdO group are involved in one N-H‚‚‚O hydrogen bond. Importantly, the linear chain motif, which is also a feature of some cocrystals of CA,2b,g,i,j is not observed in the TTCA structure nor in any cocrystals of TTCA reported to date.3 It is interesting to note that the TTCA structure could be converted into the CA structure by a displacement of every second horizontal (Type 1) tape along the direction of the tape by approximately one-quarter of the repeat distance within the tape. In terms of the structural relationship between adjacent sheets in the CA structure (Figure 3b), there is broad similarity with the TTCA structure in that there is no overlap between the π systems of the molecules in adjacent sheets. However, the CA structure has no analogy to the structural feature in TTCA that an S atom of a molecule in one sheet lies directly above the ring centroid of a molecule in an adjacent sheet. It is reasonable to propose that both CA and TTCA might be capable of forming either structure type, although to date, CA and TTCA have been found only to form one crystal structure. To obtain a more detailed understanding of the prospects for polymorphism15 of these compounds (e.g., to assess whether TTCA in the CA structure type is energetically accessible and whether CA in the TTCA structure type is energetically accessible), computational investigations of the energetic properties of the two different
(1) (a) Schmidt, G. M. J. Pure Appl. Chem. 1971, 27, 647. (b) Thomas, J. M. Philos. Trans. Royal Soc. 1974, 277, 251. (c) Adams, J. M.; Pritchard, R. G.; Thomas, J. M. J. Chem. Soc. Chem. Commun. 1976, 358. (d) Desiraju, G. R. Crystal Engineering: The Design of Organic Solids; Elsevier: Amsterdam, 1989. (e) Lehn, J. M. Supramolecular Chemistry: Concepts and PerspectiVes; VCH: Weinheim, 1995. (2) (a) Seto, C. T.; Whitesides, G. M. J. Am. Chem. Soc. 1990, 112, 6409. (b) Stainton, N. M.; Harris, K. D. M.; Howie, R. A. J. Chem. Soc. Chem. Commun. 1991, 1781. (c) Seto, C. T.; Whitesides, G. M. J. Am. Chem. Soc. 1991, 113, 712. (d) Zerkowski, J. A.; Seto, C. T.; Whitesides, G. M. J. Am. Chem. Soc. 1992, 114, 5473. (e) Harris, K. D. M.; Stainton, N. M.; Callan, A. M.; Howie, R. A. J. Mater. Chem. 1993, 3, 947. (f) Ranganathan, A.; Pedireddi, V. R.; Rao, C. N. R. J. Am. Chem. Soc. 1999, 121, 1752. (g) Ranganathan, A.; Pedireddi, V. R.; Sanjayan, G.; Ganesh, K. N.; Rao, C. N. R. J. Mol. Struct. 2000, 522, 87. (h) Pedireddi, V. R.; Belhekar, D. Tetrahedron 2002, 58, 2937. (i) Barnett, S. A.; Blake, A. J.; Champness, N. R. CrystEngComm 2003, 5, 134. (j) Akhtaruzzaman, M.; Tomura, M.; Nishida, J.; Yamashita, Y. J. Org. Chem. 2004, 69, 2953. (3) (a) Pedireddi, V. R.; Chatterjee, S.; Ranganathan, A.; Rao, C. N. R. J. Am. Chem. Soc. 1997, 119, 10867. (b) Ranganathan, A.; Pedireddi, V. R.; Chatterjee, S.; Rao, C. N. R. J. Mater. Chem. 1999, 9, 2407. (c) Ahn, S. Ph.D. Thesis, University of Birmingham, 1999. (d) Ahn, S.; PrakashaReddy, J.; Kariuki, B. M.; Chatterjee, S.; Ranganathan, A.; Pedireddi, V. R.; Rao, C. N. R.; Harris, K. D. M. Chem. Eur. J. 2005, 11, 2433. (e) Krepps, M. K.; Parkin, S.; Atwood, D. A. Cryst. Growth Des. 2001, 1, 291. (f) Dean, P. A. W.; Jennings, M.; Houle, T. M.; Craig, D. C.; Dance, I. G.; Hook, J. M.; Scudder, M. L. CrystEngComm 2004, 6, 543. (4) (a) Wiebenga, E. H.; Moerman, N. F. Z. Kristallogr. 1938, 99, 217. (b) Wiebenga, E. H. J. Am. Chem. Soc. 1952, 74, 6156. (c) Coppens, P.; Vos, A. Acta Crystallogr. Sect. B 1971, 27, 146. (d) Dietrich, H.; Cheringer, C. S.; Meyer, H.; Schulte, K. W.; Schweig, A. Acta Crystallogr. Sect. B 1979, 35, 1191. (e) Verschoor, G. C. Nature 1964, 202, 1206. (5) (a) Harris, K. D. M.; Tremayne, M.; Lightfoot, P.; Bruce, P. G. J. Am. Chem. Soc. 1994, 116, 3543. (b) Harris, K. D. M.; Tremayne, M.; Kariuki, B. M. Angew. Chem. Int. Ed. 2001, 40, 1626. (c) David, W. I. F.; Shankland, K.; McCusker, L. B.; Baerlocher, C., Eds.; Structure Determination from Powder Diffraction Data; Oxford University Press: Oxford, UK, 2002. (d) Harris, K. D. M.; Cheung, E. Y. Chem. Soc. ReV. 2004, 33, 526. (e) Baerlocher, C.; McCusker, L. B.; Eds. Z. Kristallogr. 2004, 216, 782. (6) The PXRD pattern of TTCA was recorded at ambient temperature on a Bruker D8 diffractometer [CuKR1; transmission mode; foil sample holder; linear position-sensitive VANTEC detector covering 12° in 2θ; 2θ range 8° - 70°; step size 0.0167°; data collection time 14 h]. (7) The PXRD pattern was indexed using the program TREOR (Werner, P. E.; Eriksson, L.; Westdahl, M. J. Appl. Crystallogr. 1985, 18, 367), giving the following triclinic unit cell (after cell reduction): a ) 5.86 Å, b ) 7.05 Å, c ) 8.80 Å, R ) 103.0°, β ) 92.9°, γ ) 110.4°. Density considerations suggest that there are two TTCA molecules in the unit cell. Structure solution was carried out initially in space group P1h (with one molecule in the asymmetric unit), with the intention to consider space group P1 if no satisfactory solution was obtained in P1h. Unit cell and profile refinement, using the Le Bail method, gave excellent fit (Rwp ) 2.20%).
848 Crystal Growth & Design, Vol. 6, No. 4, 2006 (8) (a) Kariuki, B. M.; Serrano-Gonza´lez, H.; Johnston, R. L.; Harris, K. D. M. Chem. Phys. Lett. 1997, 280, 189. (b) Harris, K. D. M.; Johnston, R. L.; Kariuki, B. M. Acta Crystallogr., Sect. A.: Found Crystallogr. 1998, 54, 632. (c) Habershon, S.; Harris, K. D. M.; Johnston, R. L. J. Comput. Chem. 2003, 24, 1766. (9) Habershon, S.; Turner, G. W.; Kariuki, B. M.; Cheung, E. Y.; Hanson, A. J.; Tedesco, E.; Albesa-Jove´, D.; Chao, M. H.; Lanning, O. J.; Johnston, R. L.; Harris, K. D. M. EAGER - A Computer Program for Direct-Space Structure Solution from Powder X-ray Diffraction Data; Cardiff University and University of Birmingham. (10) The GA structure solution calculation involved one TTCA molecule in the asymmetric unit, requiring six structural variables {x, y, z, θ, φ, ψ} to define the position and orientation of the rigid molecule within the unit cell. The GA calculation involved the evolution of 80 generations for a population of 100 structures, with 50 mating operations and 30 mutation operations carried out per generation.
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(11)
(12)
(13) (14) (15)
The best structure solution was taken as the starting structural model for Rietveld refinement. Final Rietveld refinement: a ) 5.8571(4) Å, b ) 7.0475(3) Å, c ) 8.7999(6) Å, R ) 102.990(6)°, β ) 92.874(6)°, γ ) 110.470(4)°, Rwp ) 3.04%, Rp ) 2.06%; 3651 profile points; 53 refined variables. Larson, A. C.; Von Dreele, R. B. GSAS; Los Alamos Laboratory Report No. LA-UR-86-748; Los Alamos National Laboratory: Los Alamos, NM, 1987. Consistent with the fact that the PXRD pattern has a peak of dominant intensity, indexed as (12h0). The S‚‚‚N and S‚‚‚C distances to all C and N atoms of the ring of the adjacent molecule are in the range 3.59-3.71 Å. Bernstein, J. Polymorphism in Molecular Crystals; Oxford University Press: Oxford, 2002.
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