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. 2024 Apr 12;2(5):221–228. doi: 10.1021/prechem.4c00019

A Hydrogen-Bonded, Hexagonally Networked, Layered Framework with Large Aperture Designed by Structural Synchronization of a Macrocycle and Supramolecular Synthon

Hiroki Yoshimura †, Ryusei Oketani †, Miki Naruoka ‡, Norimitsu Tohnai ‡, Ichiro Hisaki †,*
PMCID: PMC11504516  PMID: 39474408

Abstract

graphic file with name pc4c00019_0009.jpg

To develop porous organic frameworks, precise control of the stacking manner of two-dimensional porous motifs and structural characterization of the resultant framework are important. From these points of view, porous molecular crystals formed through reversible intermolecular hydrogen bonds, such as hydrogen-bonded organic frameworks (HOFs), can provide deep insight because of their high crystallinity, affording single-crystalline X-ray diffraction analysis. In this study, we demonstrate that the stacking manner of hydrogen-bonded hexagonal network (HexNet) sheets can be controlled by synchronizing a homological triangular macrocyclic tecton and a hydrogen-bonded cyclic supramolecular synthon called the phenylene triangle. A structure of the resultant HOF was crystallographically characterized and revealed to have a large channel aperture of 2.4 nm. The HOF also shows thermal stability up to 290 °C, which is higher than that of the conventional HexNet frameworks.

Keywords: hydrogen-bonded organic frameworks, hexagonal network, macrocycle, carboxylic acid, porosity

Introduction

Porous organic crystalline frameworks have recently been one of the most important materials for selective gas separation operating on lower energy, photocatalyst for CO2 reduction, and electrode materials.1−3 A layered assembly of two-dimensionally networked porous sheets is the most frequently observed hierarchical structure for porous crystalline organic materials. For example, tritopic motifs such as a trimer of boronic acid,4 1,3,5-trisubstituted benzene,5 and their analogous structures6 are used as a junction to link the molecules, giving a porous honeycomb sheet. The combination of other types of molecules and linkers also can give a wide range of two-dimensional (2D) network structures.7 Stacking patterns can be broadly classified into staggered, eclipsed, and slip-stacked types.8 The stacking manner is strongly related to the interlayer interactions.9 A typical example is COF-1 and COF-5 reported by Yaghi and co-workers.5 In COF-1, layers are stacked in a staggered manner such as ABA stacking in graphene, while in COF-5, layers are stacked in an eclipse manner, providing a channel structure with a large aperture. Larger triphenylene cores in COF-5 bestowed a larger number of overriding π–π interactions to guide eclipse stacking.

It is crucial for developing porous materials to control the stacking manner of the 2D porous network structures. However, COFs whose stacking manners were precisely characterized by single-crystalline X-ray or electron diffraction remain relatively limited.10−12 On the other hand, a detailed discussion for the stacking manner of 2D porous networks is possible in the case of supramolecular systems, in which molecules are bound to each other by hydrogen bonds. Duchamp and Marsh reported that trimesic acid gave a crystal structure formed by interpenetration of an undulated honeycomb network in 1969;13 meanwhile, Herbstein and co-workers achieved noninterpenetrated, almost eclipse stacking manners of the honeycomb sheets using chain-shaped template molecules in 1987.14 Similarly, the interpenetrated assembly of honeycomb networks composed of expanded tritopic carboxylic acid, 1,3,5-tris(4-carboxyphenyl)benzene, can be modified by changing the substituent groups bound to the central benzene.15,16 Such porous structures have recently been called noncovalent organic frameworks (nCOFs), supramolecular organic frameworks (SOFs), or hydrogen-bonded organic frameworks (HOFs).17−23

As compared to tricarboxylic acid, which frequently gives interpenetrated honeycomb networks, a hexasubstituted analogue hexakis(4-carboxyphenyl)benzene gives no interpenetrated but a layered assembly of hexagonal network (HexNet) sheets as reported by Kobayashi and co-workers.24 Similar layered structures are also demonstrated by Wuest and co-workers using a hexa-substituted benzene derivative with diaminotriazine (DAT) groups.25 These indicate that HexNets prefer a layered assembly because of trigonal pores unsuitable for interpenetration. We have also demonstrated that a series of hexatopic carboxylic acids with C3-symmetric π-conjugated cores26−29 and tribenzo-18-crown-6-ether30 gave layered structures composed of noninterpenetrated HexNet sheets (Figure 1). The structure is interpreted as follows. The molecules form a H-bonded triangular motif so-called phenylene triangle (PhT) by cyclotrimerization of 4,4′-dicarboxy-o-terphenyl moieties, giving a HexNet sheet. The HexNet sheets stack in an inverted fashion to give a layered crystalline porous framework.26

Figure 1.

Figure 1

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Construction of layered frameworks composed of a H-bonded hexagonal network (HexNet) of hexatropic carboxylic acids. (a) HexNet formation via the H-bonded phenylene triangle (PhT) motif composed of three 4,4′-dicarboxy-o-terphenyl moieties. (b) Layered structure with divided void formed through inverted stacking of the HexNet layers composed of the C3-symmetric tecton with a core size smaller than that of the PhT motif. (c) Layered structure retaining intrinsic aperture of the void formed through inverted stacking of HexNet layers composed of the C3-symmetric tecton with the same core size as that of the PhT motif. (d) A series of C3-symmetric hexacarboxylic acids with various sizes of π-conjugated cores. Pink dots indicate a centroid of benzene rings comprising the vertices of the macrocycles or PhT motif, and are used for estimating side lengths of the macrocycles and PhT motif.

It should be noted that the inverted stacking manner prevents eclipse stacking, while it gave only partial overlap between HexNets. Moreover, even if a single HexNet sheet has a large hexagonal aperture, the aperture is divided in the consequent layered structure by the inversion stacking. The partial overlap and divided pore results in a less stable and low crystalline framework after activation.

To construct a stable layered HexNet framework with large aperture and high crystallinity, we designed hexatopic tecton BPEx with a biphenylenediethynylene-bridged macrocycle core, which has a size and geometry closely similar to that of the H-bonded PhT motif. We hypothesized that the homology could provide a porous assembly with a large hexagonal aperture and large overlap of the frameworks when the HexNets are stacked with the inverted manner (Figure 1c). Herein, we report a highly porous and crystalline HOF constructed on the basis of the above-mentioned design strategy and hypothesis. The HOF possessing a 1D channel with aperture size of 2.4 nm shows permanent porosity with the BET surface area of 590 m2 g–1 after activation. Moreover, the structure of the HOF can be retained up to 290 °C.

Results and Discussion

Design of a Tecton

Table 1 lists the side lengths (LM) of four kinds of C3-symmetric triangular molecules Tp, T12, T18, and Ex, which we have used for the construction of HOFs (Tp-1, T12-1, T18-1, and Ex-1, respectively).26−29 The length is between the centroids of the benzene rings at the apexes of the triangle. The LM values ranging from 4.3 to 13.7 Å are clearly shorter than the side length of the H-bonded PhT motif (LH: ca. 18.1 Å). Therefore, according to strategy we proposed in Figure 1, a C3-symmetric triangular molecule with LM that is the same with LH should be developed. After exploring the candidate structures of such a triangular macrocycle, we set the biphenylenediethynylene-bridged macrocycle BPEx as a target hexatropic tecton to construct the layered HexNet HOF. The density functional theory (DFT) calculation at the B3LYP-D3/6-31G(d,p) level indicated that the geometrically optimized BPEx has an LM value of 18.08 Å (Figure S1 and Table S1), which is in good agreement with the reported value of LH.

Table 1. Side Lengths of the C3-Symmetric Triangular Molecules and the PhT Motif in HOFsa.

tecton (HOF) LMc/Å LHd/Å
Tp (Tp-1) 4.30 18.15
T12 (T12-1) 6.86 18.07
T18 (T18-1) 9.43 18.10
Ex (Ex-1) 13.71 18.10
calc. BPExb 18.08  
BPEx (BPEx-1) 17.83 17.88
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a

The values are the average for the reported crystal structures.

b

The value is for the calculated structure of BPEx.

c

Distances between the centroids of benzene rings comprising the vertices of the triangular macrocycle.

d

Distances between the centroids of benzene rings comprising the PhT motif.

Synthesis

BPEx was synthesized as shown in Scheme 1. Dissymmetric diethynylbenzene derivative 1, which was synthesized according to the literature,27 was reacted with diiodobiphenyl derivative 2 in a 1:1 stoichiometry by the Sonogashira cross-coupling reaction to give phenylethynylbiphenyl derivative 3 in moderate yield. Desilylation of 3 in the presence of tetrabutylammonium fluoride (TBAF), followed by cyclotrimerization of the resultant terminal acetylene 4, yielded macrocyclic precursor 5 in 11% in two steps from 3. Hydrolysis of 5 in the presence of KOH gave hexatropic carboxylic acid BPEx, which was characterized by 1H and 13C NMR spectroscopy and HR–MS analysis.

Scheme 1. Synthesis of BPEx.

Scheme 1

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Photophysical Properties

BPEx has a UV absorption band at 355 nm in a DMSO solution (Figure 2), which was well reproduced by theoretical calculations with CAM-B3LYP/6-31G(d,p)/PCM(DMSO) (Figures S2 and S3). The solution showed blue fluorescence with emission bands at 419 and 442 nm with a quantum yield of 0.81. A solid-state fluorescence spectrum of activated HOF BPEx-1a was slightly red-shifted by 48 nm, and its quantum yield was 0.025. The solid-state excitation spectrum monitored at 560 nm is also red-shifted as compared to the absorption band in the solution. These photophysical properties were attributed to a highly overlapped molecular packing manner in the HOF, which is discussed later.

Figure 2.

Figure 2

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UV–vis (black solid line) and fluorescence (black dashed line, λex = 355 nm) spectra of BPEx in DMSO solution (5.08 × 10–6 M–1) and solid-state excitation (red solid line, λem = 560 nm) and fluorescence (red dashed line, λex = 355 nm) spectra of HOF BPEx-1a.

Crystallography

Crystallization of BPEx was conducted by slow evaporation of a mixed solution of BPEx dissolved in N,N-dimethylformamide (DMF) and 1,2,4-trichlorobenzene (TCB) at 50 °C, giving prism-shaped single crystals of HOF BPEx-1 (Figure S4 and Table S2). A crystal structure of HOF BPEx-1 was successfully revealed by single-crystalline X-ray diffraction (SXRD) analysis using synchrotron X-ray radiation. As shown in Figure 3a, molecules of BPEx-1 are networked via H-bonding of the carboxy groups with a O···O distance of 2.58–2.63 Å to form a HexNet structure. The HexNet layer has triangular void I in the PhT motif, sexangular void II with a width of 25.1 Å, and intrinsic molecular void III. The HexNet layers are stacked alternately in an inverted manner as observed in the conventional HexNet layers.27 As designed, the layers are almost completely overlapped, allowing the 1D channel possessing a large hexagonal aperture (Figure 3b). The present highly overlapped stacking of the HexNet framework was permitted by conformity of the macrocyclic moiety of the BPEx molecule and the H-bonded PhT motif (Figure 2c and d, respectively). The observed side lengths of the macrocycle and PhT motif are 17.81–17.85 and 17.85–17.92 Å, respectively, although they are slightly shorter than those predicted probably because of the slightly twisted conformation of the BPEx molecule: the root-mean-square deviation (RMSD) for the positions of the carbon atoms in the macrocycle part except for the biphenyl moieties against the mean plane of the macrocycle was calculated to be 0.143 Å. The biphenyl moieties in the macrocycle are twisted with a small dihedral angle ranging from 6.0° to 28.5° (averaged value: 16.8°) against the mean plane of the macrocycle, which are slightly smaller than those in a molecular structure geometrically optimized by DFT calculations (4.2–38.4°, averaged value: 19.8°). The phenylene rings in the PhT motif show larger twisted angles ranging from 49.2° to 74.0° (averaged value: 56.2°) against the mean plane of the PhT motif because of steric hindrance of the o-terphenyl group.

Figure 3.

Figure 3

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Crystal structure of HOF BPEx-1. (a) H-bonded HexNet sheet with three kinds of voids (I, II, and III). (b) Alternate stacking of the three layers with large overlap of the framework, where each layer is colored orange, blue, or dark blue. (c) Cyclic structure of (c) the π-conjugated macrocycle and (d) the H-bonded PhT motif drawn in the anisotropic displacement ellipsoids with 50% probability. Twisted angles of phenylene rings against the mean plan of the macrocycle or PhT motif are presented near the corresponding phenylene ring. Side lengths of the triangular macrocycle and PhT motif (LM and LH, respectively) are defined by a distance between the centroids of the benzene rings at the vertices of the triangles. The red dot denotes a centroid of the corresponding benzene rings.

It is noteworthy that the H-bonded carboxy dimer part was held between the biphenylenethynylene moieties of the macrocycle due to alternate stacking of the HexNet sheet of BPEx (Figure 4a). This kind of stacking manner is also reported in the case of HOF composed of a stoichiometric mixture of trimetic acid and 1,3,5-tris(4-carboxyphenyl)benzene derivatives, and can stabilize the layered framework.31 Because the phenylene rings of the PhT motif have a relatively large dihedral angle against a plane of the PhT, the neighboring layers are stacked with the edge-to-face contact, where CH···π interactions and the dispersion force between C=O and the benzene ring were observed as indicated by (1) and (2) in Figure 4a. The interlayer distance is 4.11 Å, which is longer than that for π···π stacking.

Figure 4.

Figure 4

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Crystallographically solved TCB molecules accommodated in the narrow void surrounded by the macrocycle and H-bonded motif. (a) Side and top views of the packing manner of the macrocycle (dark blue) and H-bonded PhT motif (pink) with selected intermolecular interactions referred to as (1)–(6). The side view with a space-filling model is also presented. (b) Relative orientation and intermolecular interactions between the TCB molecule and macrocycle, and (c) those between the TCB molecule and H-bonded motif.

In the HOF, molecules of TCB used for recrystallization solvent were included. Two crystallographically independent TCB molecules were included in the PhT motif (void I) and covered by the macrocycles from the top and bottom. Void III in the macrocycle is probably too small to accommodate a molecule of TCB. Intermolecular interactions such as CH···Cl, CH···π, and π···π interactions referred to as (3), (4), and (5), respectively, were observed between the TCB and the biphenyl moiety of the macrocycle (Figure 4b). CH···O interactions referred to as (6) were observed between the TCB molecules and the PhT motif (Figure 4c).

The larger hexagonal channel also accommodates solvent molecules, which, however, were not refined due to severe disorder. The number of electrons in void II was estimated to be 927 by SQUEEZ treatment, indicating that an additional 10.3 TCB molecules are included in the void in the unit cell. The total solvent accessible volume and void ratio of the HOF per the unit cell were calculated to be 5829.21 Å3 and 64%, respectively, used with a probe of 1.2 Å radius (Figure 5). The channels run along the a axis, which is not perpendicular to the HexNet plane, but is inclined by 17.64° to the (100) plane. The aperture width of the larger hexagonal channel is 24 Å, which is comparable to other HOFs with large aperture.32−36

Figure 5.

Figure 5

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Visualized surface of the inclusion channel in HOF BPEx-1 viewed down from (a) the a axis and (b) the b axis.

Thermal Analysis

The TG curve showed a weight loss of 47.4% up to 213 °C, which corresponded to a loss of solvent molecules included in HOF (Figure 6a). A slight weight loss starting at ca. 380 °C is due to the thermal decomposition of the compound. Crystallinity of the framework was investigated by variable-temperature (VT)-PXRD experiments (Figure 6b). Diffraction patterns recorded at room temperature showed almost no peak because of the low contrast of the diffracted X-ray due to scattering of disordered TCB molecules in the large void, instead of the low crystallinity of the framework. This phenomenon has been often observed for HOFs accommodating chlorinated solvent molecules.27 Diffraction peaks started to appear at ca. 120 °C, and its intensity reached a plateau at 190 °C with the removal of the solvent molecules. The characteristic pattern with diffraction peaks such as those at 2.85°, 5.71°, and 8.60° is in agreement with the simulated pattern for the as-formed HOF BPEx-1 (Figure 6c). The pattern was retained up to 290 °C, indicating that the porous structures were also retained.

Figure 6.

Figure 6

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Thermal behavior of as-formed HOF BPEx-1. (a) TG-DTA curves. (b) VT-PXRD patterns. (c) Comparison of PXRD patterns of as-formed HOF BPEx-1 (top) and solvent-removed HOF BPEx-1a(bottom). The pattern of BPEx-1 is simulated from SXRD data, while that of BPEx-1a is a pattern recorded at 240 °C in the VT-PXRD experiment.

It should be mentioned that a diffraction peak corresponding to the (011) plane, which appears at 3.21° in the simulated pattern of as-formed HOF, was not observed in the experimental pattern after the solvent was removed. Assuming that the (011) and (010) diffraction peaks were merged, the activated framework could have more symmetrical structure with complete overlap of the framework. The (022) diffraction peak was not observed due to the same reason.

Elucidation of Porosity

As-formed crystalline bulk was isolated by filtration and dried at 190 °C under vacuum conditions for 2 h. The resultant activated material, however, showed no crystallinity and porosity (Figures S5–S7). After careful consideration, we finally obtained the activated HOF by applying the heating condition the same as that for TG analysis. Namely, the as-formed crystalline bulk was heated from room temperature to 210 °C at a rate of 10 °C min–1, followed by keeping the temperature for 60 min under a nitrogen flow condition. Complete removal of the solvent molecules and sustention of the structure on the activated HOF BPEx-1a were confirmed by the 1H NMR spectrum of the sample dissolved in deuterated DMSO and by the PXRD pattern (Figures S8 and S9, respectively). The powder sample of BPEx-1a was subjected to gas sorption experiments to evaluate porosity. The HOF, however, showed no uptake of N2 at 77 K, while CO2 was absorbed up to 218 mL at 195 K at P/P0 = 1 (Figure 7). Based on the CO2 adsorption isotherm, the Brunauer–Emmett–Teller (BET) surface area was estimated to be 590 m2 g–1 (Figure S10), which is lower than our expectation for HOF BPEx-1a. These results indicate that the HOF partially lost its porous structure during and/or after activation, which may be attributed to the narrow void of the macrocycle. As described, the void is too small for accommodation of TCB molecules, which also indicates that TCB molecules are not able to pass through without structural perturbations during the activation. The edge-to-face stacking manner of the layers may also cause loss of crystallinity because of the lower stability as compared to a face-to-face stacking manner.

Figure 7.

Figure 7

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N2 (black) and CO2 (green) sorption isotherms of BPEx-1a measured at 77 and 195 K, respectively. Solid symbols, adsorption; open symbols, desorption.

Conclusion

In this study, we demonstrated that the stacking manner of hydrogen-bonded hexagonal network (HexNet) sheets can be controlled by synchronizing a homological triangular macrocyclic tecton and hydrogen-bonded cyclic supramolecular synthon called a phenylene triangle. The resultant layered HOF BPEx-1 was precisely characterized by single-crystalline X-ray diffraction analysis to have a large channel aperture of 2.4 nm. The HOF retained its framework structure up to 290 °C, while the activated HOF is fragile and may be easily collapsed judging from gas sorption experiments, presumably because of the narrow void of the BPEx-1 molecule and/or less stable edge-to-face stacking of the layers. For improvement of the stability, a more suitable molecular design should be combined with the present strategy, which is currently being conducted in our laboratory.

Methods

Synthesis of 3

A three-necked flask was charged with ethynylbenzene derivative 1 (1.97 g, 3.57 mmol), 4,4′-diiodobiphenyl (2) (4.28 g, 10.5 mmol), Pd(PPh3)4 (226 mg, 0.196 mmol), and CuI (118 mg, 0.620 mmol) under argon atmosphere, and degassed THF (30 mL) and Et3N (10 mL) were added. The reaction mixture was stirred at room temperature for 3 h. After solvent was removed under vacuum, the product was extracted with CH2Cl2, washed with water (100 mL × 3) and brine (100 mL × 3), dried over anhydrous MgSO4, and purified by column chromatography (silica gel, CH2Cl2) to give 3 (1.99 g, 68%) as a yellow solid. Mp 118 °C. 1H NMR (400 MHz, CDCl3): δ 7.90 (d, J = 8.4 Hz, 2H), 7.90 (d, J = 8.8 Hz, 2H) 7.78 (d, 2H, J = 8.4 Hz), 7.65–7.54 (m, 6H), 7.36 (d, 2H, J = 8.4 Hz), 7.21–7.18 (m, 4H), 3.90 (s, 6H), 1.15–1.14 (m, 21H) ppm. 13C NMR (100 MHz, CDCl3): δ 166.9, 144.6, 140.2, 140.0, 139.6, 139.5, 138.1, 135.7, 134.9, 134.3, 132.5, 129.84, 129.82, 129.6, 129.1, 129.0, 126.8, 125.9, 125.7, 122.6, 96.8, 52.3, 18.9, 11.5 ppm. HR–MS (FAB): calcd for C47H46O4SiI [M + H]+, 829.2210; found, 829.2200.

Synthesis of 4

To a solution of 3 (1.86 g, 2.24 mmol) dissolved in THF (30 mL) was added a 1 M solution of tetrabutylammonium fluoride in THF (2.90 mL). After being stirred at room temperature for 1 h, the reaction mixture was quenched with water, extracted with CH2Cl2, and passed through a column of silica gel with CH2Cl2 to give a crude sample of 4 (1.15 g) as a brown solid, which was used in the next step without further purification. The following data were collected using a small amount of pure 4 isolated by repeated chromatography. Mp 188 °C. 1H NMR (400 MHz, CDCl3): δ 7.91 (d, J = 8.4 Hz, 2H), 7.90 (d, J = 8.4 Hz, 2H), 7.79 (d, 2H, J = 8.8 Hz), 7.65 (d, 2H, J = 8.4 Hz), 7.65 (s, 1H), 7.64 (s, 1H), 7.56 (d, 2H, J = 8.4 Hz), 7.35 (d, 2H, J = 8.4 Hz), 7.20 (d, 2H, J = 8.4 Hz), 7.19 (d, 2H, J = 8.4 Hz), 3.90 (s, 6H), 3.45 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ 144.4, 144.3, 140.4, 140.1, 139.9, 139.5, 138.1, 134.7, 133.9, 132.5, 129.8, 129.6, 129.2, 129.2, 129.0, 126.2, 124.6, 122.4, 94.5, 93.7, 88.4, 82.3, 81.7, 52.3 ppm. HR–MS (FAB): calcd for C38H25O4I [M]+, 672.0798; found, 672.0795.

Synthesis of 5

A three-necked flask was charged with the above synthesized 4 (263 mg), Pd(PPh3)4 (38.0 mg, 32.9 μmol), and CuI (37.0 mg, 0.194 mmol) under argon atmosphere, and degassed THF (12 mL) and Et3N (6 mL) were added. The reaction mixture was stirred at room temperature for 15 h. After solvent was removed under vacuum, the product was extracted with CHCl3, washed with water (100 mL × 3) and brine (100 mL × 3), dried over anhydrous MgSO4, and purified with column chromatography (silica gel, CHCl3) to give compound 10 (26.3 mg, 11% in two steps from 3) as a pale-yellow solid. Mp > 300 °C. 1H NMR (400 MHz, CDCl3): δ 7.93 (d, J = 8.4 Hz, 12H), 7.74 (s, 24H), 7.71 (s, 6H), 7.24 (d, J = 8.4 Hz, 12H), 3.92 (s, 18H) ppm. 13C NMR (100 MHz, CDCl3): δ 166.7, 144.4, 140.2, 139.5, 133.8, 132.2, 129.7, 129.5, 129.0, 127.0, 125.6, 122.6, 94.4, 88.8, 52.1 ppm. HR–MS (FAB): calcd for C114H72O12 [M]+, 1632.5024; found, 1632.5037.

Synthesis of BPEx

A round-bottomed flask was charged with compound 5 (26.3 mg, 16.0 μmol), 10% KOHaq (8 mL), and THF (10 mL). The suspension was then refluxed at 60 °C for 48 h. After THF was removed under vacuum, the resultant water suspension was neutralized by 6 M HClaq (20 mL). The precipitate was filtered and washed with water (20 mL) three times and chloroform (20 mL) once to give BPEx (21.5 mg, 87%) as a pale-yellow solid. Mp > 300 °C. 1H NMR (400 MHz, DMSO-d6): δ 7.97 (d, 12H, J = 8.8 Hz), 7.84 (d, 12H, J = 8.4 Hz), 7.78–7.76 (m, 18H), 7.31 (d, 12H, J = 8.4 Hz) ppm. 13C NMR (100 MHz, DMSO-d6): δ 143.0, 139.3, 139.0, 133.0, 131.6, 129.2, 128.8, 128.7, 126.6, 124.3, 121.3, 93.9, 88.3 ppm. HR–MS (MALDI): calcd for C108H60O12 [M]+, 1548.4085; found, 1548.4079.

Acknowledgments

This work was supported by KAKENHI (JP21H01919, JP21K18961, JP22H05461, and JP23H04029) from MEXT/JSPS, Japan. I.H. thanks the Iketani Science and Technology Foundation and the Hoansha Foundation for their financial support. I.H. thanks the Multidisciplinary Research Laboratory System for Future Developments (MRL), Graduate School of Engineering Science, Osaka University. We thank Ms. R. Miyake for HR–MS analysis. X-ray diffraction data were collected at BL40XU in SPring-8 with approval of JASRI (proposal nos. 2021A1080, 2022B1151, and 2023A1264).

Data Availability Statement

Crystallographic data for the structure reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition number CCDC 2333886. Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/prechem.4c00019.

  • General experimental methods, synthesis, theoretical calculation, 1H and 13C NMR spectra, details of crystallography, and porosity evaluation (PDF)

  • X-ray crystallographic data for BPEx-1 (CIF)

Author Contributions

H.Y. designed, synthesized, and characterized the HOF, evaluated the properties, and cowrote the paper. R.O. conducted the theoretical calculations and evaluated the data. M.N. and N.T. performed the gas sorption experiments. I.H. planned and supervised the research, analyzed the data, and cowrote the paper. All authors have given approval to the final version of the manuscript.

The authors declare no competing financial interest.

Supplementary Material

pc4c00019_si_001.pdf (2.2MB, pdf)
pc4c00019_si_002.cif (5.2MB, cif)

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

pc4c00019_si_001.pdf (2.2MB, pdf)
pc4c00019_si_002.cif (5.2MB, cif)

Data Availability Statement

Crystallographic data for the structure reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition number CCDC 2333886. Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/.

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