Finding Rules Governing Layered Architectures of Trifluoroborate

Article pubs.acs.org/crystal

Finding Rules Governing Layered Architectures of Trifluoroborate Potassium Salts in the Solid State Radosław Kamiński,*,†,§ Katarzyna N. Jarzembska,*,†,§ Marek Dąbrowski,‡ Krzysztof Durka,‡ Marcin Kubsik,† Janusz Serwatowski,‡ and Krzysztof Woźniak† Biological and Chemical Research Centre, Department of Chemistry, University of Warsaw, Ż wirki i Wigury 101, 02-089, Warsaw, Poland ‡ Department of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland †

S Supporting Information *

ABSTRACT: A set of 15 new crystal structures of aryltrifluoroborate potassium salts (ArBF−3 K+), with various substituents at the aromatic ring, is reported. The considered substituents belong to one of three groups: CF3, halogen atoms (F, Cl, Br, I), and alkoxy functions (OMe, OEt, OiPr). All crystals were obtained via solvent evaporation, and the structural features were determined using single-crystal X-ray diffraction methods (including transferred aspherical atom model, TAAM). The resulting layered crystal structures were parametrized, whereas selected ones were additionally characterized computationally (using the periodic DFT approach). The data allowed for formulating basic rules characterizing a given layered structure of the parent phenyltrifluoroborate potassium salt derivative on the basis of the type and location of the aromatic ring substituents. These layered structures can be classified as single or double sheet depending on the mutual arrangement of the potassium cations. The double-sheet type of the ionic layer is formed in the parent compound (PhBF−3 K+) and most of its simple derivatives. This motif is broken into the single-sheet type by the presence of solvent molecules (water or acetone) or alkoxy groups. Another general observation is that the electron-donating ortho-substituents are coordinated to metal centers unless a more energetically favorable interaction can be formed (e.g., Br···I). Among the studied structures, layers interact one with another via various weak intermolecular interactions, i.e., from weak C−H···π contacts, through C−H···O and C−H···F interactions, up to halogen bonds (I···I, Br···I, Br···F). The layered character of the studied crystal structures and a very significant difference in the strength of hydrophobic and hydrophilic interactions are reflected in the platelike crystal morphology and their common tendency to stratify parallel to the layer planes.

1. INTRODUCTION The understanding of structure−property relationships constitutes one of the major issues of modern materials science. Consequently, solid state materials, where crystal structures can be relatively easily elucidated and thus potentially correlated with macroscopic properties (such as optical activity, mechanical resistance, thermal or electric conductivity, etc.), have lately been the subject of significant attention. Such investigations can be, however, complex and difficult, as they require extensive multiconditioned studies of crystalline materials using various experimental and theoretical tools. Therefore, it is sensible to start the analysis with relatively simple model cases so as to find basic rules governing the crystal lattice formation and dynamics, which may be further adapted to more complicated systems. Among numerous solid state materials, extended solids, classified as either coordination polymers or ionic solids, occurred to be particularly suitable for such studies. These are usually hybrid systems consisting of organic and inorganic parts © 2016 American Chemical Society

bound together by various intermolecular forces, such as covalent or ionic bonds. Using crystal engineering tools and concepts, such 3-dimensional (3D) networks can be designed by choosing a set of nodes (e.g., metal centers) and linkers (e.g., multifunctional organic compounds). There are already numerous examples in the literature, where the crystal structure features were fine-tuned via changing these two components in a predefined fashion.1−7 The current contribution is devoted to the relationships between crystal structure and energetic features of new hybrid organic−inorganic systems based on potassium phenyltrifluoroborate salts, ArBF3K.8 This group of compounds, being arylboronic acid derivatives, can be easily prepared from a trivalent boron agent and KHF2, which serves as a source of fluoride anions.9,10 Organotrifluoroborates are very well known Received: December 13, 2015 Revised: January 6, 2016 Published: January 12, 2016 1687

DOI: 10.1021/acs.cgd.5b01760 Cryst. Growth Des. 2016, 16, 1687−1700

Crystal Growth & Design

Article

in the field of organic synthesis and are extensively used as efficient partners for transition metal-catalyzed processes, such as Suzuki-Miyaura cross-coupling reactions,11−14 Chan−Lam type C−O or C−N bond couplings,15,16 or rhodium-catalyzed addition to 1,2- and 1,4-unsaturated compounds.17,18 Because of the high energy of a B−F bond and tetracoordinative nature of a boronate complex, organotrifluoroborates show exceptional stability toward air, moisture,19,20 and various chemical reagents. Such features make them excellent reagents for the construction of complex organic systems.8,21,22 Recent efforts have resulted in the preparation of almost 7000 organotrifluoroborate salts (several hundred are commercially available),23 whereas more than 250 scientific papers dedicated to these compounds have been published to date.8,24 Despite this increased interest in the chemistry of organotrifluoroborates, they have been largely unexplored in the fields of modern crystal engineering and coordination chemistry. Nevertheless, the distinct properties of organotrifluoroborate salts, their relatively simple molecular structures, and small size make them interesting candidates for studying various aspects of selfassembly. Among the few published exceptions are the studies on the crystal structure of tripotassium benzene-1,3,5-(tris)trifluoroborate25 (Cambridge Structural Database26 (CSD) REFCODE: TUVEP) and the recent investigations by Falcicchio et al. on the dipotassium benzene-1,4-(bis)trifluoroborate crystal structure (CSD code: CCDC 1402900).27 The case of dipotassium benzene-1,2-(bis)trifluoroborate (REFCODE: ECUFUE), which can be crystallized in its monoanionic form exhibiting a symmetrical μfluoride B···F···B bridge (REFCODE: ECUGUE),28 constitutes another interesting example. To date, 90 crystal structures containing the C−BF3 group have been deposited in the CSD. Among them, there are only 9 potassium aryltrifluoroborates with well-defined separated ionic parts including the above-cited structures and excluding the cases with K+ coordinated by crown ethers (for details, see Supporting Information).25,27−33 This set contains the potassium phenyltrifluoroborate (PhBF3K, referred to as bk01, REFCODE: YUHJUG),30 which constitutes a model parent compound for the current study. As the systematic studies on a larger group of trifluoroborates yielding structuralenergetic relations and the effects of phenyl ring substituents on potassium coordination and structural organization are missing, we have decided to fill this gap. Hence, we report here a series of 15 new crystal structures of PhBF3K derivatives selected in a way to find the rules governing the molecular self-assembly in the solid state. Our structural considerations are supplemented by periodic quantum-chemistry computations, which provide a deeper insight into the nature of intermolecular interactions responsible for molecular arrangement and crystal structure stability.

2.2. X-ray Data Collection. Single-crystal X-ray measurements of bk01, bk02, bk03, bk04, and bk12 were carried out on a Bruker AXS Kappa APEX II Ultra diffractometer equipped with a TXS rotating anode (Mo Kα radiation, λ = 0.71073 Å), multilayer optics, and an Oxford Cryosystems nitrogen gas-flow device (700 Series Cryostream). Measurements of all other derivatives were performed on an Agilent Technologies KM4CCD κ-axis diffractometer (recently upgraded with an Opal area detector) equipped with a Mo Kα sealed tube, graphite monochromator, and Oxford Cryosystems nitrogen gasflow device (600 Series Cryostream). In all the cases, single crystals of suitable sizes were mounted on a MiTeGen Double-Thickness MicroMount or cryoloop using Paratone N oil positioned at 50 mm distance from the CCD camera and cooled to 100 K. Data collection strategies, based solely on ω scans (with 0.5° rotation increment), were optimized and monitored applying the appropriate algorithms implemented within the APEX234 or CRYSALIS35 suites of programs, respectively. Unit cell parameter determination and raw diffraction image integration were performed with the diffractometer software (APEX2 or CRYSALIS). Data sets were corrected for Lorentz, polarization, and oblique incidence effects. Multiscan absorption correction, frame-to-frame scaling, and merging of reflections were carried out with the SORTAV program.36−39 Final data collection parameters are summarized in the Supporting Information. 2.3. Structure Solution and Refinement. All structures were solved using a charge-flipping method40−42 implemented in the SUPERFLIP program43 and refined with the JANA package44 within the independent atom model (IAM) approximation (initially). Scattering factors, in their analytical form, were taken from the International Tables for Crystallography.45 In all of the cases, orientations of methyl groups were determined on the basis of Fourier residual maps. Subsequently, for the X-ray data of reasonable quality, transferred aspherical atom model (TAAM) refinements were performed in the JANA package44 with the aid of the newest version of the University at Buffalo Data Bank (UBDB)46 based on the Hansen−Coppens multipole model.47 During TAAM refinements, all electron density parameters are kept fixed at the databank values, whereas the scale factor, atomic positions, and atomic displacement parameters (ADPs) are iteratively varied.48 Such an approach allows for obtaining an enhanced crystal structure model in terms of lower R-factors, better residual density maps, more reliable geometrical parameter, and so forth. For more details, see the Supporting Information.46−52,84 For the purpose of this work, the UBDB databank was extended with the atom types specific for potassium trifluoroborate complexes (for details, see Supporting Information25,30,53−57). New atom types were derived according to the literature procedure.46,58 CIF files for each refinement are present in the Supporting Information or can be retrieved from the Cambridge Structural Database26 (deposition numbers: CCDC 930653−930660, CCDC 931255, CCDC 1435650− 1435652, CCDC 1435654−1435655, and CCDC 1435780− 1435781). 2.4. Interlayer Interaction Energy Calculation. All of the studied compounds form layered architectures in the solid state. As these structures contain ionic species, and solvent molecules in some cases, it is more natural and efficient to compare the interlayer interaction energies among these systems between the ionic sides and the organic sides of the repeatable molecular slab fragments than to analyze them by means of the lattice energy. Such interaction energy computations were performed with the CRYSTAL program package (CRYSTAL09 version)59,60 at the DFT(B3LYP) level of theory61,62 using the crystal geometries taken from the TAAM refinement. In general, the pVTZ63−65 molecular all-electron basis set was used. Solely in the case of the potassium cation was the 86−511G basis set66,67 employed, whereas for the iodine atom, the 6-311G** basis set was used.68 Both Grimme dispersion correction69,70 and correction for basis set superposition error (BSSE)71 were applied. Additional upper and lower molecular layers were used as ghost function sets to obtain BSSE. The evaluation of Coulomb and exchange series was controlled by five thresholds set to the values of 10−7, 10−7, 10−7, 10−7, and 10−25.

2. EXPERIMENTAL DETAILS 2.1. Materials and Crystallization Details. All studied trifluoroborate potassium salts were provided by Sigma-Aldrich Co. as 97−99% pure crystalline powders. Single crystals of these compounds were prepared by slow solvent evaporation at room temperature from the corresponding concentrated solutions. Crystals of bk01, bk03, bk04, bk06, bk07, bk08, bk12, bk11, bk13, bk14, bk15, and bk16 were obtained from acetone solutions. Crystals of bk05 and bk09 were grown from 1:1 acetone/water solutions; bk02 hydrate was crystallized from water solution, whereas crystals of bk10 were grown from tetrahydrofuran (THF) solution. 1688



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The interlayer interaction energy (Eintl) calculation formula48,72,73 is analogous to that for cohesive energy48,71

E intl =

To achieve the goals described above, we have chosen a set of bk01 modifications using three types of substituents, i.e., electron-withdrawing CF3 groups, halogen atoms, and alkoxy functions. Additionally, the bk16 structure, being the only alkyltrifluoroborate salt out of the series where the BF3 group is attached to the aromatic ring via the CH2OCH2 linker, has been included for a comparison. In this case, the linker introduces some additional flexibility to the molecule, which clearly affects the resulting crystal structure. The studied hybrid complexes are schematically presented in Scheme 1. In turn, Figure 2 shows molecular structures of anionic species, potassium cations, and solvent molecules. It should also be noted that the crystal structures of bk03, bk08, and bk10 are of significantly lower quality than the remaining systems under consideration (in the case of the two latter structures, only rough IAM refinement was possible; Supporting Information). Nevertheless, the X-ray diffraction technique provides clear atom arrangement in these latter cases, which enables further qualitative analyses. 3.1. General Structural Remarks. The majority of the investigated compounds crystallize in the monoclinic crystal setting (bk02, bk03, bk04, bk05, bk07, bk09, bk11, bk14, bk15). The remaining ones belong either to the orthorhombic (bk01, bk06, bk08, bk10, bk16) or triclinic P1̅ space groups of symmetry (bk12, bk13). It should be noted that four compounds crystallize as solvates (bk02, bk03, bk03, bk08). Molecular geometries of all compounds are summarized in the Supporting Information. All the anions constitute rather rigid moieties, which despite some differences resulting from the substituent effects generally display quite similar features. For instance, the B−F bond distances range from 1.36 to 1.46 Å. These values, however, include the poor quality crystal structures, whereas excluding them, the B−F bond lengths are in a narrower range, i.e., from 1.39 to 1.44 Å. The shortest B−C bond is found in the bk08 crystal structure (1.56(4) Å; note: large esd due to poor data quality), whereas the longest one is in bk09 (1.634(2) Å). The B−C bond length in the alkyltrifluoroborate bk16 molecule is also in the above range and equals 1.606(2) Å. In the latter case, this is most presumably due to the lack of electronic coupling between the boron atom and the aromatic ring. The differences between B− C bond lengths in the remaining cases are statistically significant, yet no clear correlation can be found between the bond length and aromatic ring substituents. Nevertheless, the longest B−C bond found in bk09 might result from the relatively low data quality (the ADPs are significantly larger when compared to the remaining structures; Figure 2). 3.2. Supramolecular Structures. As expected, the studied organic−inorganic compounds share the basic supramolecular arrangement in the solid state, i.e., all of them form layered crystal architectures similar to the parent bk01 (Figure 1). In the crystal lattice, the aromatic fragments of the adjacent molecules interact mostly one with another, consequently separating the ionic molecular parts that form parallel salt-type slabs across the crystal. Such constructs resemble double layers formed by lipids due to the surfactant-like character of small phenyltrifluoroborate species. Formation of the double layers most likely constitutes one of the key steps in the crystal growth process. This statement is later supported by computational analysis. The studied crystal structures differ depending on the nature of the substituents and their location at the aromatic ring. The most crucial weak interactions are summarized in Table 1,

1 E bulk − Eslab n

where Eslab is the energy of a molecular slab extracted from the bulk, and n indicates the slab number per unit cell. Therefore, the resulting stabilization energy falls on a part of a slab belonging to the unit cell. CRYSTAL automatically assigns the slab group symmetry and cuts out the repeatable fragment. To allow for a direct comparison, the obtained interaction energy values are shown in two ways: they are scaled to the asymmetric unit and are also related to the unit area of a given molecular slab.

3. RESULTS AND DISCUSSION The parent bk01 compound constitutes a model hybrid organic−inorganic complex arranged in a specific type of layers in the crystalline state (Figure 1). Such layers contain species

Figure 1. Representation of the layer architecture formed by bk01 potassium salt in the solid state (atom colors: K, violet; F, green; B, orange; C, gray).

tightly bound via ionic interactions between the BF3 groups and potassium cations in the inner part of the slab, whereas the organic aromatic fragments point outward the molecular construct. It is expected that this motif would be preserved in other simple phenyltrifluoroborate derivatives. However, because the molecules in layers interact one with another via π-stacking contacts or hydrogen or halogen bonding, the final crystal structure may be significantly influenced by the type and position of aromatic ring substituents. Moreover, electronegative substituents, such as halogen atoms or alkoxy groups, may also coordinate potassium cations, which should strongly affect the molecular organization. Additional degrees of complexity can be introduced by incorporation of solvent molecules into the crystal structure because crystals of trifluoroborate salts are usually obtained from polar solvent solutions (water, methanol, acetone, etc.). In the current study, we aim to verify how the mentioned factors affect the molecular arrangement in the solid state with respect to the model bk01 and whether it is possible to formulate general rules allowing for structure prediction for compounds belonging to this family. 1689



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Scheme 1. Schematic Representation of the Studied Trifluoroborate Potassium Salts Supplemented by the Abbreviations Used in the Text, Systematic Names, CSD Codes, And Solvent Molecules if Applicablea

a

Atoms involved in the ionic layer formation (excluding the BF3 group) are shown in bold italics.

double-sheet type, whereas the remaining group is classified as single-sheet (Table 2). However, such a criterion is rather arbitrary, and so there are some intermediate cases, e.g., bk10 and bk13, which shall be described in detail further in the text. To compare all structures, we also introduced five other geometrical parameters describing molecular layers. These are the interlayer distance (dL), the interlayer penetration distance (dP), the layer thickness (dT), the angle between the aromatic ring plane and the layer plane (φR), and finally the angle between the line along the B1−C1 bond (except for compound bk16) and the respective cationic layer plane (φB) (Table 2). 3.2. Parent bk01 and Its Features. The structure of the model unsubstituted trifluoroborate salt naturally opens up the analysis. Although the bk01 structure is already known in the literature,30 its detailed description has not yet been provided. Because of the simplicity of the bk01 molecule, there are no factors that could distort the layer arrangement, and also no other acceptor centers at the aromatic ring that could coordinate potassium cations. Therefore, in this case, the double-sheet motif is efficiently formed (Figure 3a). In the bk01 structure, layers propagate perpendicularly to the Y direction with the distance between two adjacent cationic layers (dL) equal to approximately 14.1 Å. Interestingly, the φB and φR angles are quite far from the right angle (72° and 73°, respectively). This is a result of weak C−H···F and C−H···π interactions between the neighboring aromatic rings. In terms

whereas the layer geometrical parameters are given in Table 2. Information regarding the coordination of potassium ions is available in the Supporting Information. Additionally, the selected representative structures were characterized computationally, and the key energetic features are shown in Table 3. For facilitating the structural comparison, the layer motifs were parametrized (Figure 4, Table 2). A single layer is understood here as two slabs of molecules joined via the ionic parts located in the middle of the layer. In all of the cases, the K···F interactions are involved in the layer formation. For the purpose of further analyses, the crystal structures of the studied trifluoroboronate potassium salts were divided on the basis of the arrangement of potassium cations in the ionic slabs, which may form “double-sheet” or “single-sheet” motifs, as shown in Figure 3. The exemplary double-sheet cationic layer is created by the bk01 complex (see Figure 3a), where the interlayer potassium cations are located in two well-separated planes. In contrast, bk16 is a good representative of the second category, i.e., of a single-sheet layer type (see Figure 3b). There is, though, no sharp border between these two layer classes. To describe the layer features, a sheet-separation distance (dS) was introduced (Table 2, Figures 3 and 4). It is defined as a distance between the two least-squares-fitted planes computed for distinct potassium-ion sheets of the same molecular layer. Hence, structures with dS > 1.5 Å shall be considered as belonging to a 1690



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Figure 2. Labeling of atoms and estimation of their thermal motion parameters as ADPs (50% probability level) after final TAAM refinements. Some hydrogen atoms were omitted for clarity. Only a part of the asymmetric part of the unit cell is shown for the bk03, bk12, bk13, and bk14 structures. The bk08 and bk10 crystal structures are not shown here (very poor data quality, IAM refinement). Full data for all of these structures are present in the Supporting Information (CIF files). The coloring scheme is retained for all figures.

problem was discussed elsewhere73), however, we tried to make the choice consistent among all of the examined crystal structures. Structural and energetic features may be linked with the crystal macroscopic properties, such as morphology,72,73 compressibility,75 thermal expansion,76 or mechanical durability.77 Figure 5 shows a planar crystal of bk01 mounted on a cryoloop together with the relative orientation of the crystal coordinate system. The most pronounced faces are the ones associated with the {010} form, whereas the remaining ones are rather small. This observation is consistent with the crystal inner structure. Clearly, in the Y direction, where the interactions are either weakest or best stabilized by solvent, the thickness of the crystal is relatively small. On the other hand, along the X and Z directions, where the interactions responsible for forming of the ionic layer architecture are strongest, the crystal grows rapidly. Both effects contribute to the shape of the crystal, which grows in the form of welldefined plates. Another interesting aspect of the bk01 crystal structure is the resemblance of interaction pattern between phenyl fragments

of energy, bk01 is characterized by the most uniform interaction energy distribution among the studied systems. It is clearly seen that the interaction between the molecular layers (i.e., between the adjacent aromatic ring fragments pointing at each other, AA-type, Table 3) is quite weak, as it is mostly dispersive in nature (C···H contacts). It is nearly three times weaker than the corresponding value for the interaction energy between the ionic parts of molecules (−14.0 kJ mol−1 vs −38.4 kJ mol−1, Table 3). Furthermore, the interactions of ionic slabs in the case of bk01, either per asymmetric unit content or per unit area, are least advantageous when compared to the other structures. This is a consequence of the widest gap describing the double-sheet motif (2.6 Å) and the absence of solvent moieties or substituents that can participate in the electrostatic interactions. On the other hand, more isotropic interactions may stimulate similar crystal growing rates in different directions, which enhances the crystal quality. Indeed, the bk01 crystals were of remarkably higher quality with respect to the remaining crystals of the series. It should also be noted here that the interaction energy between the ionic slabs may differ depending on the potassium ion assignment to a slab (a similar 1691



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the crystal architecture modifications due to the introduction of various substituents to the aromatic ring. The selected bk01 derivatives can be divided into three groups judging by the type of aromatic ring substituents. We will start the analysis with the structures containing CF3 moieties (group I); then, we will switch to the halogen substituents (group II), and finally we shall discuss the alkoxy ligands (group III) and their impact on the resulting crystal structure. 3.3.1. Group I. This group of compounds consists of three systems, namely bk02, bk03, and bk04, all containing the CF3 functional groups. The very first observation is that, in all the three cases, the respective solvent molecules, either acetone or water, are incorporated in the crystal structures. All solvent species via oxygen atoms coordinate two potassium centers each. Additionally, the ortho substituents, i.e., the electron-rich CF3 groups or fluorine atoms at the phenyl rings in bk04, support the BF3 group interactions with the metal cations. The presence of numerous electron-donating centers, including solvent moieties that can bind potassium species, leads to the formation of single-sheet layer architectures (Figure 7). This is in contrast to bk01, in which the anion molecules are more tightly packed due to their relatively small size, and they also possess only BF3 groups able to coordinate potassium cations. Hence, the potassium centers here need to be effectively arranged so as to saturate their coordination spheres, which results in the double-sheet motif. Nevertheless, potassium coordination numbers remain higher for bk02, bk03, and bk04 (in all of these structures, potassium coordination number equals 9) than that for bk01 (coordination number equals 7) (see Table 2S in the Supporting Information). This is also reflected in significantly more advantageous interaction energies between the ionic slabs characterizing the current series with respect to the corresponding values for the parent compound. Because of the presence of solvent moieties grouped in the ionic part of the layer, the interactions between ionic edges of molecular slabs are much stronger than in the other studied cases. This is especially pronounced for bk02 (Table 3), which is characterized by the most favorable BB-type interlayer interaction energy of −143 kJ mol−1 per ASU (−5.4 kJ mol−1 per unit area) among the calculated systems. On the other hand, because of the presence of solvent molecules, the anionic species are less tightly packed than in bk01. This results in very similar interactions between the hydrophobic slabs (AA-type, Table 3) per unit area for bk01 and bk02 despite the difference in the corresponding energies per analogous molecular fragments. In the case of bk04 (and what was expected for bk03), this energy is more favorable. Here, more efficient C− H···F contacts are formed due to the CF3 group located in the para position (dP = 1.3 Å). This leads to the most advantageous intermolecular interaction energy among the computationally analyzed systems, equal to −30.4 kJ mol−1 per ASU and also per unit area despite more loosely packed aryltrifluoroborate anions because of the acetone species incorporated into the layers. Additionally, in the case of bk03, the CF3 groups are disordered, which indicates a rather low-energy-barrier rotation for these molecular fragments in the interlayer environment. The para substituents in bk03 and bk04 are also responsible for greater interlayer penetration and its overall thickness, which are both outstanding when compared to the remaining systems of interest (Table 2). Also in the three systems in the current series, anionic species are less inclined to the layer plane than in bk01.

Table 1. Selected Weak Interactions Present in Studied Crystal Structures Important in the Ionic Layer Formationa compound bk02 bk03

bk04 bk05

bk06 bk07

bk08

bk09

d/Å

compound

interaction

d/Å

F4···K1 F5···K1 F4···K2b F15···K2 F14···K4b

2.943(1) 2.932(6) 2.972(5) 2.921(5) 3.066(4)

bk10

3.00(1) 2.92(2) 3.24(1) 3.543(3) 3.526(6)

F23···K3 F22···K3c F33···K4 F32···K1c F4···K1 F4···K1d F4···K1e Br1···K1d F4···K1f F4···K1g F4···K1h F4···K1 I1···I1I Br 1d···K4 Br1c···K1 Br1c···K4j Br1b···K2 Br1a···K3j Br1a··· Br1cc Br1b···Br 1dj Br1···K1 F4···K1k Br1···F5h

2.893(5) 2.804(4) 2.857(7) 2.813(6) 2.835(1) 2.896(1) 2.956(1) 3.623(1) 3.086(3) 3.109(3) 2.904(3) 2.948(3) 3.805(1) 3.38(6) 3.64(4) 3.62(4) 3.42(4) 3.56(1) 3.47(1)

bk11 bk12

F4b···K1 F4b···K2 F4a K1 I1a···Br1al I1b··· Br1bm Cl1···K1k F4···K1 O1···K3n F8···K2 O2···K1 F12···K2 O3···K4e F16···K1 O4···K2 F4···K1 F4···K1o O1···K1o K8···K2 O2···K2 F5···K1p F4···K1q F5···K1r F4···K1 F6···K1n F6···K1s

2.793(1)

O1···K1 O1···K1c O2···K1

2.799(1) 2.902(1) 2.844(1)

interaction

bk13

bk14

bk15

3.61(6) 3.563(1) 2.748(1) 3.008(1)

bk16

3.134(3) 2.825(1) 3.071(1) 2.944(1) 2.827(1) 2.738(1) 3.103(1) 2.851(1) 2.849(1) 2.809(1) 2.819(1) 2.991(1) 2.844(1) 2.851(1) 2.811(2) 2.843(3) 3.020(3) 2.842(1) 3.054(2)

a In all cases, the BF3···K interactions are present; thus, they are not shown (for more details, see the Supporting Information). bSymmetry transformations: x−0.5, −y+0.5, z−0.5; c−x, −y, −z; d−x+1, y−0.5, −z+0.5; e−x+1, −y+1, −z+1; fx + 0.5, −y+0.5, −z; g−x, −y+1, −z; hx, y+1, z; I−x+1.5, y−0.5, −z+0.5; jx−0.5, −y, −z+0.5; kx, y−1, z; lx+0.5, −y+1, z; mx+0.5, −y, z; nx, y, z−1; o−x−1, −y, −z; px−1, −y+0.5, z− 0.5; qx, −y+0.5, z+0.5; rx, −y+0.5, z−0.5; sx−1, y, z−1.

to that in the orthorhombic crystal structure of benzene.78,79 It appeared that benzene molecules form layers similar to the phenyl ring contacts between the adjacent molecular slabs present in bk01, as illustrated in Figure 6. Interaction energy characterizing benzene layers confirms the analogy between the two molecular patterns (−13.0 kJ mol−1 per ASU for benzene vs −14.0 kJ mol−1 for bk01). It also shows that, in contrast to benzene, bk01 exists as a solid material at room temperature thank to the strong ionic interactions. As mentioned earlier, although crystals of the model compound are of relatively good quality, the other investigated systems form crystals that show a more pronounced tendency to stratify along the direction perpendicular to the layer best planes. Some of them also exhibit disorder in the regions of hydrophobic contacts or bind solvent species. This is most likely caused by more fuzzy polarization of the substituted PhBF3K molecules, which makes the interactions less directional and thus introduces some instability (greater number of crystal growth pathways, etc.). 3.3. Molecule Relative to Crystal Structure in the Studied Series. In this section, we shall have a closer look at 1692



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Table 2. Selected Geometrical Parameters Describing the Supramolecular Arrangement of Layersa Compound

Miller indices

dS/Å

dL/Å

dP/Å

dT/Å

φB/°

φR/°

Layer type

bk01 bk02 bk03b bk04 bk05 bk06 bk07 bk08b bk09 bk10f bk11 bk12b bk13f bk14 bk15 bk16

(010) (100) (10̅ 1) (001) (100) (001) (100) (010) (100) (001) (100) (010) (001) (010) (010) (001)

2.6 0.6 c 0.7 1.7 1.8 2.2 c 2.3 1.3 2.4 1.2 2.1 2.3 2.3 0.7

14.1 13.7 15.0 15.0 13.6 14.1 15.5 15.8 13.0 13.4 18.1 12.7 12.6 16.4 16.7 11.7

e e 1.4 1.3 e e e e e e e e e e e 5.6

12.1 12.3 16.4 16.3 11.1 11.2 13.4 13.2 10.8 15.9 15.6 11.8 11.9 14.7 14.8 23.3

72 77 82/70/84/74 85 59 63 62 75/78/76/74 57 65/65 77 85/66/84/59 65/32 57 58 d

73 83 73/69/82/90 85 87 78 67 76/90/89/73 70 81/86 80 88/72/86/71 78/77 59 65 75d

double-sheet single-sheet single-sheet single-sheet double-sheet double-sheet double-sheet single-sheet double-sheet g double-sheet single-sheet g double-sheet double-sheet single-sheet

dS, sheet-separation distance; dL, distance between adjacent cationic layers; dP, interlayer penetration distance; dT, layer thickness; φB, angle between the B1−C1 bond vector and the layer plane; and φR, angle between the aromatic ring plane and the layer plane. bFour molecules in the asymmetric part of the unit cell (ASU). cImpossible to distinguish separate sheets. dNo CAr−B bond present. eLayers do not interpenetrate one another. fTwo molecules in ASU. gBorderline case, see text for further explanation. a

Table 3. Energetic Characterisation of Selected Layered Structuresa structure bk01 bk02 bk04 bk05 bk07 bk09 bk12 bk15

solvent 1 H2O 1 C3H9O

EAA/ kJ mol−1

ESAA/ kJ mol−1 Å−2

EBB/ kJ mol−1

ESBB/ kJ mol−1 Å−2

−14.0 −19.7 −30.4 −17.6 −13.6 −24.7 −18.8b −14.4

−1.1 −1.1 −1.4 −1.1 −1.0 −1.5 −0.8b −0.9

−38.4 −143.3 −100.2 −84.2 −58.6 −82.7 b −71.0

−2.9 −8.0 −4.7 −5.4 −4.1 −5.1 b −4.6

a

Interlayer energy is calculated per ASU (or representative formula unit) (EXY) and per unit area (ESXY) at the DFT(B3LYP)/pVTZ level of theory. AA denotes interactions between phenyl fragments, whereas BB is between the ionic parts. bConvergence problems calculated with 6-31G** basis set where possible;74 potassium treated with the 86− 511G basis set.

Figure 4. Schematic representation of distance parameters used to quantify the layer architectures. Light-blue rectangles represent K···F bound ionic layers; yellow hexagons represent aromatic ligands.

Figure 3. Two extreme cases of a layered structure: (a) double- (bk01) and (b) single-sheet (bk16). Sheet-separation distance (dS) is also depicted. 1693



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the literature systems of the kind (e.g., in the known p-F29 (REFCODE: TOJYOI) or p-OMe29 (REFCODE: TOJYUO) crystal structures). It surely may occur only for the strongly basic species at the para position, very eager to bind cations. In such cases, we may observe the formation of ionic channels80 or possibly two ionic slabs fastened together by arylfluoroborate species. 3.3.2. Group II. This section is devoted to structures denoted as bk05−bk11, which constitute modifications of the parent molecule by two or three halogen phenyl ring substituents (F, Cl, Br, or I). Two doubly substituted systems, i.e., bk05 and bk06, open the discussion. The corresponding compounds are nearly identical, both having fluorine atoms at the ortho position with either bromine (bk05) or iodine (bk06) substituents at the 3-meta position. Consequently, the layer architectures of the respective crystal structures are very much alike. Similarly as in bk04, the o-fluorine atoms are involved in the layer formation being coordinated to potassium cations. Nevertheless, in the absence of solvent species in the crystal lattice, in both cases, double-sheet motifs described by similar numerical parameters (Table 2) are observed. The main difference between these two structures is the coordination of the 3-meta located halogen atom to potassium. In the case of bk05, the bromine atoms bind to potassium (dK···Br = 3.623(1) Å). Such K···Br interactions are possible thanks to the location of the bromine atom at the same side of the phenyl ring as the fluorine atom, the sizes of fluorine and bromine atoms, which enable more distant contacts, and the sufficient electrondonating character of bromine. However, in bk06, no such interactions are observed for iodine, which is the least electronegative and weakly electron-donating halogen atom (Figure 8a,b). This is reflected in a significantly more advantageous BB-type interslab energy obtained for bk05 than that calculated for bk01 or for somewhat similar to bk06 and bk07 (Table 2). bk06 exhibits layer arrangement in which the bulky iodine atoms are pushed back (φB = 63° for bk06, and φB = 59° for bk05), when compared to the bromine substituents in bk05. This is also confirmed by the larger numerical value of φR for the bk05 structure (the aromatic ring is here less inclined toward the layer surface). Nevertheless, despite these differences, potassium coordination numbers (Table 2S) in both structures are equal and amount to 9, which is, as expected, more than in bk01. In the case of bk05, the BF3

Figure 5. bk01 (PhBF3K) crystal picture showing the orientation of real crystal axes and crystal faces.

Figure 6. (a) Arrangement of the benzene molecules in two adjacent layers present in the orthorhombic form of benzene. (b) Arrangement of model bk01 molecules across the hydrophobic layers. Small turquoise spheres represent aromatic ring centers.

The final comment in this section concerns the para substituents. It could have been expected that in some cases the para substituents may coordinate potassium cations, and so the aryltrifluoroborate species could link together two ionic slabs. Nevertheless, such a structural pattern is rarely formed in these kinds of structures. None of the systems studied here is involved in such structural motifs, and it is not encountered in

Figure 7. Layered architectures of the (a) bk02, (b) bk03, and (c) bk04 crystal structures. 1694



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Figure 8. Layered architectures of (a) bk05, (b) bk06, and (c) bk07 crystal structures. Bromine and iodine atoms are shown as small spheres.

Figure 9. Layered architecture of bk10 crystal structures. (a) Crystal packing along Y direction. (b) Molecules of the top side of a single layer showing Br···I interactions (analogous interactions are present on the bottom side, though slightly shifted in the X direction).

describing the inclination of the whole aromatic ring. It is visible in Figure 8c that molecules are inclined approximately toward the Y direction as a result of the I···I interaction formation. Nevertheless, these additional interactions do not make the AA-type interlayer interactions more favorable. They remain comparable to those characterizing bk01 or bk05 crystals, being around 1.0 kJ mol−1 per unit area (Table 3). The next structure that fits the described pattern very well is bk10. The corresponding aryltrifluoroborate group resembles that of bk06 with an additional o-bromine atom. The iodine and bromine atoms are located in the 3-meta and 6-ortho positions, respectively, whereas the fluorine atom is at the 2ortho position. The 2-o-fluorine atom is again coordinated to the cationic layer, whereas as predicted the iodine atom does not bind to the metal centers (similarly as in bk06) (Figure 9a). However, the presence of an additional bromine atom induces the formation of Br···I interactions in the crystal lattice (Figure 9b, Table 1, ⟨dBr···I⟩ = 3.53 Å).83 The observed interactions are fully symmetric, i.e., both halogen atoms act as interaction donor and acceptor. As clearly indicated in Figure 9b, the lone electron pair (LEP) of iodine donates to the σ-hole of bromine,

group accounts for 7 coordination sites, whereas the remaining 2 are occupied by the o-F atom and the m-bromine atom. For bk06, the trifluoroborate groups saturate 8 potassium sites, and the ninth is occupied by the o-fluorine atom. The following structure, i.e., bk07, can be easily compared with the two preceding ones. Its molecule is isomeric to that of bk06 and differs only by the position of the iodine atom, which is 5-meta in the current case. Similarly as in the bk06 structure, potassium coordinates 9 fluorine atoms in total, 8 from the BF3 group and the o-fluorine substituent (Table 2S). Because of the location of the iodine atom in the 5-meta position and its relatively weak electron-donating character, its coordination to potassium is not possible. Molecules are significantly inclined toward the layer plane (φB = 62°; similar to bk06: φR = 67°). Such molecular arrangement, in contrast to bk06, enables weak I···I interactions (dI···I = 3.805(1) Å) between layers (Figure 8c). They form “zigzag” chains propagating along the Y direction (C−I···I angle is equal to 109.6(1)°). Their geometrical features match well the “lump-to-hole” pattern frequently observed in molecular crystals bearing the iodine atoms.81,82 This is also the factor governing the φR parameter 1695



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and at the same time, its own σ-hole accepts the electron density from the other bromine LEP. This results in “zigzag”shape Br···I···Br···I chains propagating along the Y direction present on both sides of the layer. The φB parameters equal 65° for both molecules, but in contrast to bk07, the φR equals either 81° and 86°, indicating that the aromatic rings are almost perpendicular to the layer plane. Such geometry is obviously a consequence of the Br···I interactions as clearly visible in Figure 9b. Quite interestingly, the bk10 structure is the one where the assignment of the layer type is rather difficult (Table 2). We presume that the presence of the auxiliary Br···I interactions somehow stretches the double-sheet motif apart to the shape of a single-sheet arrangement (dS = 1.3 Å). However, the resemblance of bk10 to bk05−bk07 structures is certain, which makes it a somewhat borderline case. This observation is also reflected in potassium coordination. Two symmetryindependent potassium atoms are coordinated either by 9 or 7 fluorine atoms (Table 2S), and this asymmetry perhaps breaks the formation of a fully developed double-sheet layer. Another interesting aspect here is that solely the o-fluorine atom binds to potassium, whereas bromine remains the only ortho substituent among all studied systems that does not coordinate to metal centers. The next interesting example of layered crystal architecture is bk09 (Figure 10a). Similarly to bk05, the corresponding

Consequently, the two structures are characterized similarly and the most advantageous interaction energy of the BB-type in the second series (Table 3), both for the asymmetric unit and unit area. Additionally, the high potassium coordination number of 9 (Table 2S) again leads to a decrease of the sheet-separation distance, which is 2.3 Å for bk09 when compared to the model bk01 (dS = 2.5 Å), but it is still significantly greater than in bk05 (dS = 1.7 Å). Because of the presence of the m-fluorine atom and thanks to the effective mutual arrangements of the aromatic rings, bk09 is also described by a relatively significant BB-interlayer energy, which amounts to −1.5 kJ mol−1 per unit area, exceeding all of the corresponding calculated values for other systems. Furthermore, the m-fluorine atoms interact with the o-bromine substituents, forming the F···Br contacts (Table 1) that additionally stabilize the layers themselves. The subsequent structure, bk11, exhibits similar arrangement in the solid state to bk09, as shown in Figure 10. In both cases, the ortho substituents (F, Cl, and Br) coordinate to potassium (Table 2S), and the resultant motif can readily be described as the double-sheet. Nevertheless, the φB and φR parameters show significantly more deviation from 90° for bk09 than for bk11 (Table 2). Furthermore, the presence of the 2-o-chlorine substituent instead of fluorine and the size of chlorine atom itself are not sufficient to enable formation of the 3-m-Cl···K interactions, which is in contrast to bk05 with the respective oF and m-Br substituents. The resulting potassium coordination number in bk11 is thus lower than in bk09 and amounts to 8 (Table 2S). These observations, and the presence of the pmethyl substituent (which increases the molecular volume) pointing outward from the layer in the case of bk11 (Figure 10b), explain the considerably larger interlayer distance in the bk11 structure (dL = 18.1 Å) than that in bk09 (dL = 13.0 Å). The interlayer distance in bk11 is actually the largest among all of the crystal structures studied here (Table 2). In turn, a single layer thickness (dT) for bk11 is comparable to that observed in bk03 and bk04 with the CF3 groups in the para positions or bk10. Finally, we shall shortly discuss the bk08 structure. It contains two bromine atoms at the aromatic ring at the 2-ortho and 5-meta positions and, as expected, solely o-Br is coordinated to the potassium cation (Figure 11). However, bk08 cannot be easily compared to the other systems from the series due to the presence of acetone moieties in its crystal structure. Solvent molecules are coordinated to potassium atoms along with the fluorine (from the BF3 group) and bromine atoms. Similarly to bk02−bk04 crystal structures, incorporation of solvent species invokes the formation of single-sheet motifs. Consequently, the coordination number of potassium is increased to 8 and 9 when compared to the parent bk01 (Table 2S). Also interesting here is that the hydrophobic slabs are interacting via weak van der Waals interactions (H···H contacts) rather than via the expected Br···Br interactions. 3.3.3. Group III. This last series consists of four structures, i.e., bk12−bk15. Their common feature is the presence of an alkoxy group at the aromatic ring. Because the supplementary structure, namely bk16, in this aspect matches the series, we will add it to the discussion in this section. The molecules of bk12 and bk13 both contain two substituents at the aromatic ring, i.e., the 2-o-fluorine atoms and the 6-o-isopropoxy group or 3-m-propoxy function, respectively. Consistent with the previous observations, the oF atoms coordinate to the metal centers. Furthermore, in both

Figure 10. Layered architectures of (a) bk09 and (b) bk11 crystal structures. For bk11, note the Br···K interactions.

trifluoroborate fragments contain bromine and fluorine substituents. Two fluorine atoms are located at the 2-ortho and 3-meta positions, whereas the bromine atom is at the 6ortho position of the aromatic ring. Both mentioned crystalline systems, i.e., bk05 and bk09, belong to the double-sheet type of layered structure and are characterized by similar distances between the adjacent cationic slabs. In bk09, the fluorine atom at the ortho position naturally coordinates to potassium, but also the bromine atom at the remaining ortho position, in contrast to that in bk10, forms the K···Br interaction (3.5624(5) Å). The interaction between ionic edges of the molecular slabs is here very similar to that calculated for bk05, where the BF3 group is also supported by the fluorine and bromine substituents in coordination of potassium centers. 1696



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which is well-reflected by remarkably low φB values (65° and 32°). Therefore, no functional groups are pointing outward from the layers, which makes them quite compact and thin, similar to those of bk12. It occurs that systems bearing two fluorine atoms at the ortho positions and meta alkoxy species behave significantly differently than the ones described above. The molecules of bk14 and bk15 differ only by the presence of a p-fluorine atom at the aromatic ring in the latter case. As expected, these very similar molecules form almost identical crystal structures (Figure 13).

Figure 11. Layered architecture of bk08 crystal structure. Note the absence of interlayer Br···Br interactions and the presence of solvent molecules leading to a single-sheet layer type.

cases, the electronegative oxygen atoms from alkoxy species are also bound to potassium cations. Both systems crystallize with more than one molecule in the asymmetric part of the unit cell (4 for bk12 and 2 for bk13), which results in relatively complex molecular arrangements. In the case of bk12, because of the bulky 6-o-isopropoxy group, a single-sheet motif is formed. However, as shown in Figure 12a, it is strongly undulated. In the absence of para and

Figure 12. Layered architecture of (a) bk12 and (b) bk13 crystal structures. Figure 13. Layered architectures in the (a,b) bk14 and (c,d) bk15 crystal structures.

meta substituents, the layers are relatively thin (dL and dT parameters, Table 2) but also weakly interacting. They are characterized by one of the lowest BB-type interlayer interaction energies, which is especially visible when calculated per unit area (single-sheet motifs appear for less tightly packed crystal structures). Additionally potassium coordination numbers oscillate here between 7 and 8 (Table 2S). In turn, in the case of bk13, the potassium coordination numbers are even lower (6 and 7) because of the size of the propoxy groups, whereas the potassium sheet distance is between 1.0 and 2.1 Å. Nevertheless, the cationic arrangement can be classified as a double-sheet motif. As the meta substituent coordinates to potassium, the trifluoarylborate species are significantly rotated,

The presence of the extra fluorine atom in the para position in bk15 does not introduce any significant changes in terms of layer formation and crystal packing; however, it seems to reduce the degree of possible minor disorder that is observed in the bk14 side chain (O1 and C7 atom ellipsoids are significantly larger, Figure 2). The layers in bk14 and bk15 are described by almost equal numerical parameters, as indicated in Table 2. In bk14 and bk15, both o-fluorine atoms are coordinated to potassium centers. This results in inclination of aromatic rings toward the surface of the layer to make the F···K interactions more effective (Figure 13b,d). 1697



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In general, two ionic arrangement types are observed: double- and single-sheet motifs. The first type is present in crystals of the model bk01 compound and its simple modifications and seems to constitute the basic/initial potassium cation pattern. In turn, single-sheet motifs are observed when many atoms, usually from bulky molecular groups or solvent species, contribute to the formation of ionic slabs. Indeed, examples show that the presence of solvent molecules (water, acetone) or the ortholocated alkoxy moieties leads inevitably to single-sheet type cationic patterns. In all of these cases, the oxygen atoms are strongly coordinated to potassium. However, although the coordination of an o-alkoxy group to potassium center can be easily explained (electronegative oxygen atoms and the geometrical proximity), there is no clear indication when solvent molecules are built in a crystal structure. It seems, though, that the presence of the CF3 fragment stimulates solvent incorporation into the crystal network. The favorable location of the ortho aromatic ring substituents allows not only the mentioned alkoxy oxygen atoms to be effectively coordinated to potassium centers, as such behavior is also observed for other electron-donating species, such as halogen atoms (F, Cl, Br) and the CF3 fragments. When present, both o-halogen substituents are usually bound to potassium cations. For instance, in bk14 and bk15 both o-F atoms are coordinated to the metal centers, whereas in bk09, they are coordinated to the respective Br and F atoms. This confirms the advantage of formation of the K···X (X = halogen atoms) contacts. In turn, in bk12, we may observe simultaneous interactions of the o-isopropoxy group and o-F atom with the potassium cations. On the other hand, bk10 constitutes a notable exception with its o-Br substituent not engaged in ionic slab formation. In general, coordination of the ortho substituent changes the inclination of the whole ring toward the layer. This is naturally also coupled with the supplementary weak interactions within and/or between layers. Importantly, in some cases, the o-F atom allows for binding the meta substituent located at the same edge of the aromatic ring to potassium cations. This happens in the structures of bk05 (3-m-Br) and bk13 (3-m-propoxy). In turn, such a situation does not take place if there are two o-F atoms (then, they are both coordinated instead, e.g., bk14) or when the size and electron-donating character are not sufficient (e.g., 2-o-F and 3-m-I in bk06). Furthermore, in the case of 2-o-Cl atom in bk11, the 3-m-Cl is not bound to K+. When meta substituents support the ionic slab formation, then the aromatic ring is significantly rotated when compared to the parent bk01 structure. Thanks to the various studied substituent combinations, we can observe the formation of different weak interactions, i.e., from weak (cooperative) C−H···π contacts through the C−H··· O and C−H···F interactions up to various halogen bonds, such as I···I, Br···I, and Br···F. Such secondary interactions, however, may have a significant influence on some structural features, for example, in the mentioned case of bk10, where the more advantageous Br···I halogen bonds are formed instead of the oBr···K contacts. As might be expected, the interactions between ionic fragments are most energetically advantageous. The interaction energies in the hydrophobic region are clearly a few times lower per both ASU and unit area. Such structural and energetic features determine crystal morphology and mechanical properties. As can be expected, crystals usually exhibit plate-

Ethoxy groups are not involved in potassium cation coordination, but instead they form weak O···H interactions stabilizing the layer motif. Cationic motifs are clearly of the double-sheet type. The layers are relatively thick, as the ethoxy substituents are directed outside the layers. The very last case constitutes an example of the parent compound modification with the boron atom, which is not bound directly to the aromatic ring. The BF3 group is instead connected to the ring through the linker (CH2OCH2), which introduces some additional flexibility to the molecule. Therefore, the metal centers are not only coordinated by the trifluoroborate group but also interact strongly with the oxygen atoms from the linker and the o-OMe group. Interaction with oxygen atoms and the volume of the substituents break the double-sheet motif into the extreme case of a single-sheet pattern (as indicated before; Figure 3b). Interestingly, the layers exhibit “cavities”, which are occupied by the molecules from the adjacent layers. Such packing results in a very efficient interpenetration of layers, which is most significant among all studied structures (dP = 5.6 Å). On the other hand, such packing reduces the distance between the cationic layers (dL), which is again most outstanding in the data set, whereas the layer thickness (dT) is naturally largest (Figure 14, Table 2).

Figure 14. Layer architecture of the bk16 crystal structure. Note the large interpenetration of layers.

4. SUMMARY AND CONCLUSIONS The systematic analysis of the chosen set of aryltrifluoroborate potassium salt crystal structures allowed deriving basic rules governing crystal architectures in this kind of hybrid organic− inorganic solid state material. As expected, the studied compounds share the general supramolecular arrangement in the crystal state, i.e., they all form layered crystal structures similar to that observed for the parent bk01. In the crystal lattice, the ionic parts form parallel salt-type slabs across the crystal, whereas the aromatic fragments on the other side of trifluoroborate moieties interact mainly with one another within and between the layers. Such constructs resemble double layers formed by lipids due to the surfactant-like character of small aryltrifluoroborate species. Formation of the double layers most likely constitutes one of the key steps in the crystal growth process. 1698



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(4) Cui, Y. J.; Yue, Y. F.; Qian, G. D.; Chen, B. L. Chem. Rev. 2012, 112, 1126. (5) Dobrzycki, Ł.; Woźniak, K. CrystEngComm 2008, 10, 525. (6) Mukherjee, A.; Tothadi, S.; Desiraju, G. R. Acc. Chem. Res. 2014, 47, 2514. (7) Desiraju, G. R. J. Am. Chem. Soc. 2013, 135, 9952. (8) Hall, D. G. Boronic Acids; 2nd ed.; Wiley-VCH: Weinheim, Germany, 2011. (9) Vedejs, E.; Chapman, R. W.; Fields, S. C.; Lin, S.; Schrimpf, M. R. J. Org. Chem. 1995, 60, 3020. (10) Vedejs, E.; Fields, S. C.; Hayashi, R.; Hitchcock, S. R.; Powell, D. R.; Schrimpf, M. R. J. Am. Chem. Soc. 1999, 121, 2460. (11) Molander, G.; Ellis, N. Acc. Chem. Res. 2007, 40, 275. (12) Molander, G. A.; Biolatto, B. Efficient Ligandless PalladiumCatalyzed Suzuki Reactions of Potassium Aryltrifluoroborates. Org. Lett. 2002, 4, 1867−1870. (13) Molander, G. A.; Canturk, B. Angew. Chem., Int. Ed. 2009, 48, 9240. (14) Stefani, H. A.; Cella, R.; Vieira, A. S. Tetrahedron 2007, 63, 3623. (15) Chan, D. M. T.; Monaco, K. L.; Wang, R.-P.; Winters, M. P. Tetrahedron Lett. 1998, 39, 2933. (16) Quach, T. D.; Batey, R. A. Copper(II)-Catalyzed Ether Synthesis from Aliphatic Alcohols and Potassium Organotrifluoroborate Salts. Org. Lett. 2003, 5, 1381−1384. (17) Pucheault, M.; Darses, S.; Genet, J.-P. Chem. Commun. 2005, 4714. (18) Batey, R. A.; Thadani, A. N.; Smil, D. V. Org. Lett. 1999, 1, 1683. (19) Ting, R.; Harwig, C. W.; Lo, J.; Li, Y.; Adam, M. J.; Ruth, T. J.; Perrin, D. M. J. Org. Chem. 2008, 73, 4662. (20) Lennox, A. J. J.; Lloyd-Jones, G. C. J. Am. Chem. Soc. 2012, 134, 7431. (21) Darses, S.; Genet, J.-P. Eur. J. Org. Chem. 2003, 2003, 4313. (22) Darses, S.; Genet, J.-P. Chem. Rev. 2008, 108, 288. (23) Chemical Abstracts Service, 2015. (24) Thomson Reuters, 2015. (25) Franz, D.; Wagner, M.; Lerner, H.-W.; Bolte, M. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2010, C66, m152. (26) Allen, F. H. Acta Crystallogr., Sect. B: Struct. Sci. 2002, B58, 380. (27) Falcicchio, A.; Lill, S. O. N.; Perna, F. M.; Salomone, A.; Coppi, D. I.; Cuocci, C.; Stalke, D.; Capriati, V. Dalton Trans. 2015, 44, 19447. (28) Chase, P. A.; Henderson, L. D.; Piers, W. E.; Parvez, M.; Clegg, W.; Elsegood, M. R. J. Organometallics 2006, 25, 349. (29) Harrison, W. T. A.; Wardell, J. L. Acta Crystallogr., Sect. E: Struct. Rep. Online 2014, 70, 68. (30) Conole, G.; Clough, A.; Whiting, A. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1995, 51, 1056. (31) Crawford, A. G.; Liu, Z.; Mkhalid, I. A. I.; Thibault, M.-H.; Schwarz, N.; Alcaraz, G.; Steffen, A.; Collings, J. C.; Batsanov, A. S.; Howard, J. A. K.; Marder, T. B. Chem. - Eur. J. 2012, 18, 5022. (32) Lee, J.-K.; Gwinner, M. C.; Berger, R.; Newby, C.; Zentel, R.; Friend, R. H.; Sirringhaus, H.; Ober, C. K. J. Am. Chem. Soc. 2011, 133, 9949. (33) Gott, A. L.; Piers, W. E.; Dutton, J. L.; McDonald, R.; Parvez, M. Organometallics 2011, 30, 4236. (34) Bruker AXS: Madison, Wisconsin, USA, 2012. (35) Agilent Technologies: Yarnton, Oxfordshire, England, 2013. (36) Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421. (37) Blessing, R. H. Acta Crystallogr., Sect. A: Found. Crystallogr. 1995, 51, 33. (38) Blessing, R. H. J. Appl. Crystallogr. 1989, 22, 396. (39) Blessing, R. H. Crystallogr. Rev. 1987, 1, 3. (40) Oszlányi, G.; Sütő , A. Acta Crystallogr., Sect. A: Found. Crystallogr. 2005, 61, 147. (41) Oszlányi, G.; Sütő , A. Acta Crystallogr., Sect. A: Found. Crystallogr. 2004, 60, 134. (42) Palatinus, L. Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 2013, 69, 1. (43) Palatinus, L.; Chapuis, G. J. Appl. Crystallogr. 2007, 40, 786.

like shapes, and they frequently tend to stratify parallel to the layer planes. Finally, it should be noted here that there are some rare cases when molecular channels or molecular buckles are observed. This happens when very strongly electron-donating substituents or electronegative atoms are present in the aromatic ring. Nevertheless, for simple crystal structures derived from bk01, the outlined rules should be applicable and shall enable prediction of the layered structure architecture features. This can be further used in the sensible crystal engineering of more complex materials based on aryltrifluoroborate potassium salt units. This issue shall be investigated in the future.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01760. Additional literature information, refinement details, potassium coordination sphere geometries, and new UBDB entries (PDF) Accession Codes

CCDC 1435650−1435652, 1435654−1435655, 1435780− 1435781, 930653−930660, and 931255 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, by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Author Contributions §

R.K. and K.N.J. contributed equally to this work

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS R.K., K.N.J. and M.K. thank the Iuventus Plus grant (0220/ IP3/2011/71) of the Polish Ministry of Science and Higher Education for financial support. M.D., K.D., and J.S. thank the Warsaw University of Technology for financial support. R.K. would like to thank the Foundation for Polish Science for financial support within “International PhD Projects” program. The Wroclaw Centre for Networking and Supercomputing (Grant No. 285) is gratefully acknowledged for providing computational facilities. The authors thank Bartolomeo Civalleri (Turin, Italy) for helpful discussions concerning computational aspects and Václav Petřı ́cě k (Prague, Czech Republic) for helping with the JANA program. We also gratefully acknowledge Sigma-Aldrich Co., Milwaukee, WI, USA, for a long-term collaboration and continuous donation of chemicals.

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REFERENCES

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