Polymorphs, Solvates, Polymorphs of Solvate and Cs+–π Interactions

Sep 9, 2013 - polymorphs of dioxane solvate (2d and 2e) of bis-phenol 2 are distinguishable. The main difference ...... *E-mail: [email protected]. N...
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Polymorphs, Solvates, Polymorphs of Solvate and Cs+−π Interactions of Fluorine-Substituted bis-Phenols Bhaskar Nath and Jubaraj B. Baruah* Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India S Supporting Information *

ABSTRACT: We present here polymorphs and solvates of two isomeric bis-phenols namely 4-[(2-fluorophenyl)(4-hydroxy-3,5-dimethyl phenyl)methyl]-2,6 dimethylphenol (bis-phenol 1) and 2-[(2-fluorophenyl)(2-hydroxy-3,5-dimethylphenyl)methyl]-4, 6 dimethylphenol (bisphenol 2), and some of their interconversions. Two polymorphs of bis-phenol 1 with different crystal densities were observed. The polymorph 1a (orthorhombic, Pbca) self-assembles through O−H···O and C−H···F−C interactions and has voids of pore volume of 326 Å3 running along the crystallographic a axis, whereas the polymorph 1b (monoclinic, P21/c) that self-assembles via C−H···F−C and C−H···π interactions is without voids. The polymorph 1a or dimethylformamide solvate 1c transforms to polymorph 1b on heating. The crystal packing of the unsolvated bis-phenol 2 is devoid of C−H···F−C interactions. We obtain two dimethylsulfoxide (dmso) solvates of bis-phenol 2 with different stoichiometry, 2b (1:0.5) and 2c (1:1). The solvate 2c is formed at high temperature from bis-phenol 2 in dmso. The solvate 2b has the dimeric subunits of the parent bis-phenols in its packing pattern, whereas the solvate 2c has repeated units which are constituted by dmso-bridged bis-phenol molecules. The two polymorphs of dioxane solvate (2d and 2e) of bis-phenol 2 are distinguishable. The main difference between the structure 2d and 2e is that the latter contains C−H···F−C interactions, whereas the former does not have C−H···F−C interactions. Structure of the polymeric cesium salt of 2 has η2 and η4-types of Cs+−π interactions.

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INTRODUCTION There is a definite interest to develop stable assemblies of nanoscale networks.1 Among them, the fluorine-substituted assemblies are of interest due to their enhanced solubility and superior hydrogen absorption ability.2 Fluorine substitutions on substrates also influence the enzyme−substrate recognition.3 The van der Waals radii of fluorine (1.47 Å) and oxygen (1.57 Å) are comparable; the difluoromethylene group is isosteric and isopolar to an ethereal oxygen atom.4 Due to the nonpolarizable nature, the fluorine atom is a weak hydrogen bond acceptor, and a fluorine attached to a carbon is not readily involved in hydrogen bond formation.5 Theoretical calculations show that the strengths of C−H···F−C bonds6 lie between 2 to 3.2 kcal/mol. There are different types of interactions involving C−F bonds, such as C−H···F−C and C−F···π interactions.7 Despite the low affinity to form the C−H···F−C interactions, their presence provides directional forces in fluorine-containing organic compounds.8 Polymorphisms of organic fluorine compounds are welldocumented.9 Covalently linked fluorine atoms in crystal lattice are likely to be near hydrogen atoms, rather than being close to electronegative atoms such as oxygen. To adopt a stable packing pattern in such compounds, the interactions of fluorine atoms with adjacent atoms are not necessarily attractive.10 Recrystallization of fluorophenols under different pressure led to polymorphs, which are differentiated by C−H···F−C interactions.11 The fluorophenols with high Z′ values are also reported12 and the cocrystals of penta-fluorophenol with phenanzine in different proportions of the host−guest ratio having C−H···F−C interactions are known.13 Study on assemblies of fluorine containing © XXXX American Chemical Society

compounds possessing other strong hydrogen bond sites such as in fluoro bis-phenols (Figure 1) may result in different

Figure 1. Two isomeric fluoro bis-phenols.

polymorphic structures. We show here the self-assemblies of 4[(2-fluorophenyl)(4-hydroxy-3,5-dimethylphenyl)methyl]-2,6dimethylphenol (bis-phenol 1) and 2-[(2-fluorophenyl)(2hydroxy-3,5-dimethyl phenyl)methyl]-4,6-dimethylphenol (bis-phenol 2) (Figure 1) leading to different polymorphs and polymorphs of solvate as well as cation−π interactions. To appreciate the essence of such observations, the structural properties are related through other spectroscopic and physical properties. Received: August 10, 2013 Revised: September 3, 2013

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Figure 2. (a) Optical micrograph images of the morphologies of the two polymorphs 1a and 1b. (b) H-bond interactions in polymorph 1a. (c) C−H··· F−C and C−H···π interactions in polymorph 1a. (d) Packing pattern of the polymorph 1a.

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RESULTS AND DISCUSSION

voids has been confirmed by thermogravimetry (Figure S9 of the Supporting Information). The crystals of the polymorph 1b belong to the monoclinic space group P21/c. This polymorph is crystallized from the acetic acid solution of 1. In the crystal structure of 1b, it is observed that one of the hydroxy groups is involved in the O−H···π interaction with the fluoro-substituted aromatic ring of another molecule (dO1−H···π = 3.568 Å, π = centroid of the phenyl ring) to form dimers (Figure 3a), and the other hydroxy group is not involved in weak interactions. The O−H···π interactions were found to be responsible for generating polymorphs of 1, 1-bis-(4-hydroxyphenyl) cyclohexane.23 In that study, the cleavage of O−H···O bonds as well as the movement of H-bonded chains was shown to form the O−H···π interactions between similar rings. In the case of 1b, the O−H···π interactions are involved with the fluorosubstituted aromatic rings, which is absent in 1a. The polymorphs 1a and 1b have differences in the weak C−H···F−C interactions. In the case of 1a, C−H···F−C interactions are between dissimilar rings, whereas in 1b, such interactions are between similar rings (Figure 3b). From the separating distances between the donors and acceptors in the structure of 1b, it is clear that O−H···π and C−H···F−C interactions play a key role in the crystal packing, whereas O− H···O and C−H···F−C interactions play major roles in the packing of the polymorph 1a. The conformational polymorphs in diols24,25 are well-documented. The variations on the numbers of molecules in unit cells were also known to cause polymorphism in bis-phenols.26 The primary difference of the two polymorphs arises from voids in the packing patterns. In a recent article, we have shown existence of the porous and nonporous form of the polymorphs in an imidazole-based bis-phenol,21 in which we have shown surface area through gas absorptions. However, in the present case, the compound melts at low temperature under vacuum and transforms to a nonporous form, which deterred us to study

The fluoro substituted bis-phenols namely bis-phenol 1 and bisphenol 2 were synthesized by a conventional procedure.14 It is a well-known fact that the hydroxy groups help in assembling of organic compounds through O−H···O interactions,15 and these bis-phenols are no exception as hosts.16 The basic point which has helped in several new observations presented in this article arises from the wide variations of packing patterns in these systems. Accordingly, we have observed two polymorphs of bisphenol 1, polymorph 1a and polymorph 1b, from independent crystallization from methanol or acetic acid, respectively. Crystal morphology (Figure 2a) are easily distinguishable. The polymorph 1a crystallizes in the orthorhombic space group Pbca. The packing pattern has strong O−H···O interactions from the two hydroxy groups, which leads to the formation of a hydrogen-bonded sheetlike structure in the ac-crystallographic plane (Figure 2b). Apart from the strong hydrogen bond interactions, weak interactions such as C−H···F−C and C−H···π interactions (based on their distance of separations) also contributes to the stability of the crystal. The C−H(3)···F(1)− C distance in this structure is found to be 2.63 Å (Figure 2c). There is considerable crystal engineering on fluorophenols7,17 and halo-substituted bis-phenols,18 but there is no structural study on fluoro bis-phenols to make direct comparisons of such weak interactions. The observed H···F distances for C−H···F−C interactions with the obtuse angle reported by other researchers are in the range of 2.2 to 2.3 Å.19 The observed distances in polymorph 1a and polymorph 1b are comparable with the distances (dH···F = 2.61 to 2.95 Å) found in the polymorphs of 2-fluorophenylacetylene.7e The polymorph 1a adopts a porous structure containing voids with pore volume of 326 Å3 and a dimension of 4.5 × 8.5 Å running along the crystallographic a axis (Figure 2d). The absence of any disordered solvents in these B

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Figure 3. (a) O−H···π and C−H···π interactions in polymorph 1b. (b) C−H···F−C interactions in polymorph 1b leading to a linear chain. (c) Packing pattern of the polymorph 1b viewed along the crystallographic ac plane.

the range from 1.24 to 1.36 g/cm3. In the anhydrous carbamazepine, polymorphs have the same strong hydrogen bond interactions and the relative energy differences between the polymorphs are of the order of 0.7 kcal/mol. There is also a difference in the IR spectra of the two polymorphs, and the hydroxy stretching frequency of the polymorph 1b appears at 3609 cm−1, whereas it appears at 3441 cm−1 for the polymorph 1a (Figure S10 of the Supporting Information). The difference in the 368 cm−1 toward the higher side in the IR suggests its least participation in hydrogen bond formations. From the differential scanning calorimetry (DSC) with a heating rate of 3 °C per minute, it is found that the polymorph 1a shows an endoexothermic phase transition at 90 °C, followed by two endothermic peaks at 162 and 168.8 °C whereas DSC of the polymorph 1b obtained from heating rate at 3 °C per minute shows it to melt at 172 °C (Figure S15 of the Supporting Information). The endoexothermic peak at 90 °C may be due to partial collapse of the porous structure to form a tight-packed structure. The second melting point of the 1a at 168 °C is attributed to arise from 1b formed from 1a through partial conversion to 1b during heating. The difference in melting temperature arises due to the presence of some amount of unconverted 1a, which acts as an impurity to lower the melting point of the portion of 1b. The transformation of 1a to 1b on heating is visually noticeable, as the orange crystals of 1a turns pink on heating at ∼160 °C due to conversion to 1b; the powder XRD of the heat-treated sample has confirmed the transformation (Figure 4). However, high pressure to 11 Torr does not collapse the porous structure of 1a, as the PXRD of the sample of 1a recorded after applying such pressure does not change.

consistent gas absorption. The powder-XRD patterns of the polymorphs 1a and 1b are shown in Figures S5 and S6 of the Supporting Information. We observe that 1a has a crystal density of 1.181 g/cm3, and 1b has a crystal density of 1.240 g/cm3. In accordance with the Kitaigorodskii packing principle,20a the polymorph with larger density should have loose molecular packing, and thus, voids in the lattices of such forms are less likely. This is an indirect outcome of the Burger−Ramberger density rule,20b which suggests that at absolute zero, the lower density polymorph has less stability. In our case, to accommodate the C−H···F interactions in the two polymorphs, they adopt different packing patterns. In the case of 1a, there is strong O−H···O interactions, which is absent in the case of 1b. Such strong interactions are able to retain the voids, which is not the case in polymorph 1b. Similar logic can be suggested with our earlier reported polymorphs of 4-[(4-hydroxy-3,5-dimethylphenyl)(5-methyl-1H-imidazol-4-yl)methyl]-2,6-dimethylphenol,21 in which there are two polymorphs; one has voids and the other does not have voids in the respective packing patterns. The voids containing polymorph had a density of 1.077 g/cm3, and the one without the void was 1.223 g/cm3. The polymorph with lower density had voids, and it had dimeric assemblies guided by two N−H···π interactions with respect to one N−H···π interaction per dimer, in the case of the polymorph having no voids. Thus, in both these examples, the multiple orientations of molecules have helped them to adopt different packing patterns; the higher collective strengths of weak interactions per assembling units in one of the forms favors stabilization of the voids. Matzger et al.22 previously examined four anhydrous forms of carbamazepine polymorphs and found each of them to have identical strong hydrogen-bonding patterns, and their crystal densities were in C

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Figure 6. (I) Simulated powder XRD pattern of the polymorph 1b. Experimental powder XRD of the (II) polymorph 1b, and (III) the product of 1c after heating at 140 °C. Figure 4. Experimental powder XRD of (a) polymorph 1a, (b) polymorph 1b, and (c) polymorph 1a annealed at 160 °C for half an hour.

The DSC of the DMF solvate 1c shows two endothermic peaks at 130.4 and 174.6 °C, which correspond to the removal of dimethylformamide and to melting, respectively (Figure S15 of the Supporting Information). This suggests that the elimination of guest solvent molecules leads to collapse of the voids. Thus, the thermal conversion can be a synthetic procedure for preparation of polymorph 1b. The diffusion of DMF solvent to get back the solvate in this case was not successful. The anhydrous form 2a of the bis-phenol 2 crystallizes in the monoclinic space group P21/n. Both the hydroxy groups of the molecule are involved in intermolecular hydrogen bonding to form dimeric subassemblies (Figure 7). The dimeric assemblies further assemble through C−H···O interactions, leading to a 1D polymeric chain. Similar dimers were observed earlier in waterassisted assemblies of orthohydroxy substituted bis-phenols.27 Multiple numbers of dmso and dioxane solvates of bis-phenol 2 were observed. Two independent dmso solvates of bis-phenol abbreviated as 2b and 2c with different numbers of dmso molecules were obtained. The crystal morphology (Figure 8a) of the two solvates are distinguishable; the former crystals have a block shape, and the latter have a needle shape. The solvate 2b crystallizes in the orthorhombic space group Pbcn, and the crystallographic

The dimethylformamide (DMF) solvate 1c crystallizes in the orthorhombic space group Pna21. The crystallographic asymmetric unit of 1c contains one bis-phenol molecule and a DMF molecule. The DMF molecule acts as a bridge between two host molecules through O−H···O interactions forming a onedimensional (1D) chain (Figure 5a). The fluorine atoms of the host molecules interact with the DMF molecule through C−H··· F interaction. However, there is no C−H···F−C (aromatic) interactions among the host molecules, but there exits C−H···F− C interactions between the C−H from the methyl group of DMF with the C−F of the aromatic ring of bis-phenols. The two molecules of bis-phenols are held together by a bifurcated hydrogen bond formed between the carbonyl oxygen atom of DMF and the hydroxy group of two bis-phenol molecules (Figure 5a). From the packing pattern, it is apparent that the solvent inclusion causes the disruption of the weak C−H···F−C bonds between the bis-phenols in the polymorphs 1a and 1b. The DMF solvate 1c transforms to polymorph 1b on heating at 130−140 °C and is confirmed by powder-XRD (Figure 6).

Figure 5. (a) O−H···O and C−H···F−C interactions in the dimethylformamide solvate 1c. (b) Packing diagram of solvate 1c when viewed along the crystallographic c axis. D

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Figure 7. Assembling of dimeric subunits through O−H···O and C−H···O interactions in 2a.

Figure 8. (a) Optical micrograph of solvates 2b and 2c. (b) Dimers of the bis-phenols bridged by dmso molecules through O−H···O interactions in 2b. (c) 1D Chain of symmetry nonequivalent dmso and host molecules in 2c. (d) Packing of the molecules in solvate 2c (the solvent molecules are shown in CPK).

asymmetric unit contains one host molecule and a half dmso molecule. The sulfur atoms of dimethylsulfoxides are disordered, and it is modeled by sharing electron density at two equivalent positions. As in the structure of the anhydrous form 2a, the solvate 2b also has host components forming dimeric subassemblies through O−H···O bonds (Figure 8b). These dimeric sub- assemblies are bridged by the oxygen atoms of dmso molecules through bifurcated O−H···O bonds. On the other hand, the asymmetric unit of the dmso solvate 2c contains two symmetry independent host bis-phenol molecules and two dmso molecules. It crystallizes in the monoclinic space group P21/c. Unlike in the case of 2a or 2b; in the case of 2c, the host bisphenol molecules do not form dimeric units. It forms independent helical hydrogen-bonded chains, where the symmetry independent host molecules are bridged by dmso molecules in different symmetry relations (Figure 8c). The selected hydrogen-bond parameters of the solvates are given in the Table 1.

Recently, we have reported water-assisted assembly of dioxane solvate of an amino bis-phenol,27 but we did not observe polymorphism of such a solvate. However, crystallization of the bis-phenol 2 from 1,4-dioxane led to crystals of two polymorphs of the dioxane solvate. These two polymorphs of the solvate are abbreviated as 2d and 2e; their crystals are visually distinguishable, hence, they can be hand-picked to separate. The solvate 2d crystallizes in the triclinic P1̅ space group, and the crystallographic asymmetric unit contains one host molecule and a half dioxane molecule. The structure is mainly guided by two strong hydrogen bonding interaction, viz., O(1)−H(1)···O(3) and O(2)−H(2)···O(1) (Figure 9a). The two hydroxy groups of the host molecules involved in the intermolecular hydrogen bonds forming dimeric units and the dioxane molecules act as bridges between such units through O(1)−H(1)···O(3) interactions. They result in the formation of a 1D discrete chain (Figure 9a), and the chains self-assemble to form two-dimensional sheets (Figure S17, panels b and c, of the Supporting Information) E

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Table 1. Hydrogen Bond Parameters in 1a−1c and 2a−2e compd no.

D−H···A

dD−H (Å)

dH···A (Å)

dD···A (Å)

∠D−H···A (deg)

1a

O(1)−H(1)···O(1) [1/2 + x, y, 1/2 − z] O(2)−H(2)···O(2) [1/2 + x, 1/2 − y, −z] C(3)−H(3)···F(1) C(14)−H(14)···F(1) O(1)−H(1) ···O(3) [−1/2 + x, 1/2 − y, 1 + z] O(2)−H(2)···O(3) [1/2 + x, 1/2 − y, 1 + z] C(24)−H(24C) ···O(3) C(24)−H(24C) ···F(1) [1/2 + x, 1/2 − y, z] O(2)−H(2)···O(1) [1 − x, 1 − y, 1 − z] C(9)−H(9)···O(2) O(1)−H(1) ···O(3) [−1/2 + x, −1/2 + y, 1/2 − z] O(2)−H(2) ···O(1) [−x, −y, −z] O(1)−H(1) ···O(6) [x, 1/2 − y, 1/2 + z] O(2)−H(2) ···O(5) [1 + x, 1/2 − y, 1/2 + z] O(3)−H(3A) ···O(5) C(47)−H(47B) ···O(1) [x, 1/2 − y, −1/2 + z] C(49)−H(49A) ···F(2) C(49)−H(49B) ···O(3) [1 + x, y, z] O(1)−H(1) ···O(3) [1 − x, 1 − y, 1 − z] O(2)−H(2) ···O(1) [−x, 1 − y, 1 − z] C(9)−H(9) ···O(2) O(1)−H(1)···O(3) O(2)−H(2)···O(1) [1 − x, 1 − y, −z] C(8)−H(8A) ···F1 O(2)−H(2M) ···O(2) [2 − x, 1 − y, 1 − z] C(23)−H(23A)···F(1) [2 − x, 1 − y, 1 − z] C(23)−H(23B)···F(1) [1 + x, y, z]

0.89(5) 0.78(4) 0.93 0.931 0.82 0.82 0.96 0.96 0.86(2) 0.98 0.83(2) 0.80(2) 0.82(4) 0.80(3) 0.87(3) 0.96 0.96 0.96 0.85(2) 0.852(17) 0.98 0.82(2) 0.82(3) 0.961 0.79(7) 0.96 0.96

2.10(4) 2.26(4) 2.63 2.632 2.22 2.42 2.43 2.48 2.02(2) 2.39 1.94(2) 2.06(2) 1.87(4) 2.01(3) 1.89(3) 2.60 2.53 2.48 1.91(2) 2.14(2) 2.40 1.97(3) 2.04(3) 2.563 1.74(7) 2.46 2.38

2.923(4) 3.025(5) 3.477 3.488 2.795(8) 2.847(8) 2.760(13) 3.003(12) 2.793(3) 2.752(3) 2.7257(18) 2.799(2) 2.684(3) 2.753(3) 2.724(3) 3.451(5) 3.324(4) 3.384(5) 2.743(2) 2.905(2) 2.763(2) 2.717(5) 2.776(4) 3.308 2.463(7) 3.401(7) 3.320(8)

154(4) 167(5) 151.57 153.16 128 113 100 114 149(3) 101 158(2) 153(2) 170(3) 156(3) 160(3) 148 140 157 168(3) 148(2) 101 152(3) 153(5) 134.48 152(8) 166 166

1b 1c

2a 2b 2c

2d

2e

2f

145to 205 °C (observed weight loss of 9.7%, theoretical weight loss of 10.0%), whereas the dmso molecules of solvate 2c are lost from 135 to 170 °C (observed weight loss 18.9%, theoretical weight loss 18.2%). The higher thermal stability of 2b is attributed to the packing patterns of the bis-phenols, in which dimeric assemblies hold the dmso molecules. The dioxane solvate 2d loses the solvent molecules in the temperature range from 105 to 150 °C (observed weight loss 12.3%, theoretical weight loss 11.2%), whereas the dioxane solvate 2e loses the solvent molecules in the range from 80 to 150 °C (observed weight loss 10.4%, theoretical weight loss 11.2%). Both the solvates have similar composition but a different temperature range at which they lose the solvent molecules. On the other hand, in both cases the solvate molecules are held between the parent dimeric molecules, the difference being the C−H···F−C interactions. The 2d is having a sheetlike structure that enables a sharp release of dioxane in a relatively narrow range of temperature, whereas the 2e has channel-like structures which make slow release in a well-spread-out range of temperature. This indirectly points out the effect of the C−H···F−C interactions in such assemblies. We attempted to crystallize the sodium, potassium, and cesium salts of bis-phenol 2. We did not obtain suitable single crystals for X-ray diffraction study for sodium and potassium but obtained crystals of the cesium complex 2f. The asymmetric unit of the cesium complex 2f contains one neutral, one monodeprotonated molecule of bis-phenol 2, and a cesium cation (Figure 11a). All the oxygen atoms of the two molecules bind to the cesium cation. The coordination sphere of the cesium ion is completed by four oxygen atoms of hydroxy groups and η2 or η4 types of the cesium−π interactions with the fluoro-substituted phenyl rings of the ligands (Figure 11b). The 2f forms a 1D polymeric

parallel to the crystallographic ab plane. On the other hand, solvate 2e crystallizes in the monoclinic space group P21/n, and the crystallographic asymmetric unit contains a host molecule and a symmetric half of a 1,4-dioxane molecule. In this case also, the structure is mainly guided by O−H···O interactions to form dimeric units, and these dimeric units are connected to each other through a bridged dioxane molecule, forming a 1D chain. The chains self-assemble through C−H···F−C interaction to a 3-dimensional hydrogen-bonded channel-like structure, where the channels are occupied by dioxane molecules (Figure S17d of the Supporting Information). The main difference between the structure 2d and 2e is that the latter contains C−H···F−C interactions, whereas the former does not have C−H···F−C interactions. Apart from these, the C−H···π interactions of the dioxane molecules in solvate 2d and 2e are distinguishable (Figure S18 of the Supporting Information). Dunitz and Gavezzotti had suggested that the contribution of C−H···F−C interactions in crystal packing may either stabilize or destabilize or remain silent.10 Nonetheless, in the present case, the C−H···F−C interactions along with the C−H···π interactions distinguish the orientations and packing patterns between 2d and 2e. From the structural study, it is evident that similar dimeric subunits of the parent structure of 2 is retained in 2a, 2b, 2d, and 2e, but in the case of the 2c, disruption of the dimeric assemblies was observed. The two types of assemblies observed in 2b and 2c are shown in Figure 10. The 2c was prepared at high temperature and pressure; under such conditions, it loses dimeric assemblies of the bis-phenol molecules. This observation shows that as the temperature and pressure is raised, the amount of DMSO intake per bis-phenol molecule is doubled. From the thermogravimetry study, it is seen that the dmso molecules of solvate 2b are lost in the temperature range from F

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Figure 9. (a) The O−H···O interactions of dioxane in the solvate 2d. Packing pattern of the (b) solvate 2d and (c) solvate 2e.

Figure 10. Assemblies of two different DMSO−solvates, illustrating more DMSO uptake at drastic conditions.

Figure 11. (a) Asymmetric unit of 2f (30% thermal ellipsoids) and (b) Cs+−π interactions in the 2f.

calixarene complexes (≈ 4.0 Å).28 On the basis of such observations, the Cs−O bonds in the present case are coordinate bonds.29,30 The Cs−centroid (of aryl ring) distance between the cesium cation and the fluoro-substituted benzene rings of the bisphenol 2 are found to be 3.417 Å (η4−cesium−π interaction) and

chainlike structure, where the bis-phenol molecules act as a linker for the cesium atoms (Figure S23 of the Supporting Information). The Cs−O distances in the complex 2f are in the range of 3.05−3.12 Å (refer to Table S1 of the Supporting Information); these are shorter than the reported cesium G

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by slow evaporation of a solution of 1 in acetic acid. IR (KBr, cm−1): 3609 (s), 3587 (s), 3060 (w), 3011 (w), 2972 (m), 2948 (m), 2914 (m), 2851 (w), 1604 (w), 1584 (w), 1487 (s), 1454 (s), 1379 (w), 1328 (w), 1307 (w), 1296 (w), 1280 (w), 1220 (s), 1195 (s), 1147 (s), 1135 (m), 1090 (m), 1022 (m), 947 (m), 882 (m), 845 (w), 801 (w), 762 (s), 736 (m), 697 (w), 651(m). Solvate 1c. The solvate 1c was obtained by the slow evaporation of a solution of 1 in dimethylformamide. Elemental anal. Calcd for C26H30FNO3: C, 73.73; H, 7.14; N, 3.31. Found: C, 73.69; H, 7.12; N, 3.29. IR (KBr, cm−1): 3383 (s), 2924 (s), 2873 (w), 1657 (s), 1601 (m), 1487 (s), 1454 (w), 1393 (w), 1326 (w), 1281(w), 1193 (s), 1149 (m), 1104 (m), 1018 (w), 939 (w), 845(w), 798(w), 766(w), 662 (w), 526 (w). The compound 2 was prepared by the same procedure, except 2,4dimethylphenol was used instead of 2, 6-dimethylphenol. Yield, 87%. 1H NMR (400 MHz, methanol-d4, δ ppm): 2.09 (s, 6H), 2.17 (s, 6H), 6.33 (s, 2H), 6.36 (s, 1H), 6.79 (s, 2H), 6.80 (d, J = 8 Hz, 1H), 6.97 (m, 2H) 7.17 (dd, J = 6.8 Hz, J = 6.0 Hz, 1H). 13C NMR (100 MHz, dmso-d6, δ ppm): 159.3, 150.4, 131.9, 130.7, 130.3, 129.6, 127.9, 127.6, 127.2, 124.2, 123.9, 115.3, 115.0, 36.7, 20.7, 16.9. 19F-NMR (methanol-d4, δ ppm) −118.22 (m). The unsolvated 2a is obtained by the slow evaporation of a solution of 2 in methanol. IR (KBr, cm−1): 3486 (s), 3448 (s), 3033 (w), 2921 (s), 2860 (w), 1585 (w), 1487 (s), 1455 (s), 1380 (w), 1330 (m), 1302 (w), 1291(w), 1282 (w), 1256 (s), 1227 (s), 1194 (s), 1137 (s), 1093 (m), 1031(m), 1015 (w), 865 (m), 839 (m), 814 (w), 765 (s), 748 (s), 665 (w). ESI Mass: 350.3088 (m+/e), 349.3086 (m+/e−1). DMSO Solvate 2b. The slow evaporation of a solution of 2 in dimethylsulfoxide led to formation of 1:0.5 solvate of DMSO. Elemental anal. Calcd for C48H52F2O5S: C, 74.01; H, 6.73. Found: C, 73.97; H, 6.86. IR (KBr, cm−1): 3454 (s), 3190 (m), 3009 (w), 2973 (w), 2913 (m), 2862 (w), 1599 (m), 1586 (m), 1482 (s), 1455 (s), 1322 (m), 1303 (m), 1255 (m), 1227 (s), 1182 (s), 1169 (m), 1149 (w), 1095 (w), 1032 (w), 1014 (w), 994 (m), 940 (m), 933 (m), 892 (w), 868 (w), 856 (w), 839 (w), 817 (w), 786 (w), 753 (s), 667 (w). DMSO Solvate 2c. A solution of 2 in DMSO was heated in a sealed Teflon-lined steel autoclave at 120 °C for 4 h and allowed to cool slowly; it yielded needle-shaped crystals. Elemental anal. Calcd for C25H29FO3S: C, 70.06; H, 6.82. Found: C, 76.18; H, 6.78. IR (KBr, cm−1): 3357 (s), 3000 (w), 2915 (m), 2857 (w), 1598 (w), 1583 (w), 1483 (s), 1453 (s), 1381(w), 1316 (m), 1301 (m), 1250 (m), 1224 (s), 1181 (s), 1091 (w), 1001 (s), 941 (s), 864 (m), 839 (w), 820 (w), 750 (s), 666 (w). Dioxane Solvate 2d and 2e. When a solution of 2 in 1,4-dioxane was allowed to slowly evaporate, crystals of two different morphologies 2d and 2e appear. Elemental anal. Calcd for C25H27FO3: C, 76.12; H, 6.90. Found: C, 76.22; H, 6.94. IR (cm−1) of 2d: 3451 (s), 3009 (w), 2923 (m), 2863 (w), 1585 (m), 1483 (s), 1454 (m), 1380 (w), 1325 (w), 1298 (m), 1253 (s), 1227 (s), 1187 (s), 1146 (m), 1109 (m), 1079 (w), 1033 (w), 893 (w), 862 (s), 840 (w), 816 (w), 785 (w), 752 (s), 667 (w). For 2e: Elemental anal. Calcd for C25H27FO3: C, 76.14; H, 6.90. Found: C, 76.10; H, 6.92. IR (cm−1): 3483 (s), 3209 (m), 2922 (m), 2860 (w), 1584 (w), 1482 (s), 1453 (m), 1327 (w), 1252 (m), 1223 (s), 1189 (s), 1145 (w), 1078 (w), 1035 (w), 936 (w), 861 (s), 751 (s), 623 (w). Cesium Complex 2f. Solid Cs2CO3 (0.16 g, 0.5 mmol) was added to a well-stirred solution 2 (0.70 g, 2 mmol) in methanol. The resulting solution was refluxed for about 4 h. The reaction mixture was then filtered, and the filtrate was kept undisturbed for crystallization. After 3− 4 days, colorless needle-shaped crystals of 2e appeared. IR (KBr, cm−1): 3406 (m), 3005 (w), 2918 (m), 2851(w), 2725 (w), 1577 (w), 1482 (s), 1451(m), 1371(w), 1297 (w), 1226 (s), 1212 (s), 1146 (m), 1096 (w), 1031 (w), 1008 (w), 949 (w), 762 (s), 667 (s). 1HNMR (methanol-d4): 2.05 (s, 6H), 2.12 (s, 6H), 6.29 (s, 1H), 6.39 (s, 2H), 6.69 (s, 2H), 6.90 (d, J = 6.8 Hz, 1H), 6.97 (t, J = 7.2 Hz, 1H), 7.02 (t, J = 6.0 Hz, 1H), 7.13 (dd, J = 7.6 Hz, J = 5.2 Hz, 1H). 19FNMR: −119.62 (m). X-Ray Crystallographic Studies. Diffraction data for 1a−1c, 2a, 2c, and 2e were collected at 296 K with Mo Kα radiation (λ = 0.71073 Å) with the use of a Bruker Nonius SMART APEX CCD diffractometer equipped with a graphite monochromator and an Apex CCD camera, whereas for solvate 2b and 2d, the data were collected on a Oxford

3.638 Å (η2−cesium−π interaction). Similar interactions were earlier observed in the cesium complex of the o-alkylated p-phosphonic acid calix [4] arenes, with CAr···Cs distances from 3.41 to 3.73 Å.31 The CAr−Cs distances in the coordination polymer 2f are in the range from 3.49 to 3.68 Å, and this separation is very close to the Cs−C distance found in methyl cesium (3.53 Å).31 The interactions of calixarenes with cesium are widely studied as methods for the purification32 and analysis.33 However, the cesium complex of bis-phenol having cesium−π interactions is not reported to date. On the other hand, the calixarenes are a preorganized system for coordination of the metal, but our system is very simple, which shows interesting Cs−Cπ−interactions. The cation−π interactions are evident in the 1H NMR spectra of the cesium complex 2f. A comparison of the 1H NMR of the cesium complex with the parent bis-phenol is shown in Figure S25 of the Supporting Information. The methine proton (Hc) in the complex 2f shows a slight upfield shift, whereas the aromatic protons in the region of 6.5−7.5 are significantly affected by interactions of cesium, which are a clear indication of cesium−π interactions (Figure S25 of the Supporting Information). Further, the 19F-NMR of the cesium complex has a signal at a chemical shift of −119.62, in comparison to the parent bis-phenol 2, which appears at −118.22 ppm (Figure S26 of the Supporting Information). In conclusion, the two forms of the polymorphs 1a and 1b arise from variation of packing patterns in which the C−H···F−C interactions becomes a distinguishable factor. The polymorph 1a or dimethylfomamide solvate 1c transforms to polymorph 1b on heating. Formation of dmso solvates of the bis-phenol 2 with different compositions at different conditions is worth noting. At high temperature and pressure, disruption of the conventional dimeric assemblies of bis-phenol 2 occurs, and it allows inclusion of higher amounts of dmso than the corresponding dmso solvate formed at room temperature. This is an example to show formation of solvate with higher amounts of guest molecules at solvothermal conditions. The polymorphs of 1,4-dioxane solvate have distinguishable C−H···F−C and C−H···π interactions in their packing patterns, this opens the scope for discovering polymorphs in fluorinated host−guest systems. The strong Cs+−π interactions in the case of 2f is an exceptional observation, which may be helpful in recognition of cesium ions by fluorinated−phenolic compounds.

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EXPERIMENTAL SECTION

Synthesis of 1. 2-Fluorobenzaldehyde (0.540 mL, 5 mmol) and 2,6dimethylphenol (1.22 g, 10 mmol) were dissolved in acetic acid (20 mL), and the solution was stirred for half an hour, placing it over an ice bath. A mixture of concentrated sulphuric acid and glacial acetic acid in a 1:2 ratio (10 mL, v/v) was added dropwise to the reaction mixture. After half an hour of stirring, the mixture was kept in a deep freeze for one week. After one week, water (10 mL) was added to the reaction mixture; a light yellow-colored precipitate appeared. The precipitate was collected by filtration and was washed with aqueous sodium bicarbonate solution (20%, 25 mL). The product was then dried in air. Yield: 70%. 1 H NMR (400 MHz, CDCl3): 2.15 (s, 12H), 4.55 (s, 2H), 5.55 (s, 1H), 6.67 (s, 4H), 6.90 (t, J = 7.6 Hz, 1H), 6.94 (m, 2H), 7.15 (dd, J = 9.6 Hz, J = 5.2 Hz, 1H). 13C NMR (100 MHz, dmso-d6, δ ppm): 161.2, 158.7, 151.5, 133.4, 131.9, 131.7, 130.6, 128.6, 128.0, 124.0, 115.2, 115.0, 47.4 (methine C−H), 16.7 (CH3−). 19F-NMR (CDCl3, δ ppm): 117.20. ESI Mass: 350.3096 (m+/e), 349.3061 (m+/e−1). Polymorph 1a. The polymorph 1a was obtained by slow evaporation of a solution of 1 in methanol. IR (KBr, cm−1): 3587 (m), 3441 (s), 3011 (w), 2967 (w), 2922 (w), 2862 (w), 1604 (w), 1583 (w), 1486 (s), 1453 (s), 1385 (w), 1337 (m), 1223 (s), 1204 (s), 1145 (s), 1095 (m), 1020 (m), 948 (w), 883 (w), 753 (s). The Polymorph 1b was obtained H

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Article

Table 2. Crystallographic Parameters of Compound 1a−1c and 2a−2f compound no.

1a

formula CCDC no. Mr space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) density (mgm−3) abs. coefficient (mm−1) F(000) total no. of reflections reflections [I > 2σ(I)] max θ (deg) ranges (h, k, l)

C23 H23 F O2 937981 350.41 Pbca 4.9312(3) 19.1560(13) 41.744(2) 90.00 90.00 90.00 3943.2(4) 1.181 0.080 1488 3636 1870 25.49 −5 ≤ h ≤5, −23 ≤ k ≤15, −44 ≤ l ≤;50 complete to 2θ (%) 99.80 data/restraints/parameters 3636/0/ 241 Goof (F2) 1.087 R indices [I > 2σ(I)] 0.0708 R indices (all data) 0.1407 compound no. 2b formula CCDC no. Mr space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) density (mgm−3) abs. coefficient (mm−1) F(000) total no. of reflections reflections [I > 2σ(I)] max θ (deg) ranges (h, k, l)

C48H52F2O5S 937985 778.96 Pbcn 12.0576(9) 18.7488(11) 18.9159(14) 90.00 90.00 90.00 4276.2(5) 1.210 0.129 1656 3873 2777 25.25 −7 ≤ h ≤ 14, −22 ≤ k ≤ 21, −9 ≤ l ≤;22 complete to 2θ (%) 99.80 data/restraints/parameters 3873/2/282 Goof (F2) 1.183 R indices [I > 2σ(I)] 0.0508 R indices (all data) 0.0747

1b

1c

C23 H23 F O2 937982 350.41 P21/c 16.2856(6) 8.4173(4) 14.5989(6) 90.00 110.232(2) 90.00 1877.75(14) 1.240 0.084 744 3502 2366 25.49 −19 ≤ h ≤ 19, −8 ≤ k ≤ 10, −17 ≤ l ≤;15 1.00 3502/2/ 247 0.906 0.0435 0.0718 2c C25H29FO3S 937986 428.54 P21/c 8.3850(2) 29.3923(8) 19.4179(6) 90.00 93.876(2) 90.00 4774.7(2) 1.192 0.165 1824 8555 4814 25.25 −10 ≤ h ≤ 9, −35 ≤ k ≤ 33, −23 ≤ l ≤;22 99.20 8555/0/569 1.008 0.0527 0.1326

C26 H30 F N O3 937983 423.51 Pna21 12.006(2) 23.510(4) 8.2207(13) 90.00 90.00 90.00 2320.4(6) 1.212 0.084 904 3880 2656 25.25 −14 ≤ h ≤ 14, −27 ≤ k ≤ 27, − 9 ≤ l ≤;9 97.60 3880/1/ 288 1.103 0.0962 0.2205 2d

C25H27FO3 943939 394.47 P1̅ 9.0463(5) 9.5339(6) 13.1106(8) 98.763(4) 103.988(4) 96.474(4) 1071.13(11) 1.223 0.085 420 3850 2642 25.25 −10 ≤ h ≤ 10, −11 ≤ k ≤ 11, −15 ≤ l ≤;15 99.00 3850/2/ 274 1.084 0.0448 0.0650

SuperNova diffractometer. SMART was used for data collection and also for indexing the reflections and determining the unit cell parameters. Data reduction and cell refinement were performed using SAINT software.34 For the data collected on the SuperNova diffractometer, data refinement and cell reductions were carried out by CrysAlisPro.35 The structures were solved by direct methods and refined by full-matrix leastsquares calculations using SHELXTL. All the non-H atoms were refined in the anisotropic approximation against F2 of all reflections. In the solvate 2b, the DMSO molecule displays positional disorder around the sulfur atom, which is refined with 0.5 occupancy in SHELXTL. The H atoms attached to the heteroatoms in 1a, 1b, and 2a−2e were located in the difference Fourier synthesis maps and refined with

2a

2e

C23 H23 F O2 937984 350.41 P21/n 10.1891(3) 12.1484(4) 15.5039(4) 90.00 92.864(3) 90.00 1916.69(10) 1.214 0.083 744 3469 2533 25.25 −6 ≤ h ≤ 12, −14 ≤ k ≤ 13, −18 ≤ l ≤;18 99.90 3469/6/ 247 0.964 0.0520 0.0721 2f

C25H27FO3 937987 394.47 P21/n 10.1337(9) 11.8820(7) 18.8355(16) 90.00 104.929(8) 90.00 2191.4(3) 1.196 0.083 840 3966 2664 25.25 −12 ≤ h ≤ 7, −14 ≤ k ≤ 10, −22 ≤ l ≤;22 99.80 3966/2/274 1.124 0.0731 0.1862

C46H45F2O4Cs 937988 832.73 P1̅ 10.3787(9) 13.5980(9) 15.7691(8) 102.404(5) 102.068(6) 106.190(7) 1999.7(2) 1.383 0.977 852 7249 4236 25.25 −12 ≤ h ≤ 12, −16 ≤ k ≤ 10, −18 ≤ l ≤;18 99.80 7249/16/478 1.023 0.0621 0.1215

isotropic displacement coefficients. Crystal parameters are summarized in Table 2.

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ASSOCIATED CONTENT

S Supporting Information *

The figures show the comparison of experimentally observed powder XRD patterns with the simulated powder XRD patterns of the compounds, bond lengths, CIF files, 1H NMR, 19F-NMR, FT-IR, TGA, and DSC of the samples. This material is available free of charge via the Internet at http://pubs.acs.org. I

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS B.N. thanks the Council of Scientific and Industrial Research, New Delhi, India, for a Senior Research Fellowship. The authors thank the Department of Science and Technology, New-Delhi, for use of the X-ray facility.

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