Subscriber access provided by CMU Libraries - http://library.cmich.edu
Communication
Finding the Perfect Match: Halogen vs. Hydrogen Bonding Tanya Shirman, Meital Boterashvili, Meital Orbach, Dalia Freeman, Linda Shimon, Michal Lahav, and Milko E. van der Boom Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b01260 • Publication Date (Web): 07 Sep 2015 Downloaded from http://pubs.acs.org on September 18, 2015
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Crystal Growth & Design is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 12
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Crystal Growth & Design
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, The Weizmann Institute of Science, 234 Herzl St., Rehovot
7610001, Israel. §
Department of Chemical Research Support, The Weizmann Institute of Science, 234 Herzl St.,
Rehovot 7610001, Israel.
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.
Control over the nature and directionality of non-covalent 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
ACS Paragon Plus Environment
1
Crystal Growth & Design
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 12
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 a HB acceptor, thus inducing synthon crossover. Aakeröy and others have studied the competition and balance between the two interactions focusing on multi-component 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 co-crystals.21-29 However, the hierarchy between XB and HB in unimolecular systems whereby, competing XB/HB donor and XB/HB acceptor sites are combined in one molecular entity, has been much less explored.13,21 Nucleophilic moieties simultaneously involved in both XB and HB are rare.13 Chart 1. (A) Chemical structures of the molecular building blocks 1X and 2X (X = F, Cl, Br).30,31 (B) Possible XB- or HB-based synthons demonstrating primary motifs that direct the structure of the unimolecular assemblies.
ACS Paragon Plus Environment
2
Page 3 of 12
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Crystal Growth & Design
A
1X
2X
X = F, Cl, Br, I
B
HB > XB
HB < XB
HB ≈ XB
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 N-oxidepyr (Lewis base; Chart 1A).32 Some of these molecules and their derivatives have been used in the formation of halogen-bonded supramolecular systems, including nanoparticle assemblies in solution and on surface,12,33 and the study of interfacial XB in solution using force spectroscopy.34 Similar compounds have also been shown to have potential applications in modulating non-linear optical response 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
ACS Paragon Plus Environment
3
Crystal Growth & Design
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 12
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 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-Noxide 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). Table 1. The primary interactions expressed in the crystal packing of compounds 1X and 2X (X = F, Cl, Br, I). X:
F
Cl
Br
I
1X: Pyridine
HB
XB
XB30
XB31
2X: Pyridine-N-Oxide
HB
HB
XB+HB
XB+HB*
Acceptor:
*The HB interactions in the packing of 2I involve the pyridine-N-oxide moieties and water molecules. 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
ACS Paragon Plus Environment
4
Page 5 of 12
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Crystal Growth & Design
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
