Cocrystallization of a Tripyridyl Donor with Perfluorinated Iodobenzene Derivatives: Formation of Different N · · · I Halogen Bonds Determining Network vs Plain Packing Crystals Maida Vartanian,† André C. B. Lucassen,† Linda J. W. Shimon,‡ and Milko E. van der Boom*,†
CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 3 786–790
Departments of Organic Chemistry and Chemical Research Support, The Weizmann Institute of Science, 76100 RehoVot, Israel ReceiVed October 25, 2007; ReVised Manuscript ReceiVed January 2, 2008
ABSTRACT: Two cocrystals (4, 5) have been obtained with 1,3,5-tris[4-pyridyl(ethenyl)]benzene (1), sym-triiodo-trifluorobenzene (2), and diiodo-tetrafluorobenzene (3), respectively. Cocrystal 4 contains both compounds 1 and 2 in a molecular ratio of 1:2, whereas cocrystal 5 contains both compounds 1 and 3 in a molecular ratio of 1:0.5 and the solvent used for crystallization, namely, chloroform. Both cocrystals (4, 5) contain N · · · I halogen bonds with distances of ∼80% of the sum of the van der Waals radii. Compound 1 forms four halogen bonding interactions in cocrystal 4, resulting in an infinite halogen-bonded network with two types of N · · · I halogen bonds, whereas in cocrystal 5, compound 1 forms only one type of halogen bonding interaction with compound 3. Crystal engineering involves the design of supramolecular structures and the appraisal of their weak interactions in the solid state,1 including hydrogen bonding,2 π-π stacking,3 and metal coordination.2 One of the most common features in these intermolecular interactions is the transfer of charge density. Halogen bonding is an intriguing acceptor–donor interaction, in which relatively electron-poor halogen atoms (X ) Cl, Br, I) interact with the lone-pair electrons of heteroatoms (D ) S, N, O) or other halogen atoms.4,5 This Lewis acid/base interaction results in intermolecular X · · · D distances, which are ∼80% of the sum of the van der Waals radii. Electron-deficient halogen atoms are good acceptors and form relatively strong intermolecular halogen-bonding interactions. The preeminent way of achieving electron-poor halogens is by introducing electron-withdrawing fluorinated hydrocarbons to generate a so-called “sigma hole”.6,7 Strong intermolecular interactions result in relatively short interatomic D · · · X distances and an enhanced linear alignment of the D · · · X-C unit. The halogen-bonding interaction is often linear, which is attributed to delocalization of the free electron pair of D, which contributes electron density to an antibonding orbital of a C–X moiety (i.e., n f σ* interaction). There is much current interest in halogen bonding, and its potential is being explored in crystal engineering,8–10 nonlinear optics,11 templated synthesis,8 layer-by-layer growth of polymer-basedassemblies,12 solid-statechemistry,13 liquidcrystals,14–16 and biological systems.17,18 Several computational studies have been reported as well.19 Cocrystals often consist of two separate halogen donor and acceptor molecules, resulting in infinite linear networks: · · · A-A · · · D-D · · · A-A · · · D-D · · · , etc.20 Compounds that combine halogen-bonding donor and acceptor sides are relatively rare.21,22 An interesting challenge is to assemble highly complex XB-based structures and geometries using donor and acceptor molecules capable of multiple halogen-bonding interactions.23 Here we present two cocrystals (4, 5) that include 1,3,5-tris[4-pyridyl(ethenyl)]benzene (1)24 and perfluorinated iodobenzene derivatives: sym-triiodo-trifluorobenzene (2)25 and diiodo-tetrafluorobenzene (3).4 Compound 3 is known to form infinite halogen-bonded networks with halogen donor systems.25 Compounds 1 and 2 form a complex multiple halogen-bonded network in the solid state (cocrystal 4), including two different types of halogen-bonding interactions. In contrast, compounds 1 and 3 do not form a halogenbonded network, although there is a close N · · · I interaction * Corresponding author. E-mail:
[email protected]. Fax: +972-8-934-4142. † Department of Organic Chemistry. ‡ Department of Chemical Research Support.
Scheme 1. Cocrystallization of Compound 1 with Sym-triiodo-trifluorobenzene (2) and Diiodo-tetrafluorobenzenze (3) from Chloroform at Room Temperature
(cocrystal 5). Apparently, the acceptor systems (2-3) have a dominant role in determining the packing and the number of N · · · I interactions. Results and Discussion. Compounds 1-3 were obtained according to literature procedures24,25 and were identified by a combination of 1H, 19F{1H}, 13C{1H} NMR, and mass spectroscopy. There have been only a few solution-based studies on halogen bonding.26,27 NMR and UV/vis spectroscopy studies were performed with compounds 1-3; however, no evidence for halogenbond interactions in solution was observed. In particular, 1H and 19 F{1H} NMR measurements of a mixture of compounds 1 (15.5 mM) and 2 (31 mM) in benzene-d6 did not reveal any shifts, in comparison to the spectra of pure 1 and 2. In addition, UV/vis spectra of solutions containing both compounds 1 and 2 (0.25 mM) are nearly identical to the solution spectra of the individual compounds. The results obtained from the cocrystallizations of compounds 1 with the fluorinated halobenzenes (2, 3) are summarized in Scheme 1 and Tables 1 and 2. Cocrystal 4. Yellow cocrystals (4) of compounds 1 and 2 in a 1:2 ratio were obtained by slow evaporation of a CHCl3 solution containing these compounds in a 1:1 molar ratio at room temperature. The stoichiometry of the compounds (1, 2) in the cocrystal is different from that of the solution. However, this is not uncommon.25 Single crystal X-ray diffraction analysis revealed the formation of a halogen-bonded network (4), with both compounds (1, 2) involved in π-π stacking interactions (Figure 1). One pyridyl arm of compound 1 is involved in π-π stacking interactions with
10.1021/cg701053d CCC: $40.75 2008 American Chemical Society Published on Web 02/08/2008
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Crystal Growth & Design, Vol. 8, No. 3, 2008 787 Table 1. Selected Angles and Intermolecular Distances for Cocrystals 4 and 5
compd 1, 2
1:1
1, 3, CHCl3 a
molar ratio
1:1.5:excess
observed molar ratio
N · · · H dist (Å)
4 (1:2) a
5 (1:0.5:1)
2.160
N · · · I dist (Å)
C-I · · · N angles (deg)
π-π stacking dist (Å)
3.224 2.812 2.824
158.87 176.59 176.48
3.793
Distance between H31 of the chloroform and N2 of the pyridyl arm of compound 1 in cocrystal 5. Table 2. Crystallographic Data for Cocrystals 4 and 5
empirical formula fw (g mol-1) cryst color cryst dimensions (mm3) cryst syst space group a (Å) b (Å) c (Å) β (deg) Z V (Å3) Fcalcd (mg m-3) no. of unique data R1 wR2
cocrystal 4
cocrystal 5
C39H21N3F6I6 1406.99 yellow 0.4 × 0.4 × 0.2 monoclinic C2/c 8.8860(2) 15.9228(4) 29.1087(7) 90.323(1) 4 4118.6(2) 2.269 4813 0.0433 0.0512
C31H22N3F2Cl3I 707.77 colorless 0.3 × 0.3 × 0.21 monoclinic P21/c 18.7990(3) 5.7056(1) 27.4972(4) 99.1894(8) 4 2911.49 1.615 7346 0.0682 0.0806
compound 2 (Figure 2B). The two aromatic systems of compounds 1 and 2 are almost parallel, with a tilt angle of 13.49° and have an offset of ∼1.5 Å. The intermolecular distance between the centroids of the aromatic systems is 3.793 Å. Cocrystal 4 incorporates halogen bonding between the nitrogen atoms of the pyridyl moieties of compound 1 and the iodide atoms of compound 2 (Figure 3). Interestingly, there are two types of halogen-bonding interactions (Figure 3B). Two out of three N atoms in compound 1 have a relatively strong, single N · · · I interaction with two molecules of 2. The third N atom of compound 1 forms two N · · · I halogen bonds with two molecules of 2 (Figure 3A). The latter interaction is most probably weaker. The single N · · · I halogen-bonding interactions have a short intermolecular N · · · I distance of 2.812 Å, which is ∼80% of the sum of the van der Waals radii (3.53 Å). This distance is in good agreement with literature values.19 The N · · · I–C angle of 176.59° is in agreement with an n f σ* interaction. The other halogen-bonding interactions have an N · · · I intermolecular distance of 3.244 Å (∼90% of the van der Waals radii) between one of the pyridine units and two molecules of compound 2 (Figure 3A). The N · · · I–C angle, 158.87°, suggests that the electron density transfer is reduced in comparison to the linear geometry of the other N · · · I–C interactions. This nonlinearity enables the N atom to interact with two molecules of compound 2. Both compounds (1, 2) are involved with two different halogen-bonding interactions. The third Arf–I moiety of compound 2 is not involved with X · · · D and X · · · X interactions. Packing interactions always play an important structural role. Three linear 1:1 halogen-bonding interactions may lead to a less densely packed structure. The number of halogen bonds that can be formed with a single acceptor and donor system might be limited for electronic factors as well. Since two N atoms transfer their electron density to compound 2, the third N atom might have a somewhat lower electron density, resulting in a different type of halogen bonding. Molecules of 1 are aligned in parallel, whereas compound 2 consists of two types of planes in a “zigzag” orientation with a 41.7° angle between these planes (Figure 1). The structure (4) is discretely disordered, that is, the directionality of the positions of compound 1 varies from plane to plane. Cocrystal 5. Cocrystallization of compounds 1 and 3 in CHCl3 in a ratio of 1:1.5, respectively, resulted in the colorless cocrystal 5. Single X-ray crystal diffraction revealed the formation of both a halogen and hydrogen-bonded cocrystal of compound 1, 3 and CHCl3 in a ratio of 1:0.5:1, respectively (Figure 4). There is hydrogen bonding between CHCl3 and compound 1,29–32 as well as halogen-bonding interactions between compounds 1 and 3. In
Figure 1. Crystal lattice of cocrystal 4; compounds 1 (blue) and 2 (green) are colored according to the symmetry of equivalences. All molecules of 1 (blue) are parallel to one another, whereas compound 2 is aligned in two different planes that are oriented at 41.7° with respect to each another.
sharp contrast to system 4, only one pyridyl arm of compound 1 is involved here in halogen bonding with the acceptor (3). Both iodide atoms of compound 3 form similar halogen bonds with compound 1 (Figure 5). The intermolecular I · · · N distance is 2.824 Å (∼80% of the sum of the van der Waals radii) and the angle C-I · · · N is 176.48°. Another pyridyl arm of compound 1 is nearby an embedded CHCl3 molecule (Figure 6). The N · · · H distance between H31 and N2 is 2.160 Å, which is ∼78% of the sum of the van der Waals radii. The angle Cl3C-H · · · N is 164.81 °. The three pyridyl moieties of compound 1 are not in the same plane and have a certain digression with respect to one another (Figure 5). Most likely, this “bent” shape allows compound 1 to have a maximum number of intermolecular interactions and dense packing (Figures 4 and 5). Summary and Conclusions. Two cocrystals (4, 5) were obtained with compound 1 and the fluorinated halobenzene derivatives (1, 2). The packing arrangement and intermolecular interactions are distinctly different. The combination of compounds 1 and 2 resulted in an infinite supramolecular network consisting of two different types of N · · · I halogen bonding (cocrystal 4). Each molecule of compound 1 (having three pyridyl moieties available for halogen bonding) interacts with four molecules of 2. Two halogen-bonding interactions are relatively strong (∼80% of the sum of the N · · · I van der Waals radii) and involve two distinct N atoms and two distinct Arf–I moieties. Two halogen-bonding interactions are relatively weak (∼90% of the sum of the N · · · I van der Waals radii) and involve one only N atom. Thus, the network consists of four halogen-bonding interactions with a single Lewis base. We recently reported that cocrystallization of compound 2 with three different bipyridyl derivatives consequently yields cocrystals with only two halogen bonds.25 An identical situation is observed here with compounds 1 and 2: one out of three Arf–I moieties of compound 2 is not involved in X · · · D and X · · · X interactions. Apparently, this arrangement is preferable over a three-point halogen-bond interaction. Such motifs have been observed with hydrogen-bonded systems.33 Crystallization of compounds 1 and 3 in an equimolar donor–acceptor ratio resulted in cocrystal 5. It is remarkable that only one out of three pyridyl arms of compound 1 is involved in halogen bonding with compound 3. The latter compound is known to form infinite halogen-bonded networks with various Lewis bases;4 however, the molecular structure of compound 1 and the drive to form a densely packed structure probably prohibits it. This cocrystal also contains CHCl3, which fills up the voids and contributes much to the formation of a densely packed
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Figure 2. (A) Three possible π-π stacking interactions:28 I. Edge to face (d ∼ 5 Å), II. Offset/parallel displaced (d ∼ 3.4–3.6 Å), and III. Face to face (d ∼ 3.3–3.8 Å). (B) Mercury presentation. Cocrystal 4 contains an offset π-π stacking interaction (type II). R is ∼1.5 Å and the intermolecular distance between the pyridyl moiety of compound 1 and the aromatic system of compound 2 is 3.793 Å. Colors: carbon, gray; nitrogen, blue; fluorine, light green; iodine, magenta; hydrogen atoms are excluded for clarity.
Figure 3. (A) Mercury view of cocrystal 4 with two linear N · · · I interactions of 2.812 Å and two weaker interactions with one of the nitrogen atoms of compound 1. (B) Mercury view of cocrystal 4. Each molecule of 2 has one weak (3.224 Å) and one strong (2.812 Å) interaction with the N atoms of compound 1. The third iodide of 2 does not participate in halogen bonding or halogen-halogen interactions. Colors: carbon, gray; nitrogen, blue; fluorine, light green; iodine, magenta; hydrogen atoms are excluded for clarity.
Experimental Procedures. General Procedures. Reaction flasks were washed with deionized water (DI), followed by acetone, and then oven-dried prior to use. Deuterated solvents (99% D atom) and chemicals were purchased from Sigma-Aldrich and Holland Moran Ltd. 1,3,5-Tris[4-pyridyl(ethenyl)]benzene (1) and symtriiodo-trifluorobenzene (2) were prepared according to literature procedures24,25 and identified by NMR and mass spectroscopy. Crystals (white needles) of compound 2 were obtained by recrystallization from hexane. Analysis. The 1H and 19F{1H} NMR spectra were recorded at
Figure 4. Crystal lattice of cocrystal 5 through axis b; diiodotetrafluorobenzenze (3) (green), 1 (blue) and CHCl3 (red) colored according to symmetry of equivalence. Hydrogen atoms are not presented.
structure (Figure 4). While in cocrystal 4, the system maximized the number of N · · · I interactions, cocrystal 5 contained only one such interaction.
250 MHz on a Bruker Avance DPX 250 NMR spectrometer. The 13 C{1H} NMR spectra were recorded at 161.9 MHz on a Bruker Avance 400 NMR spectrometer. All chemical shifts (δ) are reported in ppm and coupling constants (J) are in Hz. All NMR measurements were carried out at 298 K. Mass spectrometry analysis was performed by the Chemical Support Unit of the Weizmann Institute of Science.
Formation and X-ray Analysis of Cocrystal 4. A CHCl3 solution (9 mL) containing compounds 1 (60 mg, 0.15 mmol) and 2 (78 mg, 0.15 mmol) was allowed to evaporate slowly at room temperature for two weeks, resulting in X-ray quality
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Crystal Growth & Design, Vol. 8, No. 3, 2008 789 99.1874(8)° from 20 degrees of data, T ) 120(2) K, V ) 2911.69(8) Å3, Z ) 4, Fw ) 707.77, Dc ) 1.615 Mg m-3, µ ) 1.414 mm-1. Data collection and processing: Nonius KappaCCD diffractometer, Mo KR (λ ) 0.71073 Å), graphite monochromator, -22 e h e 22, 0 e k e 6, 0 e l e 32, frame scan width ) 0.5°, scan speed 1.0° per 240 s, typical peak mosaicity 0.47°, 26 503 reflections collected, 7346 independent reflections (Rint ) 0.034). The data were processed with Denzo-Scalepack. Solution and refinement: The structure was solved by direct methods with SHELXS-97.34 Full matrix least-squares refinement was based on F2 with SHELXL-9735 341 parameters with 81 restraints, final R1 ) 0.0682 (based on F2) for data with I > 2σ(I) and, R1 ) 0.0806 on 5291 reflections, goodness-of-fit on F2 ) 0.993, largest electron density peak ) 3.564 e Å-3. There is unmodeled disorder on one of the pyridine moieties of compound 1.
Figure 5. View of cocrystal 5 around the b axis. diiodo-tetrafluorobenzene (3) has two symmetric halogen bonds with two separated N atoms of compound 1. The N · · · I bond length is 2.824 Å and the angle of C-I · · · N is 176.48°. CHCl3 is excluded for clarity. Colors: carbon, gray; nitrogen, blue; fluorine, light green; iodine, magenta.
Acknowledgment. This research was supported by Minerva and the U.S.-Israel Binational Science Foundation. M.E.vdB. is the incumbent of the Dewey David Stone and Harry Levine Career Development Chair and Head of the Minerva Junior Research Group on Molecular Materials and Interface Design. Supporting Information Available: Crystallographic information files (CIF) for cocrystals 4 and 5. This information is available free of charge via the Internet at http://pubs.acs.org.
References
Figure 6. Mercury view showing interactions of compounds 1 with 3 and CHCl3. The length of the halogen-bonding interaction between N1 and I1 is 2.824 Å, and the angle of C-I · · · N is 176.48°. The distance between N2 of compound 1 and H31 of CHCl3 is 2.160 Å (∼78% of the sum of the vdW radii). Colors: carbon, gray; nitrogen, blue; fluorine, light green; iodine, magenta; hydrogen, pink; chloride, green.
cocrystals 4. Crystal data: C27H21N3 (1) + 2(C6F3I3) (2), yellow, plate, 0.4 × 0.4 × 0.2 mm3, monoclinic, C2/c, a ) 8.8860(2) Å, b ) 15.9228(4) Å, c ) 29.1087(7) Å, β ) 90.323(1)° from 20 degrees of data, T ) 120(2) K, V ) 4118.6(2) Å3, Z ) 4, Fw ) 1406.99, Dc ) 2.269 Mg m-3, µ ) 4.585 mm-1. Data collection and processing: Nonius KappaCCD diffractometer, Mo KR (λ ) 0.71073 Å), graphite monochromator, -11 e h e 11, 0 e k e 19, 0 e l e 36, frame scan width ) 1.0°, scan speed 1.0° per 20 s, typical peak mosaicity 0.40°, 17594 reflections collected, 4813 independent reflections (R-int ) 0.045). The data were processed with Denzo-Scalepack. Solution and refinement: The structure was solved by direct methods with SHELXS-97.34 Full matrix least-squares refinement based on F2 with SHELXL-97 274 parameters with 0 restraints, final R1 ) 0.0433 (based on F2) for data with I > 2σ(I), and R1) 0.0512 on 4178 reflections, goodness-of-fit on F2 ) 1.243, largest electron density peak ) 0.874 e Å-3. The structure is discretely disordered and has been modeled as two alternate positions.
Formation and X-ray Analysis of Cocrystal 5. A CHCl3 solution (5 mL) containing compounds 1 (54 mg, 0.14 mmol) and 3 (84 mg, 0.21 mmol) was allowed to slowly evaporate at room temperature for two weeks, resulting in X-ray quality cocrystals 5. Crystal data: C27H21N3 (1), 0.5 C6F4I2 (3), CHCl3, colorless, plate, 0.3 × 0.3 × 0.21 mm3, monoclinic, P21/c, a ) 18.7990(3) Å, b ) 5.7056(1) Å, c ) 27.4972(4) Å, β )
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CG701053D
