Construction of Chiral Polar Crystals from Achiral Molecules by

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Construction of Chiral Polar Crystals from Achiral Molecules by Stacking Control of Hydrogen-Bonded Layers Using Type II Halogen Bonds Toshiyuki Sasaki,*,†,# Yoko Ida,† Ichiro Hisaki,† Seiji Tsuzuki,§ Norimitsu Tohnai,† Gérard Coquerel,∥ Hisako Sato,⊥ and Mikiji Miyata*,†,‡ †

Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan § Research Initiative of Computational Sciences (RICS), Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan ∥ Normandie Université, Crystal Genesis Unit SMS EA3233 IMR 4114, 1 Rue Tresniere Université de Rouen, Mont Saint Aignan CEDEX, France ⊥ Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan S Supporting Information *

ABSTRACT: Crystals belonging to P1 and P21 space groups are fascinating research targets because of their potential applications in various fields by taking advantage of their chirality and polarity. However, molecules intrinsically prefer symmetric, achiral nonpolar space groups due to canceling out of dipole moments and close packing in crystalline states. Therefore, it remains difficult to selectively obtain the P1 and P21 crystals, especially from achiral molecules. Here we achieve construction of the chiral P1 and P21 crystals from achiral molecules based on stacking control of chiral two-dimensional hydrogen-bonded layers by halogen bonds (XBs). Precise investigations and theoretical calculations of their crystal structures revealed that space group selectivity among the chiral P1, P21, and achiral space groups is the result of a subtle balance between the stronger interaction: charge-assisted hydrogen bonds and the weaker interactions: van der Waals interaction of alkyl chains and the bonding involving halogens, which have anisotropic nature and robustness-tunability. It is also noteworthy that type II XBs were observed in chiral crystals, while type I halogen···halogen contacts were formed in achiral crystals, indicating the importance of type II XBs for chiral crystallization.



INTRODUCTION

type II halogen bonds (XBs) for chiral stacking of the 2D layers. First, HBs, 33,34 which have anisotropic nature and complementarity, are selected as supramolecular synthons35 for constructing chiral supramolecular assemblies. Especially, charge-assisted HBs of organic salts is one of the most robust supramolecular synthons, and these characteristics let HB work effectively for constructing specific supramolecular assemblies. According to our previous reports, ammonium carboxylates form three types of hydrogen-bonded networks: 0D cubic,36,37 1D ladder,38,39 and 2D sheet,40 depending on the kinds of component substituents. All of the hydrogen-bonded networks can potentially exhibit supramolecular chirality due to their topological diversity.41 Second, 2D layer structures are useful from the viewpoint of hierarchical crystal design42−48 (Figure 1b) as well as material sciences.49−54 This comes from the idea

1−4

Numerous studies of crystal engineering have been devoted to achieve various molecular arrangements within crystals for gas absorption,5 molecular inclusion,6,7 topochemical reaction,8−11 and so on.12−16 Among them, chirality17−19 and polarity inductions20−28 are of particular interest due to their potential in elucidating the origin of homochirality29−32 and in applications such as nonlinear optical materials,13,14 respectively. However, starting from achiral molecules, construction of chiral polar crystals remains difficult because molecules intrinsically assemble to cancel out their polarity and asymmetric property. In order to overcome the difficulty, we have found an effective connection of the following three ideas (Figure 1a): (i) construction of chiral supramolecular assemblies starting from achiral molecules by hydrogen bonds (HBs), (ii) employment of two-dimensional (2D) layers rather than zero-dimensional (0D) clusters or one-dimensional (1D) columns as supramolecular buildng blocks, and (iii) usage of © XXXX American Chemical Society

Received: December 6, 2015 Revised: January 28, 2016

A

DOI: 10.1021/acs.cgd.5b01724 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 1. (a) A schematic diagram for constructing chiral polar crystals; the formation of chiral polar layers by hydrogen bonds (HBs) in the step 1 and the stacking of those layers by halogen bonds (XBs) in the step 2. (b) Schematic representation of difference in the numbers of assembly directions among 0D clusters, 1D columns, and 2D layers. (c) Two types of the interactions involving halogen atoms: (i) type I halogen···halogen contacts (XCs) and (ii) type II XBs, observed in achiral and chiral crystals, respectively. (d) Molecular structures of achiral p-halo-substituted benzylammonium carboxylates employed in this study. without further purification. 1:1 Molar ratio of p-chlorobenzylamine (ClBA) or p-bromobenzylamine (BrBA) and n-alkyl carboxylic acid (CH3(CH2)n‑2CO2H, CAn: n = 5−14) or ω-bromocarboxylic acid (BrCH2(CH2)n‑2CO2H, BrCAn: n = 7−12) with various chain length were dissolved in ethanol. Slow evaporation of the solution afforded single crystals of their salts (4-chlorobenzylammonium carboxylate, ClBA·CAn; 4-chlorobenzylammonium bromocarboxylate, ClBA· BrCAn; 4-bromobenzylammonium carboxylate, BrBA·CAn; 4-bromobenzylammonium bromocarboxylate, BrBA·BrCAn). When powdered salts were yielded, the salts were then recrystallized from organic solvents: diethyl ether, CHCl3/hexane, ethanol, 2-propanol, and 2butanol, in glass vials (10 mL) affording single crystals for single crystal or powder X-ray diffraction measurements. X-ray Crystallography. X-ray diffraction data were collected on a Rigaku RAXIS-RAPID imaging plate diffractometer with a 2D area detector using graphite monochromated CuKα radiation (λ = 1.54187 Å). Lattice parameters were obtained by least-squares analysis from reflections for three oscillation images. Structure solution was achieved by direct methods with the programs SIR92, SIR2004, or SHELXL97.64 The structures were refined by a full-matrix least-squares procedure with all the observed reflections based on F2. All nonhydrogen atoms were refined with anisotropic displacement parameters, and hydrogen atoms were placed in idealized positions with isotropic displacement parameters relative to the connected nonhydrogen atoms, and not refined. Calculations for ClBA·CA13 were performed using the TEXSAN65 crystallographic software of the Molecular Structure Corp. Calculations for ClBA·CA7, ClBA·BrCA7, ClBA·BrCA12, BrBA·CA5, BrBA·CA8, BrBA·CA13, and BrBA·BrCA12 were performed using CrystalStructure crystallographic software package66 except for refinement, which was performed using SHELXL-97. The crystallographic data for this study have been deposited at the Cambridge Crystallographic Data Center (Tables 1, S1, and S2). For powder X-ray diffraction measurements, their data were collected on the powdered salts, which were prepared by grinding the single crystals, with a Rigaku RINT-2000 diffractometer using

that 2D structures assemble in only one direction to afford 3D crystals, while 0D or 1D structures assemble in three or two directions, respectively. Third, it is remarkable that the interactions involving halogen atoms,21,55−63 especially type II XBs, are available for chiral and/or polar stacking of the layers. This finding is attributable to the directionality difference between type I halogen···halogen contacts (XCs) and type II XBs, resulting in completely different molecular arrangements owing to the specific interaction angles (Figure 1c). The above-mentioned ideas reached a supramolecular layer with the 2D hydrogen-bonded network which is schematically shown in Figure 1a. All substituents of the component ammoniums and carboxylates in the 2D supramolecular layer are on opposite sides of the 2D hydrogen-bonded network from each other, forming a three-layered structure. It should be noted that the 2D supramolecular layer motif reported in our previous work has a unique chiral polar structure without any symmetric operation except for translation40,41 (Step 1 in Figure 1a), while 2D hydrogen-bonded networks are normally achiral nonpolar.41,43 This characteristic prompted us to control the stacking of the chiral polar 2D layers for construction of chiral polar crystals. This paper describes usage of XBs for construction of chiral polar P1 and P21 crystals consisting of achiral ammonium carboxylates, which is based on chiral stacking of the 2D layers (Step 2 in Figure 1a). This is the first achievement of construction of chiral polar P1 and P21 crystals from achiral components based on layer-based crystal design by tuning interaction balance among HBs, van der Waals interactions, and type II XBs.



EXPERIMENTAL SECTION

Preparations of Organic Salts and Their Crystals. All of materials employed in this study were commercially available and used B

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Table 1. Crystallographic Parameters of ClBA·CA7, ClBA·CA13, ClBA·BrCA7, ClBA·BrCA12, BrBA·CA5, BrBA·CA8, BrBA·CA13 and BrBA·BrCA12 ClBA·CA7

ClBA·CA13

ClBA·BrCA7

ClBA·BrCA12

formula formula weight solvent crystal shape space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z D (g/cm3) T (K)

C14H22ClNO2 271.79 CHCl3/hexane platelet P1̅ (#2) 5.74 8.19 17.8 99.3 92.0 115 744.18(3) 2 1.213 213.1 BrBA·CA5

C20H34ClNO2 367.96 CHCl3/hexane platelet P1̅ (#2) 5.05 5.91 39.2 93.0 93.6 97.8 1153(2) 2 1.059 213.2 BrBA·CA8

C14H21BrClNO2 350.68 2-butanol chunk P1̅ (#2) 5.76 8.1 18.4 81.6 86.3 65.0 769.60(3) 2 1.513 213.1 BrBA·CA13

C19H31BrClNO2 420.82 2-propanol prism P21 (#4) 4.73 38.0 5.62 90 97.7 90 1000.83(9) 2 1.396 213.1 BrBA·BrCA12

formula formula weight solvent crystal shape space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z D (g/cm3) T (K)

C12H18BrNO2 288.18 diethyl ether platelet P1̅ (#2) 5.82 7.73 15.1 81.3 88.0 72.6 642.46(3) 2 1.490 213.1

C15H24BrNO2 330.26 2-butanol platelet P1̅ (#2) 5.74 8.25 18.6 82.1 88.4 65.2 789.91(8) 2 1.388 213.1

C20H34BrNO2 400.40 CHCl3/hexane block P1̅ (#2) 4.73 5.65 38.4 85.1 85.3 83.4 1014.09(3) 2 1.311 213.1

C19H31Br2NO2 465.27 ethanol block P1 (#1) 4.72 5.65 19.1 86.4 88.1 82.2 503.06(3) 1 1.536 173

Layer(P1̅)b

Layer(P21)c

Layer(P1)d

Table 2. Structural Motifs of the Salts entries ClBA·CAn BrBA·CAn ClBA·BrCAn BrBA·BrCAn a

Column(P1̅)a n n n n

= = = =

n = 10−14 n = 10−14

5−9 5−9 7, 9, 11 7, 9, 11

Crystals composed of hydrogen-bonded columns. and P1, respectively.

n = 8, 10, 12 n = 8, 10, 12 b−d

Crystals composed of hydrogen-bonded layers with the corresponding space groups, P1̅, P21,

graphite-monochromatized CuKα radiation (λ = 1.54187 Å) at room temperature (Supporting Information, Figures S1−S4). Measurements of Second Harmonic Generation (SHG) Activity. The SHG activities of the powder samples of ClBA· BrCA12 and BrBA·BrCA12 were measured by the Kurtz and Perry method67 with the experimental setup previously described by Galland et al.68 Theoretical Calculation. Optimizations of P21 and P1 crystal structures of the salts: ClBA·BrCA12 and BrBA·BrCA12, respectively, were conducted by DMol3 module of Materials Studio 6.0 SP1.69−71 The first-principles density functional theory (DFT) calculations were carried out using generalized gradient approximation (GGA) with formulas of Perdew, Burke, and Ernzerhof (PBE)72 in conjunction with the DNP basis set, a real-space cut off of 4.0 Å and a 3 × 3 × 1 k points generated with the Monkhorst−Pack scheme. The dispersion interactions are incorporated by the DFT-D approach using Grimme (G06) correction73 to PBE. For the geometry optimization, FINE convergence criteria were employed (energy 1 × 10−5 Hartree, gradient 2 × 10−3 Hartree Å−1, displacement 5 × 10−3 Å) for both

atomic coordinates and lattice vector optimizations. Interaction energies were calculated using Gaussian 09.74 The aug-cc-pVTZ basis set was used for the calculations. The basis set superposition error (BSSE)75 was corrected for all the interaction energy calculations using the counterpoise method.76



RESULTS AND DISCUSSION A series of achiral organic salts of p-halo-substituted benzylammonium carboxylates was employed to investigate the selective formation of the chiral layered structures (Figure 1d). The crystal structures of these salts were determined and classified based on the results of single-crystal and powder Xray diffraction measurements (Supporting Information, Figures S1−S4). Each of the four types of salts, ClBA·CAn, ClBA·BrCAn, BrBA·CAn, and BrBA·BrCAn, exhibited characteristic tendencies in their crystal structures. The crystal structures of the four types of salts are summarized in Table 2, and the representative C

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Figure 2. (a) Achiral crystal structures of ClBA·CA7 (Column(P1̅)), (b) ClBA·BrCA7 (Column(P1̅)), and (c) BrBA·CA13 (Layer(P1̅)), which involve (i) representation in a space-filling model, (ii) hydrogen-bonded networks, (iii) asperities between layers, and (iv) type I halogen···halogen contacts (XCs); db = 3.60 Å, θ1b = θ2b = 147°, dc = 3.54 Å, θ1c = θ2c = 160°.

Figure 3. (a) Chiral crystal structures of ClBA·BrCA12 (Layer(P21)) and (b) BrBA·BrCA12 (Layer(P1)), which involve (i) representation in a spacefilling model, (ii) hydrogen-bonded networks, (iii) layer contacts and (iv) type II halogen bonds (XBs) between the layers; da = 3.63 Å, θ1a = 165°, θ2a = 93°, db = 4.16 Å, θ1b = 157°, θ2b = 91°, dc = 3.80 Å, θ1c = 159°, θ2c = 98°, dd = 3.59 Å, θ1d = 174°, θ2d = 104°.

intercolumnar type I XCs are observed between the bromine atoms of the ω-bromide carboxylic acids in the ClBA·BrCAn and BrBA·BrCAn crystals, as exemplified in Figure 2b(iv). All columns have inversion centers in and between the columns, and the crystals belong to achiral P1̅ space group. The other three types of crystal structures are constructed by stacking of similar layer supramolecular motifs with 2D hydrogen-bonded networks, which are repetition of a R-HB

crystal structures are depicted in Figures 2 and 3. The one is an achiral nonpolar crystal (Column(P1̅)) constructed by bundling columnar supramolecular motifs with achiral 1D hydrogen-bonded networks, which consist of two repeating ring-type hydrogen-bonded (R-HB) networks, R44(12) and R24(8), according to the graph-set analysis41,77−80 (Figure 2a,b). The columns assemble by intercolumnar CH/π interactions and by fitting their surface asperities. Additional D

DOI: 10.1021/acs.cgd.5b01724 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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network, R56(16), according to the graph set analysis, but their stacking patterns are different (Figures 2c and 3a,b). One of them has inversion centers between the layers and belongs to an achiral nonpolar P1̅ space group (Layer(P1̅)) (Figure 2c). Contrary to this, the others have no inversion centers between the layers and belong to a chiral polar P21 (Layer(P21)) (Figure 3a) or P1 space groups (Layer(P1)) (Figure 3b). In the crystal of Layer(P21), there are 21 screw axes which are vertical to the layers, meaning the unit layer stacking in 2-fold rotational manners with 180 degree rotations, while that in translational manners with 0 degree rotation in the crystal of Layer(P1). Table 2 indicates three characteristics of the salts: (i) chain length, (ii) halogen atoms on terminals, and (iii) parity, in constructing supramolecular motifs and crystals. First, a certain length of an alkyl chain is required for the layer formation. The salts of ClBA·CAn and BrBA·CAn with more than nine carbon atoms (n = 10−14) form only Layer(P1̅), suggesting that van der Waals interactions between the alkyl chains are critical to form the layer 2D motifs. Moreover, the salts of ClBA·BrCAn and BrBA·BrCAn with more than seven and even number of carbon atoms (n = 8,10,12) produce Layer(P21) and Layer(P1), respectively, while the Column(P1)̅ is constructed by those with an odd number of carbon atoms (n = 7, 9, 11). Such an introduction of type I XCs or type II XBs to this benzyl ammonium carboxylate system caused a drastic change in the crystal structures, depending on the number and type of halogen atoms. These observations allow the effect of the type I XCs and type II XBs on the crystal structures to be explained based on the steric and electronic properties of the halogen atoms48 between the surfaces of the contacting layers (Figures 2 and 3). Second, as for halogen atoms on terminals, the ClBA·CAn and BrBA·CAn salts with halogen atoms only on terminals of the ammoniums form achiral crystals (Layer(P1̅)) in which the unit layer stacks in an inverted manner (Figure 2c), creating either XCs or alkyl···alkyl contacts. In contrast, the ClBA· BrCAn and BrBA·BrCAn salts, which have halogen atoms on both terminals of ammoniums and carboxylates, form chiral crystals (Layer(P21), Figure 3a) and (Layer(P1), Figure 3b), respectively. Roles of the XCs and XBs in constructing the achical nonpolar P1̅ or the chiral polar P21 and P1 crystals are schematically drawn in Figure 4. After construction of the chiral polar layers by HBs and van der Waals interactions, the layers stack by forming XCs or XBs. With regard to the layers composed of the ClBA·CAn and BrBA·CAn salts, the ammonium surfaces face each other to form type I XCs (Figure 4b). As easily expected, the type I XCs between the same (super)molecules generate an inversion center due to unique anisotropic nature of the type I XBs, or specific contact angles (θ1 = θ2). As a result, there are inversion centers between the layers, affording the achiral nonpolar P1̅ crystal. On the other hand, the layers composed of the ClBA·BrCAn and BrBA· BrCAn salts, the ammonium and carboxylate surfaces face each other to form type II XBs (Figure 4c). In this case, there are no inversion centers due to unique anisotropic nature of the type II XBs, or vertical contacts (θ1 ≈ 180°, θ2 ≈ 90°), affording either the chiral polar P21 or P1 crystals. Third, one can see a parity effect that is easily attributable to the bromine atom on the edge of the linear alkyl chain. The direction of the interaction depends on whether n is odd or even due to the alkyl chain conformation that, in turn, depends on the anisotropic nature of the type I XCs and type II XBs. When the number of n is odd, columns are constructed, and

Figure 4. Difference between type I halogen···halogen contacts (XCs) and type II halogen bonds (XBs) in layer stacking. (a) Construction of supramolecular structures: a chiral polar layer and an achiral nonpolar column by hydrogen bonds (HBs) and van der Waals (vdWs) interactions. (b) Achiral centrosymmetric stacking of the layers in a P1̅ manner by type I XCs which generate inversion centers. (c) Chiral non-centrosymmetric stacking of the layers in P1 and P21 manners by type II XBs which generate no inversion centers. HBs and type I XCs/ type II XBs are represented by blue and green dotted lines, respectively.

they assembled by intercolumnar type I XCs and a fitting of surface asperities (Figure 2b(iv)). On the other hand, when n is even, effective type II XBs are formed by constructing the layers (Figure 3a(iv), 3b(iv)). As a result, crystal structures Layer(P1) and Layer(P21) become preferable to those of Column(P1̅). It is also noteworthy that the ClBA·BrCAn and BrBA·BrCAn crystals form identical layer motifs, but their stacking patterns are different. The type II XBs between chlorine···bromine atoms induce 2-fold rotational stacking of the layers, while those between bromine···bromine atoms induce translational stacking of the layers, resulting in P21 and P1 crystals, respectively. Precise investigations on interlayer type II XBs were conducted crystallographically and theoretically to elucidate origins of the stacking difference. Figure 5 represents layer stacking manners in the crystals of ClBA·BrCA12 (Layer(P21)) and BrBA·BrCA12 salts (Layer(P1)). The surface asperities of the BrCAn, ClBA, and BrBA sides on the unit layers are depicted in Figure 5a(ii), (iii) and 5b(ii), (iii). Two types of concaves, sites A and B, are present on the BrCAn side, and the surface asperities of the BrCAn sides are similar in both salts (Figure 5a(iii) and 5b(iii)). On the other hand, two types of convexes are present on the ClBA and BrBA sides due to the halogen and neighboring hydrogen atoms. Accordingly, in the case of Layer(P21) (Figure 5a(iv) and 5a(v)), the halogen and hydrogen atoms contact to sites A and B, respectively. In contrast, in the case of Layer(P1) (Figure 5b(iv) and 5b(v)), the halogen and hydrogen atoms contact to sites B and A, respectively. Such differences cause the similar type II XBs with a slight difference as follows. Four of the bromine atoms on the BrCAn side form a parallelogram around one halogen atom on the amine side, and sites A and B are located on its long and short sides of the parallelogram, respectively. The chlorine atom on ClBA is located at site A and forms type II XBs with two of the bromine atoms along the long side of the parallelogram. In contrast, the bromine atom on BrBA is located at site B and forms type II XBs with two of the bromine atoms along the short side of the parallelogram. E

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Figure 5. Layer stacking manners in the crystals of (a) ClBA·BrCA12 (Layer(P21)) and (b) BrBA·BrCA12 (Layer(P1)), which involve (i) representation in a space-filling model, (ii) surfaces of the layers of the carboxylic acid (CA) sides, (iii) surfaces of the amine (BA) sides. Schematic representations of (iv) asperities on the surfaces and (v) overlapping manners of the layers. Site A (light blue circles) and Site B (white circles) are concaves on long and short edges, respectively, of the parallelogram which is composed of four bromine atoms (brown circles) on the surfaces of the CA side. Hydrogen atoms (black circles) and chlorine (green circles) or bromine atoms (brown circles) on the surfaces of the BA sides fit in the two sites when the layers stack with each other. Carbon, hydrogen, nitrogen, oxygen, chlorine, and bromine atoms are represented in gray, white, light blue, red, green and brown, respectively.

Table 3. Optimized and Simulated Crystallographic Parameters of ClBA·BrCA12 (P1, P21) and BrBA·BrCA12 (P1, P21) formula crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z D (g/cm3) model structure a

ClBA·BrCA12

ClBA·BrCA12

BrBA·BrCA12

BrBA·BrCA12

C19H31BrClNO2 triclinic P1 (#1)a 4.5558 5.5569 18.6242 84.7399 88.7894 81.5183 464.358 1 1.50484 ClBr(Me)-S-P1

C19H31BrClNO2 monoclinic P21 (#4)b 4.5437 37.3475 5.5514 90 97.4320 90 934.135 2 1.49611 ClBr(Me)-O-P21

C19H31Br2NO2 triclinic P1 (#1)b 4.5845 5.5708 18.6768 84.4029 88.3014 81.6845 469.670 1 1.64499 BrBr(Me)-O-P1

C19H31Br2NO2 monoclinic P21 (#4)a 4.5288 37.4335 5.6218 90 98.5877 90 942.372 2 1.63969 BrBr(Me)-S-P21

Simulated structure. bOptimized structure.

crystal structures are listed in Table 3. The calculated crystal structures showed no drastic changes in the crystallographic parameters from those of the experimentally obtained crystal structures (Table 1), demonstrating the reliability of the calculation. Therefore, the subsequent energy calculations could reasonably be conducted based on the optimized and simulated structures. Two pairs of interacted molecules (Figure 6a−d(i) and (ii)), which form different kinds of interlayer type II XBs from the viewpoints of interaction distances and angles, were picked up from each of the optimized and simulated crystal structures. The following two modifications were made on the molecules. First, the ammonium cations were removed to eliminate any interactions due to their charges. Second, the undecyl group was exchanged for a methyl group to evaluate the type II XBs by eliminating additional van der Waals interactions. These

Therefore, it is considered that type II XBs in the case of the BrBA·BrCAn salt become closer than those in the case of the ClBA·BrCAn salt, suggesting that the former can potentially form more effective and robust type II XBs than the former. Then, interaction energies of interlayer type II XBs were evaluated theoretically. Experimentally obtained crystal structures: ClBA·BrCA12 (Layer(P21)) and BrBA·BrCA12 (Layer(P1)) were optimized, or modified to the most energetically stable crystal structures, by DMol3 module of Materials Studio 6.0 SP1.69−71 Crystal structure of ClBA·BrCA12 (Layer(P1)) was simulated by exchanging the bromine atoms for chlorine atoms in the crystal structure of BrBA·BrCA12 (Layer(P1)). Similarly, crystal structure of BrBA·BrCA12 (Layer(P21)) was simulated by exchanging the chlorine atoms for bromine atoms in the crystal structure of ClBA·BrCA12 (Layer(P21)). The crystallographic parameters of the optimized and simulated F

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the stacked structures (Figure 7a(iv)). At this stage, the 2-fold rotational stacking is more stable than the translational stacking due to canceling out of dipole moments and formation of the type II XBs as demonstrated in the theoretical calculations. The type II XBs in the 2-fold rotational stacking work more effectively than those in the translational stacking when the layers are closely packed, e.g., in crystalline states (Figure 7a(v)). As a result, the P21 crystal is obtained from the ClBA· BrCA12 salt with type II XBs between chlorine and bromine atoms. As for the BrBA·BrCA12 salt, the type II XBs are sufficiently robust to form a multilayered structure in a translational manner (Figure 7b(iii) and 7b(iv)). Further stacking and close packing of the layers, which affords P1 crystals (Figure 7b(v)). That is, the interlayer type II XBs affect not only the packing state stabilization but also the assembly manner of the supramolecular layers. Finally, second harmonic generation (SHG) activities of the crystals, ClBA·BrCA12 and BrBA·BrCA12, were measured by the Kurtz and Perry method.67 As previously reported, XBs have good potential to induce NLO properties.83−85 Both of the crystals showed positive signals which are 2.7 and 6.6 times compared to that of quartz without optimization of their particle sizes. The values are not remarkable, but the existence of the SHG activity suggests that this crystal design strategy could be applicable to construct chiral polar crystals for developing nonlinear optical materials using highly polarized molecules.

Figure 6. Molecular pairs by type II halogen bonds (XBs) extracted from optimized and simulated crystal structures. Molecules from (a) a simulated P1 crystal (ClBr(Me)-S-P1) and (b) an optimized P21 crystal (ClBr(Me)-O-P21) of ClBA·BrCA12. Molecules from (c) an optimized P1 crystal (BrBr(Me)-O-P1) and (d) a simulated P21 crystal (ClBr(Me)-S-P21) of BrBA·BrCA12. Two kinds of type II XBs in the crystal structures are described separately in (i) and (ii).

models were named ClBr(Me)-S-P1, ClBr(Me)-O-P21, BrBr(Me)-O-P1, and BrBr(Me)-S-P21 for the simulated (S) P1 crystal structure from BrBA·BrCA12, the optimized (O) P21 crystal structure from ClBA·BrCA12, the optimized (O) P1 crystal structure from BrBA·BrCA12 and the simulated (S) P21 crystal structure from BrBA·BrCA12, respectively, and are presented in Figure 6. Then interaction energies of type II XBs between the molecules were calculated and are listed in Table 4. The type II XBs in the P1 crystals were shorter than those in the P21 crystals for both salts, which indicates that potentially more robust type II XBs can form in P1 crystals than those in P21 crystals. However, the calculated interaction energies indicate that type II XBs in the P21 crystals are more robust than those in the P1 crystals, suggesting that the bond lengths and angles in the P1 crystals are not the most favored situation. With regard to difference in kinds of halogen atoms, the type II XBs between bromine atoms are stronger than those between chlorine and bromine atoms. According to the aforementioned investigations based on crystallographic studies and theoretical calculations, the selectivity of the P1 and P21 crystals can be explained as follows: the ion pairs of the ammonium carboxylates are assembled via robust, charge-assisted HBs to yield 2D layered structures (Figure 7a(i),(ii) and 7b(i),(ii)). The layers stack to form multilayered structures through type II XBs (Figure 7a(iii) and 7b(iii)). In the case of the ClBA·BrCA12 salt, the type II XBs are too weak to give selectivity between the translational and 2-fold rotational stacking, and further stacking of the layers generates additional van der Waals interactions that stabilize



CONCLUSIONS In conclusion, we demonstrated the usefulness of the layerbased hierarchical crystal design strategy due to 1D stacking control by achieving construction of P1 and P21 crystals from achiral organic salts using hydrogen-bonded chiral polar layers assembled by type II XBs. The results obtained here suggest the following three important crystal design strategies. First, utilization of supramolecular motifs with high dimensionality, especially 2D ones, is useful for crystal design because of restriction of assembly direction. Second, combinations of different halogen atoms could lead to crystal design incorporating XBs with variable robustness. The introduction of robustness-tunable XBs enables us to tune the energy balance among the other intermolecular interactions such as van der Waals interactions, resulting in control of the supramolecular assembly manner. Third, the type II XBs could be used for chiral crystallization due to their specific contact angles, while the type I halogen···halogen contacts (XCs) generate inversion centers, affording achiral crystals. Because of these features, this study will contribute to set up an

Table 4. Calculated Interaction Energies of the Type II XBs in the Optimized and Simulated Crystal Structures

a

space group

dX‑X (Å)a

θ1/θ2 (deg)a

HF (kcal/mol)a

MP2 (kcal/mol)a

ClBr(Me)-S-P1

P1

ClBr(Me)-O-P21

P21

BrBr(Me)-O-P1

P1

BrBr(Me)-S-P21

P21

3.518 3.708 3.686 3.787 3.526 3.720 3.643 3.799

105/174 98/157 84/162 93/157 104/175 99/159 83/163 91/158

1.462 1.183 1.071 1.844 1.577 1.599 1.514 2.049

−0.940 −1.185 −1.111 −1.424 −1.424 −1.195 −1.489 −1.592

Upper and lower columns in each of the cells represent the values calculated from models in Figure 6(i) and (ii), respectively. G

DOI: 10.1021/acs.cgd.5b01724 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 7. Stacking of hydrogen-bonded layers: in the case of (a) ClBA·BrCA12 and (b) BrBA·BrCA12 salt. (i) An ion pair, (ii) formation of a layer by hydrogen bonds (HBs), (iii) stacking of the layers by type II halogen bonds (XBs), (iv) further stacking of the layers by type II XBs and additional van der Waals (vdWs) interactions of alkyl chains, (v) construction of a crystal.



effective crystal design strategy for layered crystals, which reflect properties of the component layers, as well as conglomerates.



AUTHOR INFORMATION

Corresponding Authors

*(T.S.) E-mail: [email protected]. *(M.M.) E-mail: [email protected].

ASSOCIATED CONTENT

S Supporting Information *

Present Addresses #

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01724. Crystallographic information files are also available from the Cambridge Structural Data Center (CCDC) (http://www. ccde.cam.ac.uk/data_request/cif, CCDC numbers: CCDC975973 (ClBA·CA7), 976950 (ClBA·CA13), 975978 (ClBA· BrCA7), 975979 (ClBA·BrCA12), 975974 (BrBA·CA5), 975976 (BrBA·CA8), 975977 (BrBA·CA13), and 975975 (BrBA· BrCA12).

(T.S.) Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan. ‡ (M.M.) The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan. Notes

The authors declare no competing financial interest.



Details of crystallographic parameters and powder X-ray diffraction patterns (PDF)

ACKNOWLEDGMENTS

This work was financially supported by KAKENHI Grant Numbers 24350072, 24108723, 25763, 15J00237, 26620068, and the GCOE Program of Osaka University and Grants for Excellent Graduate Schools, MEXT, Japan. We are grateful to Dr. S. Clevers, and Ms. L. Yuan for measurements of SHG activities and to Dr. K. Miura, Dr. S. Baba, and Dr. N. Mizuno for crystallographic data collection at the BL38B1 (proposal numbers 2013A1605 and 2015B1234) in the SPring-8, JASRI.

Accession Codes

CCDC 975973−975979 and 976950 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/ cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. H

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ABBREVIATIONS HBs, hydrogen bonds; XBs, halogen bonds; XCs, halogen··· halogen contacts; TPAA, triphenylacetic acid; ClBA, pchlorobenzylamine; BrBA, p-bromobenzylamine; CAn, n-alkyl carboxylic acid; BrCAn, ω-bromocarboxylic acid; SHG, second harmonic generation; 1D, one-dimensional; 2D, two-dimensional; 3D, three-dimensional; DFT, density functional theory; GGA, generalized gradient approximation; PBE, Perdew, Burke and Ernzerhof; BSSE, Basis set superposition error; R-HB, ringtype hydrogen-bonded



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