Communication pubs.acs.org/crystal
Finding the Perfect Match: Halogen vs Hydrogen Bonding Tanya Shirman,‡,† Meital Boterashvili,‡ Meital Orbach,‡ Dalia Freeman,‡ Linda J. W. Shimon,§ Michal Lahav,‡ and Milko E. van der Boom*,‡ ‡
Department of Organic Chemistry and §Department of Chemical Research Support, The Weizmann Institute of Science, 234 Herzl Street, Rehovot 7610001, Israel
Crystal Growth & Design 2015.15:4756-4759. Downloaded from pubs.acs.org by UNIV OF SUNDERLAND on 10/26/18. For personal use only.
S Supporting Information *
ABSTRACT: The prediction of supramolecular structures involving different weak interactions is challenging. In this study, single-atom modifications to the molecular structure allow us to address their hierarchy. The resulting series of unimolecular assemblies are mainly based on halogen bonding (XB), hydrogen bonding (HB), or a combination of both. By varying the XB donor (F, Cl, Br, and I) and the XB and HB acceptors (pyridine vs pyridine-N-oxide) we can control the primary motifs directing the structure.
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competing XB/HB donor and XB/HB acceptor sites are combined into one molecular entity, has been much less explored.13,21 Nucleophilic moieties simultaneously involved in both XB and HB are rare.13 Herein, we study a series of substituted pyridine and pyridine-N-oxide-based compounds, 1X and 2X, each containing both XB (F, Cl, Br, I) and HB donors (Cα−Hpyr, Cα− HN‑oxide; Lewis acids), as well as the XB/HB acceptor Npyr or Noxidepyr (Lewis base; Chart 1A).32 Some of these molecules and their derivatives have been used in the formation of halogenbonded supramolecular systems, including nanoparticle assemblies in solution and on surface,12,33 and the study of interfacial XB using force spectroscopy.34 Similar compounds have also been shown to have potential applications in modulating nonlinear optical responses through XB.32a We show that single-atom modifications to the molecular structure will determine the primary interactions directing the packing: HB, XB, or a combination of both. More specifically, changing the electrophilicity of the halogen atom determined the crystal packing of the compounds. As expected, the more electrophilic halogens (I > Br > Cl > F) are more likely to form halogen bonds. However, predicting the behavior of the HB donors relative to the XB donors is not trivial. We found that the pyridine-N-oxide derivatives (2X) are more likely to form hydrogen bonds than the pyridine derivatives (1X). Furthermore, pyridine-N-oxide can simultaneously participate in the formation of both the XB- and HB-based synthons through O−···X and O−···H interactions,13 which can be used to further control the 3D-arrangement of the assemblies. Some of the
ontrol over the nature and directionality of noncovalent interactions is of fundamental importance for designing supramolecular architectures.1 The information encoded in the molecular building blocks will determine the forces involved. Synergy, interplay, and competition between the different forces play important roles in determining the final structure and function of the assembly.2 For example, hydrogen bonding (HB) interactions can be used to disrupt extensive π−π stacking, resulting in morphologies that lead to higher photovoltaic efficiencies.3 Nonetheless, the factors that control the fine balance between the supramolecular interactions are still not fully understood. HB and halogen bonding (XB) are two interactions that have been used to control molecular packing, although the former has been more extensively studied.2,4−6 Both attractive interactions involve a nucleophilic moiety (XB/HB acceptor) and an electrophilic hydrogen atom (HB donor) or an electrophilic halogen atom (XB donor), respectively. This definition emphasizes the analogy between the two interactions.7 Indeed, XB is considered a World Parallel to Hydrogen Bonding.8 In recent years it has been increasingly used in diverse fields, including crystal engineering,9−11 hybrid materials,12 thin films,13 and even drug design.14−16 Nonetheless, predicting structures involving both XB and HB is still very challenging, since the XB acceptor might act as an HB acceptor, thus inducing synthon crossover. Aakeröy and others have studied the competition and balance between the two interactions focusing on multicomponent systems.17 It was shown that complexes where one interaction dominates over the other can be obtained.18−20 Other studies demonstrated how both interactions can work together to determine the structure of the corresponding cocrystals.21−29 However, the hierarchy between XB and HB in unimolecular systems, whereby © 2015 American Chemical Society
Received: August 30, 2015 Published: September 7, 2015 4756
DOI: 10.1021/acs.cgd.5b01260 Cryst. Growth Des. 2015, 15, 4756−4759
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Chart 1. (A) Chemical Structures of the Molecular Building Blocks 1X and 2X (X = F, Cl, Br, I).30,31 (B) Possible XB- or HB-Based Synthons Demonstrating Primary Motifs That Direct the Structure of the Unimolecular Assemblies
Figure 1. The primary motifs expressed in the packing of compounds (A) 1F, (B) 1Cl, (C) 2Cl, and (D) 2Br. The red and blue dashed lines correspond to XB and HB interactions, respectively. Thermal ellipsoids are set at 50% probability.
consists of infinite 1D-linear chains that are aligned in a headto-tail fashion due to attractive XB interactions. Adjacent chains are oriented in opposite directions and stacked on one side with an equivalent aromatic ring and on the other side with a nonequivalent ring. This arrangement results in an alternating sheet-like structure (Figure S2A and B). The distance between the sheets is 3.508 Å, which falls well within the range of π−π interactions. The crystals of 1Br30 and 1I31 have similar structures (Table S1). Introducing the more electron-rich N-oxide moiety into the molecular structure (2X), instead of the Npyr (1X), resulted in different molecular packing (Figure 1C and D, and Figures S1C and D, S2C and D, and S3−4). Interestingly, the crystal structure of 2Cl displays a completely different packing from that of the analogue pyridine derivative 1Cl. A single crystal Xray diffraction study revealed that the solid-state network of 2Cl is based on HB rather than XB interactions (Figures 1C and S2C and D). Homomeric HB-based synthons involving two pyridine-N-oxide moieties are obtained. Most probably, the Cα−HN‑oxide group is activated by the N-oxide electron withdrawing substituent, resulting in a stronger Lewis acidity of the Cα−HN‑oxide proton compared to the Cl, driving the system toward hydrogen-bond formation (Table S1). When the Lewis acidity of X is increased further, the bromine (2Br) and iodine (2I) derivatives display a XB-based motif, through C− X···O− interactions (Figures 1D and S3−S4). However, unlike in the case of 1X, the formation of an XB-based motif does not interfere with the HB-based motif. The crystal structure of 2Br reveals that the N-oxide moiety forms C−H···O− interactions. These results suggest that the N-oxide moiety simultaneously acts as both an XB and a HB acceptor (Figures 1D and S3). Noxides are known for their ability to form bifurcated noncovalent bonds.40,41 This behavior is probably due to the higher electron density resulting from the multiple lone pair electrons around the oxygen atom of the N-oxidepyr moiety compared with that of the Npyr. The different geometric
possible supramolecular motifs expected for these structures are shown in Chart 1B. Crystals suitable for single-crystal X-ray analysis were obtained by crystallization from solution (Supporting Information). The primary supramolecular motifs expressed in the crystal structures of 1X (X = F, Cl, Br, and I) are listed in Table 1. The pyridine and pyridine-N-oxide Table 1. The Primary Interactions Expressed in the Crystal Packing of Compounds 1X and 2X (X = F, Cl, Br, I) X Acceptor
F
Cl
Br
I
1X: Pyridine 2X: Pyridine-N-oxide
HB HB
XB HB
XB30 XB+HB
XB31 XB+HBa
a
The HB interactions in the packing of 2I involve the pyridine-Noxide moieties and water molecules.
moieties play a dual role; Npyr and N-oxide can potentially act as HB acceptors interacting with the Cα−Hpyr or Cα−HN‑oxide acting as HB donors, forming the corresponding Cα−Hpyr···N or Cα−HN‑oxide···O− interactions.35−37 These interactions might interfere with the formation of a halogen-bonded network (Chart 1B). The selected geometrical parameters of the intermolecular interactions in the crystal packing of compounds 1X (X = F, Cl, Br, I), as obtained from single-crystal X-ray analysis, are listed in Table S1. Fluorine is not expected to participate in XB due to the negative electrostatic potential around its surface, making it a poor XB donor.38 Indeed, crystals of compounds 1F consist of homomeric HB-based synthons (Chart 1B, Figures 1A and S1A and B).39 As expected, increasing the Lewis acidity of X (Cl < Br < I) resulted in crystal structures consisting of primarily XB interactions, with Npyr acting as the XB acceptor (Figures 1B and S2A and B). The crystal structure of 1Cl 4757
DOI: 10.1021/acs.cgd.5b01260 Cryst. Growth Des. 2015, 15, 4756−4759
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requirements of the two Lewis bases due to the extra degree of freedom of the N-oxide moiety cannot be ruled out as a factor in determining the molecular packing. The crystal structure of 2F consists of hydrogen-bonded chains (Figures S1C and D and S5, and Table S1). In conclusion, we found that the relative Lewis acid−Lewis base complementarity plays a crucial role in the competitive formation of supramolecular halogen and hydrogen bonding motifs. Our results show that the stronger XB donors (i.e., I and Br) in 2Br and 2I can readily interact with the stronger Lewis base (N-oxide), unlike the weaker XB donor Cl in 2Cl, where HB is preferred. Since halogen bonds have large electrostatic components, the strength of this interaction is also governed by the Lewis acidity−basicity of the XB donor and acceptor, respectively. Whereas Br and I are strong XB donors, Cl is a significantly weaker Lewis acid. The crystallographic data indicates that the interaction of the Cl-derivative with the strong Lewis base N-oxide moiety is overcomed by the more favorable HB, due to the higher Lewis acidity of the Cα− HN‑oxide proton. Using pyridine as the Lewis base results in XB rather than HB interactions (Figure 1B vs C). Understanding those factors that govern the balance between halogen and hydrogen bonds will assist in developing strategies for the formation of supramolecular architectures.
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REFERENCES
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01260. Experimental methods, characterization, and crystallographic data (PDF) Crystallographic data 1F (CIF) Crystallographic data 1Cl (CIF) Crystallographic data 2F (CIF) Crystallographic data 2Cl (CIF) Crystallographic data 2Br (CIF) Crystallographic data 2I (CIF)
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Communication
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Present Address †
Tanya Shirman, School of Engineering and Applied Sciences, Harvard University, 9 Oxford St., Cambridge, MA 02138, USA. Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Tanya Shirman and Meital Boterashvili contributed equally. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research was supported by the Helen and Martin Kimmel Center for Molecular Design, The Schmidt Minerva Center, and the US-Israel Binational Science Foundation (BSF). M.E.vdB. is the incumbent of the Bruce A. Pearlman Professorial Chair in Synthetic Organic Chemistry.
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ABBREVIATIONS HB, hydrogen bonding; XB, halogen bonding 4758
DOI: 10.1021/acs.cgd.5b01260 Cryst. Growth Des. 2015, 15, 4756−4759
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Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Righetto, S.; Terraneo, G.; Tordin, E. Cryst. Growth Des. 2011, 11, 5642−5648. (33) Shirman, T.; Kaminker, R.; Freeman, D.; van der Boom, M. E. ACS Nano 2011, 5, 6553. (34) (a) Boterashvili, M.; Shirman, T.; Cohen, S. R.; Evmenenko, G.; Dutta, P.; Milko, P.; Leitus, G.; Lahav, M.; van der Boom, M. E. Chem. Commun. 2013, 49, 3531. (b) Ebralidze, I. I.; Hanif, M.; Arjumand, R.; Azmi, A. A.; Dixon, D.; Cann, N. M.; Crudden, C. M.; Horton, J. H. J. Phys. Chem. C 2012, 116, 4217. (c) Maruccio, G.; Arima, V.; Cingolani, R.; Liantonio, R.; Pilati, T.; Rinaldi, R.; Metrangolo, P. CrystEngComm 2009, 11, 510. (35) Saha, B. K.; Nangia, A.; Jaskolski, M. CrystEngComm 2005, 7, 355. (36) Yamada, S.; Sako, N.; Okuda, M.; Hozumi, A. CrystEngComm 2013, 15, 199. (37) Reddy, L. S.; Babu, N. J.; Nangia, A. Chem. Commun. 2006, 1369. (38) Clark, T.; Hennemann, M.; Murray, J.; Politzer, P. J. Mol. Model. 2007, 13, 291. (39) Mondal, B.; Captain, B.; Ramamurthy, V. Photochem. Photobiol. Sci. 2011, 10, 891. (40) Koehn, S. K.; Tran, N. L.; Gronert, S.; Wu, W. J. Am. Chem. Soc. 2010, 132, 390. (41) Aakeröy, C. B.; Wijethunga, T. K.; Desper, J. CrystEngComm 2014, 16, 28.
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DOI: 10.1021/acs.cgd.5b01260 Cryst. Growth Des. 2015, 15, 4756−4759
