Isostructural Co-crystals Derived from Molecules with Different

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Isostructural Co-crystals Derived from Molecules with Different Supramolecular Topologies Michael C. Pfrunder,† Aaron S. Micallef,‡ Llewellyn Rintoul,† Dennis P. Arnold,† Karl J. P. Davy,‡ and John McMurtrie*,† †

School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Queensland 4001, Australia ‡ Australian Institute for Bioengineering and Nanotechnology and School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072, Australia S Supporting Information *

ABSTRACT: In this article, we report the crystal structures of five halogen bonded co-crystals comprising quaternary ammonium cations, halide anions (Cl− and Br−), and one of either 1,2-, 1,3-, or 1,4-diiodotetrafluorobenzene (DITFB). Three of the co-crystals are chemical isomers: 1,4-DITFB[TEA-CH 2 Cl]Cl, 1,2-DITFB[TEA-CH 2 Cl]Cl, and 1,3DITFB[TEA-CH2Cl]Cl (where TEA-CH2Cl is chloromethyltriethylammonium ion). In each structure, the chloride anions link DITFB molecules through halogen bonds to produce 1D chains propagating with (a) linear topology in the structure containing 1,4-DITFB, (b) zigzag topology with 60° angle of propagation in that containing 1,2-DITFB, and (c) 120° angle of propagation with 1,3-DITFB. While the individual chains have highly distinctive and different topologies, they combine through π-stacking of the DITFB molecules to produce remarkably similar overall arrangements of molecules. Structures of 1,4DITFB[TEA-CH2Br]Br and 1,3-DITFB[TEA-CH2Br]Br are also reported and are isomorphous with their chloro/chloride analogues, further illustrating the robustness of the overall supramolecular architecture. The usual approach to crystal engineering is to make structural changes to molecular components to effect specific changes to the resulting crystal structure. The results reported herein encourage pursuit of a somewhat different approach to crystal engineering. That is, to investigate the possibilities for engineering the same overall arrangement of molecules in crystals while employing molecular components that aggregate with entirely different supramolecular connectivity.

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INTRODUCTION The ultimate achievement in crystal engineering is the construction of a crystal to meet a particular set of design criteria (most likely, although not exclusively) to solve a technological problem. Consider first the dilemma faced by civil engineers tasked with facilitating transport across a chasm. There are many possible solutions to the problem, but perhaps the most obvious is the design and construction of a bridge. How much weight will the bridge be required to carry? What will be the height of the bridge? How far is the span? The answers to questions such as these provide the design criteria from which the bridge may be engineered. Now, while the methodologies for civil engineering are well-advanced, the same cannot be said for crystal engineering. Ab initio structure prediction remains an enigma, and methodologies for the design and preparation of crystals with specific and tunable physical properties (e.g., spin-crossover, piezoelectric, ferromagnetic properties, to name just a few) are, at this stage, still in their infancy.1 A common approach to crystal engineering, and the one we were following here, is to study the propensity for molecules with specific geometric arrangements of supramolecular synthons to assemble in predictable arrays. The © XXXX American Chemical Society

outcomes of such studies will lead to a greater capability to engineer crystals from first principles. Just as there are many different ways to engineer a bridge suitable for a particular application, it is reasonable to expect that there will be more than one way to engineer a crystal for a particular purpose. By way of schematic illustration, Figure 1a shows the resulting aggregation of a molecule that assembles as a linear topological node to create linear chains of molecules. By contrast, a molecule that acts as a ditopic node with a 90° angle of propagation as in Figure 1b results in the formation of a zigzag chain. With topological nodes of the 1D chains stacking on one another, both cases lead to the formation of structures in which square channels propagate through space bounded by the supramolecular architecture (Figures 1c,d). As the field of crystal engineering matures over the next decade, it will be important to show that particular crystal structure design criteria can be accommodated by a range of different engineering solutions. Received: August 14, 2014 Revised: September 17, 2014

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tures, by comparison with the more widely explored parasubstituted analogue, 1,4-DITFB.12−22 The para-substituted isomer (1,4-DITFB) has been shown to behave as a linear ditopic halogen bond donor linker in the presence of a range of halogen bond acceptors, especially halide ions.23−26 Our previous report showed that the ortho-substituted isomer (1,2-DITFB) can act as a 60° ditopic halogen bond donor node when combined with chloride ion acceptors. While there have been no structures reported that we are aware of in which the meta-substituted isomer (1,3-DITFB) forms halogen bonds with halide ions, this isomer has the potential to act as a 120° ditopic halogen bond donor node (Figure 2).27 Among our findings, reported herein, is a remarkable set of three structures that are co-crystals (containing DITFB, quaternary ammonium cation, halide anion) that (1) are absolute chemical isomers (i.e., share the same chemical formula), (2) each exhibit distinctly different geometric halogen bonding topology (due to regioisomeric differences between the iodine atoms on the DITFB molecules), but (3) feature supramolecular connectivity that leads to essentially the same arrangement of molecules in 3D space. Through variation of the cation and anion, we demonstrate that the featured supramolecular architecture is robust enough to resist change despite significant changes in the molecular components, to give a total of five new crystal structures with almost identical crystal packing. These results have some interesting consequences for crystal engineering that are developed and discussed below.

Figure 1. Schematic illustration of the aggregation of two different topological supramolecular nodes generating one overall arrangement of molecules. (a) Aggregation of linear ditopic nodes; (b) aggregation of ditopic nodes with 90° angle of propagation; (c, d) 3D stacking of topological nodes in panels a and b, respectively, each leading to a structure with square channels bounded by aggregating nodes.

Halogen bonds are attractive for use in the development of crystal engineering methodologies. The nature of the halogen bond is now well established and described in detail in the literature.2−7 Briefly, a halogen bond occurs between an electron donor (called the halogen bond acceptor) and a polarized halogen atom (called the halogen bond donor) to form an interaction of the type A···X−Y (A is the halogen bond acceptor, X is the electronically polarized halogen donor, and Y is the molecule or atom to which the polarized halogen is attached). Halogen bonds have energies ranging from 5 to 180 kJ mol−1,8 and they are typically linear across A···X−Y, the predictability of which makes them particularly useful for crystal engineering applications. In a recent article,9 we reported a new methodology for the construction of halogen-bonded supramolecular architectures mediated by the Menshutkin reaction.10,11 We have been expanding our investigation of this methodology to compare the topological diversity and controllability/predictability of assemblies incorporating a range of diiodotetrafluorobenzene (DITFB) analogues, specifically 1,2-DITFB, 1,3-DITFB, and 1,4-DITFB (Figure 2). These three regioisomers (otherwise

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EXPERIMENTAL SECTION

1,2-DITFB (99%), 1,4-DITFB (98%), 1,4-diazabicyclo[2.2.2]octane (DABCO) (99%), dichloromethane (DCM, ≥99%), and dibromomethane (DBM, 99%) were purchased from Sigma-Aldrich and used as received. Triethylamine (TEA) (99%) was purchased from MERCK and used as received. 1,3-DITFB was prepared from 1,2,3,5tetrafluorobenzene by a previously reported method.28 Elemental microanalyses were determined on a Carlo Erba NA1500 elemental microanalyzer. Raman spectra were obtained on a Renishaw System 1000 Raman microscope, with a laser of wavelength 632.8 nm, giving a maximum power of approximately 5 mW at the sample. The spectrometer was calibrated by reference to the silicon wafer band of 520.5 cm−1 and spectra were recorded with a resolution better than 4 cm−1. 1,4-DITFB[TEA-CH2Cl]Cl (1). Crystals formed in a sealed vessel containing a solution of 1,4-DITFB (162 mg, 400 μmol) and TEA (40.8 mg, 400 μmol) in DCM (1.0 cm3) over a period of 2−3 weeks. Yield: 164.8 mg, 70%; mp 177 °C (dec.); Found: C, 26.45; H, 2.76; N, 2.43. Anal. Calcd for 1:1 complex C33H51Cl6F8I4N3: C, 26.55; H, 2.91; N, 2.38. Selected Raman data (solid): v ̅ (cm−1) = 2987, 2945, 1609, 1579, 1366, 866, 495, 301, 152; powder XRD (Cu Kα1 1.540598 Å): °2θ = 7.52, 8.79, 13.69, 15.07, 17.24, 17.60, 19.13, 19.84, 20.48, 21.95, 23.04, 24.19, 25.16, 25.80, 26.46, 27.76, 30.58, 33.05, 35.18. 1,2-DITFB[TEA-CH2Cl]Cl (2). A solution of 1,2-DITFB (10.0 mg, 24.9 μmol) and TEA (3.8 mg, 37.3 μmol) in DCM was sealed in a vial for 5 days, resulting in the growth of colorless crystals. Powder XRD suggested the presence of two phases, with crystals of 2 making up the phase in lower proportion. The major phase consisted of the hydrated polymorph 1,2-DITFB[TEA-CH2C]3Cl3·4H2O, which has been described previously.9 Efforts to produce a phase-pure sample of 2 proved to be unsuccessful and hence powder XRD and elemental microanalysis data for a pure sample could not be collected for this compound. Selected Raman data (solid): v ̅ (cm−1) = 2985, 2947, 1455, 1288, 1179, 1156, 1008, 806, 902, 847, 478, 356, 222, 146, 117, 104. 1,3-DITFB[TEA-CH2Cl]Cl (3). Crystals of 3 formed in a sealed vessel containing a solution of 1,3-DITFB (164 mg, 400 μmol) and TEA (41.3 mg, 400 μmol) in DCM (0.7 cm3) over a period of 2−3

Figure 2. Molecules 1,4-DITFB, 1,2-DITFB, and 1,3-DITFB have the potential to produce halogen-bonded motifs with the same connectivity (ditopic) but with different supramolecular directionality.

known as positional isomers) are all potentially ditopic nodes in halogen-bonded supramolecular assemblies. Significantly, though, the differing spatial dispositions of the iodine atoms must lead to different geometric supramolecular connectivity. One goal for this continuing investigation was to address the current dearth of crystallographic information available to assess the potential for halogen bond donors 1,2-DITFB and 1,3-DITFB to produce predictable supramolecular architecB

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Table 1. Crystal and Refinement Data for 1−5

formula M crystal system space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 T/K Dc/g cm−3 Z color habit dimensions μ(Mo Kα)/mm−1 Tmin,max Nind (Rint) Nobs − (I > 2σ(I)) Nvar. R1a wR2a A, B GoF Δρmin,max/e− Å−3 Flack

1,4-DITFB

1,2-DITFB

1,3-DITFB

1,4-DITFB

1,3-DITFB

[TEA-CH2Cl]Cl (1)

[TEA-CH2Cl]Cl (2)

[TEA-CH2Cl]Cl (3)

[TEA-CH2Br]Br (4)

[TEA-CH2Br]Br (5)

C13H17Cl2F4I2N 587.97 monoclinic Cc 11.5522(4) 23.5906(7) 7.0881(2)

C13H17Cl2F4I2N 587.97 monoclinic I2/a 22.7006(7) 7.2522(2) 24.5928(8)

C13H17Cl2F4I2N 587.97 monoclinic P21/n 7.2585(1) 22.6912(2) 11.6527(2)

C13H17Br2F4I2N 676.89 monoclinic Cc 11.6862(5) 24.0917(9) 7.1603(3)

C13H17Br2F4I2N 676.89 monoclinic P21/c 7.3618(2) 23.1141(5) 11.7718(3)

105.784(4)

114.651(4)

107.655(1)

106.682(5)

107.919(3)

1858.84(10) 150(2) 2.101 4 colorless prism 0.21 × 0.16 × 0.14 3.702 0.714, 1 2232 (0.015) 2214 200 0.0132 0.0325 0.02, 0.5 1.059 −0.287, 0.395 0.00(2)

3679.7(2) 173(2) 2.123 8 colorless prism 0.15 × 0.11 × 0.09 3.740 0.797, 1 3231 (0.026) 2769 208 0.0257 0.0649 0.03, 3.5 1.101 −1.735, 1.464

1828.86(4) 173(2) 2.135 4 colorless prism 0.27 × 0.15 × 0.13 3.762 0.707, 1 3215 (0.023) 3052 199 0.0188 0.0475 0.025, 2 1.074 −0.427, 0.323

1931.07(14) 173(2) 2.328 4 colorless prism 0.30 × 0.07 × 0.07 7.425 0.349, 1 2803 (0.027) 2610 200 0.0252 0.0499 0.02, 0 1.084 −0.702, 0.525 0.063(15)

1905.96(8) 173(2) 2.359 4 colorless prism 0.12 × 0.09 × 0.07 7.523 0.607, 1 3348 (0.028) 2865 199 0.0233 0.0540 0.03, 0 1.031 −0.963, 0.600

Reflections with [I > 2σ(I)] were considered to be observed. R1 = Σ∥F0| − |Fc∥/Σ|F0| for F0 > 2σ(F0) and wR2(all) = {Σ[w(F02 − Fc2)2]/ Σ[w(Fc2)2]}1/2, where w = 1/[σ2(F02) + (AP)2 + BP], P = (F02 + 2Fc2)/3. a

weeks. Yield: 157.0 mg, 68%; mp 160 °C; Found: C, 26.52; H, 2.87; N, 2.48. Anal. Calcd for 1:1 complex C33H51Cl6F8I4N3: C, 26.55; H, 2.91; N, 2.38. Selected Raman data (solid): v ̅ (cm−1) = 2984, 2945, 1355, 1216, 1206, 1060, 1042, 869, 855, 649, 575, 458, 371, 329, 215, 190, 155, 107; powder XRD (Cu Kα1 1.540598 Å): °2θ = 8.75, 13.00, 15.30, 16.89, 17.32, 17.68, 19.48, 20.08, 20.74, 22.83, 23.36, 23.97, 25.06, 25.81, 26.12, 28.09, 29.96, 31.32, 31.89, 33.52, 35.41. 1,4-DITFB[TEA-CH2Br]Br (4). 1,4-DITFB (15.0 mg, 37.3 μmol) and TEA (3.8 mg, 37.6 μmol) were dissolved in neat DBM (0.15 cm3) in a sealed vial. Crystals formed over a 36 h period. Crystals were washed with DBM, filtered, and dried over silica gel. SCXRD analysis revealed the crystal structure to be 1,4-DITFB[TEA-CH2Br]Br. Yield: 22.7 mg, 90%; Found: C, 23.26; H, 2.53; N, 2.04. Anal. Calcd for 1:1 complex C13H17Br2F4I2N: C, 23.07; H, 2.53; N, 2.07. Powder XRD (Cu Kα1 1.540598 Å): °2θ = 7.346, 8.405, 8.660, 13.46, 14.51, 14.69, 15.70, 17.16, 17.37, 18.76, 19.50, 20.03, 21.58, 22.09, 22.56, 22.72, 23.96, 24.85, 25.60, 26.05, 26.15, 26.67, 27.06, 27.24, 28.16, 28.46, 28.55, 29.00, 29.15, 29.64, 30.01, 30.12, 31.03, 31.72, 32.06, 32.15, 32.36, 32.45, 33.72, 34.18, 34.38, 34.48, 35.13, 35.23, 35.43, 35.53, 35.97, 37.14, 37.52, 37.79, 38.02, 38.13, 38.32, 39.17, 39.54, 39.66. 1,3-DITFB[TEA-CH2Br]Br (5). 1,3-DITFB (17.1 mg, 42.5 μmol) and TEA (4.3 mg, 42.5 μmol) were dissolved in a sealed vial containing neat DBM (0.15 cm3). Colorless crystals formed over 36 h. SCXRD analysis revealed the crystal structure to be isostructural with 1,3-DITFB[TEA-CH2Cl]Cl. Yield: 27.4 mg, 95%; Found: C, 22.86; H, 2.56; N, 2.06. Anal. Calcd for 1:1 complex C13H17Br2F4I2N: C, 23.07; H, 2.53; N, 2.07. Powder XRD (Cu Kα1 1.540598 Å): °2θ = 7.667, 8.258, 8.757, 10.98, 12.39, 12.59, 13.14, 13.93, 14.70, 15.25, 15.35, 15.73, 16.20, 16.74, 16.97, 17.20, 17.50, 18.48, 19.49, 19.84, 20.38, 20.75, 22.00, 22.75, 23.07, 23.33, 23.95, 24.27, 24.35, 24.87, 25.16, 25.48, 26.34, 27.79, 28.11, 28.55, 29.03, 29.82, 29.91, 30.16, 30.25,

30.61, 30.89, 31.14, 31.68, 31.91, 32.00, 32.34, 32.78, 32.87, 33.45, 33.79, 34.41, 34.73, 34.82, 35.35, 35.45, 35.77, 35.97, 36.66, 37.20, 37.30, 37.41, 37.86, 38.27, 38.44, 38.90, 39.25, 39.72. X-ray Structure Determination. Single-crystal X-ray diffraction data were collected for co-crystals 1−5 under the software control of CrysAlis CCD29 on an Oxford Diffraction Gemini Ultra diffractometer using Mo Kα radiation generated from a sealed tube. Data reduction was performed using CrysAlis RED.29 Multiscan empirical absorption corrections were applied using spherical harmonics, implemented in the SCALE3 ABSPACK scaling algorithm, within CrysAlis RED,29 and subsequent computations were carried out using the WinGX-32 graphical user interface.30 The structures were solved by direct methods using SIR9731 and refined with SHELXL-2014.32 Full occupancy non-hydrogen atoms were refined with anisotropic thermal parameters. C−H hydrogen atoms were included in idealized positions, and a riding model was used for their refinement. Crystal data and refinement details for 1−5 are supplied in Table 1. The CIF files have been deposited into the Cambridge Structural Database (CCDC reference numbers 1019347−1019351) and can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]). Rhombic channel volumes were calculated by applying a PLATON: SQUEEZE operation on the structures after removal of [TEA-CH2Cl]+ ions.33 Powder X-ray diffraction data were collected for all samples on an XPERT-PRO diffractometer with graphite-monochromated Cu radiation, Kα1 = 1.540598 Å. The powder XRD patterns were compared to patterns simulated from the single-crystal X-ray structures in order to confirm structural purity of the samples. The powder patterns for the bulk samples were in excellent agreement with simulated patterns indicating structural C

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purity, except in the case of 2. Reasons for this are detailed and discussed above.

are bounded by halogen-bonded chains and propagate parallel to the c axis. These channels are occupied by [TEA-CH2Cl]+ ions (Figure 3c). The structures of co-crystals 2 (1,2-DITFB[TEA-CH2Cl]Cl) and 3 (1,3-DITFB[TEA-CH2Cl]Cl) are closely related to that of 1 in terms of halogen bond connectivity. Both 2 and 3 feature infinite 1D halogen-bonded chains comprising DITFB molecules and chloride anions; however, zigzag topologies are adopted rather than the linear topology observed in the structure of 1 (Figure 4). The zigzag topologies of the halogen-

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RESULTS AND DISCUSSION In the structure of co-crystal 1 (1,4-DITFB[TEA-CH2Cl]Cl), halogen bonding is observed between the iodine atoms of 1,4DITFB (donors) and chloride ions (acceptors). The iodine atoms of both 1,4-DITFB molecules form halogen bonds with a chloride ion and thus 1,4-DITFB behaves as a linear ditopic halogen bond donor linker. Likewise, each chloride ion is ditopic, forming halogen bonds with two 1,4-DITFB molecules. The resulting connectivity is a 1D halogen-bonded chain that propagates in the ab plane (Figure 3a). The para-substitution of

Figure 4. Zigzag topology of the halogen-bonded chains observed in the structures of 2 and 3 reflect the iodine substitution of the DITFB isomer present. Halogen bond details for 2: I1···Cl2, 3.09 Å; C−I1··· Cl2, 170.2°; I2···Cl1, 3.16 Å; C−I2···Cl1, 169.4°. Halogen bond details for 3: I2···Cl2, 3.15 Å; C−I2···Cl2, 172.7°; I1···Cl2 3.08 Å; C−I1··· Cl2, 176.0°.

bonded chains in 2 and 3 are the consequence of the geometrical dispositions of iodine atoms of 1,2-DITFB and 1,3DITFB. The ortho-substitution of iodine atoms in 1,2-DITFB leads to ca. 60° vertices in the halogen-bonded chains in 2 (Figure 4), while the corresponding meta-substitution found in 1,3-DITFB results in vertices of ca. 120° in the halogen-bonded chains found in 3 (Figure 4). The I···Cl−···I halogen bond linkages are not responsible for the zigzag topologies, as they remain relatively close to linear (angles range from 138−180°). In the structure of 2, 1,2-DITFB molecules π-stack such that adjacent molecules have their iodine atoms alternating in opposite directions, which, as in 1, effectively minimizes any iodine−iodine steric repulsion that might disrupt efficient stacking of the aromatic rings. The result of the combination of this π-stacking motif with zigzagging halogen-bonded chains is a supramolecular framework featuring rhombic channels filled with [TEA-CH2Cl]+ ions very similar to that observed in the structure of 1 (Figure 5). The structure of 3 also features DITFB molecules (the meta-substituted analogue in this case) arranged in a π-stacking motif, with iodine atoms of one molecule projecting on opposite sides of the stack from the contiguous molecules, again avoiding potentially disruptive steric contact between iodine atoms, leading to overall crystal packing that is isostructural with 1 and 2 despite containing 120° ditopic halogen-bonded nodes rather than the linear or 60° nodes found in 1,4- and 1,2-DITFB. In the structure of 3, the rhombic channels bounded by the supramolecular frame-

Figure 3. (a) In crystals of 1 (1,4-DITFB[TEA-CH2Cl]Cl), 1,4DITFB molecules and chloride ions are arranged in linear 1D halogenbonded chains. (b) Chains are linked by π-stacking of 1,4-DITFB molecules and switch orientation back and forth from one chain to the next by ca. 60° forming layers. (c) The relative orientation of halogenbonded chains generates rhombic channels that are occupied by TEACH2Cl+ ions (gold; hydrogens omitted for clarity). Halogen bond details: I1···Cl1, 3.01 Å; C−I1···Cl1, 174.3°; I2···Cl1, 3.07 Å; C−I2··· Cl1, 177.5°. Color code: iodine, purple; chloride, green; fluorine, yellow; carbon, gray.

iodine atoms of 1,4-DITFB along with the near-linearity of the C−I···Cl− angles and the I···Cl−···I angle (177.5, 174.3, and 165.8°, respectively) give the halogen bond chains a linear topology. These chains overlap forming π-stacking interactions (along the c axis) between molecules of 1,4-DITFB. Adjacent molecules in the stack are oriented so that the chains propagate in directions subtended by ca. 60°. The rotated orientation of adjacent 1,4-DITFB molecules allows optimal π-stacking distances, as it places the relatively large iodine atoms on opposite sides alternating through the stack and thus minimizes any steric interference that they might otherwise cause (Figure 3b). This arrangement results in rhombic-shaped channels that D

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Figure 5. Crystal structures of chemical isomers 1−3 are strikingly similar in terms of the arrangement of molecules in 3D space. The combination of π-stacking, minimization of iodine−iodine steric repulsion, and linear halogen bond connections allows the molecules to assume the same arrangement despite obvious differences in topological nodes and halogen bond topologies.

work of DITFB and chloride house [TEA-CH2Cl]+ ions, as in the structures of 1 and 2 (Figure 5). When directly comparing the structures of chemical isomers 1−3, one notices their remarkable resemblance. All three structures exhibit a similar criss-cross type halogen-bonded framework that results in rhombic channels that are occupied by cations. The construction of frameworks from tectons with such different geometric supramolecular connectivity would normally be expected to result in vastly different overall crystal packing. However, in this case, the rotational freedom provided by π−π interactions (around the axis of propagation) allows DITFB molecules to settle into relative orientations that, when combined, lead to formation of the same overall architecture. Clearly, an important factor is the disposition of iodine atoms in adjacent molecules, which are oriented in all three structures such that steric interference is minimized. Figure 5 provides comparisons between the halogen-bonded topologies in 1−3 while illustrating schematically how the same overall crystal packing derives from each. Interestingly, the structure of DABCO−CH 2 Cl[(1,2DITFB)(Cl−)] (which we reported previously)9 also features this crystal packing arrangement despite containing the significantly larger DABCO−CH2Cl+ cations rather than TEA-CH2Cl+ cations. Noting this, we then began to explore the extent to which this crystal packing motif might be preserved in other similar co-crystals.

Substitution of the dichloromethane (DCM) solvent/ reactant with dibromomethane (DBM) in the presence of 1,4-DITFB resulted in the formation of 4 (1,4-DITFB[TEACH2Br]Br), which is isomorphous with the DCM-derived analogue 1, while in the presence of 1,3-DITFB, the cocrystallization resulted in 5 (1,3-DITFB[TEA-CH2Br]Br), which is isomorphous with the DCM-derived analogue 3. Cocrystals 4 and 5 contain [TEA-CH2Br]+ quaternary ammonium cations, which were produced in situ through the Menshutkin reaction along with the liberated bromide ions that act as the halogen bond acceptors in place of the chloride ions in 1 and 3 (Figure 6). A statistical survey of the Cambridge Structural Database (v5.34)34 revealed that C−I···Br− halogen bonds generally exhibit longer interaction distances of 3.2−3.4 Å across I···Br− when compared to the typical I···Cl− interaction distances of 3.05 and 3.25 Å in C−I···Cl− halogen bonds. This is not unexpected given that bromide ions are larger than chloride ions (Pauling ionic radii of 195 pm for Br− compared to 181 pm for Cl−). What is important though is that changes in interaction distances of this magnitude more often than not result in formation of completely different supramolecular architectures. However, it is apparent that the structural motif obtained here is robust enough to accommodate the change in this case. The difference in bond length clearly does not appear to have a major effect on the halogen bond motifs obtained or on the overall crystal structures for these two systems. One E

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of 2. This suggests that, at least for this particular combination, there are other supramolecular possibilities and that while the structure observed for 2 is possible, it is not the only one and is not even necessarily the preferred one. It is not surprising therefore that when the molecular system is changed further to include bromide anions and [TEA-CH2Br]+ cations, a structure isomorphous with 2 remains elusive.

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CONCLUSIONS Despite significant differences in halogen-bonded network topology, co-crystals 1−5 exhibit strikingly similar arrangements of molecules in space, where quaternary ammonium ions are housed within rhombic channels bounded by a halogenbonded framework. This remarkable structural arrangement is facilitated through the combination of linear C−I···X− (X = Cl− or Br−) halogen bond connections, leading to predictable formation of (a) linear chains for 1,4-DITFB, (b) zigzag chains with 60° angle of propagation for 1,2-DITFB, and (c) zigzag chains with 120° angle of propagation for 1,3-DITFB. Overlap of the chains at the DITFB nodes leads to formation of rhombic channels that are occupied by the quaternary ammonium cations. The directional influence resulting from the orientation of iodine atoms of adjacent molecules in the stack drives the formation of the remarkably similar overall arrangement of the molecules in space. One of the ongoing challenges in crystal engineering is the modification and tuning of structural features of molecular components to produce crystals with specific and designed arrangements of those molecules in space. The compounds presented herein clearly demonstrate that one overall crystal packing arrangement can be achieved, not just for systems with almost identical molecular components such as the isomorphous pairs 1/4 and 3/5 (as has been commonly found and reported) but also where the molecular components aggregate with very different supramolecular topologies. One of the most common approaches to crystal engineering has been to make systematic changes to the molecular components to produce predictable changes in crystal structure. We propose that another, equally worthwhile, approach is to attempt to engineer the same crystal packing arrangement by use of molecular components with different supramolecular topologies.

Figure 6. Crystal structures of 4 and 5 viewed down the axis of the rhombic channels containing the cations. Color code: cations, gold; bromide, brown.

aspect of these structures of these crystals that is affected (however subtly) by the lengthening of halogen bond connections is the size of the rhombic channels formed by the halogen bond architecture. The “calc void” function of the crystallographic software PLATON33 was used to calculate estimates of the volume of the channels in each of these four structures. It was calculated that each rhombic channel in the structure 1 features an internal volume of 996.0 Å3 per unit cell. In comparison, the volume of a channel in the analogous bromide structure (3) was estimated to be 1040 Å3 per unit cell. Likewise, the channel volumes in the structures of 3 and 5 were estimated to be 980 and 1030 Å3, respectively. These values indicate an increase in channel volume of 4 to 5% when bromide ions are substituted for chloride ions. Of course, the [TEA-CH2Br]+ cations that occupy these channels are also slightly larger than the chloro analogue [TEA-CH2Cl]+ in 1 and 3. Choice of the halide ion therefore provides a convenient handle with which to finely tune the size of channels or cavities generated upon the assembly of halogen-bonded frameworks. In this case, the larger size of the cations is no doubt accommodated by the increase in the sizes of the pores they occupy. Interestingly, attempts to obtain an isomorphous analogue of 2, by crystallization of 1,2-DITFB in the presence of DBM, proved to be unsuccessful. Other crystalline products did form, and we are currently investigating their significance, but there was no evidence of formation of the architecture displayed by 1−5. As described in detail in the Experimental Section, crystallization of 1,2-DITFB in dichloromethane leads to a twophase mixture of crystals, of which only the minor proportion is 2. The structure of the major phase comprises 1,2-DITFB[TEA-CH2Cl]Cl3·4H2O, with intermolecular connectivity including both halogen and hydrogen bonds (possibly due to the presence of water of crystallization) and which, as a result, displays an entirely different supramolecular architecture to that

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ASSOCIATED CONTENT

S Supporting Information *

Powder XRD patterns of 1, 3, 4, and 5; Raman spectra of 1−3; and crystallographic data in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS M.P. acknowledges QUT for a Strategic Masters Scholarship and the Australian Government for an Australian Postgraduate Award. The authors gratefully acknowledge the QUT Central Analytical Research Facility (CARF) for access to scientific instrumentation used in this research project. F

dx.doi.org/10.1021/cg501210t | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Article

REFERENCES

(1) Desiraju, G. R. J. Am. Chem. Soc. 2013, 135, 9952−9967. (2) Desiraju, G. R.; Shing Ho, P.; Kloo, L.; Legon, A. C.; Marquardt, R.; Metrangolo, P.; Politzer, P.; Resnati, G.; Rissanen, K. Pure Appl. Chem. 2013, 85, 1711−1713. (3) Priimagi, A.; Cavallo, G.; Metrangolo, P.; Resnati, G. Acc. Chem. Res. 2013, 46, 2686−2695. (4) Politzer, P.; Murray, J. S.; Clark, T. Phys. Chem. Chem. Phys. 2013, 15, 11178−11189. (5) Politzer, P.; Murray, J. S. ChemPhysChem 2013, 14, 278−294. (6) Metrangolo, P.; Resnati, G. Cryst. Growth Des. 2012, 12, 5835− 5838. (7) Beale, T. M.; Chudzinski, M. G.; Sarwar, M. G.; Taylor, M. S. Chem. Soc. Rev. 2013, 42, 1667−1680. (8) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. Acc. Chem. Res. 2005, 38, 386−395. (9) Pfrunder, M. C.; Micallef, A. S.; Rintoul, L.; Arnold, D. P.; Davy, K. J. P.; McMurtrie, J. Cryst. Growth Des. 2012, 12, 714−712. (10) Menshutkin, N. Z. Phys. Chem. 1890, 6, 41−57. (11) Abboud, J. L. M.; Notario, R.; Bertran, J.; Sola, M. Prog. Phys. Org. Chem. 1993, 19, 1−182. (12) Liantonio, R.; Metrangolo, P.; Pilati, T.; Resnati, G. Acta Crystallogr. 2002, E58, o575−o577. (13) Jay, J. I.; Padgett, C. W.; Walsh, R. D. B.; Hanks, T. W.; Pennington, W. T. Cryst. Growth Des. 2001, 1, 501−507. (14) Cinčić, D.; Frišcǐ ć, T.; Jones, W. J. Am. Chem. Soc. 2008, 130, 7524−7525. (15) Cauliez, P.; Polo, V.; Roisnel, T.; Llusar, R.; Fourmigue, M. CrystEngComm 2010, 12, 558−566. (16) Arman, H. D.; Gieseking, R. L.; Hanks, T. W.; Pennington, W. T. Chem. Commun. 2010, 46, 1854−1856. (17) Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G. Acta Crystallogr. 2007, E63, o4243. (18) Prasang, C.; Whitwood, A. C.; Bruce, D. W. Chem. Commun. 2008, 2137−2139. (19) Roper, C. L.; Präsang, C.; Kozhevnikov, V. N.; Whitwood, A. C.; Karadakov, P. B.; Bruce, D. W. Cryst. Growth Des. 2010, 10, 3710− 3720. (20) Cinčić, D.; Frišcǐ ć, T.; Jones, W. Chem.Eur. J. 2008, 14, 747− 753. (21) Walsh, R. B.; Padgett, C. W.; Metrangolo, P.; Resnati, G.; Hanks, T. W.; Pennington, W. T. Cryst. Growth Des. 2001, 1, 165− 175. (22) Liu, P.; Ruan, C.; Li, T.; Ji, B. Acta Crystallogr. 2012, E68, o1431. (23) Grebe, J.; Geiseler, G.; Harms, K.; Dehnicke, K. Z. Naturforsch., B: J. Chem. Sci. 1999, 54, 77−86. (24) Abate, A.; Biella, S.; Cavallo, G.; Meyer, F.; Neukirch, H.; Metrangolo, P.; Pilati, T.; Resnati, G.; Terraneo, G. J. Fluorine Chem. 2009, 130, 1171−1177. (25) Raatikainen, K.; Rissanen, K. Cryst. Growth Des. 2010, 10, 3638−3646. (26) Cavallo, G.; Biella, S.; Lü, J.; Metrangolo, P.; Pilati, T.; Resnati, G.; Terraneo, G. J. Fluorine Chem. 2010, 131, 1165−1172. (27) Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G. Angew. Chem., Int. Ed. 2008, 47, 6114−6127. (28) Neenan, T. X.; Whitesides, G. M. J. Org. Chem. 1988, 53, 2489− 2496. (29) CrysAlis CCD and CrysAlis RED; Oxford Diffraction Ltd: Abingdon, Oxfordshire, England, 2007. (30) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838. (31) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giocovazzo, C.; Guagliardi, A.; Moliterni, A. G. C.; Polidori, G.; Spagna, S. J. J. . Appl. Crystallogr. 1999, 32, 115−119. (32) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122. (33) Spek, A. L. Acta Crystallogr. 2009, D65, 148−155. (34) Allen, F. Acta Crystallogr. 2002, B58, 380−388.

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