Subscriber access provided by University of Chicago Library
Article
Edge-to-Edge C-H···N Hydrogen Bonds in TwoComponent Co-crystals Aide a [2+2] Photodimerization Cristian M. Santana, Eric W. Reinheimer, Herman R. Krueger, Leonard R. MacGillivray, and Ryan H. Groeneman Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b00040 • Publication Date (Web): 13 Mar 2017 Downloaded from http://pubs.acs.org on March 19, 2017
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 8
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
Edge-to-Edge C-H···N Hydrogen Bonds in Two-Component Co-crystals Aide a [2+2] Photodimerization Cristian M. Santana,a Eric W. Reinheimer,b Herman R. Krueger Jr.,a and Leonard R. MacGillivray*c and Ryan H. Groeneman*a a
Department of Biological Sciences, Webster University, St. Louis, MO, USA. Rigaku Americas Corporation, The Woodlands, TX, USA. c Department of Chemistry, University of Iowa, Iowa City, Iowa, USA. b
Supporting Information Placeholder C-H···N hydrogen bonds support an intermolecular [2+2] photodimerization in the solid state. The photocycloaddition occurs in a co-crystal of composition (tbrb)·(4,4’-bpe) (where: tbrb = 1,2,4,5-tetrabromobenzene; 4,4’-bpe = trans-1,2-bis(4pyridyl)ethylene) that consists of one-dimensional (1D) chains that self-assemble to form corrugated sheets. Stacking of 4,4’bpe between sheets conforms to the topochemical postulate of Schmidt. The alkene reacts to form rctt-tetrakis(4pyridyl)cyclobutane (4,4’-tpcb) stereoselectively and in quantitative yield. C-H···N hydrogen bonds also support the assembly of the components in (tbrb)·(4,4’-azo) (where: 4,4’-azo = 4,4’-azopyridine) into planar sheets. Density-functional theory calculations reveal identical face-to-face stacks of tbrb to aide in the stabilization of the structures of the co-crystals.
show here that co-crystallization of 1,2,4,5-tetrabromobenzene (tbrb) with 4,4’-bpe affords the two-component co-crystal (tbrb)·(4,4’-bpe) wherein the components form 2D sheets with aromatic rings that interact via edge-to-edge C-H···N hydrogen Face-to-face π-stacks of adjacent layers bonds (Scheme 1). preorganize the C=C bonds of 4,4’-bpe into a geometry to undergo a topochemical [2+2] photocycloaddition according to the postulates of Schmidt.7 Ultraviolet (UV) irradiation of (tbrb)·(4,4’-bpe) results in the formation of rctt-tetrakis(4-pyridyl)cyclobutane (4,4’tpcb) stereoselectively and in quantitative yield. We also demonstrate that C-H···N forces involving the related linear bipyridine 4,4’-azopyridine (4,4’-azo) support planar sheets in the co-crystal (tbrb)·(4,4’-azo). Density-functional theory (DFT) calculations are consistent with the face-to-face π-stackings of tbrb to contribute to the stabilization of the assembly of the components in each solid.
Introduction
- insert Scheme 1 here
There are ongoing interests to employ principles of supramolecular chemistry to conduct [2+2] photodimerizations in the organic solid state.1 The solid-state reaction, when mediated by the strength and directionality of noncovalent forces, can provide means to synthesize molecules in solids (e.g. ladderanes) that are difficult to form in solution. To date, hydrogen bonds2 and coordination bonds3 have supported photodimerizations of carbon-carbon double (C=C) bonds in co-crystals and metal-organic materials, respectively. The hydrogen bonds used to form the co-crystals have been of the traditional, or conventional, type.4 That conventional hydrogen bonds have been a focus is generally predicated on the idea that such forces [e.g. O-H(acid)···N(pyridine)] are sufficiently strong and directional to overcome detrimental effects of crystal packing that make organizing C=C bonds in solids difficult to control. The forces are also regarded strong enough to provide a driving force to support co-crystal formation.5 Here, we wish to report on the use of weak, or non-conventional, hydrogen bonds to support the formation of a co-crystal wherein the bipyridine trans-1,2-bis(4-pyridyl)ethylene (4,4’-bpe) undergoes an intermolecular [2+2] photodimerization in the solid state. C-H···N hydrogen bonds are now recognized as supramolecular synthons able to dictate the assembly and geometry of molecules in solids.4 A common geometry of two interacting aromatic partners of a C-H···N hydrogen bond involves edge-to-edge contacts of N-heterocycles.6 Applications of C-H···N forces to problems of crystal engineering, however, remain admittedly scarce, with a recent example being the generation of two-dimensional (2D) wavy layered topologies.6a We
Scheme 1.
Experimental Section Co-crystal Syntheses and Photochemical Studies. Solvent toluene, tbrb, 4,4’-bpe, and 4,4’-azo were each purchased from Sigma Aldrich Chemical (St. Louis, MO, USA) and used as received. The formation of each co-crystal was achieved utilizing a 20 mL glass scintillation vial. Co-crystals of (tbrb)·(4,4’-bpe) and (tbrb)·(4,4’-azo) were synthesized by dissolving 108 mg of tbrb in 2 mL of toluene. Each resulting solution was then combined with a 2 mL solution of 1.0 mol equiv of either 4,4’-bpe or 4,4’-azo under gentle heating. Within a period of 1 day, colorless single crystals of each sample formed. The solids were filtered, dried, and analyzed using 1H NMR spectroscopy and single-crystal X-ray diffraction. Single crystals of (tbrb)·(4,4’-bpe) were finely ground using a mortar and pestle, and then placed between a pair of Pyrex glass plates. The sample was irradiated using a 450 W medium-pressure mercury lamp in a photochemical safety cabinet. The progress of the photoreaction was monitored using 1H NMR spectroscopy. X-ray Crystallography. Single crystals of (tbrb)·(4,4’-bpe) and (tbrb)·(4,4’-azo) were secured to Mitegen magnetic mounts using Paratone oil. Single-crystal data were collected at 290 K and 100 K with a Bruker APEX II Kappa Diffractometer equipped with an Oxford Cryostream low temperature device using Mo Kα radiation (λ
ACS Paragon Plus Environment
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
= 0.71073 Å). The same crystals were utilized to collect room and low temperature data sets. The room temperature data was collected first then the single crystal was cooled under a stream of liquid nitrogen. Data collection strategies to ensure maximum data redundancy and completeness were calculated using Apex II. Data collection, initial indexing, frame integration, Lorentz-polarization corrections and final cell parameter calculations were carried out with Apex II. Multi-scan absorption corrections were performed using SADABS. All structures were solved via direct methods using ShelXT and refined using ShelXL in the Olex2 graphical user interface. The space groups were unambiguously verified by PLATON. Final structural refinements included anisotropic temperature factors on all non-hydrogen atoms. All hydrogen atoms were attached via the riding model at calculated positions using HFIX commands. Major and minor occupancies for the disordered C=C core of 4,4’-bpe converged to respective ratios. Crystallographic data for (tbrb)·(4,4’-bpe) and (tbrb)·(4,4’-azo) are summarized (Table 1).
Page 2 of 8
Rebek’s imide
N-H(imide), COO-H(acid)
4,6-di-Cl-res
O-H(phenol)
thiourea
N-H(thiourea)
5-CN-res
O-H(phenol)
cyclobutane tetraacid
COO-H(acid)
urea
N-H(urea)
semicarbazole
N-H(carbazole)
tbrb
C-H(benzene)
8d 8e 8f 8g 8h 8i 8j this work
- insert Table 1 here DFT Calculations. Interaction energies were estimated using the GAMESS package. All calculations were performed with the M062X functional and an aug-cc-pVTZ basis set. Positions of all atoms except hydrogen were obtained from the X-ray diffraction data. Positions of hydrogen atoms were determined via structure optimizations. The model system consisted of two tbrb molecules. Interaction energies were computed as the difference between the energy of a pair of tbrb molecules and that of separated components. Corrections were made for basis set superpositon error (BSSE) without incorporating fragment relaxation. The geometry for a tbrbpyridine pair was obtained by replacing a tbrb from the diffraction data with pyridine. Positions of the pyridine atoms were then optimized using a molecular mechanics routine with a MMFF94 force field within Avogadro. The interaction energy between the tbrb-pyridine pair was calculated employing the electronic structure method described for the tbrb-tbrb pair.
Results and Discussion There have been a number of recent reports on the use of smallmolecule templates with two or more convergent binding sites that assemble and preorganize 4,4’-bpe in the solid state for an intermolecular [2+2] photodimerization (Table 2).8 The templates have been developed to operate via conventional hydrogen bonds, typically organizing the alkene into discrete molecular assemblies to react. Photocycloadditions of 4,4’-bpe within the solids have generated 4,4’-tpcb in up to quantitative yield. As a pure form, 4,4’bpe is photostable, crystallizing with nearest-neighbor C=C bonds separated on the order of 6.5 Å.9 While templates with multiple convergent sites have been successful assembling 4,4’-bpe to react, it is also clear that monotopic and/or co-crystal formers with divergent sites can be used to generate photoreactive solids.10 In this study, our use of tbrb to support a [2+2] photodimerization of 4,4’bpe principally falls in the latter category. The interaction between the co-former and alkene, however, is the weakest among those of reported co-crystals to facilitate a photocycloaddition of 4,4’-bpe in a solid (Table 2).
Co-crystals of (tbrb)·(4,4’-bpe) and (tbrb)·(4,4’-azo) were each prepared by mixing toluene solutions of tbrb and either 4,4’-bpe or 4,4’-azo (1:1 ratio) with gentle heating and allowing the resulting solutions to slowly cool and stand for a period of ca. 1 day. The formulation of each co-crystal was confirmed using single-crystal Xray diffraction and 1H NMR spectroscopy. Single-crystal X-ray diffraction analysis reveals the components of (tbrb)·(4,4’-bpe) to crystallize in the triclinic space group P-1 (Fig. 1). The asymmetric unit is composed of two unique tbrb and 4,4’bpe molecules. The C=C bond of one bipyridine lies disordered over two positions (occupancies: 0.87 and 0.13). A low temperature (100 K) single-crystal X-ray dataset when compared to the room temperature (290 K) structure shows the disorder of the C=C bonds to be dynamic (occupancies: 0.94 and 0.06), which is consistent with the C=C bonds undergoing pedal-like rotation in the solid.11 The components of (tbrb)·(4,4’-bpe) assemble by edge-to-edge CH···N hydrogen bonds (Fig. 1, Table 3). The C-H···N forces are defined by aromatic rings that lie relatively close to co-planarity (5.0o and 18.1o), with the largest twist angle being associated with the disordered alkene. As a consequence of the assembly process, the components form 1D chains that run parallel to the crystallographic c-axis (Fig. 1a). Adjacent chains interact via Type I Br···Br forces12 (|θ1-θ2| ~ 14°) (Fig. 1b) such that the chains form a corrugated 2D sheet (cant angle 30.9˚) (Fig. 1c) (Table 3). The sheets stack slightly offset along the crystallographic a-axis with identical molecules of tbrb and 4,4’-bpe participating in face-to-face π-stacks (Fig. 1d). The stacks consist of tbrb in a parallel and slipped orientation (centroid-to-centroid: 3.49 and 3.47 Å), with the stacking of both co-crystal components being propagated infinitely. The stacking of 4,4’-bpe places the C=C bonds in a position suitable for an intermolecular [2+2] photocycloaddition reaction (centroid-tocentroid: 4.02 Å).
Table 2. Hydrogen-bond donors involving N(pyridine) to support [2+2] photodimerizations of 4,4’-bpe in co-crystals. Co-crystal former
Hydrogen-bond donor
resorcinol (res)
O-H(phenol)
1,8-naphthalenedicarboxylic acid
COO-H(acid)
tricarballylic acid
COO-H(acid)
Ref 8a 8b 8c
ACS Paragon Plus Environment
Page 3 of 8
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 interactions that involve the central N=N unit (Fig. 2b).10,12 Type I Br···Br contacts (|θ1-θ2| 0°) also support the assembly of the chains into coplanar sheets (Fig. 2c). Similar to (tbrb)·(4,4’-bpe), identical tbrb molecules form infinite face-to-face π-stacks along the crystallographic a-axis (centroid-to-centroid distances: 3.52 Å) (Fig. 2d). That tbrb and 4,4’-azo assemble form 1D chains that assemble to form sheets attests to robustness of the C-H···N hydrogen bond.4
Figure 1. X-ray structure (tbrb)·(4,4’-bpe): (a) 1D chain with edgeto-edge C-H···N hydrogen bonds, (b) parallel chains showing Br···Br forces, (c) side view of corrugated sheets, and (d) face-toface π-stacks of tbrb and 4,4’-bpe. Table 3. Hydrogen- and halogen-bond metrics of (tbrb)·(4,4’-bpe) and (tbrb)·(4,4’-azo). Co-crystal
C···N (Å)
C-H-N (°)
Br···Br (Å)
(tbrb)·(4,4’-bpe)
3.327(6) 3.337(6)
165.6(3) 167.3(3)
3.813(1)
(tbrb)·(4,4’-azo)
3.349(3)
176.0(2)
3.553(1)
When (tbrb)·(4,4’-bpe) was exposed to UV-irradiation (medium power Hg lamp) for a period of ca. 30 hours, 4,4’-bpe reacted to generate 4,4’-tpcb stereoselectively and in quantitative yield (Scheme 2). The progress of the photoreaction was monitored in six hour intervals (Table 4). The formation of 4,4’-tpcb was evidenced by the disappearance of the C=C bond proton (7.55 ppm) and emergence of the cyclobutane proton (4.67 ppm) in the 1H NMR spectrum. That 4,4’-tpcb formed quantitatively despite 4,4’-bpe forming infinite stacks may be a result of cooperative movements of the disordered C=C bonds during the course of the photoreaction.13 We note that an examination of powder X-ray diffraction diffractograms before and after the photocycloaddition is also consistent with the solid also undergoing a change in phase following the photoreaction. - insert Scheme 2 here Table 4. Progress of [2+2] photodimerization of (tbrb)·(4,4’-bpe) as measured by 1H NMR spectroscopy.
Time (h)
Percent Yield
6
66
12
86
18
92
24
96
30
100
Figure 2. X-ray structure (tbrb)·(4,4’-azo): (a) edge-to-edge CH···N hydrogen bonds, (b) Br···Br and Br···N forces, (c) side view of sheets, and (d) face-to-face π-stacks of tbrb and 4,4’-azo. DFT calculations were performed to gain insight into the energies of the face-to-face π-stacks adopted by tbrb in each co-crystal. The stacking interactions were, thus, calculated between neighboring tbrb molecules by comparing interaction energies of a stacked pair obtained directly from our X-ray data (290 K) and two isolated molecules. Interaction energies of -6.99 and -7.09 kcal/mole were determined in the case of (tbrb)·(4,4’-bpe) and (tbrb)·(4,4’-azo), respectively. We note that similar face-to-face stacks are present in pure tbrb.14 The calculated energies were greater than that of a calculated tbrb-pyridine pair (-3.89 kcal/mole), as also derived from the X-ray data.
Conclusion In this report, we have described a photoactive co-crystal generated using nonconventional hydrogen bonds in the form of CH···N forces. Face-to-face π-stacks of tbrb and 4,4’-bpe have enabled the C=C bonds to be stacked in a geometry suitable for a [2+2] photodimerization that occurs stereoselectively and quantitatively. We are currently studying the scope of generating photoactive co-crystals involving tbrb and other bis(pyridyl)ethylenes, as well as related stilbazoles, in efforts to understand and further study the robustness of the C-H···N hydrogen bond to influence packing and afford to photoreactive materials.
The ability of C-H···N hydrogen bonds to support a co-crystal of tbrb with an additional bipyridine was realized in the case of 4,4’azo (Fig. 2). As with (tbrb)·(4,4’-bpe), the components of (tbrb)·(4,4’-azo) crystallize in the triclinic space group P-1 (Fig. 2, Table 3). In contrast to (tbrb)·(4,4’-bpe), however, the asymmetric unit contains only one half of each of a molecule of tbrb and 4,4’azo, with the central azo core being ordered. The components form 1D chains with a twist angle (29.6˚) larger than (tbrb)·(4,4’-bpe) (Fig 2a). The larger twist angles may be a result of Type II Br···N
Supporting Information Electronic supplementary information (ESI) available: 1H NMR spectra and powder X-ray diffractogram. CCDC 1413332-1413335. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c000000x/.
ACS Paragon Plus Environment
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
AUTHOR INFORMATION Corresponding Author E-mail:
[email protected]; Tel: +1 319-335-3504.
(7) (8)
[email protected]; Tel: +1 314-246-7466.
Funding Sources No competing financial interests have been declared.
ACKNOWLEDGMENT L.R.M. gratefully acknowledges the National Science Foundation (DMR-1408834) for funding. R.H.G. gratefully acknowledges financial support from Webster University from both a Faculty Research Grant and Faculty Development Fund.
REFERENCES (1)
(2)
(3)
(4) (5) (6)
(a) Ramamurthy, V.; Sivaguru, J. Chem. Rev. 2016, 116, 9914. (b) Biradha, K.; Santra, R. Chem. Soc. Rev., 2013, 42, 950;.(c) MacGillivray, L.R.; Papaefstathiou, G.S.; Friščić, T.; Hamilton, T.D.; Bučar, D.-K.; Chu, Q.; Varshney, D.B.; Georgiev, I.G. Acc. Chem. Res., 2008, 41, 280. (d) Georgiev, I.G.; MacGillivray, L.R. Chem. Soc. Rev., 2007, 36, 1239. (a) MacGillivray, L.R. J. Org. Chem., 2008, 73, 3311. (b) Hutchins, K.M.; Sumrak, J.C.; MacGillivray, L.R. Org. Lett., 2014, 16, 1052. (c) Elacqua, E.; Kaushik, K.; Groeneman, R.H.; Sumrak, J.C.; Bučar, D.-K.; MacGillivray, L.R. Angew. Chem. Int. Ed., 2012, 51, 1037. (a) Kole, G.K; Vittal J.J. Chem. Soc. Rev., 2013, 42, 1755. (b) Kole, G.K.; Tan, G.K.; Vittal, J.J. Cryst. Growth Des., 2012, 12, 326. (c) Santra, R.; Biradha, K. Cryst. Growth Des., 2010, 10, 3315. (d) Toh, N.L.; Nagarathinam, M.; Vittal, J.J. Angew. Chem. Int. Ed., 2005, 44, 2237. (e) Elacqua, E.; Sinnwell, M.A.; Loren, B.P.; Jurgens, P.T.; Groeneman, R.H.; Reinheimer, E.W.; MacGillivray, L.R. ChemPlusChem 2016, 81, 893. Desiraju, G.R. Chem. Commun. 2005, 2995. Adachi, T.; Ward, M.D. Acc. Chem. Res. 2016, 49, 2669. (a) Shivakumar, K.; Vidyasagar,A.; Naidu, A.; Gonnadec, R.G.; Sureshan, K.M. CrystEngComm, 2012, 14, 519. (b) Bosch, E.; Bowling, N.P.; Darko, J. Cryst. Growth Des., 2015, 15, 1634.
(9) (10) (11) (12) (13) (14)
Page 4 of 8
(c) Kimball, D.; Starnes, J.; Groeneman, R.H.; Krueger, H.R.; Reinheimer, E.W. Supramol. Chem., 2015, 27, 465. Schmidt, G.M.J. Pure Appl. Chem., 1971, 27, 647-678. (a) MacGillivray, L.R.; Reid, J.L.; Ripmeester, J.A. J. Am. Chem. Soc., 2000, 122, 7817. (b) Papaefstathiou, G.S.; Kipp, A.J.; MacGillivray, L.R. Chem. Commun., 2001, 2462. (c) Shan, N.; Jones, W. Tetrahedron Lett., 2003, 44, 3687. (d) Varshney, D.B.; Gao, X.; Friščić T.; MacGillivray, L.R. Angew. Chem. Int. Ed., 2006, 45, 646; (e) Atkinson, M.B.J.; Bučar, D.-K.; Sokolov, A.N.; Friščić, T.; Robinson, C.N.; Bilal, M.Y.; Sinada, N.G.; Chevannes, A.; MacGillivray, L.R. Chem. Commun., 2008, 5713; (f) Bhogala, B.R.; Captain, B.; Partasarathy, A.; Ramamurthy, V. J. Am. Chem. Soc., 2010, 132, 13434; (g) Karunatilaka, C.; Bučar, D.-K.; Ditzler, L.R.; Friščić, T.; Swenson, D.C.; MacGillivray, L.R.; Tivanski, A.V. Angew. Chem. Int. Ed., 2011, 50, 8642; (h) Bhattacharya, S.; Stojaković, J.; Saha, B.K.; MacGillivray, L.R. Org. Lett., 2013, 15, 2013; (i) Bhogala, B.R.; Captain, B.; Ramamurthy, V. Photochem. Photobiol., 2015, 91, 696; (j) Stojakovic, J.; Whitis, A.M.; MacGillivray, L.R., Angew. Chem., Int. Ed. 2013, 52, 12127. Vansant, J.; Toppet, S.; Smets, G.; Declercq, J.P.; Germain, G.; Van Meerssche, M. J. Org. Chem.1980, 45, 1565. Hutchins, K.M.; Sumrak, J.C.; Swenson, D.C.; MacGillivray, L.R. CrystEngComm. 2014, 16, 5762. Harada, J.; Ogawa, K. Chem. Soc. Rev., 2009, 38, 2244. Mukherjee, A.; Tothadi, S.; Desiraju, G.R. Acc. Chem. Res., 2014, 47, 2514. Wenick, D.K.; Schochet, S. J. Phys. Chem. 1988, 92, 6773. (a) Gafner, G.; Herbstein, F.H. Acta Crystallogr., 1960, 13, 706. (b) Mrse, A.A.; Lee, P.; Bryant, P.L.; Fronczek, F.R.; Butler, L.G.; Simeral, L.S. Chem. Mater., 1998, 10, 1291.
ACS Paragon Plus Environment
Page 5 of 8
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
Scheme 1
ACS Paragon Plus Environment
5
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
Br
Page 6 of 8
Br
H
H Br
N
N
Br
Br
H
Br
H
H Br
Br
H
Br Br
Br
N
N
Br
Br
Br
Br
H
Br
H
hv solid state
N
N
N
N 100% yield
Scheme 2
ACS Paragon Plus Environment
6
Page 7 of 8
Crystal Growth & Design
Table 1. Crystallographic data for (tbrb)·(4,4’-bpe) and (tbrb)·(4,4’-azo) (100 and 290 K).
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
Compound
(tbrb)·(4,4’-bpe)
(tbrb)·(4,4’-bpe)
(tbrb)·(4,4’-azo)
(tbrb)·(4,4’-azo)
CCDC code
1413332
1413333
1413334
1413335
Formula
C18H12Br4N2
C18H12Br4N2
C16H10Br4N4
C16H10Br4N4
Formula weight
575.94
575.94
577.92
577.92
Temp.
100(2)
290(2)
100(2)
290(2)
Space group
P-1
P-1
P-1
P-1
a, Å
3.93570(10)
4.0191(2)
3.8608(4)
3.9319(5)
b, Å
13.4625(3)
13.5460(6)
9.6506(11)
9.6874(12)
c, Å
17.2236(4)
17.3723(8)
12.2022(14)
12.2125(13)
α, deg
102.783(2)
102.782(3)
75.744(2)
76.396(6)
β, deg
92.360(2)
93.568(3)
86.061(2)
86.097(6)
94.3690(10)
94.343(3)
80.648(2)
80.478(6)
volume, Å
885.80(4)
916.67(8)
434.59(8)
445.69(9)
Z
2
2
1
1
Density (calculated), g/cm3
2.159
2.087
2.208
2.153
µ, mm-1
9.089
8.783
9.266
9.035
Scan
ω and φ scans
ω and φ scans
ω and φ scans
ω and φ scans
θ range for data collection, deg
1.214-31.552
1.206-27.084
1.723-31.026
1.716-30.748
Reflections measured
17424
13824
8388
9373
Independent observed reflns.
5876
3976
2723
2684
Independent reflns. [I>2σ]
3903
2353
2433
2070
Data/restraints/parameters
5876/8/227
3976/7/227
2723/0/129
2684/0/129
Rint
0.0320
0.0366
0.0199
0.0220
Final R Indices [I>2σ]
R1 = 0.0273
R1 = 0.0371
R1 = 0.0177
R1 = 0.0253
wR2 = 0.0551
wR2 = 0.0657
wR2 = 0.0425
wR2 = 0.0517
R1 = 0.0430
R1 = 0.0760
R1 = 0.0217
R1 = 0.0418
wR2 = 0.0606
wR2 = 0.0781
wR2 = 0.0440
wR2 = 0.0566
1.007
1.009
1.026
1.028
γ, deg 3
R Indices (all data)
Goodness-of-fit on F2
ACS Paragon Plus Environment
7
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 8 of 8
Edge-to-Edge C-H···N Hydrogen Bonds in Two-Component Co-crystals Aide a [2+2] Photodimerization
solid state hv
The robustness of the C-H···N hydrogen bond is exploited to support a [2+2] photodimerization in a cocrystal.
ACS Paragon Plus Environment
8
