Synthesis, Structures and Co-Crystallizations of Perfluorophenyl Substituted β-Diketone and Triketone Compounds

Abstract

Perfluorophenyl-substituted compounds, 3-hydroxy-1,3-bis(pentafluorophenyl)-2- propen-1-one (H1) and 1,5-dihydroxy-1,5-bis(pentafluorophenyl)-1,4-pentadien-3-one (H₂2), were prepared in 56 and 30% yields, respectively, and only the enol forms were preferentially obtained among the keto-enol tautomerism. Molecular conformations and tautomerism of the fluorine-substituted compounds were certified based on X-ray crystallographic studies and density functional calculations. The solvent dependency of the absorption spectra was only observed for the fluorinated compounds. The compounds H1 and H₂2 quantitatively formed co-crystals with the corresponding non-perfluorinated compounds, dibenzoylmethane (H3) and 1,5-dihydroxy-1,5-diphenyl-1,4-pentadien-3-one (H₂4), respectively, through the arene–perfluoroarene interaction to give the 1:1 co-crystals H1•H3 and H₂2•H₂4, which were characterized by X-ray crystallographic and elemental analysis studies.

1. Introduction

Fluorine-substituted organic molecules are being widely explored by materials scientists in various applications encompassing battery, catalysis, and many other technological fields [1,2,3,4,5]. Ring fluorination dramatically changes molecular characteristics through intramolecular electron withdrawing nature and intermolecular electrostatic interactions. One of the unique properties of perfluoroaromatic compounds is the opposite quadrupole moment [6], which is positive for hexafluorobenzene, 31.7 × 10⁻⁴⁰ C m², and negative for benzene, −29.0 × 10⁻⁴⁰ C m² [7,8]. Thus, unique π-interactions, such as arene–perfluoroarene [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27] and CH···F [28,29,30], are observed in the crystals of perfluorinated compounds and co-crystals containing perfluorinated and non-perfluorinated aromatic compounds. The co-crystals have alternating layered structures and are found to possess unique molecular recognition capabilities [10]. In this area, we have been interested in the perfluoroarene coordination compounds and their molecular self-assembled systems for a decade; e.g., bis[bis(pentafluorobenzoyl)]copper(II), [Cu(1)₂], was prepared and applied to metal-ordered co-crystals with unique one-dimensional metal chains [31] and several guest encapsulations in the crystal states [32,33,34,35]. However, the corresponding ligand, 3-hydroxy-1,3-bis(pentafluorophenyl)-2- propen-1-one (H1) (Scheme 1) [36], which is a unique target for the fluorine-substituted dibenzoylmethane [37], has never been characterized by crystallographic studies, whereas the corresponding coordination complexes have been reported. This fact encouraged us to characterize and develop the structure of the perfluorinated compound H1 and also prepare the expanded triketone-type compound H₂2, of which both structures always involve the problems of keto-enol tautomerism [38,39,40,41,42,43,44,45,46,47]. In this study, we investigated the molecular structures and the supramolecular associations of H1 and H₂2 in the solution and solid states, which further co-crystallize with the corresponding non-perfluorinated compounds H3 and H₂4, respectively, to give the unique 1:1 co-crystals of H1• H3 and H₂2•H₂4.

2. Materials and Methods

2.1. General

All the chemicals were of reagent grade and used without further purification. Non-perfluorinated compounds H3 and H₂4 were commercially available. The ¹H NMR spectral data were recorded by a Bruker DRX600 (600 MHz) or JEOL ECS400 (400 MHz) spectrometer. The melting points were determined by a Yanako MP-500D melting point apparatus. The infrared spectra were recorded by a Shimadzu IR 8400s using a KBr disk. The electronic absorption spectra were recorded by a JASCO V-660 spectrometer. The results of the elemental analysis (EA) of C and H were determined by a Perkin-Elmer PE2400 analyzer. The DFT calculations were performed by the Spartan’16 package with B3LYP/6-31G* [48,49].

2.2. Synthesis of H1 and H₂2

The synthesis of 3-hydroxy-1,3-bis(pentafluorophenyl)-2-propen-1-one (H1) was previously reported [36,50]. Typically, pentafluorobenzoyl chloride and vinyl acetate were combined in 1,1,2,2-tetrachloroethane in the presence of anhydrous AlCl₃. The reaction mixture was separated by a column chromatography (silica, benzene). The H1 product was obtained at R_f = 0.8, and two other byproducts corresponding to the aluminum complex and acethylpentafluorobenzoylmethane were obtained at R_f = 0.9 and 0.5, respectively. With sufficient acid treatment after the reaction, the H1 product was preferentially obtained instead of the corresponding aluminum (III) complex. Compound H1 was further purified by gel permeation chromatography (GPC) and recrystallized from an ethanol solution to give colorless prismatic crystals with the constant melting point of 83–84 °C in 56% yield. ¹H NMR (600 MHz, CDCl₃): δ 15.12 (s, OH), 6.26 (s, CH). ¹³C NMR (150 MHz, CDCl₃): δ 177.0 (CO), 144.9 (d(m), J = 257 Hz, C₆F₅), 143.2 (d(m), J = 257 Hz, C₆F₅), 137.9 (d(m), J = 257 Hz, C₆F₅), 111.3 (m, C₆F₅), 106.3 (CH). IR (KBr disk, cm⁻¹): 3457, 3144, 2926, 1651, 1593, 1524, 1497, 1335, 1319, 1206, 1180, 1099, 995, 932, 827, 642. EA: Calcd. for C₁₅H₂F₁₀O₂ (%): C, 44.58; H, 0.50. Found: C, 44.65; H, 0.38.

1,5-Dihydroxy-1,5-bis(pentafluorophenyl)-1,4-pentadien-3-one (H₂2) was prepared by adding a solution of hexamethyldisilazine (7.2 mL, 32 mmol) in dry tetrahydrofuran (THF, 15 mL) to n-BuLi (19.4 mL, 32 mmol, hexane) at 0 °C under an N₂ atmosphere with continuous stirring for 15 min. Subsequently, freshly distilled acetone (0.75 mL, 11 mmol), dissolved in 15 mL of THF, was dropwise added to the mixture, then a solution of methylpentafluorobenzoate (5 mL, 22 mmol) in THF (25 mL) was added. The mixture was stirred for 20 h at room temperature. During the stirring, the solution color changed from colorless to dark orange. Subsequently, the mixture was added to an aqueous solution of 3M HCl (100 mL), neutralized by NaHCO₃, and extracted with diethylether. The obtained mixture was purified by column chromatography (silica, CH₂Cl₂). The first product was assigned to methylpentafluorobenzoate (R_f = 0.7), and the second product with R_f = 0.5 was characterized as H₂2. Compound H₂2 was further purified by GPC and recrystallized from ethanol to give yellow prismatic crystals. Yield 30%. mp 87–88 °C. ¹H NMR (600 MHz, CDCl₃, TMS): δ 14.26 (s, 2H, OH), 5.73 (s, 2H, CH). ¹³C NMR (150 MHz, CDCl₃): δ 194.0 (COH), 164.4 (CO), 144.8 (d(m), J = 254 Hz, C₆F₅), 142.6 (d(m), J = 254 Hz, C₆F₅), 137.9 (d(m), J = 254 Hz, C₆F₅), 110.0 (m, C₆F₅), 104.5 (CH). IR (KBr disk, cm⁻¹): 3148, 1651, 1607, 1522, 1495, 1377, 1196, 1167, 1084, 1011, 837, 716. EA: Calcd. for C₁₇H₄F₁₀O₃ (%): C, 45.76; H, 0.90. Found: C, 45.84; H 0.83.

2.3. Co-Crystallizations of H1•H3 and H₂2•H₂4

The perfluorinated compound and the corresponding non-perfluorinated compound were completely dissolved in EtOH, then combined for co-crystallization. Stoichiometric co-crystals grew slowly under slow solvent evaporation conditions.

Co-crystal H1•H3. The crystal was obtained as a colorless prismatic. Isolated yield: 74%. mp 106–108 °C. IR (KBr disk, cm⁻¹): 3457, 3119, 3082, 1672, 1653, 1524, 1497, 1371, 1107, 993, 768, 691. EA: Calcd. for C₃₀H₁₄F₁₀O₄ (%): C, 57.34; H, 2.25. Found: C, 57.39; H 1.88.

Co-crystal H₂2•H₂4. The crystal was obtained as a yellow prismatic. Isolated yield: 94%. Mp 125–126 °C. IR (KBr disk, cm^-1): 1653, 1609, 1520, 1493, 1157, 1082, 1007, 982, 824, 775, 691. EA: Calcd. for C₃₄H₁₈F₁₀O₆ (%): C, 57.32; H, 2.55. Found: C, 57.05; H 2.46.

2.4. Crystal Structure Determination

The single crystal X-ray structures were determined by a Bruker SMART APEX CCD diffractometer with a graphite monochrometer and MoKα radiation (λ = 0.71073 Å) generated at 50 kV and 30 mA. All the crystals were coated by paratone-N oil and measured at 120 K. SHELXT program was used for solving the structures [51]. Refinement and further calculations were carried out using SHELXL [52]. The crystal data and structure refinement of the perfluorinated compounds (H1 and H₂2) and their co-crystals (H1•H3 and H₂2•H₂4) are summarized in Table 1. CCDC 1827049 (H1), 1827050 (H₂2), 1827051 (H1•H3), and 1827052 (H₂2•H₂4) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html.

3. Results and Discussion

3.1. Enol-Type Structures of H1 and 2

Compounds H1 and H₂2 were prepared by using previously described protocols, purified by column chromatography, GPC, and recrystallized to give pure single products. The ¹H NMR results of both structures in CDCl₃ clearly suggested enol-type structures. The ¹H NMR spectrum of H1 in CDCl₃ shows only two single peaks at δ 15.12 (OH) and 6.26 (CH), indicating the enolic form; the enol tautomeric species generally contains a hydrogen bonded ring comprised of two equivalent structures with C_s symmetry connected through a transition state with C_2v symmetry [38]. The ¹H NMR spectrum of H₂2 in CDCl₃ also shows two single peaks at δ 14.26 (OH) and 5.73 (CH), indicating the highly symmetric structure of H₂2, while several keto- and enol-type corresponding isomers are expected. Single crystals of H1 and H₂2 were obtained from ethanol as colorless and pale yellow prismatic crystals, respectively, which were suitable for X-ray crystallographic studies.

The molecular structures in the single crystals of H1 and H₂2 are shown in Figure 1a,b, respectively, with the numbering schemes. In the crystal of H1, the whole structure is an asymmetric unit, that is distinguishable as the C_s structure; the bond lengths of O1-C7, C7-C8, C8-C9, and C9-O2 are 1.2636(17), 1.4246(18), 1.3722(18) and 1.3103(16) Å, respectively, showing the localization of the π-conjugated system in the O1=C7-C8=C9-O2 coordination sites. The hydrogen proton is close to O2 to give C_s symmetry of the hydrogen bonded ring, such as the β-diketonato moiety: The distance of O1···O2 and the angle of O1···H2-O2 are 2.4857(14) Å and 146°, respectively. The enol form, which means keto-enol type structure, is stabilized by intramolecular hydrogen bonds to form a six-membered ring structure of the β-ketonate O1-C7-C8-C9–O2-H2, indicating the same orientation of the corresponding non-perfluorinated H3 [53]. This phenomenon is well known as a resonance-assisted hydrogen bond (RAHB) by Gilli et al. [40,41]. Two pentafluorophenyl rings are highly twisted to the ring; the dihedral angles between the two pentafluorophenyl rings and the β-ketonate six-membered ring are 25.47° and 49.29°: the torsion angles of C1-C6-C7-O1 and O2-C9-C10-C11 are 24.47(18)° and 47.80(17)°, respectively. The low planarity of the molecules was compromised due to the twisting induced by the steric hindrance between the fluorine at the o-positions of the pentafluorophenyl group and the hydrogen at the ketonate sites. The related dihedral angles between two phenyl rings and the β−ketonate six-membered ring of H3 are 4.69° and 17.42°, showing a flatter structure [53].

In the crystal of H₂2, O1 and O3 are also crystallographically independent. The bond lengths of O1-C7, O2-C9, and O3-C11 are 1.3363(15), 1.2784(15), and 1.3332(15) Å, respectively, indicating the enol-keto-enol type structure (proposed structure in Scheme 1). In this configuration, the bond lengths of C8-C9 and C9-C10 [1.4429(17) Å and 1.4403(16) Å] are longer than those of C7-C8 and C10-C11 [1.3617(17) Å and 1.3591(17) Å], which indicates that the localization of the π system with RAHB: the distances of O1···O2 and O2···O3 and the angles of O1-H1···O2 and O1···H3-O3 are 2.5565(13) Å, 2.5724(13) Å, 147°, and 146°, respectively. The two pentafluorophenyl rings of H₂2 were highly twisted; the torsion angles of C1-C6-C7-O1 and O3-C11-C12-C13 are 22.61(16)° and −42.47(16)°, respectively. The corresponding torsion angles of the non-perfluorinated H₂4 were flatter: 2.6(3)° and −21.4(3)° [54]. The enol structures based on the difference in the predominant bond length and the twist of the aromatic ring in the two compounds H1 and H₂2 are very similar. In the crystal packings of H1 and H₂2, no remarkable π-π stacking was observed; the closest intermolecular distances between the two centroids of the pentafluorophenyl groups are sufficiently long (5.629 Å for H1 and 4.991 Å for H₂2) due to the sliding orientations of the molecular planes along the b axis (Figure 1c).

3.2. UV-Vis Studies of the Perfluorinated Compounds

The UV-spectra for H1~H₂4 were obtained in chloroform (CHCl₃), acetonitrile (CH₃CN), methanol (CH₃OH), and benzene (C₆H₆) solutions. The electronic absorption spectra of the four ligands in CHCl₃ are shown in Figure 2a. The maximum absorptions for H1, H3, H₂2, and H₂4 are observed at 315, 343, 351, and 383 nm, respectively. The absorption bands of the perfluorinated ligands H1 and H₂2 (shown in solid lines) were broad and more symmetric but those of the non-perfluorinated ligands H3 and H₂4 (dashed lines) showed a peak shoulder on the side of the long wavelength (around 370 and 400 nm for H3 and H₂4, respectively) [38]. The spectra of the triketonate ligands H₂2 and H₂4 (green lines) were about 36~40 nm red shifted in comparison to the corresponding diketone ligands H1 and H3 (black lines). The shift of each peak can be explained by expansion of the π-conjugated system. The spectra of the perfluorinated ligands H1 and H₂2 were blue shifted about 30 nm in comparison to the corresponding non-perfluorinated ligands H3 and H₂4. The blue shift can be explained by a loss of planarity of both molecules [53,54]. The planarity of the molecules was compromised due to the twisting induced by the steric hindrance between the fluorine at the o-positions of the pentafluorophenyl group and the hydrogen at the ketonate sites, as suggested by the crystal structures.

The maximum absorption wavelength and the shape of the spectrum of the perfluorinated ligands H1 and H₂2 were different depending on the solvent. The λ_max of H1 in polar solvents, such as CH₃OH, was 305 nm and in the aprotic polar CH₃CN solvent, it was ca. 310 nm. The spectrum in the nonpolar CHCl₃ (λ_max 315 nm) was red shifted nearly 5 nm compared with that in the polar solvents as shown in Figure 2b. The λ_max of H₂2 in the polar solvents was at 348–349 nm and slightly shifted from that in CHCl₃ (351 nm), and the intensity of the small shoulder peak around 280 nm increased in CH₃CN (Figure 2c). These solvent effects were not observed in the solution of H3 and H₂4. The H1 and H₂2 absorption spectra in the benzene solution were almost the same as those observed in the CHCl₃ solution. This indicates that solvatochromism occurs only in the polar solvents.

3.3. Co-Crystallization by Arene-Perfluoroarene Interactions

The perfluorinated compound and the non-perfluorinated compound were combined to give 1:1 co-crystal. Typically, H1 (121 mg, 0.30 mmol) in EtOH solution (2.5 mL) and H3 (67 mg, 0.30 mmol) in EtOH solution (2.5 mL) were combined, then the mixture was slowly evaporated to give the colorless prismatic crystals H1•H3. Although the reaction proceeded quantitatively, the co-crystal was isolated before the filtrate disappeared so that the microcrystals did not stick to the precipitated single crystal. The H₂2•H₂4 co-crystal was obtained as a yellow prismatic crystal using the same synthetic protocol. The results of the elemental analysis for H1•H3 (C₃₀H₁₄F₁₀O₄) and H₂2•H₂4 (C₃₄H₁₈F₁₀O₆) clearly showed that the crystallized products were pure with a 1:1 stoichiometry. The melting points of the co-crystals are expected to be higher than the single perfluorinated compounds: H1•H3 (106 °C) > H1 (83 °C) and H3 (76 °C); H₂2•H₂4 (125 °C) > H₂2 (87 °C) and H₂4 (107 °C).

The molecular structures of the co-crystals H1•H3 and H₂2•H₂4 are shown in Figure 3 with the corresponding numbering schemes. The major intra- and intermolecular interactions of H1•H3 and H₂2•H₂4 are summarized in Table 2. In Figure 3a, the co-crystal H1•H3 is comprised of H1 and H3 in a 1:1 ratio. The mean planes of both molecular structures were highly overlapped by the arene–perfluoroarene interaction. The bond lengths of O1-C7 and O2-C9 in H1 are 1.2607(17) Å and 1.3063(16) Å, respectively, and those of O3-C22 and O4-C24 in H3 are 1.2757(16) Å and 1.3054(16) Å, respectively, indicating the same type of π-conjugated structure of each molecular component. The two phenyl rings of H3 were twisted to the plane of the β-diketonate moiety, and the torsional angles of the C1-C6-C7-O1 and O2-C9-C10-C11 are -30.64(19)° and 32.78(18)°, respectively. Similarly, the pentafluorophenyl groups of H1 are twisted, producing 18.14(18)° and -12.71(18)° angles for C16-C21-C22-O3 and O4-C24-C25-C26, respectively.

Parts of the packing structure of H1•H3 are shown in Figure 4. The alternate stacking of the two compounds was observed along the b axis with alternating H1 and H3 layers (Figure 4a). The closest intermolecular distances between the two centroids of the pentafluorophenyl group in H1 and the phenyl group in H3 are 3.6671(8) Å [Ring C1-C2-C3-C4-C5-C6 (x, y, z) and Ring C25-C26-C27-C28-C29-C30 (x, y-1, z) indicating a weak arene–perfluoroarene interaction as shown in Figure 3a and Figure 4a. Remarkable intermolecular interactions were observed along the c axis (Figure 4b); two molecules, H1 and H3, are very close between the two edges of the compounds next to each other on the same plane by C-H···F interactions [28,31]. The corresponding distances of C20···F4, C23···F4, C30···F4, C29···F5, and C29···F10 are 3.418(2), 3.604(2), 3.541(2), 3.282(2), and 3.366(2) Å, respectively. Due to the CH···F interaction, the alternating columnar layers through arene–perfluoroarene interactions are further alternately staggered to form checkered patterns. No intermolecular hydrogen bonds are observed because of the stabilized intramolecular hydrogen bonds of each compound.

The molecules in the co-crystal of H₂2•H₂4 have almost the same orientation (Figure 3b and Figure 5) as the molecules in the H1•H3 co-crystal (Figure 3a and Figure 4). The bond lengths of O1-C7, O2-C9, and O3-C11 are 1.3276(16), 1.2729(16), and 1.3313(16) Å, respectively, and those of O4-C24, O5-C26, and O6-C28 are 1.3304(15), 1.2746(16), and 1.3343(16) Å, respectively. The torsional angle of the C1-C6-C7-O1 and O3-C11-C12-C13 are -29.51(17)° and 30.12(17)°, respectively, and that of C18-C23-C24-O4 and O6-C28-C29-C30 are 16.08(17)° and -11.66(17)°, respectively. The closest intermolecular distances between the two centroids of the pentafluorophenyl group in H₂2 and the phenyl group in H₂4 are 3.6949(8) Å, indicating that the driving force of the co-crystal is the arene–perfluoroarene interactions in the crystal. The C-H···F intermolecular interactions were also observed in H₂2•H₂4, but the remarkable short distance was only observed in C25···F4 [3.344(2) Å].

For understanding the intermolecular association of the two co-crystals, density functional theory (DFT) calculations using B3LYP/6-31G* [48,49] were performed for each compound [55,56]. The electrostatic potential (ESP) surfaces for H1~H₂4 are shown in Figure 6. Based on the orientation of the two aromatic rings of each compound, two stable structures with a bowl shape (the twisted direction of the aromatic rings is the same and the corresponding twist angle is small) and twisted shape (the twisted direction of the aromatic rings is opposite and the corresponding twist angle is large) were obtained. For example, the torsion angles of C5-C6-C10-C15 for the diketones H1 and H3 and C5-C6-C12-C17 for the triketones H₂2 and H₂4, of which the numbering schemes are assigned in Figure 1, were calculated to be around 1° and 60° for the bowl and twisted shapes, respectively. Typically, the torsion angle of C5-C6-C10-C15 in compound H1 is 0.13° for the bowl shape and 61.63° for the twisted shape. In the ESP, the property range of the bowl and twisted shapes are very similar to +118.3 ~ −142.1 kJ mol^-1 and +112.6 ~ −143.8 kJ mol⁻¹, respectively. Since all the co-crystals have a bowl shape, the ESP shows only bowl shapes in Figure 6. In the map, the blue color shows electron poor regions, indicating the proton atoms and the center parts of the pentafluorophenyl groups; the highest potential energies of H1, H3, H₂2, and H₂4 are +118.3, +109.6, +119.1, and +99.6 kJ mol⁻¹, respectively, of the hydroxy protons. The lowest potential energies are assigned to the oxygen atoms. The most interesting information is the inverted potential energy of the aromatic rings between the perfluorinated and non-fluorinated compounds. In the pentafluorophenyl rings of H1 and H₂2, the higher potentials due to electron poor regions (blue color) are occupied in the aromatic center (max. +106.7 kJ mol⁻¹ for H1 and +100.2 kJ mol⁻¹ for H₂2). The lower potentials due to the electron-rich regions (green–yellow color) are occupied in the edge of the fluorine atoms, and both of the F1 atoms in H1 and H₂2 shows smaller values, approximately −40 ~ −60 kJ mol⁻¹, which gives the intermolecular CH···F interactions in the co-crystals, as shown in Figure 4b and Figure 5b. On the other hand, in the phenyl rings of H3 and H₂4, the higher regions (blue color) are occupied on the edge of the protons (max. +104.3 kJ mol⁻¹ for proton H30 bound on C30 in H3 and +99.6 kJ mol⁻¹ for the proton H34 bound to C34 in H₂4) and the lower regions (green–yellow color) are occupied in the aromatic center (min. −67.6 kJ mol^-1 for H3 and −63.0 kJ mol⁻¹ for H₂4). These opposite electron distributions between the perfluorinated and non-fluorinated compounds indicate co-crystallizations through the arene-perfluoroarene and CH···F interactions [55,56], when two molecules approach each other.

4. Conclusions

We have demonstrated arene–perfluoroarene interactions between fully-fluorinated compounds and the corresponding non-perfluorinated compounds to give alternate layered supramolecular associations in the crystal states. Two fully-fluorinated compounds, the diketone H1 and triketone H₂2, were prepared and characterized by ¹H NMR, elemental analysis and X-ray crystallography. The UV-Vis spectra of H1 and H₂2 show keto-enol and enol-keto-enol structures, respectively. The compounds further interacted with the corresponding non-perfluorinated compounds to give 1:1 alternating co-crystals, which were characterized by elemental analysis and single crystal X-ray analysis. In the co-crystals, the intermolecular arene–perfluoroarene interactions were observed between the pentafluorophenyl rings and phenyl rings showing that the opposite quadrupole moments are responsible for their association as indicated by the DFT calculations.

Author Contributions

Syntheses: T.K., S.S. & K.N.; calculations, measurements and original draft preparation: T.K.; supervision: H.Y. & I.I.R.; manuscript review and editing: I.I.R & A.H.; crystal structure analysis, conceptualization, funding acquisition and project administration: A.H.

Funding

This research was funded by Grant-in-Aid for Scientific Research C (No. 18K05153) of JSPS KAKENHI.

Conflicts of Interest

The authors declare no conflict of interest.

Figures, Scheme and Tables

Scheme 1. Molecular structures of perfluorinated compounds, H1 and H22, and non-perfluorinated compounds, H3 and H24.

Figure 1. ORTEP drawings of the crystal structure of (a) H1 and (b) H22 at 120 K with 50% probability thermal ellipsoids and (c) the packing structure of H22 viewed from the ac axis.

Figure 2. UV-Vis absorption spectra of (a) H1~H24 in CHCl3 solution (40 μM, 1 cm, rt.); and (b) H1 and (c) H22 in following solvents, CHCl3, CH3CN, and CH3OH (1.0 mM, 1 mm, rt).

Figure 3. ORTEP drawings of the crystal structure of (a) H1•H3 and (b) H22•H24 with 50% probability thermal ellipsoids.

Figure 4. Packing structures of H1•H3: (a) the comprehensive view of the stacking structure and (b) major intermolecular interactions.

Figure 5. Packing structure of H22•H24: (a) the comprehensive view of the stacking structure and (b) major intermolecular interactions.

Figure 6. The energy potential maps [−162 kJ mol−1 (red) to +120 kJ mol−1 (blue)] of four compounds: (a) H1 vs. H3 and (b) H22 vs. H24.

Table 1

Crystal data and structure refinement for H1, H₂2, H1•H3, and H₂2•H₂4.

	H1	H22	H1•H3	H22•H24
Chemical formula	C15H2F10O2	C17H4F10O3	C30H14F10O4	C34H18F10O6
Formula weight	404.17	446.20	628.41	712.48
Crystal system	monoclinic	monoclinic	monoclinic	monoclinic
Space group	P21/n	P21/c	P21/c	P21/c
a [Å]	10.3800(11)	17.4336(12)	13.4003(10)	15.7397(14)
b [Å]	5.6285(6)	4.9910(3)	7.0784(5)	7.0887(6)
c [Å]	23.196(3)	18.3069(12)	26.1345(18)	25.835(2)
β [°]	94.2233(12)	106.929(1)	95.2152(8)	98.842(1)
V [Å3]	1351.5(2)	1523.88(17)	2468.7(3)	2848.3(4)
Z	4	4	4	4
Dc [Mg m−3]	1.986	1.945	1.691	1.662
μ [mm−1]	0.223	0.213	0.162	0.156
F(000)	792	880	1264	1440
R int	0.0240	0.0194	0.0238	0.0265
GOF	1.061	1.033	1.047	1.035
R [(I) > 2σ (I)]	0.0303	0.0301	0.0337	0.0334
wR (Fo2)	0.0845	0.0849	0.0930	0.0952
CCDC No.	1827049	1827050	1827051	1827052

Table 2

Major intra- and intermolecular interactions of H1•H3 and H₂2•H₂4.

	H1•H3	H22•H24
Intramolecular hydrogen bonds (O-H···O)	O1···O2, 2.5313(15) Å	O1···O2, 2.5495(14) Å
		O2···O3, 2.5811(14) Å
	O3···O4, 2.4882(15) Å	O4···O5, 2.5584(14) Å
		O5···O6, 2.5632(14) Å
	O1···H2-O2, 147°	O1-H1···O2, 147°
		O2···H3-O3, 146°
	O3···H4-O4, 148°	O4-H4···O5, 146°
		O5···H6-O6, 147°
Intermolecular hydrogen bonds (O-H···O)	not found	not found
Arene-perfluoroarene[Cg(C6F5)···Cg(C6H5)]	π(C1-6)···π(C29-34), 3.6671(8) Å	π(C1-6)···π(C29-34), 3.6949(8) Å
	π(C10-15)···π(C16-21), 4.1008(9) Å	π(C12-17)···π(C18-23), 4.0439(8) Å
C-F···π [C-F···Cg(C6F5)]	C4-F4···π(C29-34), 3.4806(11) Å	C4-F4···π(C29-34), 3.4959(11) Å
	C14-F9···π(C16-21), 3.2877(11) Å	C16-F9···π(C18-23), 3.2621(11) Å
	C15-F10···π(C16-21), 3.2364(10) Å	C17-F10···π(C18-23), 3.3073(11) Å