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

Perfluorophenyl-substituted compounds, 3-hydroxy-1,3-bis(pentafluorophenyl)-2propen-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.


General
All the chemicals were of reagent grade and used without further purification. Nonperfluorinated compounds H3 and H24 were commercially available. The 1 H 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].

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 1,1,2,2tetrachloroethane in the presence of anhydrous AlCl3. The reaction mixture was separated by a column chromatography (silica, benzene). The H1 product was obtained at Rf = 0.8, and two other byproducts corresponding to the aluminum complex and acethylpentafluorobenzoylmethane were obtained at Rf = 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. 1 H NMR (600 MHz, CDCl3): δ 15.12 (s, OH), 6.26 (s, CH). 13   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

General
All the chemicals were of reagent grade and used without further purification. Non-perfluorinated compounds H3 and H 2 4 were commercially available. The 1 H 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].

Synthesis of H1 and H 2 2
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 AlCl 3 . 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. 1  1,5-Dihydroxy-1,5-bis(pentafluorophenyl)-1,4-pentadien-3-one (H 2 2) 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 N 2 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 NaHCO 3 , and extracted with diethylether. The obtained mixture was purified by column chromatography (silica, CH 2 Cl 2 ). The first product was assigned to methylpentafluorobenzoate (R f = 0.7), and the second product with R f = 0.5 was characterized as H 2 2. Compound H 2 2 was further purified by GPC and recrystallized from ethanol to give yellow prismatic crystals. Yield 30%. mp 87-88 • C. 1  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.

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 H 2 2) and their co-crystals (H1•H3 and H 2 2•H 2 4) are summarized in Table 1. CCDC 1827049 (H1), 1827050 (H 2 2), 1827051 (H1•H3), and 1827052 (H 2 2•H 2 4) 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.

Enol-Type Structures of H1 and 2
Compounds H1 and H 2 2 were prepared by using previously described protocols, purified by column chromatography, GPC, and recrystallized to give pure single products. The 1 H NMR results of both structures in CDCl 3 clearly suggested enol-type structures. The 1 H NMR spectrum of H1 in CDCl 3 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 1 H NMR spectrum of H 2 2 in CDCl 3 also shows two single peaks at δ 14.26 (OH) and 5.73 (CH), indicating the highly symmetric structure of H 2 2, while several keto-and enol-type corresponding isomers are expected. Single crystals of H1 and H 2 2 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 H 2 2 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.

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 nonperfluorinated 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 Figure 1. ORTEP drawings of the crystal structure of (a) H1 and (b) H 2 2 at 120 K with 50% probability thermal ellipsoids and (c) the packing structure of H 2 2 viewed from the ac axis.
In the crystal of H 2 2, 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 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 H 2 2 are very similar. In the crystal packings of H1 and H 2 2, 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 H 2 2) due to the sliding orientations of the molecular planes along the b axis (Figure 1c).

UV-Vis Studies of the Perfluorinated Compounds
The UV-spectra for H1~H 2 4 were obtained in chloroform (CHCl 3 ), acetonitrile (CH 3 CN), methanol (CH 3 OH), and benzene (C 6 H 6 ) solutions. The electronic absorption spectra of the four ligands in CHCl 3 are shown in Figure 2a. The maximum absorptions for H1, H3, H 2 2, and H 2 4 are observed at 315, 343, 351, and 383 nm, respectively. The absorption bands of the perfluorinated ligands H1 and H 2 2 (shown in solid lines) were broad and more symmetric but those of the non-perfluorinated ligands H3 and H 2 4 (dashed lines) showed a peak shoulder on the side of the long wavelength (around 370 and 400 nm for H3 and H 2 4, respectively) [38]. The spectra of the triketonate ligands H 2 2 and H 2 4 (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 H 2 2 were blue shifted about 30 nm in comparison to the corresponding non-perfluorinated ligands H3 and H 2 4. 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.

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 nonperfluorinated 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 H 2 2 were different depending on the solvent. The λ max of H1 in polar solvents, such as CH 3 OH, was 305 nm and in the aprotic polar CH 3 CN solvent, it was ca. 310 nm. The spectrum in the nonpolar CHCl 3 (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 H 2 2 in the polar solvents was at 348-349 nm and slightly shifted from that in CHCl 3 (351 nm), and the intensity of the small shoulder peak around 280 nm increased in CH 3 CN (Figure 2c). These solvent effects were not observed in the solution of H3 and H 2 4. The H1 and H 2 2 absorption spectra in the benzene solution were almost the same as those observed in the CHCl 3 solution. This indicates that solvatochromism occurs only in the polar solvents.

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 H 2 2•H 2 4 co-crystal was obtained as a yellow prismatic crystal using the same synthetic protocol. The results of the elemental analysis for H1•H3 (C 30 H 14 F 10 O 4 ) and H 2 2•H 2 4 (C 34 H 18 F 10 O 6 ) 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); H 2 2•H 2 4 (125 • C) > H 2 2 (87 • C) and H 2 4 (107 • C).
The molecular structures of the co-crystals H1•H3 and H 2 2•H 2 4 are shown in Figure 3 with the corresponding numbering schemes. The major intra-and intermolecular interactions of H1•H3 and H 2 2•H 2 4 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. The maximum absorption wavelength and the shape of the spectrum of the perfluorinated ligands H1 and H22 were different depending on the solvent. The λmax 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 (λmax 315 nm) was red shifted nearly 5 nm compared with that in the polar solvents as shown in Figure 2b. The λmax 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.

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 cocrystal 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 areneperfluoroarene interaction. The bond lengths of O1-C7 and O2-C9 in H1 are 1.2607 (17) 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 Figures 3a and 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.    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 Figures 3a and  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 (Figures 3b and 5) as the molecules in the H1•H3 co-crystal (Figures 3a and 4). The bond lengths of O1-C7, O2-C9, and O3-C11 are 1.3276 (16)  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 Figures 4b and 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. 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~H 2 4 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 H 2 2 and H 2 4, 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, H 2 2, and H 2 4 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 H 2 2, 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 H 2 2). 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 H 2 2 shows smaller values, approximately −40~−60 kJ mol −1 , which gives the intermolecular CH···F interactions in the co-crystals, as shown in Figures 4b and 5b. On the other hand, in the phenyl rings of H3 and H 2 4, 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 H 2 4) 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 H 2 4). 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. perfluorinated and non-fluorinated compounds indicate co-crystallizations through the areneperfluoroarene and CH···F interactions [55,56], when two molecules approach each other.

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 1 H 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.

Conflicts of Interest:
The authors declare no conflict of interest.