Pressure-Induced Solvate Crystallization of 1,4-Diazabicyclo[2.2.2]octane Perchlorate with Methanol

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1 This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. pubs.acs.org/crystal Pressure-Induced Solvate Crystallization of 1,4-Diazabicyclo[2.2.2]octane Perchlorate with Methanol Michalina Anioła, Anna Olejniczak, and Andrzej Katrusiak* Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, Poznan, Poland *S Supporting Information Downloaded via on October 14, 2018 at 18:57:22 (UTC). See for options on how to legitimately share published articles. ABSTRACT: 1,4-Diazabicyclo[2.2.2]octane perchlorate, [C 6 H 13 N 2 ] + ClO 4, dabcohclo 4, the first NH + N hydrogen-bonded ferroelectric, exhibits at least ten unsolvated polymorphs, depending on temperature and pressure. When crystallized from the methanol solution above 2 GPa, dabcohclo 4 crystallizes with two molecules of methanol to form solvate dabcohclo 4 2CH 3 OH. This solvate structure has been determined by single-crystal X-ray diffraction up to 3 GPa. High pressure transforms the H-bonding pattern and the hierarchy of different cohesion forces. The solvate formation is additionally favored by its molecular volume lower than the sum of the molar equivalents of unsolvated components. INTRODUCTION Formation of solvates is one of the challenges of modern crystal engineering. The crystallization of solvates is often hard for predicting theoretically, while their application in pharmaceutical, agricultural, and even electronic technologies is most desired. 1,2 The formation of nonsolvated and solvated crystals depends on the concentration and temperature. 3 Recently, while investigating the ferroelectric and relaxor properties of NH + N bonded 1,4-diazabicyclo[2.2.2]octane monosalts, it was found that pressure efficiently induces their polymorphic transitions and preferential crystallization of hydrates and other solvates. 4 Ten unsolvated polymorphs of 1,4-diazabicyclo [2.2.2]octane hydroiodide (dabcohi) have been documented so far. 5 The crystallization of aqueous solution at ambient conditions yields exclusively unsolvated dabcohi crystals, whereas above 0.5 and 0.7 GPa two polymorphs of hydrate dabcohi H 2 O were obtained; 6 the recrystallization above 1.2 GPa led to unsolvated dabcohi again. The recrystallization of the dabcohi methanol solution was even more intriguing: 4 above 1.8 GPa, the trimethanol solvate of disalt 1,4- diazabicyclo[2.2.2]octane (dabco2hi 3CH 3 OH) precipitated (Scheme 1), while residue free-base dabco remained dissolved; above 2.4 GPa, the reaction of N-methylation yielded N- Scheme 1. Pressure Ranges and Types of dabcohi and dabcohclo 4 Solvation methyl-1,4-diazabicyclo[2.2.2]octanium iodide (dabcoch 3 I) and its dimethanol solvate crystals (dabcoch 3 I 2CH 2 OH) were obtained. The reluctance of dabcohi to cocrystallize with methanol was investigated further and, after circumventing the N-methylation, at 3.1 GPa another solvate dabcohi H 2 O CH 3 OH was formed. However, no dabcohi solvate with methanol alone could be obtained. Hence, our present investigation on the cocrystallization of the perchlorate salt, dabcohclo 4, with methanol. At ambient pressure dabcohclo 4 crystallizes from aqueous and from methanol solutions exclusively in the unsolvated form. We intended to check if the perchlorate anion in dabcohclo 4 would facilitate the formation of its methanol solvate. We have found that indeed the crystallization of dabcohclo 4 above 2.0 GPa yields solvated crystals with methanol, dabcohclo 4 2CH 3 OH. In accordance with our previous studies, the high-pressure formation of the solvate can be due to its volume gain, compared to the sum of the solvate components separately, as well as to new types of interactions to the solvate molecules. Moreover, pressure can reverse the balance between different types of interactions. For example, high pressure significantly enhances the CH O bonds, 7,8 which leads to a polymorphic transition in sucrose at 4.8 GPa 9 and in formamide at 0.45 GPa. 10 These effects have been explored in the dabcohclo 4 and dabcohclo 4 2CH 3 OH (Figure 1) structures below. EXPERIMENTAL SECTION High Pressure Crystal Growth. The high-pressure diffraction experiments on dabcohclo 4 were performed on the samples in situ crystallized in a modified high-pressure diamond anvil-cell (DAC), 11 with the anvils directly supported on steal-backing plates. Pressure in the DAC chamber was calibrated by the ruby-fluorescence method, 12,13 with a Photon Control spectrometer affording the Received: November 13, 2013 Revised: March 5, 2014 Published: March 20, American Chemical Society 2187

2 Crystal Growth & Design were grown at isochoric conditions. After loading the solution into the DAC chamber, it was sealed and pressure was increased till polycrystalline mass formed. All crystals except one were dissolved by heating the DAC, and this single crystal was grown by slowly cooling the DAC to room temperature. The crystallizations and X-ray diffraction measurements were performed at 2.16, 2.30, 2.40, and 3.00 GPa. We tried to recover the crystal from the DAC; however, while releasing pressure the cocrystal crushed at about 1.00 GPa. The rounded edges of the sample at 2.30 GPa (Figure 2, panels c and d) could suggest that the solvate is stable at high temperature only and that it slowly decomposes at 296 K. On the other hand, we have not noted any decrease of the sample volume by measuring its size under the microscope. In fact, the surface of the sample after the experiment (d) is bigger than before (c). This has been confirmed by inspecting the X-ray diffraction data, as we did not detect intensity changes of reflections in the reference frames. We also observed this effect of rounding edges for the sample at 2.40 GPa (Figure S2 of the Supporting Information). X-Ray Diffraction Analysis. The diffraction data have been measured with a KUMA KM4-CCD diffractometer. CrysAlis14 was used for recording reflections15 and preliminary reduction of the data. Then reflections overlapping with diamond reflections were eliminated and the intensities were corrected for the DAC absorption, sample shadowing by the gasket, and the sample absorption.16,17 The structures were solved straightforwardly by direct methods18 and refined by full-matrix least-squares.18 In this solvate, there are two methanol molecules per one cation dabcoh+ and anion ClO4 pair. Anisotropic temperature factors were applied for all nonhydrogen atoms at 2.16 and 2.30 GPa, except the disordered methanol molecules where the isotopic atoms were refined; in the structure at 2.40 GPa, the anisotropic thermal parameters were retained only for the ClO4 anion. The ethylene H-atoms were located from molecular geometry (distance C H of 0.97 Å) and their Uiso s constrained to 1.2 Ueq of the carrier atoms. The model with the amine proton disordered was assumed. The proton sites were calculated from geometry (dn H = 0.86 Å; their Uiso = 1.2 Ueq of the nitrogen atom) and their site occupation factor (SOF) was refined with constrain SOF(H1) + SOF(H2) = 1. In all experiments, SOF(H1) and SOF(H2) were refined to the values close to 0.5 and it was further assumed that the structure is disordered, as shown in Figures 3 and 4. The methanol molecule B is disordered in two orientations, hence two sets of labels of atomic sites have been used: C(12)H 3 O(11)H and C(14)H3O(13)H, respectively. Additionally, in both methanol molecules A and B, the hydroxyl H-atoms are disordered each in three sites. The SOFs of the disordered atoms were initially refined as free variables and then fixed in the final refinement. The selected crystal and refinement data are listed in Table 1; complete experimental details are given in Table S1 of the Supporting Information. Structural drawings have been prepared using the XSeed interface of POV-Ray.19,20 Figure 1. Atomic labels of the H-bonded symmetry-independent ions and CH3OH molecules in dabcohclo4 2CH3OH. The methanol molecules and the proton in dabcoh+ cation have been shown in their disordered sites for illustrating possible hydrogen bonds, indicated as the dashed lines. accuracy of 0.02 GPa; pressure was measured before and after each diffraction measurement. The in situ crystallizations of dabcohclo4 were performed from methanol or methanol:ethanol:water (16:3:1) solutions. An addition of ethanol significantly improves the crystallization conditions, compared with the crystallization of dabcohclo4 dissolved in methanol only. We grew large and well-shaped crystals from the solution in the 16:3:1 methanol:ethanol:water mixture (Figure 2 and Figures S1 and S2 of the Supporting Information). The single crystals DISCUSSION Above 2 GPa, none of dabcohclo4 crystallizations of solutions containing methanol succeeded in unsolvated crystals and only the solvate dabcohclo4 2CH3OH with methanol could be obtained. In accordance with our study, only the monoclinic solvate in the form described in Table 1 is stable up to at least 3 GPa. The crystal structure of the solvate is strongly disordered: (i) the proton of dabcoh+ cation is disordered close to 50:50 in two sites at nitrogen atoms N(1) and N(4); (ii) in the methanol molecule A, the hydroxyl atom H(9) is disordered in three sites, each hydrogen bonded either to N(1) or N(4) of the neighboring dabcoh+ cations or to O(3) of the anion; (iii) methanol molecule B is disordered in two orientations, each with the C O bond inclined by 97 to the other, and the hydroxyl atom H(11) is disordered in three sites, similarly as that in molecule A. High pressure usually eliminates orientational disorder, but it often promotes the disorder of protons in Figure 2. Isochoric growth of the single-crystal dabcohclo4 2CH3OH solvate from 16:3:1 metanol:ethanol:water solution: one crystal seed at (a) 423 K, (b) 373 K, (c) 296 K/2.30 GPa, and (d) the crystal after the measurement ended. A ruby chip for pressure calibration lies by the left wall of the chamber. 2188

3 Figure 3. Schematic diagram of hydrogen-bonding network in the dabcohclo 4 2CH 3 OH co-crystal: (a) the average structure with the disordered dabcoh + protons and methanol molecules discriminated by colors red and black, but the perchlorate anions omitted for clarity and (b) the structural fragment of drawing (a) simplified by eliminating the disordered sites of amine protons and hydroxyl groups. Table 1. Selected Crystal Data for High-Pressure Structure of dabcohclo 4 2CH 3 OH pressure (GPa) 2.16(2) 2.30(2) 2.40(2) temperature (K) 296(2) 296(2) 296(2) crystal system monoclinic monoclinic monoclinic space group P2 1 /c P2 1 /c P2 1 /c unit cell (Å, ) a 7.771(2) (9) 7.660(11) b 9.800(2) 9.782(3) (6) c (13) (19) (8) β (14) (10) 90.42(2) Z/Z 4/1 4/1 4/1 volume (Å 3 ) (4) (4) (16) D calc (g/cm 3 ) final R 1 /wr 2 (I > 2σ 1 ) / / / Figure 4. The chain of NH + O and OH O bonded cations, anions and methanol molecules in the dabcohclo 4 2CH 3 OH solvate: (a and b) viewed in two projections perpendicular to the chain direction and (c) in the projection along the chain. This drawing shows all sites of the disordered cations and molecules. H-Bonds are indicated by dashed lines. hydrogen bonds, like in OH O-bonded KH 2 PO 4 (KDP) ferroelectrics 21 and their NH N-bonded analogues (e.g., pyrazole 22 ). In the dabcohclo 4 2CH 3 OH solvate, all the disorder described above, except that of (i) amine protons, involves reorientations of (iii) methanol molecules or at least the (ii) hydroxyl groups. It is characteristic of all structures of unsolvated dabcohclo 4 polymorphs determined so far that the dabcoh + cations are NH + N hydrogen-bonded into chains. The plot in Figure 5 shows that this NH + N bond is hardly dependent on pressure up to the limit of unsolvated dabcohclo 4 stability at about 2.0 GPa. Of other short contacts in unsolvated dabcohclo 4, the most pressure-dependent are NH + OCl distances, reduced by nearly 1 Å at 1.8 GPa. In methanol solvate dabcohclo 4 2CH 3 OH, the NH + N hydrogen bonds are not formed and NH + O(Cl) bonds have become longer by 0.2 Å. The shortest are NH + O bonds disordered with OH N bonds, joining the alternatively located dabcoh + cations and methanol molecule A into chains along crystal direction [001]. The distance between methanol molecules A and B approaches the sum of van der Waals radii, and both of the methanol molecules form short contacts to the ClO 4 anion (Figures 3 and 4). The structure of dabcohclo 4 2CH 3 OH is mainly governed by hydrogen bonds NH + O(methanol) and OH N, of the distances shorter than the sum of van der Waals radii (Figure 5), 23 but also by many other contacts of distances comparable to the sum of van der Waals radii. Distances H acceptor in 2189

4 Figure 5. Short interionic and intermolecular contacts: (a) in unsolvated dabcohclo 4 polymorphs (labeled by Roman numbers) below 2.0 GPa and these contacts in solvate dabcohclo 4 2CH 3 OH above 2.1 GPa and (b) new short contacts formed in the solvate. The contacts of unsolvated dabcohclo 4 retained in the solvate and the short contacts characteristic of the solvate only have been shown separately in plots (a) and (b). Short contacts involving methyl groups of the methanol molecules have been skipped for clarity. The lines joining the points have been drawn for guiding the eye; these lines for CH O and NH N distances in unsolvated polymorphs have been indicated with thick dashed and dotted lines. bonds NH + O(methanol) and OH N are longer and angles donor-h acceptor are sharper (divert more from 180 ) than those in hydrogen bonds NH + N in unsolvated dabcohclo 4. On the other hand, many short CH O contacts, which can be classified as weak hydrogen bonds, are formed between the cation, anion and methanol molecules. It was established that pressure enhances the CH O and CH N interactions. 9,24 In sucrose 9 and formamide, 10 the transformation to high-pressure phases were associated with competition between OH O and CH O hydrogen bonds, the latter becoming increasingly important at high pressure. It can be seen in Figure 5 that pressure gradually reduces the N O and (N)H O distances in dabcohclo 4 polymorphs, while distances NH + N and CH O are hardly compressed up to 2.0 GPa. The formation of dabcohclo 4 2CH 3 OH eliminates the NH + N contacts (the shortest in the unsolvated polymorphs) and slightly lengthens distances CH O and NH + O, but the number of CH O contacts is increased (Figure 5). Thus there are new types of intermolecular interactions which promote the formation of the dabcohclo 4 2CH 3 OH solvate above 2.0 GPa. The weak hydrogen bonds are relevant also for the formation of new polymorphs at high pressure. 25,26 It is also characteristic of dabcohclo 4 2CH 3 OH that its molecular volume, calculated of the unit-cell volume (V/Z), is smaller than the molecular volume of unsolvated dabcohclo 4 and two methanol molecules (Figure 6). Thus the formation of the solvate is consistent with Le Cha telier s principle. It can also be noted that the solvate crystal is pseudosymmetric, as the monoclinic angle β is close to 90 (Table 1) and the structure approximates space group Pmc2 1 and Pmma. CONCLUSIONS The formation of solvate dabcohclo 4 CH 3 OH above 2.0 GPa and at high temperature sharply contracts with the reluctance of dabcohi to form methanol solvates. On the other hand, N- Figure 6. Molecular volume of high-pressure phases II, III, and IV of unsolvated dabcohclo 4 (red ) and its methanol solvate (blue ). The blue vertical arrows indicate the difference of the volume of two methanol molecules subtracted from the molecular volume of the solvate (i.e. of dabcohclo 4 alone in the solvate; blue ). The molecular volume of methanol molecules has been assessed for the high-pressure conditions based on the volumetric 27 and diffraction 28 data methylated 1,4-diazabicyclo[2.2.2]octane, dabcoch 3 I, cocrystallizes with two CH 3 OH molecules in dabcoch 3 I 2CH 3 OH above 2.4 GPa. Despite analogous stoichiometry, solvates dabcohclo 4 2CH 3 OH and dabcoch 3 I 2CH 3 OH have different structures. 29 It is particularly striking that even in the same crystals of isostructural dabcoch 3 I 2CH 3 OH and analogous dabcoch 3 Br 2CH 3 OH, the H-bonding patterns are different. In the structures of all dabcoha (where A = Br, I, or ClO 4 ) solvates investigated so far, new types of hydrogen bonds are formed. This is also the case in the present results, although it is 2190

5 apparent that the close packing of the ions and molecules also play an important role for the dabcohclo 4 CH 3 OH solvate formation in the high-pressure conditions. ASSOCIATED CONTENT *S Supporting Information Stages of growth of crystal at 2.16 GPa (Figure S1) and at 2.4 GPa (Figure S2), molecular packing (Figure S3), hydrogen bonding in dabcohclo 4 2CH 3 OH (Figure S4), detailed crystallographic information on high-pressure measurements (Table S1), and CIF files. This material is available free of charge via the Internet at CIF format (CCDC ) are available free of charge via the Internet AUTHOR INFORMATION Corresponding Author * katran@amu.edu.pl. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This study was partly supported by the Polish Ministry of Science and Higher Education, Grant N , and partly by the Foundation for Polish Science, TEAM project /6. REFERENCES (1) Shan, N.; Zaworotko, M. J. Drug Discovery Today 2008, 13, 440. (2) Vishweshwar, P.; McMahron, J. A.; Bis, J. A.; Zaworotko, M. J. J. Pharm. Sci. 2006, 95, 499. (3) Tung, H. H.; Paul, E. L.; Midler, M.; McCauley, J. A. Crystallization of Organic Compounds: An Industrial Perspective, John Willey & Sons, Inc.: Hoboken, NJ, (4) Olejniczak, A.; Katrusiak, A. CrystEngComm 2010, 12, (5) Olejniczak, A.; Katrusiak, A.; Szafranśki, M. Cryst. Growth Des. 2010, 10, (6) Olejniczak, A.; Katrusiak, A. Cryst. Growth Des. 2011, 11, (7) Dziubek, K. F.; Jęczminśki, D.; Katrusiak, A. J. Phys. Chem. Lett. 2010, 1, (8) Chang, H.-C.; Jiang, J.-C.; Chuang, C.-W.; Lin, J.-S.; Lai, W.-W; Yang, Y.-C.; Lin, S. H. Chem. Phys. Lett. 2005, 410, (9) Patyk, E.; Skumiel, J.; Podsiadło, M.; Katrusiak, A. Angew. Chem., Int. Ed. 2012, 51, (10) Gajda, R.; Katrusiak, A. Cryst. Growth Des. 2011, 11, (11) Merrill, L.; Bassett, W. A. Rev. Sci. Instrum. 1974, 45, (12) Piermarini, G. J.; Block, S.; Barnett, J. D.; Forman, R. A. J. Appl. Phys. 1975, 46, (13) Mao, H. K.; Xu, J.; Bell, P. M. J. Geophys. Res. 1985, 91, (14) Xcalibur CCD System, CrysAlisPro Software System, version ; Oxford Diffraction Ltd.: Wrocław, Poland, (15) Budzianowski, A.; Katrusiak, A. High-pressure Crystallography; Katrusiak, A.; McMillan, P. F., Eds.; Kluwer: Dordrecht, 2004, pp (16) Katrusiak, A. REDSHABS, Program for the correcting reflections intensities for DAC absorption, gasket shadowing and sample crystal absorption; Adam Mickiewicz University: Poznan, Poland, (17) Katrusiak, A. Z. Krystallogr. 2004, 219, (18) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, (19) Barbour, L. J. J. Supramol. Chem. 2001, 1, (20) Persistence of Vision (TM) Raytracer, version 2.6; Persistence of Vision Pty. Ltd.: Williamstown, Victoria, Australia., (21) Sikora, M.; Pojawis, P.; Katrusiak, A. J. Phys. Chem. C. 2013, 117, (22) Sikora, M.; Katrusiak, A. J. Phys. Chem. C 2013, 117, (23) Bondi, A. J. Phys. Chem. 1964, 68, (24) Dziubek, K. F.; Katrusiak, A. J. Phys. Chem. B 2008, 112, (25) Fabbiani, F. P. A.; Allan, D. R.; David, W. I. F.; Moggach, S. M.; Parsons, S.; Pulham, C. R. CrystEngComm 2004, 6, (26) Boldyreva, E. V. Cryst. Growth Des. 2007, 7, (27) Bridgman, P. W. Proc. Am. Acad. Arts Sci. 1942, 74, (28) Allan, D. R.; Clark, S. J.; Brugmans, M. J. P.; Ackland, G. J.; Vos, W. L. Phys. Rev. 1988, B58, R (29) Andrzejewski, M.; Olejniczak, A.; Katrusiak, A. CrystEngComm 2012, 14,