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Highly Selective p-Xylene Separation from Mixtures of C8 Aromatics by a Nonporous Molecular Apohost
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Journal of the American Chemical Society

Cite this: J. Am. Chem. Soc. 2023, 145, 50, 27316–27324
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https://doi.org/10.1021/jacs.3c07198
Published December 6, 2023

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Abstract

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High and increasing production of separation of C8 aromatic isomers demands the development of purification methods that are efficient, scalable, and inexpensive, especially for p-xylene, PX, the largest volume C8 commodity. Herein, we report that 4-(1H-1,2,4-triazol-1-yl)-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (TPBD), a molecular compound that can be prepared and scaled up via solid-state synthesis, exhibits exceptional PX selectivity over each of the other C8 isomers, o-xylene (OX), m-xylene (MX), and ethylbenzene (EB). The apohost or α form of TPBD was found to exhibit conformational polymorphism in the solid state enabled by rotation of its triazole and benzene rings. TPBD-αI and TPBD-αII are nonporous polymorphs that transformed to the same PX inclusion compound, TPBD-PX, upon contact with liquid PX. TPBD enabled highly selective capture of PX, as established by competitive slurry experiments involving various molar ratios in binary, ternary, and quaternary mixtures of C8 aromatics. Binary selectivity values for PX as determined by 1H NMR spectroscopy and gas chromatography ranged from 22.4 to 108.4, setting new benchmarks for both PX/MX (70.3) and PX/EB (59.9) selectivity as well as close to benchmark selectivity for PX/OX (108.4). To our knowledge, TPBD is the first material of any class to exhibit such high across-the-board PX selectivity from quaternary mixtures of C8 aromatics under ambient conditions. Crystallographic and computational studies provide structural insight into the PX binding site in TPBD-PX, whereas thermal stability and capture kinetics were determined by variable-temperature powder X-ray diffraction and slurry tests, respectively. That TPBD offers benchmark PX selectivity and facile recyclability makes it a prototypal molecular compound for PX purification or capture under ambient conditions.

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Introduction

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Purification of the C8 aromatic isomers o-xylene (OX), m-xylene (MX), p-xylene (PX), and ethylbenzene (EB) occurs at an industrial scale as each is a high-volume product of the chemical industry. (1−3) Among these isomers, PX is of note as it is a precursor for terephthalic acid, which in turn is used to produce polyester and polyethylene terephthalate. Demand for PX is increasing at 6–8% per year and accounts for >86% of the global mixed xylenes market in 2021. (4) The similarity of the C8 aromatic isomers with respect to their physicochemical properties (Table S1) (5) complicates their separation from each other, and conventional purification methods such as distillation or fractional crystallization require controlled environments with either high or low temperatures, respectively. Therefore, there is interest in the development of novel sorbents or membrane-based technologies that can provide more energy-efficient purification of PX. (6,7) Whereas selective PX adsorption using FAU-type zeolites has been validated, relatively high temperatures and pressures on simulated moving beds (SMBs) are required and PX selectivity is usually <10. (5)
Physisorbents such as metal–organic materials (MOMs), (8−14) especially flexible MOMs (FMOMs), (15−19) have exhibited promising characteristics for C8 separation. (18,20−27) Notably, two-dimensional (2D) layered coordination networks, (28,29) one-dimensional (1D) chain coordination polymers, (30,31) and zero-dimensional (0D) coordination complexes (32−35) can offer selective binding of C8 guests through C8-induced structural phase transformations from guest-free apohosts (α-phases) to inclusion compounds (β-phases). (36) Organic molecular solids can also undergo phase transformations induced by guest molecules (37−41) and offer selective binding of C8 isomers. (32,33,42−46) In terms of selectivity, a cage host with intrinsic porosity was found to offer across-the-board PX selectivity ranging between 6.60 and 12.10. (36) In addition, studies suggest that flexibility in molecular compounds can enable selective clathration and accelerated diffusion of PX through porous structures. (43,47,48) Stimuli-induced phase transformations of 0D apohosts conducted by the Atwood and Barbour groups provided insight into how external stimuli can trigger structural changes and their potential applications. (33,44,49,50) We have recently coined the term switching adsorbent molecular materials (SAMMs) (32) for those molecular compounds that switch between nonporous and porous phases when exposed to gas, vapor, or liquid adsorbates.
Organic inclusion compounds, exemplified by urea, thiourea, quinol, phenol, and Dianin’s compound, have been extensively studied with respect to their host–guest chemistry (51−55) and selective enclathration of guest molecules. However, despite combining low cost and comparative simplicity, this class of materials remains understudied in the context of C8 separations. It has been reported that nonporous molecular solids, e.g., bishydrazones, (56) can distinguish one isomer from a mixture of C8 aromatics, highlighting the significance of phase transformations and conformational flexibility in adapting host cavities to fit guest molecules. (57) We herein report the C8 aromatic inclusion properties of a hitherto unstudied molecular compound, 4-(1H-1,2,4-triazol-1-yl)-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione, TPBD, which was prepared by cocrystal-controlled solid-state synthesis (58−60) (solvent-drop grinding, SDG, (61−63) followed by heating). TPBD’s selection is rooted in its inherent structural features and the aforementioned studies on molecular compounds such as Werner complexes. (32−34) The studies of Werner clathrates highlight that molecular compounds comprising aromatic rings and conformational diversity can form host–guest complexes with C8 isomers. TPBD is also attractive because it can be prepared in high yield using mechanochemistry. (64) Single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), and solubility studies provide insight into phase switching of TPBD upon exposure to liquid C8 aromatic mixtures at room temperature.

Results and Discussion

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Crystal Structure of TPBD and its Polymorphism

A 1:1 mixture of 1,8-naphthalic anhydride (1,8-NA) and 4-(1,2,4-triazol-1-yl) aniline (4-TA) was wet ground with EtOH before heating at 270 °C for 1 h to form TPBD (Figures 1 and S1a). SCXRD data revealed that the colorless blocks, grown by crystallizing TPBD from EtOH, belong to the monoclinic space group P21/c with one TPBD in the asymmetric unit (Tables S2 and S3). This crystal form, TPBD-αI, was also crystallized from water, methanol, ethanol, acetone, acetonitrile, n-hexane, isopropanol, and n-propanol (Figure S2). Recrystallization of TPBD-αI from dimethylformamide and dichloromethane afforded colorless needle-like crystals of a second polymorph, TPBD-αII, which adopted orthorhombic space group P21212 (Figures 2a, S1b and Table S3). The main difference between TPBD-αI and TPBD-αII is the orientation of the triazole and benzene moieties, resulting in different unit cell parameters and a slightly reduced unit cell volume (Table S3). During a study of reaction conditions to optimize the synthesis of TPBD (Figures S3a,b), two additional polymorphs were found. TPBD-αIII and TPBD-αIV were isolated as minor crystalline impurities from the bulk reaction product but could not be reproduced with bulk phase purity using solvent-mediated methods, which consistently afforded TPBD-αI or TPBD-αII. TPBD-αIII crystallized in the orthorhombic space group P21212, whereas TPBD-αIV crystallized in the triclinic space group P1̅ (Table S3). The relative stability of these polymorphs is suggested by their respective densities (65,66) of 1.495, 1.533, 1.423, and 1.506 g/cm3.

Figure 1

Figure 1. Synthesis of TPBD-αI via solid-state synthesis.

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Figure 2

Figure 2. (a) Solvent and temperature-mediated conformational polymorphism of TPBD. (a) Illustration of the formation of TPBD-αII from the recrystallization of TPBD-αI in DMF or DCM and subsequent recovery of TPBD-αI by heating. (b) VT-PXRD indicates that conversion of TPBD-αII to TPBD-αI occurs after heating to temperatures ≥200 °C and that this structure is maintained when cooled to 25 °C.

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To simplify the analysis of TPBD’s conformational features, we label the 1,2,4-triazole ring A, the benzene ring B, and the rest of the structure C (Figure 1). TPBD’s structural flexibility is evident from rotation of the triazole and benzene rings as depicted in Table S4 and Figure S4. The magnitude of the torsion angles formed between the planes of A and B are 33.6, 4.9, 14.6, and 32.4° in TPBD-αI-αIV, respectively. Figure S4 shows that TPBD-αI and TPBD-αII have opposite orientations for rings A and B compared to TPBD-αIII and TPBD-αIV. TPBD-αI and TPBD-αII have similar orientations, but the triazole ring in TPBD-αI is twisted more significantly, while TPBD-αIII and TPBD-αIV have similar conformations. The conformational variability of the A/B rings and B/C moieties (Figure S4) can explain the conformational polymorphism seen herein. CH···π and π···π stacking interactions play a key role in the crystal packing in TPBD-αI-αIV (Figure S5).
The four TPBD polymorphs were optimized with density functional theory (DFT) to determine their relative stability in kilojoules per molTPBD at 0 K. The cell parameters for structures before and after cell optimization are displayed in Tables S5 and S6. In decreasing order of stability, we found TPBD-αII (0.0) > TPBD-αI (1.3) > TPBD-αIII (3.4) > TPBD-αIV (4.4). The relative energy differences between these four cell-optimized TPBD polymorphs are thus small, and with the cell-optimized structures, qualitative stability trends at different temperatures can be predicted (Table S7). Furthermore, other synthesis parameters, such as temperature, pressure, and solvation, will also contribute to the relative stability, as observed experimentally.
Following unsuccessful attempts to reproduce TPBD-αIII and TPBD-αIV, our focus shifted to preparing bulk samples of TPBD-αI and TPBD-αII and an analysis of their properties. Thermogravimetric analysis (TGA) revealed that TPBD-αI and TPBD-αII did not exhibit weight loss below 300 °C (Figure S6a). Differential scanning calorimetry (DSC) (closed pan) revealed one endothermic event in the DSC curve of TPBD-αI (Figure S6b), which we attribute to melting at 328 °C. The DSC curve of TPBD-αII showed two endotherms, the first consistent with a phase transition at 185 °C, followed by a sharp endothermic peak at 334 °C consistent with melting. Interestingly, the free energies of formation for both TPBD-αI and TPBD-αII polymorphs become endergonic at approximately 330 °C, which agrees with the experimentally observed melting temperatures (Figure S7). Variable-temperature powder X-ray diffraction (VT-PXRD) revealed that TPBD-αII converted to TPBD-αI at 175–200 °C (Figure 2b). This experimentally observed stability reversal is also observed computationally: the Helmholtz free energy differences between TPBD-αI and TPBD-αII are negligible at 50 °C; however, at higher temperatures, TPBD-αI becomes the thermodynamically stable polymorph (Table S7). Furthermore, accelerated stability testing (67,68) in a humidity chamber (75% RH, 40 °C) revealed that TPBD-αI and TPBD-αII are hydrolytically stable, as confirmed by PXRD patterns remaining unchanged (Figure S8).

C8 Aromatic Inclusion and Separation Studies

Single-Component Enclathration of C8 Aromatic Isomers

The flexibility of TPBD prompted us to study its potential to serve as a host for C8 aromatic isomers. We first studied the effect of subjecting TPBD-αI and TPBD-αII to pure C8 isomers at room temperature (25 ± 3 °C) by slurry or liquid immersion in sealed vials. We observed through PXRD, 1H NMR, and SCXRD analyses that only PX induced transformation to an inclusion compound, TPBD-PX, despite prolonged exposure to the C8 isomers (ambient conditions for 4 days, Figures 3a and S9–S15): TPBD-PX crystallized in the space group P21/n with two TPBD molecules and one PX in the asymmetric unit (Table S3). Saturation was attained in 20 min for TPBD-αI and within 25 min for TPBD-αII (Figure S16). Slurry experiments revealed that whereas both polymorphs are practically insoluble after several hours, 3.7 and 8.6 ng/mL for TPBD-αI and TPBD-αII, respectively, the dissolution profiles revealed a rapid initial increase in solubility (Cmax = 66.8 ± 28.1 ng/mL for TPBD-αI; Cmax = 82.1 ± 17.5 ng/mL for TPBD-αII). This “spring-and-parachute” effect (Figure S24 and Table S8) is well-known in pharmaceutical science and is consistent with dissolution followed by recrystallization of a less soluble phase, e.g., a hydrate, solvate, or more stable polymorph. (69) In this case, it indicates dissolution of TPBD followed by the crystallization of TPBD-PX. PXRD analysis (Figure S16) of aliquots removed from TPBD slurries indicates that conversion from TPBD-αI or TPBD-αII to TPBD-PX had occurred. To investigate the mechanism of phase change, time-lapse photomicroscopy experiments were conducted (Movies S1, S2, S3, S4 and Figures S17–S22). These PX immersion experiments revealed that smaller particles (<100 μm) of TPBD-αI and all particles of TPBD-αII dissolved during PX exposure (1300 min) before recrystallizing as TPBD-PX. Larger particles of TPBD-αI did not dissolve, and SCXRD analysis (Figure S23) of a single crystal after PX exposure (15 h) revealed that transformation to TPBD-PX had occurred in the solid state (see SI for details). These data are consistent with concomitant recrystallization and adsorption. PX desorption from TPBD-PX was studied by using VT-PXRD under N2 flow. Peaks corresponding to TPBD-αI appeared after heating to ca. 60–90 °C, and phase transformation was complete by ca. 100 °C (Figure 3b). Upon cooling the sample to 25 °C, TPBD-αI was maintained (Figure 3b). TGA analysis revealed that loss of PX occurred at 120 °C with a weight loss of 13.5% and that the apohost remained stable up to 297 °C (Figure S25a). The DSC curve of TPBD-PX (closed pan) revealed a first endothermic event at approximately 185 °C, corresponding to loss of PX, and a second endotherm at ca. 328 °C that we attribute to melting (Figure S25b). Conducting PX dynamic vapor sorption tests on TPBD-αI did not result in a phase transformation (Figure S26). However, exposing TPBD-αI to pure PX vapor or the vapor formed from an equimolar mixture of C8 isomers at 25 °C (30 days) and 50 °C (14 days) resulted in phase transformation to TPBD-PX (Figure S27).

Figure 3

Figure 3. (a) Interconversion of TPBD-αI, TPBD-αII, and TPBD-PX; (b) VT-PXRD study of TPBD-PX reveals transformation to TPBD-αI upon heating.

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Multicomponent Enclathration of C8 Aromatic Isomers

Since C8 aromatics are usually separated in the liquid phase at an industrial scale, we evaluated the specificity of the apohost by immersing TPBD-αI in binary liquid mixtures of different ratios (1:1, 1:4, 1:9, 1:19, 1:49, and 1:99 mol/mol, Figures S28–S30). 1H NMR was employed to determine selectivity after slurry-assisted immersion of ca. 34 mg of TPBD-αI in ca. 1 mL of liquid mixture for 4 days at ambient temperature. For PX-containing mixtures, the apohost displayed strong preference toward PX. Equimolar binary separations revealed selectivity of 76.1, 22.1, and 49.2 for PX/OX, PX/MX, and PX/EB, respectively (Table 1 and Figures S31–S33). High selectivity of TPBD-αI toward PX was corroborated by exposing it to binary mixtures with lower PX concentration. It was determined that TPBD-αI exhibited PX/OX selectivity of 108.4, 105.6, and 97.1 for PX/OX mixtures with ratios of 1:4, 1:9, and 1:19, respectively (Table 1 and Figures S34–S38). Additionally, PX/MX selectivity values of 45.9, 65.8, and 70.3 for mixtures with ratios of 1:4, 1:9, and 1:19 were observed (Table 1 and Figures S39–S43).
Table 1. Selectivity Coefficients for Liquid Mixtures of C8 Isomers at 25 °C
compositionratio in liquidratio absorbedselectivity coefficient
TPBD-αI
PX/MX1:159.7:1.250.6G
1:122.122.1N
1:411.645.9N
1:97.365.8N
1:193.770.3N
1:49No C8 uptakeNo C8 uptake
1:99No C8 uptakeNo C8 uptake
PX/OX1:149.6:0.954.1G
1:176.176.1N
1:427.5108.4N
1:910.8105.6N
1:195.097.1N
1:49No C8 uptakeNo C8 uptake
1:99No C8 uptakeNo C8 uptake
PX/EB1:152.0:1.147.3G
1:149.249.2N
1:414.659.9N
1:96.558.4N
1:193.057.1N
1:490.946.0N
1:99No C8 uptakeNo C8 uptake
PX/OX/MX1:1:149.4:0.9:0.84d60.4G
66.3:1.0:2.4lh39.4N
104.2:1.0:2.74d56.3N
PX/OX/MX/EB1:1:1:187.1:1.0:1.1:0.94d85.7G
89.6:1.0:3.1:1.54d48.5N
50.7:1.2:1.9:1.0a37.5N
TPBD-αII
PX/OX/MX1:1:178.7:1.0:2.61h43.7N
82.4:1.0:2.84d43.6N
PX/OX/MX/EB1:1:1:184.6:1.0:2.5:1.84d47.9N
a

Selectivity after 10 cycles in 2 h′ immersion. N = 1H NMR G = GC.

Overlapping of PX and MX 1H NMR peaks impact the accuracy of values at higher amounts of PX. For PX/EB; selectivities were determined to be 59.9, 58.4, 57.1, and 46.0 for 1:4, 1:9, 1:19, and 1:49 mixtures, respectively (Table 1 and Figures S44–S49).
No PX uptake was observed for PX/MX or PX/OX in 1:49 and 1:99 binary mixtures or with PX/EB in 1:99 binary mixtures. In the absence of PX, TPBD does not form inclusion compounds with the other C8 isomers, further emphasizing the high selectivity of TPBD for PX. For binary C8 mixtures, PX selectivity increased for PX/MX mixtures as a function of MX concentration (Figure S50a), while for other mixture compositions (PX/OX, PX/EB), no clear trend was observed. TGA showed PX uptake from the binary mixtures consistent with that of single-component PX (14.8 wt % loss), indicating preferential PX enclathration from binary mixtures (Table 1 and Figure S50a). TPBD-αI displayed selectivities, ranging from 76 to 108, that exceed the current benchmarks for PX/OX binary mixtures: Previously, the highest selectivities were reported for a 0D Cu-metallocycle, (44) a 1D coordination polymer, Mn-dhbq, (31) and three-dimensional (3D) MOFs ZIF-67 and ZIF-8, (22) with PX/OX selectivities of 51.6, 66.8, 98.9, and 81.2, respectively. MAF-89, comprised of 3D-connected quasi-discrete pores, shows PX/OX selectivity of 221 that surpasses TPBD-αI (Figure S50b and Table S9).
The separation performances of TPBD-αI and TPBD-αII for ternary and quaternary mixtures (Figure S51) were also investigated by using slurries at 25 °C (Figure S52). TPBD-αI and TPBD-αII were immersed in equimolar PX/MX/OX and PX/MX/OX/EB mixtures, filtered, and air-dried under ambient conditions. TGA curves of TPBD-αI after exposure to ternary and quaternary mixtures resulted in weight losses consistent with the PX loading obtained from binary mixtures and pure PX (14.9 wt %, Figure S53). TPBD-αI exhibited a selectivity of 56.3 (104.2/2.7/1.0) for equimolar ternary PX/MX/OX mixtures (Table 1 and Figure S54). These values surpass the selectivity of current benchmark sorbents MAF-36–3C (51.3 at 25 °C), (19) Mn-dhbq (48.3 at 120 °C), (31) and MAF-89 (46.4 at 35 °C). (20) Furthermore, while TPBD-αII (SPX/OX/MX = 43.6) displayed a slightly lower selectivity than previous benchmarks, its performance remains high (Figures 4a and S55).

Figure 4

Figure 4. (a) Comparison of nonporous (●) and porous (⧫) absorbents for PX separation from ternary and quaternary mixtures. The experimental conditions may vary, like temperature and composition (E: equimolar, NE: nonequimolar mixture). (b) Gas chromatograms used to quantify the composition of TPBD crystals exposed to pure C8 isomers or approximately equimolar mixtures of C8 isomers at RT.

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Concerning purification of PX from EB, literature reports are limited, likely reflecting that sorbents tend to exhibit relatively low PX/EB selectivity, making them unsuitable for purifying PX when EB is present. (70) TPBD retained its high PX selectivity in the presence of EB in binary, ternary, and even quaternary mixtures (Table 1 and S9). According to our findings, TPBD sets a new benchmark for the extraction of PX from EB despite their similar kinetic diameters, not only in equimolar binary mixtures but also at low PX concentrations (2%). At ambient conditions, TPBD-αI and TPBD-αII yielded PX/OX/MX/EB selectivities of 48.5 and 47.9 (Figures S56 and S57), respectively, higher than the value of 25.1 for Mn-dhbq (Figure 4a, Tables 1 and S9). Owing to the consistent presence of EB in industrial feed mixtures, the affinity of TPBD toward PX compared to EB enables both forms of TPBD to outperform existing sorbents. Our data reveal that one cycle of uptake/release involving TPBD-αI afforded PX with purity levels of 96.6 and 94.1% from equimolar mixtures of PX/OX/MX and PX/OX/MX/EB, respectively. Values of 95.6 and 94.1% were obtained for TPBD-αII (Figure 5a). Notably, molecular solids, as exemplified by EtP6β, can exhibit higher PX purity in equimolar ternary mixtures, but this purity decreases in the presence of EB in quaternary mixtures. (41,43,45,71) However, due to a lack of data on selectivities of current benchmark sorbents under ambient conditions, it is challenging to compare their overall performance with TPBD.

Figure 5

Figure 5. (a, b) Separation performance of TPBD-αI and TPBD-αII upon exposure to equimolar ternary and quaternary mixture of C8 isomers at 293 K. (c) TPBD-αI recyclability after 11 consecutive cycles of PX enclathration/release. (d) Asymmetric unit and crystal packing of TPBD-PX.

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Enclathration of PX from equimolar ternary mixtures after 1 or 4 days of slurrying revealed almost identical outcomes (Figures 5a, S54, and S55). This indicates that the PX inclusion compound is both the kinetic and thermodynamic product. Table 1 reveals that PX selectivity improved only slightly with time, corresponding to PXRD (Figure S16) and solubility test (Figure S24 and Table S8) analyses of slurry-assisted immersions, indicating that PX exposure for 1 h is sufficient for TPBD-αI to reach its capacity. PXRD data revealed that TPBD-αI had converted to TPBD-PX upon exposure to an equimolar quaternary mixture of C8 aromatic isomers within 35 min (Figure S58), indicating relatively fast kinetics under slurry-assisted immersion at room temperature. This sorption time is comparable to MOFs, PCPs, and PMCs with high selectivities. (20,31,44,72) In the liquid phase, MAF-36-3C (SPX/OX/MX = 51.3) and 3B (SPX/OX/MX = 16) exhibited varying adsorption rates, taking 24 and 3 h, respectively, whereas form 1B (SPX/OX/MX = 15) exhibited fast uptake in 2 min attributed to smaller crystal size. (19) MAF-89 achieved over 90% capacity of its equilibrium amount within 15 min upon exposure to an equimolar ternary xylene mixture. (20) We note that comparison to kinetics reported in the literature is only qualitative/indicative, as uptake kinetics depend on multiple factors such as sample mass, particle shape/size, and grain size. Carefully controlled experimental conditions are needed for quantitative comparison of sorption kinetics. (73,74)
For practical applications, stability over multiple sorption cycles is required, so recyclability of TPBD-αI was studied. TPBD-αI retained its working capacity (approximately 13.5 wt % or 156.5 mg/g uptake) after 11 consecutive cycles of static immersion in pure PX and enclathration, followed by PX removal by heating to 150 °C (Figure 5c and S59). TPBD-αI could be regenerated after 11 cycles as indicated by its unchanged PXRD pattern (Figure S60). TPBD-αI also maintained selectivity of SPX/OX/MX/EB = 37.5 from an equimolar mixture of PX/OX/MX/EB, confirming sustained enclathration performance after 11 cycles (Figure S61). The dynamic column separation performance of TPBD-αI toward liquid equimolar quaternary C8 mixtures at ambient conditions (25 ± 3 °C) was investigated and revealed selectivity of 27.39 (Figure S62). Despite the energy-efficient advantage of separation by enclathration over distillation, subjecting TPBD-αI to higher temperatures in contact with pure or mixed C8 isomers offers insights into its selectivity behavior under various conditions. Gas chromatography was also used to analyze the PX selectivity of TPBD-αI exposed to C8 mixtures at 25 and 80 °C (Table S10, Figure 4b and S63). Selectivity coefficients at 25 °C for binary (PX/MX, PX/OX, PX/EB), ternary (PX/OX/MX), and quaternary mixtures were determined to be 50.6, 54.1, 47.3, 60.4, and 85.7, respectively. At 80 °C, selectivity coefficients decreased compared to room temperature, with corresponding values of 32.6, 36.0, 25.4, 31.9, and 36.7, respectively. As revealed in Table 1, the values obtained by GC are consistent with those obtained by 1H NMR.
To gain insight into the PX selectivity of TPBD, we recrystallized TPBD from PX and determined the single-crystal structure of TPBD-PX (Figure 5d). The conformation of the two TPBD molecules differed due to slight rotation around the bond between the A and B rings (Table S4). TPBD dimers formed through CH···N interactions (C···N distances of 3.503 Å) between adjacent triazole rings (Figure S64a). TPBD molecules arrange to form 1D rectangular channels (5.44 Å × 9.07 Å) during PX uptake that propagate along [100], with void spaces of 20.1% that were sufficiently large to accommodate PX molecules (Figure S65). An analysis of the interactions in TPBD-PX revealed no significant π···π interactions in terms of guest–guest or host–guest binding. As shown in Figure S61b, the PX molecules do not interact with one another. Instead, PX molecules form several C–H···π interactions (Figure S64b) and CH···O hydrogen bonds (C···O distances of 3.503(3) and 3.529(3) Å with associated angles of 163.0(8) and 153.0(7)°), and CH···N (C···N distances of 3.785(3) and 3.859(3) Å with associated angles of 135.9(6) and 140.3(6)°) with TPBD molecules (Figures 6 and S64a).

Figure 6

Figure 6. Illustration depicting the arrangement of PX molecules in TPBD-PX, highlighting that multiple C–H···π interactions occur in the yellow area, along with CH···O interactions (PX guest molecules are purple).

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Usually, enhanced binding of guest molecules occurs when pores exhibit a size and shape match for a specific molecule, allowing for improved selectivity over other guest species. Indeed, the 1D pores in TPBD-PX have dimensions of 10.30–9.07 Å at the solvent-accessible surface, comparable to the dimensions of PX (Table S1), making it a suitable match for PX inclusion but not for the other isomers. While simulation studies have previously reported the ideal dimensions of rectangular 1D channels for separating PX from other C8 isomers, (75,76) it is important to note that the ideal size also depends on supramolecular interactions within the host–guest system and the arrangement of PX molecules.
To corroborate the experimental results showing the preference for capture of PX over other C8 isomers, the relative stability of TPBD inclusion compounds was determined via DFT calculations. Since PX-loaded TPBD could be refined by XRD, i.e., (TPBD)8(PX)4, the other guest-loaded structures were built from TPBD-PX. These hypothetical C8-loaded structures and TPBD-PX were then optimized and subsequently cell-optimized to determine the crystallization energies and Gibbs free energies starting from TPBD-αI and the gas phase of C8 isomers (pC8 = 1 bar) at 25, 50, 100, and 150 °C (in kJ/molC8). The crystallization energies, i.e., −78.8 (PX), −67.8 (MX), −61.9 (OX), and −65.6 (EB) kJ/mol, are indicative of strongly exothermic crystallization processes and show a strong preference to enclathrate PX over the other C8 aromatic isomers (see Table S11). Analyses of various modeled TPBD-C8 aromatic structures revealed predominant H···O, H···N, and C···H interactions, which control crystal packing (Figure S66). Notably, in TPBD-PX, stronger CH···O hydrogen bonds compared with other models influence crystal packing and selectivity for PX over the other C8 aromatic isomers.
In previous work, sorbents that exhibit discrimination for PX, typically adapt to the size and shape of PX molecules, controlling their pore structure via a gating mechanism, leading to a guest-loaded complex with the lowest binding energy and preference for PX over other C8 aromatic isomers. (19,20,77) PX clathrate TPBD-PX offers precise size/shape matching to accommodate PX molecules, establishing favorable positions for C–H···π interactions along the a-axis. CH···O and CH···N interactions formed between the host and guest serve to anchor the PX molecules. The cavity in TPBD-PX formed by the triazole and benzene rings of the host is such that the second methyl group in MX and OX and the ethyl moiety of EB are hindered from the formation of favorable C–H···π, C–H···O, and CH···N interactions. We therefore attribute the separation performance of TPBD to its ability to adapt to PX molecules through a channel that is an excellent shape and size fit for PX vs the other C8 aromatic isomers. This feature enables TPBD to more selectively separate PX from the other C8 aromatic isomers in comparison to existing PX selective sorbents.

Conclusions

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In summary, our results reveal that a nonporous molecular apohost (TPBD) enables the highly selective separation of PX from mixtures of C8 aromatics, setting new benchmark selectivity values. PX can thereby be separated by TPBD as a sole substrate, even in the presence of low concentrations (5%) of PX. Whereas separation of xylene isomers has tended to focus upon porous frameworks such as zeolites and MOFs, TPBD further highlights (7) that certain nonporous apohost molecules can form inclusion compounds with suitable binding sites that offer across-the-board selectivity for one of the C8 isomers. TPBD also offers low cost, facile synthesis, a metal-free composition, high thermal stability, high hydrolytic stability, and recyclability. Further, that the uptake kinetics in slurry are relatively rapid at room temperature means that PX can be isolated from OX, MX, and EB with high purity in only one cycle with a relatively low energy footprint. Our findings emphasize the potential utility of molecular compounds that, although nonporous as apohosts, can be highly selective through structural adaptability and induced fit, thereby enabling phase transformations to generate cavities that offer shape and size matching for a particular guest. Such sorbents are also advantageous as they are inherently facile to recycle, relying only upon weak noncovalent interactions.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.3c07198.

  • Experimental details; materials and methods; computational studies; summary of reported adsorbents for separation of C8 aromatics; modeling section (PDF)

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CCDC 2243659–2243664 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Author Information

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  • Corresponding Author
  • Authors
    • Maryam Rahmani - Bernal Institute, Department of Chemical Sciences, University of Limerick, Limerick V94 T9PX, Republic of Ireland;  Orcidhttps://orcid.org/0000-0002-9699-1317
    • Catiúcia R. M. O. Matos - Bernal Institute, Department of Chemical Sciences, University of Limerick, Limerick V94 T9PX, Republic of Ireland
    • Shi-Qiang Wang - Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, 138634 Singapore;  Orcidhttps://orcid.org/0000-0003-1213-8317
    • Andrey A. Bezrukov - Bernal Institute, Department of Chemical Sciences, University of Limerick, Limerick V94 T9PX, Republic of Ireland
    • Alan C. Eaby - Bernal Institute, Department of Chemical Sciences, University of Limerick, Limerick V94 T9PX, Republic of Ireland
    • Debobroto Sensharma - Bernal Institute, Department of Chemical Sciences, University of Limerick, Limerick V94 T9PX, Republic of Ireland;  Orcidhttps://orcid.org/0000-0002-4918-0730
    • Yassin Hjiej-Andaloussi - Bernal Institute, Department of Chemical Sciences, University of Limerick, Limerick V94 T9PX, Republic of Ireland
    • Matthias Vandichel - Bernal Institute, Department of Chemical Sciences, University of Limerick, Limerick V94 T9PX, Republic of Ireland;  Orcidhttps://orcid.org/0000-0003-1592-0726
  • Funding

    This research was funded by Science Foundation Ireland (SFI) through Synthesis and Solid State Pharmaceutical Center (SSPC), 12/RC/2275_P2 and 16/IA/4624.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The authors gratefully acknowledge Science Foundation Ireland (SFI, 12/RC/2275_P2 and 16/IA/4624) for financial support. M.V. acknowledges the Irish Centre for High-End Computing (ICHEC) for providing computational facilities and support.

References

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    Wang, Shi-Qiang; Mukherjee, Soumya; Zaworotko, Michael J.
    Faraday Discussions (2021), 231 (MOFs for Energy and the Environment), 9-50CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
    Coordination networks (CNs) are a class of (usually) cryst. solids typically comprised of metal ions or cluster nodes linked into 2 or 3 dimensions by org. and/or inorg. linker ligands. Whereas CNs tend to exhibit rigid structures and permanent porosity as exemplified by most metal-org. frameworks, MOFs, there exists a small but growing class of CNs that can undergo extreme, reversible structural transformation(s) when exposed to gases, vapors or liqs. These "soft" or "stimuli-responsive" CNs were introduced two decades ago and are attracting increasing attention thanks to two features: the amenability of CNs to design from first principles, thereby enabling crystal engineering of families of related CNs; and the potential utility of soft CNs for adsorptive storage and sepn. A small but growing subset of soft CNs exhibit reversible phase transformations between nonporous (closed) and porous (open) structures. These "switching CNs" are distinguished by stepped sorption isotherms coincident with phase transformation and, perhaps counterintuitively, they can exhibit benchmark properties with respect to working capacity (storage) and selectivity (sepn.). This review addresses fundamental and applied aspects of switching CNs through surveying their sorption properties, analyzing the structural transformations that enable switching, discussing structure-function relationships and presenting design principles for crystal engineering of the next generation of switching CNs.
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  16. 16
    Schneemann, A.; Bon, V.; Schwedler, I.; Senkovska, I.; Kaskel, S.; Fischer, R. A. Flexible metal–organic frameworks. Chem. Soc. Rev. 2014, 43 (16), 6062– 6096,  DOI: 10.1039/C4CS00101J
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    16
    Flexible metal-organic frameworks
    Schneemann, A.; Bon, V.; Schwedler, I.; Senkovska, I.; Kaskel, S.; Fischer, R. A.
    Chemical Society Reviews (2014), 43 (16), 6062-6096CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Advances in flexible and functional metal-org. frameworks (MOFs), also called soft porous crystals, are reviewed by covering the literature of the five years period 2009-2013 with ref. to the early pertinent work since the late 1990s. Flexible MOFs combine the cryst. order of the underlying coordination network with cooperative structural transformability. These materials can respond to phys. and chem. stimuli of various kinds in a tunable fashion by mol. design, which does not exist for other known solid-state materials. Among the fascinating properties are so-called breathing and swelling phenomena as a function of host-guest interactions. Phase transitions are triggered by guest adsorption/desorption, photochem., thermal, and mech. stimuli. Other important flexible properties of MOFs, such as linker rotation and sub-net sliding, which are not necessarily accompanied by crystallog. phase transitions, are briefly mentioned as well. Emphasis is given on reviewing the recent progress in application of in situ characterization techniques and the results of theor. approaches to characterize and understand the breathing mechanisms and phase transitions. The flexible MOF systems, which are discussed, are categorized by the type of metal-nodes involved and how their coordination chem. with the linker mols. controls the framework dynamics. Aspects of tailoring the flexible and responsive properties by the mixed component solid-soln. concept are included, and as well examples of possible applications of flexible metal-org. frameworks for sepn., catalysis, sensing, and biomedicine.
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  17. 17
    Chang, Z.; Yang, D.-H.; Xu, J.; Hu, T.-L.; Bu, X.-H. Flexible Metal–Organic Frameworks: Recent Advances and Potential Applications. Adv. Mater. 2015, 27 (36), 5432– 5441,  DOI: 10.1002/adma.201501523
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    17
    Flexible Metal-Organic Frameworks: Recent Advances and Potential Applications
    Chang, Ze; Yang, Dong-Hui; Xu, Jian; Hu, Tong-Liang; Bu, Xian-He
    Advanced Materials (Weinheim, Germany) (2015), 27 (36), 5432-5441CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Flexible metal-org. frameworks (MOFs) receive much attention owing to their attractive properties that originate from their flexibility and dynamic behavior, and show great potential applications in many fields. Here, recent progress in the discovery, understanding, and property studies of flexible MOFs are reviewed, and the examples of their potential applications in storage and sepn., sensing, and guest capture and release are presented to highlight the developing trends in flexible MOFs.
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  18. 18
    Mukherjee, S.; Joarder, B.; Manna, B.; Desai, A. V.; Chaudhari, A. K.; Ghosh, S. K. Framework-Flexibility Driven Selective Sorption of p-Xylene over Other Isomers by a Dynamic Metal-Organic Framework. Sci. Rep. 2014, 4 (1), 5761  DOI: 10.1038/srep05761
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    18
    Framework-Flexibility Driven Selective Sorption of p-Xylene over Other Isomers by a Dynamic Metal-Organic Framework
    Mukherjee, Soumya; Joarder, Biplab; Manna, Biplab; Desai, Aamod V.; Chaudhari, Abhijeet K.; Ghosh, Sujit K.
    Scientific Reports (2014), 4 (), 5761CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    Chem. sepn. has great importance in industrial applications. Sepn. of xylene isomers still prevails to be one of the most important challenges in chem. industry, due to the large amt. of com. use of p-xylene in the prodn. of beverage bottles, fibers and films. A novel Zn(II)-based dynamic coordination framework based on flexible ether-linkage, exhibiting selective adsorption of p-Xylene over its congener C8-alkyl arom. isomers at ambient conditions is reported. Notably, no dynamic structure based MOF compd. is known in the literature which shows clear preference of p-xylene over other isomers. This type of framework-breathing and guest-induced reversible solid-state structural transformations with unique adsorption selectivity can be exploited purposefully to develop smart functional host materials capable of industrially important chem. sepns.
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  19. 19
    Yang, X.; Zhou, H.-L.; He, C.-T.; Mo, Z.-W.; Ye, J.-W.; Chen, X.-M.; Zhang, J.-P. Flexibility of Metal-Organic Framework Tunable by Crystal Size at the Micrometer to Submillimeter Scale for Efficient Xylene Isomer Separation. Research 2019, 2019, 9463719  DOI: 10.34133/2019/9463719
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    19
    Flexibility of metal-organic framework tunable by crystal size at the micrometer to submillimeter scale for efficient xylene isomer separation
    Yang, Xiao; Zhou, Hao-Long; He, Chun-Ting; Mo, Zong-Wen; Ye, Jia-Wen; Chen, Xiao-Ming; Zhang, Jie-Peng
    Research (Washington, DC, United States) (2019), 2019 (), 9463719CODEN: RESECF; ISSN:2639-5274. (American Association for the Advancement of Science)
    Understanding, controlling, and utilizing the flexibility of adsorbents are of great importance and difficulty. Analogous with conventional solid materials, downsizing to the nanoscale is emerging as a possible strategy for controlling the flexibility of porous coordination polymers (or metal-org. frameworks). We report a unique flexibility controllable by crystal size at the micrometer to submillimeter scale. Template removal transforms [Cu2(pypz)2] ·0.5p-xylene (MAF-36, Hpypz=4-(1H-pyrazol-4-yl)pyridine) with one-dimensional channels to α-[Cu2(pypz)2] with discrete small cavities, and further heating gives a nonporous isomer β-[Cu2(pypz)2]. Both isomers can adsorb p-xylene to give [Cu2(pypz)2] ·0.5p-xylene, meaning the coexistence of guest-driven flexibility and shape-memory behavior. The phase transition temp. from α-[Cu2(pypz)2] to β-[Cu2(pypz)2] decreased from ~ 270 °C to ~ 150°C by increasing the crystal size from the micrometer to the submillimeter scale, ca. 2-3 orders larger than those of other size-dependent behaviors. Single-crystal X-ray diffraction showed coordination bond reconstitution and chirality inversion mechanisms for the phase transition, which provides a sufficiently high energy barrier to stabilize the metastable phase without the need of downsizing to the nanoscale. By virtue of the cryst. mol. imprinting and gate-opening effects, α-[Cu2(pypz)2] and β-[Cu2(pypz)2] show unprecedentedly high p-xylene selectivities of 16 and 51, resp., as well as ultrafast adsorption kinetics (<2minutes), for xylene isomers.
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  20. 20
    Ye, Z.-M.; Zhang, X.-F.; Liu, D.-X.; Xu, Y.-T.; Wang, C.; Zheng, K.; Zhou, D.-D.; He, C.-T.; Zhang, J.-P. A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation. Sci. China Chem. 2022, 65 (8), 1552– 1558,  DOI: 10.1007/s11426-022-1304-1
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    20
    A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation
    Ye, Zi-Ming; Zhang, Xue-Feng; Liu, De-Xuan; Xu, Yan-Tong; Wang, Chao; Zheng, Kai; Zhou, Dong-Dong; He, Chun-Ting; Zhang, Jie-Peng
    Science China: Chemistry (2022), 65 (8), 1552-1558CODEN: SCCCCS; ISSN:1869-1870. (Springer International Publishing AG)
    Adsorptive sepn. of p-xylene (pX) from xylene isomers is a key process in chem. industry, but known adsorbents cannot simultaneously achieve high adsorption selectivity, capacity, and rate. Here, we demonstrate gating ultramicropore as a soln. for this challenge. Slight modification of the synthetic condition gives rise to isomeric metal-org. frameworks α-[Zn(pba)] (MAF-88, H2pba = 4-(1H-pyrazol-4-yl)benzoic acid) and β-[Zn(pba)] (MAF-89) possessing similar pillared-column structures, porosities, and high pX capacities of 2.0 mmol g-1, but very different framework/pore topologies, pore sizes, and pX selectivities. For binary and ternary mixts. of liq. xylene isomers, MAF-88 with narrow one-dimensional (1D) channels shows pX selectivity of 11 and 1.6, while MAF-89 with 3D-connected quasi-discrete pores shows pX selectivity up to 221 and 46, resp. Thermogravimetry, differential scanning calorimetry, and time-dependent sepn. expts. reveal that the kinetic effects of the gating pores play more important roles than the thermodn. effects, which is further confirmed by single-crystal X-ray diffraction and computational simulations.
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  21. 21
    Sapianik, A. A.; Dudko, E. R.; Kovalenko, K. A.; Barsukova, M. O.; Samsonenko, D. G.; Dybtsev, D. N.; Fedin, V. P. Metal–Organic Frameworks for Highly Selective Separation of Xylene Isomers and Single-Crystal X-ray Study of Aromatic Guest–Host Inclusion Compounds. ACS Appl. Mater. Interfaces 2021, 13 (12), 14768– 14777,  DOI: 10.1021/acsami.1c02812
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    21
    Metal-Organic Frameworks for Highly Selective Separation of Xylene Isomers and Single-Crystal X-ray Study of Aromatic Guest-Host Inclusion Compounds
    Sapianik, Aleksandr A.; Dudko, Evgeny R.; Kovalenko, Konstantin A.; Barsukova, Marina O.; Samsonenko, Denis G.; Dybtsev, Danil N.; Fedin, Vladimir P.
    ACS Applied Materials & Interfaces (2021), 13 (12), 14768-14777CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Sepn. of hydrocarbon mols., such as benzene/cyclohexane and o-xylene/m-xylene/p-xylene, is relevant due to their widespread application as chem. feedstock but challenging because of their similar b.ps. and close mol. sizes. Physisorption sepn. could offer an energy-efficient soln. to this problem, but the design and synthesis of sorbents that exhibit high selectivity for one of the hydrocarbons remain a largely unmet challenge. Herein, we report a new heterometallic MOF with a unique tortuous shape of channels decorated with arom. sorption sites [Li2Zn2(bpy)(ndc)3] (NIIC-30(Ph), bpy = 4,4'-bipyridine, ndc2- = naphthalene-1,4-dicarboxylate) and study of its benzene/cyclohexane and xylene vapor and liq. sepn. For an equimolar benzene/cyclohexane mixt., it is possible to achieve a 10-fold excess of benzene in the adsorbed phase. In the case of xylenes, microporous framework NIIC-30(Ph) demonstrates outstanding selective sorption properties and becomes a new benchmark for m-/o-xylene sepn. In addn., NIIC-30(Ph) is stable enough to carry out at least three sepn. cycles of benzene/cyclohexane mixts. or ternary o-xylene/m-xylene/p-xylene mixts. both in the liq. and in the vapor phase. Insights into the performance of NIIC-30(Ph) are gained from X-ray structural studies of each arom. guest inclusion compd.
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  22. 22
    Polyukhov, D. M.; Poryvaev, A. S.; Sukhikh, A. S.; Gromilov, S. A.; Fedin, M. V. Fine-Tuning Window Apertures in ZIF-8/67 Frameworks by Metal Ions and Temperature for High-Efficiency Molecular Sieving of Xylenes. ACS Appl. Mater. Interfaces 2021, 13 (34), 40830– 40836,  DOI: 10.1021/acsami.1c12166
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    22
    Fine-Tuning Window Apertures in ZIF-8/67 Frameworks by Metal Ions and Temperature for High-Efficiency Molecular Sieving of Xylenes
    Polyukhov, Daniil M.; Poryvaev, Artem S.; Sukhikh, Aleksandr S.; Gromilov, Sergey A.; Fedin, Matvey V.
    ACS Applied Materials & Interfaces (2021), 13 (34), 40830-40836CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Sepn. of structurally similar components from their mixts. is one of the most promising applications of metal-org. frameworks (MOFs). A high efficiency of such mol. sieving requires fine tuning of the MOF structure. In this work, we investigate subtle metal- and temp.-induced changes in window dimensions of zeolitic imidazolate frameworks (ZIF-8(Zn) and ZIF-67(Co)) and apply such structural tuning for efficient sepn. of xylene isomers (p-, m-, and o-xylenes). The use of Co instead of Zn favorably modifies window geometry: it accelerates the diffusion of all components by a factor of 2-3 while maintaining closely the same sepn. efficiency as that of ZIF-8(Zn). Outstanding selectivity above 18:1 and faster isolation of demanded p-xylene from the ternary mixt. using ZIF-67(Co) have been demonstrated at room temp., opening new horizons for its energy-efficient xylene sepn. More generally, our findings suggest the prospective ways to tune various MOFs for target liq.-state sepns.
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  23. 23
    Polyukhov, D. M.; Poryvaev, A. S.; Gromilov, S. A.; Fedin, M. V. Precise Measurement and Controlled Tuning of Effective Window Sizes in ZIF-8 Framework for Efficient Separation of Xylenes. Nano Lett. 2019, 19 (9), 6506– 6510,  DOI: 10.1021/acs.nanolett.9b02730
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    23
    Precise Measurement and Controlled Tuning of Effective Window Sizes in ZIF-8 Framework for Efficient Separation of Xylenes
    Polyukhov, Daniil M.; Poryvaev, Artem S.; Gromilov, Sergey A.; Fedin, Matvey V.
    Nano Letters (2019), 19 (9), 6506-6510CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Metal-org. frameworks (MOFs) are the promising nanomaterials for sepn. of mols. with close dimensions and structures, such as various types of isomers. The efficiency of sepn. can be greatly enhanced if the apertures of the nanosized windows, controlling the diffusion of a particular mol. inside the cavities, are fine-tuned by external stimuli. The authors report the new approach for precise measurement of window sizes in ZIF-8 MOF and employ it in efficient sepn. of xylenes, which is of high practical importance. For this sake, the authors synthesized ZIF-8 with embedded stable nitroxides in the pores and applied ESR spectroscopy for in situ kinetic measurement of the diffusion of various guest mols. through the material. Slight variation of temp. within 298-333 K allowed tuning of the windows and reaching optimum conditions for sepn. of p-, m-, and o-xylenes with the efficiency up to 92-95%. The developed methodol. provides deeper understanding of steric and kinetic aspects of mol. diffusion in ZIF-8 and paves the way to rational optimization of other MOF-based sepn. applications.
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    Mukherjee, S.; Desai, A. V.; Ghosh, S. K. Potential of metal–organic frameworks for adsorptive separation of industrially and environmentally relevant liquid mixtures. Coord. Chem. Rev. 2018, 367, 82– 126,  DOI: 10.1016/j.ccr.2018.04.001
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    Potential of metal-organic frameworks for adsorptive separation of industrially and environmentally relevant liquid mixtures
    Mukherjee, Soumya; Desai, Aamod V.; Ghosh, Sujit K.
    Coordination Chemistry Reviews (2018), 367 (), 82-126CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
    Metal-org. frameworks (MOFs) or porous coordination polymers (PCPs) are defined as cryst., open, coordination network architectures with potential voids. They have drawn momentous attention across several crossroads of material chem. since their discovery, owing to an exciting plethora of application-oriented footprints left by this class of supramol. network solids. The unmatched aspect of tunable coordination nanospace arising from the countless choice of pre-functionalized org. struts pertaining to varying lengths alongside multivariate coordination geometries/oxidn. states of the metal nodes, bestows a distinct chem. tailorability facet to this class of porous materials. Amidst the two-decade long attention dedicated to the adsorption-governed purifn. of gases, the MOF literature has substantially expanded its horizon into the manifestation of industrially relevant liq. mixts.' adsorptive sepn.-driven purifn. Such chem. sepn. phenomena categorically encompasses high importance to the manufg. and processing industry sectors, apart from the fundamental scientific pursuit of discovering novel physicochem. principles. Aimed at the energy-economic prepn. of pure industrial feedstocks and their consequent usage as end products, structure-property correlations pursued in the alleys of coordination chem. has led to major advancements in a no. of crit. sepn. frontiers, inclusive of biofuels (alc./water), diverse hydrocarbon mixts., and chiral species. This comprehensive review summarizes the topical developments accrued in the field of MOF based liq. mixts.' adsorptive sepn. phenomena, structure-selectivity relationships as well as the assocd. plausible mechanisms substantiating such behavior.
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    Vermoortele, F.; Maes, M.; Moghadam, P. Z.; Lennox, M. J.; Ragon, F.; Boulhout, M.; Biswas, S.; Laurier, K. G. M.; Beurroies, I.; Denoyel, R.; Roeffaers, M.; Stock, N.; Düren, T.; Serre, C.; De Vos, D. E. p-Xylene-Selective Metal–Organic Frameworks: A Case of Topology-Directed Selectivity. J. Am. Chem. Soc. 2011, 133 (46), 18526– 18529,  DOI: 10.1021/ja207287h
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    25
    p-Xylene-Selective Metal-Organic Frameworks: A Case of Topology-Directed Selectivity
    Vermoortele, Frederik; Maes, Michael; Moghadam, Peyman Z.; Lennox, Matthew J.; Ragon, Florence; Boulhout, Mohammed; Biswas, Shyam; Laurier, Katrien G. M.; Beurroies, Isabelle; Deboyel, Renaud; Roeffaers, Maarten; Stock, Norbert; Duren, Tina; Serre, Christian; De Vos, Dirk E.
    Journal of the American Chemical Society (2011), 133 (46), 18526-18529CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Para-disubstituted alkylaroms. such as p-xylene are preferentially adsorbed from an isomer mixt. on three isostructural metal-org. frameworks: MIL-125(Ti) ([Ti8O8(OH)4(BDC)6]), MIL-125(Ti)-NH2 ([Ti8O8(OH)4(BDC-NH2)6]), and CAU-1(Al)-NH2 ([Al8(OH)4(OMe)8(BDC-NH2)6]) (BDC = 1,4-benzenedicarboxylate). Their unique structure contains octahedral cages, which can sep. mols. from differences in packing and interaction with the pore walls, as well as smaller tetrahedral cages, which are capable of sepg. mols. by mol. sieving. These exptl. data are in line with predictions by mol. simulations. Addnl. adsorption and microcalorimetric expts. provide insight in the complementary role of the two cage types in providing the para selectivity.
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  26. 26
    Gonzalez, M. I.; Kapelewski, M. T.; Bloch, E. D.; Milner, P. J.; Reed, D. A.; Hudson, M. R.; Mason, J. A.; Barin, G.; Brown, C. M.; Long, J. R. Separation of Xylene Isomers through Multiple Metal Site Interactions in Metal–Organic Frameworks. J. Am. Chem. Soc. 2018, 140 (9), 3412– 3422,  DOI: 10.1021/jacs.7b13825
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    26
    Separation of xylene isomers through multiple metal site interactions in metal-organic frameworks
    Gonzalez, Miguel I.; Kapelewski, Matthew T.; Bloch, Eric D.; Milner, Phillip J.; Reed, Douglas A.; Hudson, Matthew R.; Mason, Jarad A.; Barin, Gokhan; Brown, Craig M.; Long, Jeffrey R.
    Journal of the American Chemical Society (2018), 140 (9), 3412-3422CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Purifn. of the C8 alkylaroms. o-xylene, m-xylene, p-xylene, and ethylbenzene remains among the most challenging industrial sepns., due to the similar shapes, b.ps., and polarities of these mols. Herein, we report the evaluation of the metal-org. frameworks Co2(dobdc) (dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate) and Co2(m-dobdc) (m-dobdc4- = 4,6-dioxido-1,3-benzenedicarboxylate) for the sepn. of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co2(dobdc) distinguishes among all four mols., with binding affinities that follow the trend o-xylene > ethylbenzene > m-xylene > p-xylene. Multicomponent liq.-phase adsorption measurements further demonstrate that Co2(dobdc) maintains this selectivity over a wide range of concns. Structural characterization by single-crystal X-ray diffraction reveals that both frameworks facilitate the sepn. through the extent of interaction between each C8 guest mol. with two adjacent cobalt(II) centers, as well as the ability of each isomer to pack within the framework pores. Moreover, counter to the presumed rigidity of the M2(dobdc) structure, Co2(dobdc) exhibits an unexpected structural distortion in the presence of either o-xylene or ethylbenzene that enables the accommodation of addnl. guest mols.
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    Peng, B.; Wang, S. Separation of p-xylene and m-xylene by simulated moving bed chromatography with MIL-53(Fe) as stationary phase. J. Chromatogr. A 2022, 1673, 463091  DOI: 10.1016/j.chroma.2022.463091
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    27
    Separation of p-xylene and m-xylene by simulated moving bed chromatography with MIL-53(Fe) as stationary phase
    Peng, Bo; Wang, Shaoyan
    Journal of Chromatography A (2022), 1673 (), 463091CODEN: JCRAEY; ISSN:0021-9673. (Elsevier B.V.)
    The sepn. of p-xylene (PX) and m-xylene (MX) isomers with near b.ps. is a worldwide problem. The metal-org. framework material is an ideal stationary phase for chromatog. sepn. because of its high porosity, homogeneous pore diam. and good chem. stability. In this paper, a simulated moving bed (SMB) chromatog. system with MIL-53(Fe) as the stationary phase and petroleum ether-dichloromethane as the mobile phase was designed to sep. PX and MX at ambient temp. Firstly, according to the elution curves of a single column, nonlinear competitive Langmuir adsorption isotherm equation was confirmed by equil. dispersive chromatog. model. Then, the SMB sepn. zone was detd. based on triangle theory, and the SMB operating conditions were optimized. Finally, the purity, recovery and productivity of PX reached 100.0%, 99.1% and 93.1 g/L/h, resp.; the purity, recovery and productivity of MX reached 96.4%, 100.0% and 23.5 g/L/h, resp.; the solvent consumption was 0.42 L/g.
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    Kumar, N.; Wang, S.-Q.; Mukherjee, S.; Bezrukov, A. A.; Patyk-Kaźmierczak, E.; O’Nolan, D.; Kumar, A.; Yu, M.-H.; Chang, Z.; Bu, X.-H.; Zaworotko, M. J. Crystal engineering of a rectangular sql coordination network to enable xylenes selectivity over ethylbenzene. Chem. Sci. 2020, 11 (26), 6889– 6895,  DOI: 10.1039/D0SC02123G
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    Crystal engineering of a rectangular sql coordination network to enable xylenes selectivity over ethylbenzene
    Kumar, Naveen; Wang, Shi-Qiang; Mukherjee, Soumya; Bezrukov, Andrey A.; Patyk-Kazmierczak, Ewa; O'Nolan, Daniel; Kumar, Amrit; Yu, Mei-Hui; Chang, Ze; Bu, Xian-He; Zaworotko, Michael J.
    Chemical Science (2020), 11 (26), 6889-6895CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Sepn. of the C8 arom. isomers, p-xylene (PX), m-xylene (MX), o-xylene (OX) and ethylbenzene (EB), is relevant thanks to their widespread application as chem. feedstocks but challenging because of their similar b.ps. and close mol. dimensions. Physisorptive sepn. could offer an energy-efficient soln. to this challenge but sorbents which exhibit strong selectivity for one of the isomers remain a largely unmet challenge despite recent reports of OX or PX selective sorbents with high uptake capacity. For example, the square lattice, sql, topol. coordination network [Co(bipy)2(NCS)2]n (sql-1-Co-NCS) exhibits the rare combination of high OX selectivity and high uptake capacity. Herein we report that a crystal engineering approach enabled isolation of the mixed-linker sql coordination network [Co(bipy)(bptz)(NCS)2]n (sql-1,3-Co-NCS, bipy = 4,4'-bipyridine, bptz = 4,4'-bis(4-pyridyl)tetrazine) and study of its C8 vapor and liq. sorption properties. sql-1,3-Co-NCS was found to exhibit high adsorption capacity from liq. xylenes (~ 37 wt%) and is to our knowledge the first sorbent to exhibit high selectivity for each of xylene isomer over EB (SOX/EB, SMX/EB, SPX/EB > 5). Insights into the performance of sql-1,3-Co-NCS are gained from structural studies which reveal stacking interactions between electron-deficient bptz linkers and the resp. xylenes. sql-1,3-Co-NCS is the first N-donor mixed-linker sql coordination network studied for its gas/vapor sorption properties and represents a large and diverse class of understudied coordination networks.
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  29. 29
    Wang, S.-Q.; Mukherjee, S.; Patyk-Kaźmierczak, E.; Darwish, S.; Bajpai, A.; Yang, Q.-Y.; Zaworotko, M. J. Highly Selective, High-Capacity Separation of o-Xylene from C8 Aromatics by a Switching Adsorbent Layered Material. Angew. Chem., Int. Ed. 2019, 58 (20), 6630– 6634,  DOI: 10.1002/anie.201901198
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    29
    Highly selective, high-capacity separation of o-xylene from C8 aromatics by a switching adsorbent layered material
    Wang, Shi-Qiang; Mukherjee, Soumya; Patyk-Kazmierczak, Ewa; Darwish, Shaza; Bajpai, Alankriti; Yang, Qing-Yuan; Zaworotko, Michael J.
    Angewandte Chemie, International Edition (2019), 58 (20), 6630-6634CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Purifn. of the C8 aroms. (xylenes and ethylbenzene) is particularly challenging because of their similar phys. properties. It is also relevant because of their industrial utility. Physisorptive sepn. of C8 aroms. has long been suggested as an energy efficient soln. but no physisorbent has yet combined high selectivity (>5) with high adsorption capacity (>50 wt %). Now a counterintuitive approach to the adsorptive sepn. of o-xylene from other C8 aroms. involves the study of a known nonporous layered material, [Co(bipy)2(NCS)2]n (sql-1-Co-NCS), which can reversibly switch to C8 aroms. loaded phases with different switching pressures and kinetics, manifesting benchmark o-xylene selectivity (SOX/EB≈60) and high satn. capacity (>80 wt %). Structural insight into the obsd. selectivity and capacity is gained by anal. of the crystal structures of C8 aroms. loaded phases.
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    Wright, J. S.; Vitórica-Yrezábal, I. J.; Thompson, S. P.; Brammer, L. Arene Selectivity by a Flexible Coordination Polymer Host. Chem. - Eur. J. 2016, 22 (37), 13120– 13126,  DOI: 10.1002/chem.201601870
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    Arene Selectivity by a Flexible Coordination Polymer Host
    Wright, James S.; Vitorica-Yrezabal, Inigo J.; Thompson, Stephen P.; Brammer, Lee
    Chemistry - A European Journal (2016), 22 (37), 13120-13126CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The coordination polymers [Ag4(O2CCF3)4(phen)3]·phen·arene (1·phen·arene) (phen = phenazine; arene = toluene, p-xylene or benzene) were prepd. from the soln. phase in arene solvents and crystallog. characterized. By contrast, analogous syntheses from o-xylene and m-xylene as solvent yield the solvent-free coordination polymer [Ag4(O2CCF3)4(phen)2] (2). Toluene, p-xylene and benzene were successfully used in mixed-arene syntheses to template the formation of coordination polymers 1·phen·arene, which incorporate o- or m-xylene. The selectivity of 1·phen·arene for arene guests was detd. through pairwise competition expts. to be p-xylene > toluene ≈ benzene o-xylene m-xylene. The largest selectivity coeff. was 14.2 for p-xylene:m-xylene and the smallest was 1.0 for toluene:benzene.
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    Li, L.; Guo, L.; Olson, D. H.; Xian, S.; Zhang, Z.; Yang, Q.; Wu, K.; Yang, Y.; Bao, Z.; Ren, Q.; Li, J. Discrimination of xylene isomers in a stacked coordination polymer. Science 2022, 377 (6603), 335– 339,  DOI: 10.1126/science.abj7659
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    Discrimination of xylene isomers in a stacked coordination polymer
    Li, Liangying; Guo, Lidong; Olson, David H.; Xian, Shikai; Zhang, Zhiguo; Yang, Qiwei; Wu, Kaiyi; Yang, Yiwen; Bao, Zongbi; Ren, Qilong; Li, Jing
    Science (Washington, DC, United States) (2022), 377 (6603), 335-339CODEN: SCIEAS; ISSN:1095-9203. (American Association for the Advancement of Science)
    The sepn. and purifn. of xylene isomers is an industrially important but challenging process. Developing highly efficient adsorbents is crucial for the implementation of simulated moving bed technol. for industrial sepn. of these isomers. Herein, we report a stacked one-dimensional coordination polymer {[Mn(dhbq)(H2O)2], H2dhbq = 2,5-dihydroxy-1,4-benzoquinone} that exhibits an ideal mol. recognition and sieving of xylene isomers. Its distinct temp.-adsorbate-dependent adsorption behavior enables full sepn. of p-, m-, and o-xylene isomers in both vapor and liq. phases. The delicate stimuli-responsive swelling of the structure imparts this porous material with exceptionally high flexibility and stability, well-balanced adsorption capacity, high selectivity, and fast kinetics at conditions mimicking industrial settings. This study may offer an alternative approach for energy-efficient and adsorption-based industrial xylene sepn. and purifn. processes.
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    Kałuża, A. M.; Mukherjee, S.; Wang, S.-Q.; O’Hearn, D. J.; Zaworotko, M. J. [Cu(4-phenylpyridine)4(trifluoromethanesulfonate)2], a Werner complex that exhibits high selectivity for o-xylene. Chem. Commun. 2020, 56 (13), 1940– 1943,  DOI: 10.1039/C9CC09525J
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    [Cu(4-phenylpyridine)4(trifluoromethanesulfonate)2], a Werner complex that exhibits high selectivity for o-xylene
    Kaluza, Adrianna M.; Mukherjee, Soumya; Wang, Shi-Qiang; O'Hearn, Daniel J.; Zaworotko, Michael J.
    Chemical Communications (Cambridge, United Kingdom) (2020), 56 (13), 1940-1943CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    [Cu(4-phenylpyridine)4(trifluoromethanesulfonate)2] is a new Werner complex that exhibits switching behavior between non-porous (apohost) and porous (guest-loaded) phases upon exposure to o-xylene but not when exposed to other C8 isomers. High o-xylene selectivity (>6) vs. the other C8 isomers was obsd. from binary mixts., only the third occurrence across all sorbent types.
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    Lusi, M.; Barbour, L. J. Solid–Vapor Sorption of Xylenes: Prioritized Selectivity as a Means of Separating All Three Isomers Using a Single Substrate. Angew. Chem., Int. Ed. 2012, 51 (16), 3928– 3931,  DOI: 10.1002/anie.201109084
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    Solid-Vapor Sorption of Xylenes: Prioritized Selectivity as a Means of Separating All Three Isomers Using a Single Substrate
    Lusi, Matteo; Barbour, Leonard J.
    Angewandte Chemie, International Edition (2012), 51 (16), 3928-3931, S3928/1-S3928/7CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Soln.-state and solid-vapor prepns. of the xylene clathrates of [Ni(NCS)2(ppp)4] (I) (ppp = p-phenylpyridine) are reported. The previously unknown structure of [Ni(NCS)2(ppp)4]·3p-xylene was detd. Significant selectivity of 1 for ortho- over meta- and para-xylene from a ternary mixt., and then similar selectivity for meta- over para-xylene from a binary mixt. were obsd. The reason for such selectivity is discussed.
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    Lusi, M.; Barbour, L. J. Solid–vapour reactions as a post-synthetic modification tool for molecular crystals: the enclathration of benzene and toluene by Werner complexes. Chem. Commun. 2013, 49 (26), 2634– 2636,  DOI: 10.1039/c3cc40521d
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    Solid-vapour reactions as a post-synthetic modification tool for molecular crystals: the enclathration of benzene and toluene by Werner complexes
    Lusi, Matteo; Barbour, Leonard J.
    Chemical Communications (Cambridge, United Kingdom) (2013), 49 (26), 2634-2636CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    The enclathration of benzene and toluene by Werner complexes has been described. In the case of toluene, time-lapse PXRD anal. reveals that solid-liq. and solid-vapor reactions proceed according to different pathways. These preliminary results suggest that solid-liq. reactions destroy the host structure, whereas the solid-vapor reactions allow post-synthetic modification.
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    Sun, N.; Wang, S.-Q.; Zou, R.; Cui, W.-G.; Zhang, A.; Zhang, T.; Li, Q.; Zhuang, Z.-Z.; Zhang, Y.-H.; Xu, J.; Zaworotko, M. J.; Bu, X.-H. Benchmark selectivity p-xylene separation by a non-porous molecular solid through liquid or vapor extraction. Chem. Sci. 2019, 10 (38), 8850– 8854,  DOI: 10.1039/C9SC02621E
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    Benchmark selectivity p-xylene separation by a non-porous molecular solid through liquid or vapor extraction
    Sun, Na; Wang, Shi-Qiang; Zou, Ruqiang; Cui, Wen-Gang; Zhang, Anqi; Zhang, Tianzhen; Li, Qi; Zhuang, Zhan-Zhong; Zhang, Ying-Hui; Xu, Jialiang; Zaworotko, Michael J.; Bu, Xian-He
    Chemical Science (2019), 10 (38), 8850-8854CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Solid-liq. sepn. of similarly sized org. mols. utilizing sorbents offers the potential for new energy-efficient approaches to a no. of important industrial sepns. such as xylenes (C8) sepns. Research on selective C8 sorption has tended to focus upon rigid porous materials such as zeolites and MOFs but has revealed generally weak selectivity that is inconsistent across the range of C8 mols. Nevertheless, there are a few recent examples of non-porous mol. materials that exhibit relatively high selectivity for p-xylene (pX) from pX/oX, approaching that of the current benchmark pX sorbent, the zeolite H/ZSM-5. Herein, we report that a L-shaped Ag(I) complex, AgLClO4 (M), which crystallizes as a non-porous mol. solid material, offering exceptional performance for pX selectivity across the range of C8 isomers with liq. extn. selectivity values of 24.0, 10.4 and 6.2 vs. oX, eB and mX, resp. The pX selectivities over oX and eB are among the highest yet reported. Moreover, M also exhibits strong vapor extn. selectivity and can be regenerated by exposure to vacuum drying.
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    Nassimbeni, L. R. Physicochemical Aspects of Host–Guest Compounds. Acc. Chem. Res. 2003, 36 (8), 631– 637,  DOI: 10.1021/ar0201153
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    Physicochemical Aspects of Host-Guest Compounds
    Nassimbeni, Luigi R.
    Accounts of Chemical Research (2003), 36 (8), 631-637CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. The macro properties of cryst. inclusion compds. depend on their structures. Their thermal stabilities are a function of the strength and the directionality of the various nonbonded interactions occurring in the host-guest assembly. Their lattice energies, as measured by the method of atom-atom potentials, correlate with the thermodn. of the guest-release reactions and the selectivity that a given host displays for a particular guest. The kinetics of solid-host:vapor-guest reactions and of guest exchange are important in our understanding of catalytic processes. Crystal engineering, in which materials of predetd. properties may be synthesized, is still at the empirical stage.
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    Barbour, L. J. Crystal porosity and the burden of proof. Chem. Commun. 2006, (11), 1163– 1168,  DOI: 10.1039/b515612m
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    Crystal porosity and the burden of proof
    Barbour, Leonard J.
    Chemical Communications (Cambridge, United Kingdom) (2006), (11), 1163-1168CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A review. The study of porosity in the context of crystal engineering is rapidly growing in intensity. However, claims of porosity are often highly subjective and use of the term porous is susceptible to abuse. This contribution discusses some of the criteria to be considered when stating that a particular crystal structure is porous.
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    Wang, Z.; Sikdar, N.; Wang, S.-Q.; Li, X.; Yu, M.; Bu, X.-H.; Chang, Z.; Zou, X.; Chen, Y.; Cheng, P.; Yu, K.; Zaworotko, M. J.; Zhang, Z. Soft Porous Crystal Based upon Organic Cages That Exhibit Guest-Induced Breathing and Selective Gas Separation. J. Am. Chem. Soc. 2019, 141 (23), 9408– 9414,  DOI: 10.1021/jacs.9b04319
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    Soft Porous Crystal Based upon Organic Cages That Exhibit Guest-Induced Breathing and Selective Gas Separation
    Wang, Zhifang; Sikdar, Nivedita; Wang, Shi-Qiang; Li, Xia; Yu, Meihui; Bu, Xian-He; Chang, Ze; Zou, Xiaolong; Chen, Yao; Cheng, Peng; Yu, Kuang; Zaworotko, Michael J.; Zhang, Zhenjie
    Journal of the American Chemical Society (2019), 141 (23), 9408-9414CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Soft porous crystals (SPCs) that exhibit stimuli-responsive dynamic sorption behavior are attracting interest for gas storage/sepn. applications. However, the design and synthesis of SPCs is challenging. Herein, we report a new type of SPC based on a [2 + 3] imide-based org. cage (NKPOC-1) and find that it exhibits guest-induced breathing behavior. Various gases were found to induce activated NKPOC-1 crystals to reversibly switch from a "closed" nonporous phase (α) to two porous "open" phases (β and γ). The net effect is gate-opening behavior induced by CO2 and C3 hydrocarbons. Interestingly, NKPOC-1-α selectively adsorbs propyne over propylene and propane under ambient conditions. Thus, NKPOC-1-α has the potential to sep. binary and ternary C3 hydrocarbon mixts., and the performance was subsequently verified by fixed bed column breakthrough expts. In addn., mol. dynamics calcns. and in situ X-ray diffraction expts. indicate that the gate-opening effect is accompanied by reversible structural transformations. The adsorption energies from mol. dynamics simulations aid are consistent with the exptl. obsd. selective adsorption phenomena. The understanding gained from this study of NKPOC-1 supports the further development of SPCs for applications in gas sepn./storage because SPCs do not inherently suffer from the recyclability problems often encountered with rigid materials.
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    Jie, K.; Zhou, Y.; Li, E.; Huang, F. Nonporous Adaptive Crystals of Pillararenes. Acc. Chem. Res. 2018, 51 (9), 2064– 2072,  DOI: 10.1021/acs.accounts.8b00255
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    Nonporous Adaptive Crystals of Pillararenes
    Jie, Kecheng; Zhou, Yujuan; Li, Errui; Huang, Feihe
    Accounts of Chemical Research (2018), 51 (9), 2064-2072CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. The authors focus on the discussion of pillararene-based nonporous adaptive crystals (NACs) for adsorption and sepn. and the crystal structure transformations from the initial nonporous cryst. state to new guest-loaded structures during the adsorption and sepn. processes. Single-crystal X-ray diffraction, powder X-ray diffraction, gas chromatog., and soln. NMR spectroscopy are the main techniques to verify the adsorption and sepn. processes and the structural transformations. Compared with traditional porous materials, NACs of pillararenes have several advantages. First, their prepn. is simple and cheap, and they can be synthesized on a large scale to meet practical demands. Second, pillararenes have better chem., moisture, and thermal stability than cryst. MOFs, COFs, and POCs, which are usually constructed on the basis of reversible chem. bonds. Third, pillararenes are sol. in many common org. solvents, which means that they can be easily processed in soln. Fourth, their regeneration is simple and they can be reused many times with no decrease in performance. It is expected that this class of materials will not only exert a significant influence on scientific research but also show practical applications in chem. industry.
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    Jie, K.; Zhou, Y.; Li, E.; Zhao, R.; Liu, M.; Huang, F. Linear Positional Isomer Sorting in Nonporous Adaptive Crystals of a Pillar[5]arene. J. Am. Chem. Soc. 2018, 140 (9), 3190– 3193,  DOI: 10.1021/jacs.7b13156
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    Linear Positional Isomer Sorting in Nonporous Adaptive Crystals of a Pillar[5]arene
    Jie, Kecheng; Zhou, Yujuan; Li, Errui; Zhao, Run; Liu, Ming; Huang, Feihe
    Journal of the American Chemical Society (2018), 140 (9), 3190-3193CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Here we show a new adsorptive sepn. approach using nonporous adaptive crystals of a pillar[5]arene. Desolvated perethylated pillar[5]arene crystals (EtP5α) with a nonporous character selectively adsorb 1-pentene (1-Pe) over its positional isomer 2-pentene (2-Pe), leading to a structural change from EtP5α to 1-Pe loaded structure (1-Pe@EtP5). The purity of 1-Pe reaches 98.7% in just one cycle and EtP5α can be reused without losing sepn. performance.
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    Zhang, G.; Hua, B.; Dey, A.; Ghosh, M.; Moosa, B. A.; Khashab, N. M. Intrinsically Porous Molecular Materials (IPMs) for Natural Gas and Benzene Derivatives Separations. Acc. Chem. Res. 2021, 54 (1), 155– 168,  DOI: 10.1021/acs.accounts.0c00582
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    Intrinsically Porous Molecular Materials (IPMs) for Natural Gas and Benzene Derivatives Separations
    Zhang, Gengwu; Hua, Bin; Dey, Avishek; Ghosh, Munmun; Moosa, Basem A.; Khashab, Niveen M.
    Accounts of Chemical Research (2021), 54 (1), 155-168CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. Conspectus: Sepg. and purifying chems. without heat would go a long way toward reducing the overall energy consumption and the harmful environmental footprint of the process. Mol. sepn. processes are crit. for the prodn. of raw materials, commodity chems., and specialty fuels. Over 50% of the energy used in the prodn. of these materials is spent on sepn. and purifn. processes, which primarily includes vacuum and cryogenic distns. Chem. manufacturers are now investigating modest thermal approaches, such as membranes and adsorbent materials, as they are more cognizant than ever of the need to save energy and prevent pollution. Porous materials, such as zeolites, metal-org. frameworks (MOFs), and covalent org. frameworks (COFs), have dominated the field of industrial sepns. as their high surface areas and robust pores make them ideal candidates for mol. sepns. of gases and hydrocarbons. Sepn. processes involving porous materials can save 70%-90% of energy costs compared to that of thermally driven distns. However, most porous materials have low thermal, chem., and moisture stability, in addn. to limited soln. processability, which tremendously constrain their broad industrial translation. Intrinsically porous mol. materials (IPMs) are a subclass of porous mol. materials that are comprised of mol. host macrocycles or cages that absorb guests in or around their intrinsic cavity. IPMs range from discrete porous mols. to assemblies with amorphous or highly cryst. structures that are held together by weak supramol. interactions. Compared to the coordination or dynamic covalent bond-constructed porous frameworks, IPMs possess high thermal, chem., and moisture stability and maintain their porosity under crit. conditions. Moreover, the intrinsic porosity endows IPMs with excellent host-guest properties in solid, liq. (org. or aq.), and gas states, which can be further utilized to construct diverse sepn. strategies, such as solid-gas adsorption, solid-liq. absorption, and liq.-liq. extn. The diversity of host-guest interactions in the engineered IPMs affords a plethora of possibilities for the development of the ideal "mol. sieves". Herein, we present a different take on the applicability of intrinsically porous materials such as cyclodextrin (CD), cucurbiturils (CB), pillararene (P), trianglamines (T), and porous org. cages (POCs) that showed an impressive performance in gas purifn. and benzene derivs. sepn. IPMs can be easily scaled up and are quite stable and soln. processable that consequently facilitates a favorable technol. transformation from the traditional energy-intensive sepns. We will account for the main advances in mol. host-guest chem. to design "on-demand" sepn. processes and also outline future challenges and opportunities for this promising technol.
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    Moosa, B.; Alimi, L. O.; Shkurenko, A.; Fakim, A.; Bhatt, P. M.; Zhang, G.; Eddaoudi, M.; Khashab, N. M. A Polymorphic Azobenzene Cage for Energy-Efficient and Highly Selective p-Xylene Separation. Angew. Chem., Int. Ed. 2020, 59 (48), 21367– 21371,  DOI: 10.1002/anie.202007782
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    A Polymorphic Azobenzene Cage for Energy-Efficient and Highly Selective p-Xylene Separation
    Moosa, Basem; Alimi, Lukman O.; Shkurenko, Aleksander; Fakim, Aliyah; Bhatt, Prashant M.; Zhang, Gengwu; Eddaoudi, Mohamed; Khashab, Niveen M.
    Angewandte Chemie, International Edition (2020), 59 (48), 21367-21371CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Developing the competence of mol. sorbents for energy-saving applications, such as C8 sepns., requires efficient, stable, scalable, and easily recyclable materials that can readily transition to com. implementation. Herein, we report an azobenzene-based cage for the selective sepn. of p-xylene isomer across a range of C8 isomers in both vapor and liq. states with selectivity that is higher than the reported all-org. sorbents. The crystal structure shows non-porous cages that are sepd. by p-xylene mols. through selective CH-π interactions between the azo bonds and the Me hydrogen atoms of the xylene mols. This cage is stable in soln. and can be regenerated directly under vacuum to be used in multiple cycles. We envisage that this work will promote the investigation of the azo bond as well as guest-induced crystal-to-crystal phase transition in non-porous org. solids for energy-intensive sepns.
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  43. 43
    Jie, K.; Liu, M.; Zhou, Y.; Little, M. A.; Pulido, A.; Chong, S. Y.; Stephenson, A.; Hughes, A. R.; Sakakibara, F.; Ogoshi, T.; Blanc, F.; Day, G. M.; Huang, F.; Cooper, A. I. Near-Ideal Xylene Selectivity in Adaptive Molecular Pillar[n]arene Crystals. J. Am. Chem. Soc. 2018, 140 (22), 6921– 6930,  DOI: 10.1021/jacs.8b02621
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    Near-ideal xylene selectivity in adaptive molecular pillar[n]arene crystals
    Jie, Kecheng; Liu, Ming; Zhou, Yujuan; Little, Marc A.; Pulido, Angeles; Chong, Samantha Y.; Stephenson, Andrew; Hughes, Ashlea R.; Sakakibara, Fumiyasu; Ogoshi, Tomoki; Blanc, Frederic; Day, Graeme M.; Huang, Feihe; Cooper, Andrew I.
    Journal of the American Chemical Society (2018), 140 (22), 6921-6930CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The energy-efficient sepn. of alkylarom. compds. is a major industrial sustainability challenge. The use of selectively porous extended frameworks, such as zeolites or metal-org. frameworks, is one soln. to this problem. Here, we studied a flexible mol. material, perethylated pillar[n]arene crystals (n = 5, 6), which can be used to sep. C8 alkylarom. compds. Pillar[6]arene is shown to sep. para-xylene from its structural isomers, meta-xylene and ortho-xylene, with 90% specificity in the solid state. Selectivity is an intrinsic property of the pillar[6]arene host, with the flexible pillar[6]arene cavities adapting during adsorption thus enabling preferential adsorption of para-xylene in the solid state. The flexibility of pillar[6]arene as a solid sorbent is rationalized using mol. conformer searches and crystal structure prediction (CSP) combined with comprehensive characterization by X-ray diffraction and 13C solid-state NMR spectroscopy. The CSP study, which takes into account the structural variability of pillar[6]arene, breaks new ground in its own right and showcases the feasibility of applying CSP methods to understand and ultimately to predict the behavior of soft, adaptive mol. crystals.
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  44. 44
    du Plessis, M.; Nikolayenko, V. I.; Barbour, L. J. Record-Setting Selectivity for p-Xylene by an Intrinsically Porous Zero-Dimensional Metallocycle. J. Am. Chem. Soc. 2020, 142 (10), 4529– 4533,  DOI: 10.1021/jacs.9b11314
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    44
    Record-Setting Selectivity for p-Xylene by an Intrinsically Porous Zero-Dimensional Metallocycle
    du Plessis, Marike; Nikolayenko, Varvara I.; Barbour, Leonard J.
    Journal of the American Chemical Society (2020), 142 (10), 4529-4533CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    In its cryst. state, a dinuclear Cu-based metallocycle discriminates between the three isomers of xylene with liq.-phase selectivity in the order p-xylene » m-xylene » o-xylene. This selectivity holds over a wide concn. range, with p-xylene concns. as low as 5%. Single-crystal X-ray diffraction and gas chromatog. further indicate that the metallocyclic host exts. trace amts. of p-xylene from com. pure o-xylene (≥99%); using NMR spectroscopy, we show that the metallocycle exhibits exclusive selectivity for p-xylene. Crystallog. studies show that the selectivity is based on the size and shape of the guest in combination with the flexibility of the host.
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  45. 45
    Barton, B.; Caira, M. R.; de Jager, L.; Hosten, E. C. N,N′-Bis(9-phenyl-9-thioxanthenyl)ethylenediamine: Highly Selective Host Behavior in the Presence of Xylene and Ethylbenzene Guest Mixtures. Cryst. Growth Des. 2017, 17 (12), 6660– 6667,  DOI: 10.1021/acs.cgd.7b01284
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    45
    N,N'-Bis(9-phenyl-9-thioxanthenyl)ethylenediamine: Highly Selective Host Behavior in the Presence of Xylene and Ethylbenzene Guest Mixtures
    Barton, Benita; Caira, Mino R.; de Jager, Lize; Hosten, Eric C.
    Crystal Growth & Design (2017), 17 (12), 6660-6667CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    Host compd. N,N'-bis(9-phenyl-9-thioxanthenyl)ethylenediamine formed 1:1 host:guest complexes with o- and p-xylene, and ethylbenzene, when recrystd. from them. The meta-isomer was not included. Competition expts. using equimolar binary and ternary mixts. of the three xylenes demonstrated that this host is markedly selective for p-xylene (≥94% on both a milligram- and gram-scale), while 68% of this guest was extd. from an equimolar quaternary mixt. of the three xylenes and ethylbenzene. This selectivity was also evident when guest ratios in binary mixts. contg. p-xylene were varied. The obsd. high affinity for the para-isomer was explained using single crystal X-ray diffraction, Hirshfeld surface anal. and thermoanal. expts. Furthermore, the host was subjected to gas phase guests in order to establish whether the ability existed for complexation of these guests from the solid state.
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  46. 46
    Barton, B.; Senekal, U.; Hosten, E. C. trans-α,α,α′,α′-Tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol and its tetra(p-chlorophenyl) derivative: roof-shaped host compounds for the purification of aromatic C8H10 isomeric guest mixtures. J. Inclusion Phenom. Macrocyclic Chem. 2022, 102 (1), 77– 87,  DOI: 10.1007/s10847-021-01102-5
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    trans-α,α,α',α'-Tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol and its tetra(p-chlorophenyl) derivative: roof-shaped host compounds for the purification of aromatic C8H10 isomeric guest mixtures
    Barton, Benita; Senekal, Ulrich; Hosten, Eric C.
    Journal of Inclusion Phenomena and Macrocyclic Chemistry (2022), 102 (1-2), 77-87CODEN: JIPCF5; ISSN:1388-3127. (Springer)
    Roof-shaped host compds. trans-α,α,α',α'-tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12sda-dimethanol H3 and trans-α,α,α',α'-tetra(p-chlorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol H6 were assessed for their host potential and selectivity behavior when presented with single or mixed guest solvents comprising o-xylene, m-xylene, p-xylene and ethylbenzene (o-Xy, m-Xy, p-Xy and EB). H3 included each solvent with 3:1 host:guest ratios, while the ratios preferred by H6 were more varied (4:3, 1:1 and 3:2). More importantly, the selectivity behavior of these two host compds. was obsd. to be entirely different: H3 possessed only a very modest preference for o-Xy (37.9-68.2%) when recrystd. from various equimolar binary, ternary and quaternary guest mixts., while H6 was considerably more selective, preferring m-Xy (the least favored guest of H3) with selectivities ranging from 57.7 to 91.4% in analogous conditions. The latter result was obtained in o-Xy/m-Xy mixts. and demonstrates that H6 may be employed as a purifn. tool for mixts. of these two xylenes via host-guest chem. protocols. A single crystal diffraction expt. on 3(H3)·o-Xy (contg. the preferred guest of H3) revealed that the guest was retained in the host crystal by means of a singular (host)m-Ar-H···π(guest) interaction that measured 2.73 Å (148°) as well as numerous other host···guest interactions involving only the arom. protons of the free host Ph groups and the guest Me protons or arom. carbons and protons (2.20-2.54 Å, 121-125°). Thermal analyses explained the preference of H3 for o-Xy, while these were less informative for the complexes of H6.
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    Little, M. A.; Cooper, A. I. The Chemistry of Porous Organic Molecular Materials. Adv. Funct. Mater. 2020, 30 (41), 1909842  DOI: 10.1002/adfm.201909842
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    The Chemistry of Porous Organic Molecular Materials
    Little, Marc A.; Cooper, Andrew I.
    Advanced Functional Materials (2020), 30 (41), 1909842CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Porous org. mol. materials are a subclass of porous solids that are defined by their modular, mol. structures, and the absence of extended covalent or coordination bonding in the solid-state. As a result, porous mol. materials are sol. and they can be processed into different forms, such as mixed matrix membranes. The structure of the porous modules can be fine-tuned for specific applications, such as gas isotope sepns., and in some cases the solid-state properties of these materials can be defined by the structure of the porous mol. as viewed in isolation. In this review, the authors focus on the design of porous org. mol. materials and how their properties can be tuned for specific applications by using crystal engineering techniques. The authors distinguish between strategies where porosity is defined largely by the mol. itself, for example, in porous org. cages, and cases where porosity is generated by the solid-state cryst. assembly. They emphasize the importance of computational techniques in the de novo design of functional, porous org. mol. materials, and how mol. modeling is applied to understand the properties of these materials.
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    Mitra, T.; Jelfs, K. E.; Schmidtmann, M.; Ahmed, A.; Chong, S. Y.; Adams, D. J.; Cooper, A. I. Molecular shape sorting using molecular organic cages. Nat. Chem. 2013, 5 (4), 276– 281,  DOI: 10.1038/nchem.1550
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    Molecular shape sorting using molecular organic cages
    Mitra, Tamoghna; Jelfs, Kim E.; Schmidtmann, Marc; Ahmed, Adham; Chong, Samantha Y.; Adams, Dave J.; Cooper, Andrew I.
    Nature Chemistry (2013), 5 (4), 276-281CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
    The energy-efficient sepn. of chem. feedstocks is a major sustainability challenge. Porous extended frameworks such as zeolites or metal-org. frameworks are one potential soln. to this problem. Here, we show that org. mols., rather than frameworks, can sep. other org. mols. by size and shape. A mol. org. cage is shown to sep. a common arom. feedstock (mesitylene) from its structural isomer (4-ethyltoluene) with an unprecedented perfect specificity for the latter. This specificity stems from the structure of the intrinsically porous cage mol., which is itself synthesized from a deriv. of mesitylene. In other words, cryst. org. mols. are used to sep. other org. mols. The specificity is defined by the cage structure alone, so this solid-state 'shape sorting' is, uniquely, mirrored for cage mols. in soln. The behavior can be understood from a combination of atomistic simulations for individual cage mols. and solid-state mol. dynamics simulations.
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    Ye, J.; du Plessis, M.; Loots, L.; van Wyk, L. M.; Barbour, L. J. Solid–Liquid Separation of Xylene Isomers Using a Cu-Based Metallocycle. Cryst. Growth Des. 2022, 22 (4), 2654– 2661,  DOI: 10.1021/acs.cgd.2c00082
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    Solid-Liquid Separation of Xylene Isomers Using a Cu-Based Metallocycle
    Ye, Jiajia; du Plessis, Marike; Loots, Leigh; van Wyk, Lisa Mercene; Barbour, Leonard J.
    Crystal Growth & Design (2022), 22 (4), 2654-2661CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    Industrial sepn. of xylene isomers is a challenge due to their similarity in size, shape, d., b.p. and polarity. Xylene isomers have been sepd. using zero-dimensionally porous crystals composed of a Cu-based metallocycle, with selectivity in the order p-xylene » m-xylene > o-xylene. The selectivity trend follows that of increasing kinetic diams. of the xylenes. Crystallog. studies show that the flexible host transforms from one phase to another to adapt to the inclusion of xylenes.
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    Atwood, J. L.; Barbour, L. J.; Jerga, A.; Schottel, B. L. Guest Transport in a Nonporous Organic Solid via Dynamic van der Waals Cooperativity. Science 2002, 298 (5595), 1000– 1002,  DOI: 10.1126/science.1077591
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    Guest Transport in a Nonporous Organic Solid via Dynamic van der Waals Cooperativity
    Atwood, Jerry L.; Barbour, Leonard J.; Jerga, Agoston; Schottel, Brandi L.
    Science (Washington, DC, United States) (2002), 298 (5595), 1000-1002CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    A well-known org. host compd. undergoes single-crystal-to-single-crystal phase transitions upon guest uptake and release. Despite a lack of porosity of the material, guest transport through the solid occurs readily until a thermodynamically stable structure is achieved. In order to actively facilitate this dynamic process, the host mols. undergo significant positional and/or orientational rearrangement. This transformation of the host lattice is triggered by weak van der Waals interactions between the mol. components. In order for the material to maintain its macroscopic integrity, extensive cooperativity must exist between the mols. throughout the crystal, such that rearrangement can occur in a well-orchestrated fashion. We demonstrate here that even weak dispersive forces can exert a profound influence over solid-state dynamics.
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    Barrer, R. M.; Shanson, V. H. Dianin’s compound as a zeolitic sorbent. J. Chem. Soc., Chem. Commun. 1976, (9), 333– 334,  DOI: 10.1039/c39760000333
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    Dianin's compound as a zeolitic sorbent
    Barrer, Richard M.; Shanson, Vivien H.
    Journal of the Chemical Society, Chemical Communications (1976), (9), 333-4CODEN: JCCCAT; ISSN:0022-4936.
    Dianin's compd., suitably agitated, sorbed freely Ar, Kr, Xe, CO2, CH4, C2H6, C3H8, C4H10, iso-C4H10, and neo-C5H12, and behaved in some respects like an org. zeolite because of the permanent character of its porous host lattice. The nos. of mols. filling each cavity in the host lattice varied from 6 for Ar at -196° and CH4 at -183° to 2 for iso-C4H10 and neo-C5H12 at 0°, and satn. nos. depended on the size and shape of the guest mols., as for zeolites.
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    Enright, G. D.; Ratcliffe, C. I.; Ripmeester, J. A. Crystal structure and 13C CP/MAS NMR of the p-xylene clathrate of Dianin’s compound. Mol. Phys. 1999, 97 (11), 1193– 1196,  DOI: 10.1080/00268979909482920
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    Crystal structure and 13C CP/MAS NMR of the p-xylene clathrate of Dianin's compound
    Enright, G. D.; Ratcliffe, C. I.; Ripmeester, J. A.
    Molecular Physics (1999), 97 (11), 1193-1196CODEN: MOPHAM; ISSN:0026-8976. (Taylor & Francis Ltd.)
    Single-crystal x-ray diffraction and 13C solid-state NMR spectroscopy were used to characterize the structure and dynamics of the p-xylene clathrate of Dianin's compd. In contrast to conclusions obtained from single-crystal 2H NMR and modeling, the diffraction results suggest there is a single (symmetry disordered) guest site without any significant distortion of the host framework. S single xylene guest statistically disordered over 6 overlapping equiv. positions can account for the 13C NMR spectrum at room temp. The high crystallog. symmetry arises from space averaging. At high temps. the 13C spectrum is consistent with the onset of dynamic processes that result in higher effective symmetry.
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    Harris, K. D. M. Meldola Lecture: understanding the properties of urea and thiourea inclusion compounds. Chem. Soc. Rev. 1997, 26 (4), 279– 289,  DOI: 10.1039/cs9972600279
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    Meldola lecture: understanding the properties of urea and thiourea inclusion compounds
    Harris, Kenneth D. M.
    Chemical Society Reviews (1997), 26 (4), 279-290CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review with 49 refs.; much of the intrinsic appeal of structural science arises from the fact that structural behavior at the mol. level often resembles macroscopic structures that we can see in the world around us. In the same way that we perceive beauty in the symmetries and forms of macroscopic objects, there is an equally enthralling beauty in the way that nature fashions symmetry and diversity within the architectures of cryst. solids. In the field of inclusion chem., for example, many direct analogies can be drawn between the concepts of inclusion in the microscopic and macroscopic worlds, but the scientific interest and importance of inclusion chem. extends far beyond such structural comparisons. As this article demonstrates, solid org. inclusion compds. can exhibit a diversity of interesting and important fundamental properties, which can form the basis of a range of important applications.
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    Palin, D. E.; Powell, H. M. 50. The structure of molecular compounds. Part III. Crystal structure of addition complexes of quinol with certain volatile compounds. J. Chem. Soc. (Resumed) 1947, 0, 208– 221,  DOI: 10.1039/jr9470000208
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    Terres, E.; Vollmer, W. Solubility of Mineral Oil and tar constituents in liquid Hydrogen Sulphide. Petroleum 1935, 31, 1– 12
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    The solubility of petroleum and tar constituents in liquid hydrogen sulfide
    Terres, Ernst; Vollmer, Walter
    (1935), 31 (No. 19), 1-12 ISSN:.
    Development of solvent extn. methods and the early works on the behavior of liquid H2S with org. substances are reviewed. Binary systems of the following constituents of petroleum and tar and H2S were investigated: benzene, toluene, phenol, o-cresol, naphthalene, β-methylnaphthalene, anthracene,phenanthrene, octadecane, hexahydrobenzene and quinoline. Benzene, toluene, hexahydrobenzene and quinoline, and the paraffin hydrocarbons are miscible in all proportions at 0° with liquid H2S. The soly. of phenol, o-cresol, naphthalene and β-methyl-naphthalene is very high. The f.-p. curve of anthracene and phenanthrene cuts the crit. line of H2S. All the org. substances investigated form only 1 liquid phase with liquid H2S; in no case was a miscibility gap present. Toluene, phenol, β-methylnaphthalene and quinoline form intermediate compds.: 2C6H5CH3.H2S, 2C6H5OH.H2S, 4C10H7CH3.H2S and C8H7N.H2S. Octadecane and hexahydrobenzene form solid solns. with H2S.
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    Dwivedi, B.; Kumar, S.; Das, D. Selective inclusion of p-xylene by bis-hydrazone compounds. CrystEngComm 2022, 24 (6), 1161– 1165,  DOI: 10.1039/D1CE01569A
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    Selective inclusion of p-xylene by bis-hydrazone compounds
    Dwivedi, Bhavna; Kumar, Sunil; Das, Dinabandhu
    CrystEngComm (2022), 24 (6), 1161-1165CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
    The sepn. of xylene isomers from their mixt. is a challenging task. The present study describes the highly selective inclusion of p-xylene (p-XY) from a mixt. of xylene isomers by three novel org. bis-hydrazone compds., ethanedial-1,2-bis(4,4'-dichlorobenzophenone hydrazone) (1), ethanedial-1,2-bis(4,4'-dibromobenzophenone hydrazone) (2) and ethanedial-1,2-bis(4,4'-diiodobenzophenone hydrazone) (3). These van der Waals host compds. specifically enclathrate p-XY from a mixt. of xylene isomers. Crystn. of the host compds. in all possible mixts. of xylene isomers, X-ray diffraction (both single-crystal and powder) and thermogravimetric anal. (TGA) confirm the selective inclusion property of the bis-hydrazone compds. Compds. 1, 2 and 3 might be suitable candidates for the sepn. of p-XY from a mixt. of xylene isomers.
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    Pivovar, A. M.; Holman, K. T.; Ward, M. D. Shape-Selective Separation of Molecular Isomers with Tunable Hydrogen-Bonded Host Frameworks. Chem. Mater. 2001, 13 (9), 3018– 3031,  DOI: 10.1021/cm0104452
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    Shape-Selective Separation of Molecular Isomers with Tunable Hydrogen-Bonded Host Frameworks
    Pivovar, Adam M.; Holman, K. Travis; Ward, Michael D.
    Chemistry of Materials (2001), 13 (9), 3018-3031CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    The propensity of H-bonded guanidinium (G) organodisulfonates (S) to form cryst. inclusion compds. was studied in the context of sepg. isomeric mixts. of xylenes and dimethylnaphthalenes via selective inclusion. Pairwise competition expts., in which inclusion compds. are grown from solns. contg. an isomeric mixt. of guests, map the inclusion selectivity of a particular host as a function of guest content in soln. Whereas the G2[4,4'-biphenyldisulfonate] host is minimally selective with respect to inclusion of o-, m-, or p-xylene, the homologous G2[2,6-naphthalenedisulfonate] is highly selective toward the inclusion of p-xylene, by a factor of 36 and 160 vs. o-xylene and m-xylene, resp. Similarly, the hosts of the homologous series G2[2,6-naphthalenedisulfonate], G2[4,4'-biphenyldisulfonate], G2[2,6-anthracenedisulfonate], and G2[4,4'-azobenzenedisulfonate] display different selectivity for the 10 isomers of dimethylnaphthalene. The details of the selectivity behavior are highly dependent on the mol. structure of the GS host and the solid-state structures of the corresponding inclusion compds. Single crystal structure detns. reveal that isomer selectivity is most pronounced when the structures of corresponding inclusion compds. are significantly different, i.e., when the isomeric guests template different architectural isomers of the host. also, selectivity appears to be a consequence of size and shape compatibility between the host and guest. The observation of selective inclusion demonstrates the feasibility of a crystn.-based sepn. process based on these host compds.
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    Matos, C. R. M. O.; Sanii, R.; Wang, S.-Q.; Ronconi, C. M.; Zaworotko, M. J. Reversible single-crystal to single-crystal phase transformation between a new Werner clathrate and its apohost. Dalton Trans. 2021, 50 (37), 12923– 12930,  DOI: 10.1039/D1DT01839F
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    Reversible single-crystal to single-crystal phase transformation between a new Werner clathrate and its apohost
    Matos, Catiucia R. M. O.; Sanii, Rana; Wang, Shi-Qiang; Ronconi, Celia M.; Zaworotko, Michael J.
    Dalton Transactions (2021), 50 (37), 12923-12930CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    The authors report the synthesis and structural characterization of the ligand 2-(pyridin-3-yl)-benzo[de]isoquinoline-1,3(2H)-dione, 5, its isostructural Werner complexes ML4(NCS)2 (L = 5; M = Co(II) and Ni(II)), and five clathrates with three arom. guests, ML4(NCS)2·2G (M = Co(II) and Ni(II), G = nitrobenzene (NB); M = Co, G = 1,2-dichlorobenzene (1,2-DCB); M = Co(II) and Ni(II), G = o-xylene (OX)). 5 was prepd. in high yield by condensation in the solid-state (C3S3, Cocrystal Controlled Solid-State Synthesis). The Werner complexes ML4(NCS)2 (M = Co(II) and Ni(II)) (apohosts) were prepd. by reacting M(NCS)2 (M = Co(II) and Ni(II)) and 5 in 1-butanol at 60° for 24 h. The Werner clathrates were prepd. by reacting M(NCS)2 (M = Co(II) and Ni(II)), G and 5 in 1-butanol at 60° for 48-96 h. The clathrates transform to the apohost ML4(NCS)2 upon heating. CoL4(NCS)2·2NB was subsequently regenerated by exposing CoL4(NCS)2 to liq. NB at 60° for 48 h. This phase change occurred as a single-crystal to single-crystal phase transformation and was studied by single crystal X-ray diffraction, powder X-ray diffraction and thermal analyses. Structural analyses of the apohost CoL4(NCS)2 and its Werner clathrate CoL4(NCS)2·2NB indicated that rotational freedom of the Co-N bonds together with torsional flexibility of the ligand between the imide bond and the pyridine moiety are key to enabling the structural switching induced by exposure to NB or its removal.
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    Cheney, M. L.; McManus, G. J.; Perman, J. A.; Wang, Z.; Zaworotko, M. J. The Role of Cocrystals in Solid-State Synthesis: Cocrystal-Controlled Solid-State Synthesis of Imides. Cryst. Growth Des. 2007, 7 (4), 616– 617,  DOI: 10.1021/cg0701729
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    The Role of Cocrystals in Solid-State Synthesis: Cocrystal-Controlled Solid-State Synthesis of Imides
    Cheney, Miranda L.; McManus, Gregory J.; Perman, Jason A.; Wang, Zhenqiang; Zaworotko, Michael J.
    Crystal Growth & Design (2007), 7 (4), 616-617CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    1,4,5,8-Naphthalenetetracarboxylic dianhydride (I) and arylamines such as 2-methyl-4-nitroaniline and 3-aminobenzoic acid form cocrystals upon grinding of the solids in the presence of a small amt. of solvent; the cocrystals undergo cyclocondensation reactions [cocrystal-controlled solid-state synthesis (C3S3)] upon heating in the solid state to yield imides II (R = Me; R1 = H; R2 = O2N) and II (R = R2 = H; R1 = HO2C) in 75% and 99% yields, resp. The effect of solvent on the formation of either imides or cocrystals of I with arylamines is studied by both IR spectroscopy and by X-ray powder diffraction. Phase transitions of the cocrystals are studied by differential scanning calorimetry. Charge transfer bands are obsd. in the UV/visible spectra of the cocrystals of I with 2-methyl-4-nitroaniline and 3-aminobenzoic acid. Structures for the 1:2 cocrystal of I and 2-methyl-4-nitroaniline, the 1:2:1 cocrystal of I, 3-aminobenzoic acid, and 1,4-dioxane, the mono-DMF solvate of II (R = Me; R1 = H; R2 = O2N), and the 2:5 solvate of II (R = R2 = H; R1 = HO2C) with pyridine are detd. by X-ray crystallog.
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    Sanii, R.; Bajpai, A.; Patyk-Kaźmierczak, E.; Zaworotko, M. J. High Yield, Low-Waste Synthesis of a Family of Pyridyl and Imidazolyl-Substituted Schiff Base Linker Ligands. ACS Sustainable Chem. Eng. 2018, 6 (11), 14589– 14598,  DOI: 10.1021/acssuschemeng.8b03204
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    High Yield, Low-Waste Synthesis of a Family of Pyridyl and Imidazolyl-Substituted Schiff Base Linker Ligands
    Sanii, Rana; Bajpai, Alankriti; Patyk-Kazmierczak, Ewa; Zaworotko, Michael J.
    ACS Sustainable Chemistry & Engineering (2018), 6 (11), 14589-14598CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
    Solid-state synthesis (S3) is an attractive approach to org. synthesis as in principle it offers minimal solvent waste and high yield. However, many functional groups are ill-suited for S3 reactions, which tend to only proceed when substrates are aligned in the solid-state according to the topochem. principle. The aim of this work is to use high yield, low-waste synthetic methods to develop a library of novel Schiff bases that can be used as linker ligands to prep. coordination networks. Herein, the authors report that eight pyridyl- and/or imidazolyl-substituted Schiff bases, five of which are new chem. entities, can be prepd. via reaction of an amine and an aldehyde without the use of solvent. All eight compds. were prepd. via solvent-drop grinding (SDG) in multigram scale in >95% yield and each was characterized by FTIR, 1H and 13C NMR spectroscopies and single crystal x-ray diffraction. One of the aldehydes used is a liq. under ambient conditions so its reactions to form the corresponding Schiff bases are not classified as S3 reactions whereas the other aldehydes are solids and the other four Schiff bases are therefore obtained by S3. The SDG solvents were selected in accordance with guidelines used by industry. Four Schiff bases were also prepd. quant. via addn. of the liq. aldehyde (4-pyridinecarboxaldehyde) to a soln. of the corresponding amine. That the Schiff bases contain functional groups suitable for coordinating with metal cations will enable them to serve as linker ligands in coordination networks as exemplified by one nickel complex, which forms a parallel interpenetrated coordination network with square lattice, sql, topol.
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    Friščić, T.; Trask, A. V.; Jones, W.; Motherwell, W. S. Screening for inclusion compounds and systematic construction of three-component solids by liquid-assisted grinding. Angew. Chem. 2006, 118 (45), 7708– 7712,  DOI: 10.1002/ange.200603235
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    Shan, N.; Toda, F.; Jones, W. Mechanochemistry and co-crystal formation: effect of solvent on reaction kinetics. Chem. Commun. 2002, (20), 2372– 2373,  DOI: 10.1039/b207369m
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    Mechanochemistry and co-crystal formation: effect of solvent on reaction kinetics
    Shan, Ning; Toda, Fumio; Jones, William
    Chemical Communications (Cambridge, United Kingdom) (2002), (20), 2372-2373CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    Significant improvements in kinetics of co-crystal formation by grinding can be achieved by the addn. of minor amts. of appropriate solvent.
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    Solvent-assisted mechanochemistry
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    Chemical Communications (Cambridge, United Kingdom) (2013), 49 (4), 334-348CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A review. The literature on solvent-assisted mechanochem. is reviewed with a view to linking observations concerning the applicability of the technique to theories of its mechanism, and summarizing the advantages and limitations of the technique when applied to a variety of different reaction types. Previously unnoticed links between "solvent-free" and solvent-assisted reaction mechanisms are presented, and reasons why the method should be considered more widely by synthetic chemists are given.
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    Cheney, M. L.; Zaworotko, M. J.; Beaton, S.; Singer, R. D. Cocrystal Controlled Solid-State Synthesis. A Green Chemistry Experiment for Undergraduate Organic Chemistry. J. Chem. Educ. 2008, 85 (12), 1649  DOI: 10.1021/ed085p1649
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    Cocrystal controlled solid-state synthesis. A green chemistry experiment for undergraduate organic chemistry
    Cheney, Miranda L.; Zaworotko, Michael J.; Beaton, Steve; Singer, Robert D.
    Journal of Chemical Education (2008), 85 (12), 1649-1651CODEN: JCEDA8; ISSN:0021-9584. (Journal of Chemical Education, Dept. of Chemistry)
    The article presents expts. that can be adapted to a typical undergraduate org. chem. course easily and are inexpensive, relatively safe, require no solvent (or extremely small quantities of solvent), have high atom economy, make use of non-toxic or low toxicity compds., and generate negligible quantities of waste. The expts. can be accomplished through the use of a new technique known as cocrystal controlled solid-state synthesis, C3S3.
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    Burger, A.; Ramberger, R. On the polymorphism of pharmaceuticals and other molecular crystals. I. Microchim. Acta 1979, 72 (3), 259– 271,  DOI: 10.1007/BF01197379
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    Burger, A.; Ramberger, R. On the polymorphism of pharmaceuticals and other molecular crystals. II. Microchim. Acta 1979, 72 (3), 273– 316,  DOI: 10.1007/BF01197380
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    Burtch, N. C.; Jasuja, H.; Walton, K. S. Water Stability and Adsorption in Metal–Organic Frameworks. Chem. Rev. 2014, 114 (20), 10575– 10612,  DOI: 10.1021/cr5002589
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    Water Stability and Adsorption in Metal-Organic Frameworks
    Burtch, Nicholas C.; Jasuja, Himanshu; Walton, Krista S.
    Chemical Reviews (Washington, DC, United States) (2014), 114 (20), 10575-10612CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review; water stability and adsorption in metal-org. frameworks are discussed.
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    Waterman, K. C.; Huynh-Ba, K. Understanding and Predicting Pharmaceutical Product Shelf-Life. In Handbook of Stability Testing in Pharmaceutical Development: Regulations, Methodologies, and Best Practices; Springer New York: New York, NY, 2009; pp 115– 135.
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    Brouwers, J.; Brewster, M. E.; Augustijns, P. Supersaturating drug delivery systems: the answer to solubility-limited oral bioavailability?. J. Pharm. Sci. 2009, 98 (8), 2549– 2572,  DOI: 10.1002/jps.21650
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    Supersaturating drug delivery systems: The answer to solubility-limited oral bioavailability?
    Brouwers, Joachim; Brewster, Marcus E.; Augustijns, Patrick
    Journal of Pharmaceutical Sciences (2009), 98 (8), 2549-2572CODEN: JPMSAE; ISSN:0022-3549. (Wiley-Liss, Inc.)
    A review. Contemporary pharmaceutical pipelines are often highly populated with poorly water-sol. drug candidates necessitating novel formulation technologies to provide dosage forms with appropriate biopharmaceutical properties. The configuration of supersaturating drug delivery systems (SDDS) is a promising concept to obtain adequate oral bioavailability. SDDS contain the drug in a high energy or otherwise rapidly dissolving form such that intraluminal concns. above the satn. soly. of the drug are generated. For the strategy to be useful, the formed supersatd. soln. must then be stabilized to allow for significant absorption and eventually sufficient bioavailability. The stabilization of a supersatd. soln. can be accomplished by adding pptn. inhibitors which may act through a variety of mechanisms. The goal of this review is to assess methods and excipients assocd. with the development of SDDS and provide some context for their use. In addn., the future directions and factors likely to contribute to or detract from optimal dosage form selection are assessed. This includes a discussion on the potential effect of the gastrointestinal physiol. on the ability to attain and maintain supersatn. as this information is essential in designing useful formulations based on the supersaturating concept. © 2009 Wiley-Liss, Inc. and the American Pharmacists Assocn. J Pharm Sci 98:2549-2572, 2009.
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    Peralta, D.; Chaplais, G.; Paillaud, J.-L.; Simon-Masseron, A.; Barthelet, K.; Pirngruber, G. D. The separation of xylene isomers by ZIF-8: A demonstration of the extraordinary flexibility of the ZIF-8 framework. Microporous Mesoporous Mater. 2013, 173, 1– 5,  DOI: 10.1016/j.micromeso.2013.01.012
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    The separation of xylene isomers by ZIF-8: A demonstration of the extraordinary flexibility of the ZIF-8 framework
    Peralta, David; Chaplais, Gerald; Paillaud, Jean-Louis; Simon-Masseron, Angelique; Barthelet, Karin; Pirngruber, Gerhard D.
    Microporous and Mesoporous Materials (2013), 173 (), 1-5CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Inc.)
    The present work describes the adsorption and sepn. of xylene isomers by ZIF-8. Although the formal pore diam. of ZIF-8 is much smaller than the mol. diam. of the xylene isomers, ZIF-8 is able to sep. the isomers by mol. sieving. A structural study indicates that the diffusion of the xylenes into the pore structure of ZIF-8 happens via a transitory deformation of the pore aperture which is based on a tilt of the imidazolate linkers, followed by a return to the initial conformation. The rate of adsorption depends on the size of the isomer, i.e. it decreases from para- to meta- and to ortho-xylene. The sepn. of the xylene isomers is good in the gas phase. In liq. phase breakthrough expts., the quality of the sepn. is deteriorated. Moreover, as expected for a sepn. based on mol. sieving, para-xylene cannot be well sepd. from ethyl-benzene.
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    Barton, B.; de Jager, L.; Hosten, E. C. Minor modifications afford improved host selectivities in xanthenyl-type host systems. CrystEngComm 2019, 21 (19), 3000– 3013,  DOI: 10.1039/C9CE00265K
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    Minor modifications afford improved host selectivities in xanthenyl-type host systems
    Barton, Benita; de Jager, Lize; Hosten, Eric C.
    CrystEngComm (2019), 21 (19), 3000-3013CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
    In this work, we examine the selectivity of host N,N'-bis(9-phenyl-9-xanthenyl)ethylenediamine in the presence of two different guest series', namely the C8 arom. fraction of crude oil (i.e., ethylbenzene, and o-, m- and p-xylene) and anisoles (anisole, and o-, m- and p-methylanisole). Of the four alkyl aroms., only p-xylene formed a complex with this host when it was recrystd. from each one, while both anisole and p-methylanisole from the second guest series were clathrated in this way. Host : guest ratios were consistently 1 : 1. When this host was recrystd. from various mixts. of the solvents from the two guest groups, an unequivocal bias towards p-xylene and p-methylanisole, resp., was obsd., with the other competing guests essentially being excluded from the host crystal in these expts. Furthermore, this host displayed significantly enhanced selectivities relative to the structurally-related compd., N,N'-bis(9-phenyl-9-thioxanthenyl)ethylenediamine, in the presence of the xylenes and ethylbenzene, when considering a previous report. The latter compd. was also assessed for inclusion behavior in the presence of the anisoles and, once more, its inferior selectivity compared with the oxo-host counterpart was strikingly evident. Both single crystal X-ray diffraction and thermal expts. were conducted in order to investigate the noted selectivity differences.
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    Gee, J. A.; Zhang, K.; Bhattacharyya, S.; Bentley, J.; Rungta, M.; Abichandani, J. S.; Sholl, D. S.; Nair, S. Computational Identification and Experimental Evaluation of Metal–Organic Frameworks for Xylene Enrichment. J. Phys. Chem. C 2016, 120 (22), 12075– 12082,  DOI: 10.1021/acs.jpcc.6b03349
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    Computational Identification and Experimental Evaluation of Metal-Organic Frameworks for Xylene Enrichment
    Gee, Jason A.; Zhang, Ke; Bhattacharyya, Souryadeep; Bentley, Jason; Rungta, Meha; Abichandani, Jeevan S.; Sholl, David S.; Nair, Sankar
    Journal of Physical Chemistry C (2016), 120 (22), 12075-12082CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    We report the computational discovery and exptl. evaluation of nanoporous materials targeted at the adsorptive sepn. of p-xylene from a C8 aroms. mixt. We first introduce a computational method that is capable of efficiently predicting the p-xylene selectivities and capacities for a large database of porous materials. We then demonstrate the application of this method to screen a database of several thousand metal-org. framework (MOF) structures. Our computational screening methodol. predicted that two MOFs with good solvothermal stability and com. available linkers give comparable performance to the state-of-the-art zeolite BaX currently used in industrial p-xylene sepns. The best-performing MOFs are then synthesized, and their xylene sepn. characteristics are evaluated in detail through breakthrough adsorption expts. and modeling. We find that the selectivities obtained in these materials are higher than that of any MOF previously reported in the literature and in some cases exceed the measured performance of zeolite BaX. In the case of the p-xylene selective material MOF-48, we use calcd. free energy profiles to show how the presence of Me substituents on the linkers allows the inversion of selectivity from the equiv. MOF with no Me substituents (MIL-47, which is o-xylene selective). This combined computational and exptl. methodol. is a useful step in the development of MOFs for sepn. of arom. hydrocarbons and can also be applied to other chem. sepns. and other classes of porous materials as long as the appropriate intermol. force fields are available.
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    Wang, J.-Y.; Mangano, E.; Brandani, S.; Ruthven, D. M. A review of common practices in gravimetric and volumetric adsorption kinetic experiments. Adsorption 2021, 27 (3), 295– 318,  DOI: 10.1007/s10450-020-00276-7
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    A review of common practices in gravimetric and volumetric adsorption kinetic experiments
    Wang, Jin-Yu; Mangano, Enzo; Brandani, Stefano; Ruthven, Douglas M.
    Adsorption (2021), 27 (3), 295-318CODEN: ADSOFO; ISSN:0929-5607. (Springer)
    Abstr.: The availability of com. gravimetric and volumetric systems for the measurement of adsorption equil. has seen also a growth of the use of these instruments to measure adsorption kinetics. A review of publications from the past 20 years has been used to assess common practice in 180 cases. There are worrying trends obsd., such as lack of information on the actual conditions used in the expt. and the fact that the anal. of the data is often based on models that do not apply to the exptl. systems used. To provide guidance to users of these techniques this contribution is divided into two parts: a discussion of the appropriate models to describe diffusion in porous materials is presented for different gravimetric and volumetric systems, followed by a structured discussion of the main trends in common practice uncovered reviewing a large no. of recent publications. We conclude with recommendations for best practice to avoid incorrect interpretation of these expts.
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    Bezrukov, A. A.; O’Hearn, D. J.; Gascón-Pérez, V.; Darwish, S.; Kumar, A.; Sanda, S.; Kumar, N.; Francis, K.; Zaworotko, M. J. Metal-organic frameworks as regeneration optimized sorbents for atmospheric water harvesting. Cell Rep. Phys. Sci. 2023, 4 (2), 101252  DOI: 10.1016/j.xcrp.2023.101252
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    Metal-organic frameworks as regeneration optimized sorbents for atmospheric water harvesting
    Bezrukov, Andrey A.; O'Hearn, Daniel J.; Gascon-Perez, Victoria; Darwish, Shaza; Kumar, Amrit; Sanda, Suresh; Kumar, Naveen; Francis, Kurt; Zaworotko, Michael J.
    Cell Reports Physical Science (2023), 4 (2), 101252CODEN: CRPSF5; ISSN:2666-3864. (Elsevier Inc.)
    As the freshwater crisis looms, metal-org. frameworks (MOFs) with stepped isotherms lie at the forefront of desiccant development for atm. water harvesting (AWH). Despite numerous studies on water sorption kinetics in MOF desiccants, the kinetics of AWH sorbents are a challenge to quantify. Here, we report that the AWH kinetics of seven known MOFs and the industry-std. desiccant Syloid are limited by diffusion to the sorbent bed surface. A quant. model that exploits isotherm shape enables simulation of sorption cycling to evaluate sorbent performance through productivity contour plots ("heatmaps"). These heatmaps reveal two key findings: steady-state oscillation around partial loading optimizes productivity, and dense ultramicroporous MOFs with a step at low relative humidity afford superior volumetric performance under practically relevant temp. swing conditions (27°C, 30% relative humidity [RH] - 60°C, 5.4% RH). Cellulose-desiccant composites of two such regeneration optimized sorbents retain the kinetics of powders, producing up to 7.3 L/kg/day of water under these conditions.
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    Snurr, R. Q.; Bell, A. T.; Theodorou, D. N. Prediction of adsorption of aromatic hydrocarbons in silicalite from grand canonical Monte Carlo simulations with biased insertions. J. Phys. Chem. A 1993, 97 (51), 13742– 13752,  DOI: 10.1021/j100153a051
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    Prediction of adsorption of aromatic hydrocarbons in silicalite from grand canonical Monte Carlo simulations with biased insertions
    Snurr, Randall Q.; Bell, Alexis T.; Theodorou, Doros N.
    Journal of Physical Chemistry (1993), 97 (51), 13742-52CODEN: JPCHAX; ISSN:0022-3654.
    Adsorption isotherms and isosteric heats of adsorption for benzene and p-xylene in silicalite have been calcd. from mol. simulations. The simulations were performed using newly developed grand canonical ensemble Monte Carlo (GCMC) techniques in which insertion attempts are biased toward the most favorable regions of the zeolite pore space. The new techniques result in a substantial improvement in the efficiency of the simulations compared to traditional GCMC. The adsorption thermodn. and mol.-level structure were studied for benzene and p-xylene in silicate with Pnma symmetry (ORTHO) and P212121 symmetry (PARA). The subtle differences between ORTHO and PARA silicate result in qual. different sorption behavior. An explanation of the exptl. obsd. step in the adsorption isotherm is presented, based on the results of the simulations and the ORTHO to PARA framework transformation that is obsd. exptl. Prediction of the adsorption isotherms, isosteric heats, and siting locations of the adsorbates are in good agreement with expt.
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    Torres-Knoop, A.; Krishna, R.; Dubbeldam, D. Separating Xylene Isomers by Commensurate Stacking of p-Xylene within Channels of MAF-X8. Angew. Chem., Int. Ed. 2014, 53 (30), 7774– 7778,  DOI: 10.1002/anie.201402894
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    Separating Xylene Isomers by Commensurate Stacking of p-Xylene within Channels of MAF-X8
    Torres-Knoop, Ariana; Krishna, Rajamani; Dubbeldam, David
    Angewandte Chemie, International Edition (2014), 53 (30), 7774-7778CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The development of energy-efficient processes for selective sepn. of p-xylene from mixts. with its isomers is of vital importance in the petrochem. industries. Current industrial practice uses BaX zeolite that has high adsorption selectivity for p-xylene. Finding para-selective structures is challenging. With state-of-the-art simulation methodologies the authors systematically screened a wide variety of zeolites and metal-org. frameworks (MOFs). The authors' studies highlight the crucial importance of the channel dimension on the sepn. MAF-X8 is particularly noteworthy because the channel dimensions and geometry allow commensurate stacking which the authors exploit as a sepn. mechanism at satn. conditions. Due to a significantly improved capacity compared to BaX, the cycle times for p-xylene with MAF-X8 are about a factor of 4.5 longer. This is expected to result in significant process improvements.
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    Yan, H.; Quan, J.; Qu, H.; Zhu, F.; Wang, Y.; Dhinakaran, M. K.; Han, T.; Li, H. Membranes with Nanochannels Based on Pillar[6]arenes to Separate Xylenes. ACS Appl. Nano Mater. 2022, 5 (12), 18637– 18644,  DOI: 10.1021/acsanm.2c04408
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    Membranes with Nanochannels Based on Pillar[6]arenes to Separate Xylenes
    Yan, Hewei; Quan, Jiaxin; Qu, Haonan; Zhu, Fei; Wang, Yingqian; Dhinakaran, Manivannan Kalavathi; Han, Ting; Li, Haibing
    ACS Applied Nano Materials (2022), 5 (12), 18637-18644CODEN: AANMF6; ISSN:2574-0970. (American Chemical Society)
    Membrane sepn. technol. has been widely applied in material sepn. fields. However, it still has the disadvantage of poor selectivity at nanometer and sub-nanometer scales. Here, two kinds of pillar[6]arene with opposite charges were prepd. by modification, and the aligned nanochannel composite membrane was successfully constructed by directional assembly on a neg. charged silicon interface. The precise sieving properties of aligned channels were studied using the xylene isomer as a model mol. It has been proved that the aligned channel can better maintain the pore size close to the macrocyclic mols., which is beneficial to realize the customized construction of the through-ordered nanochannel. The exptl. results show that the aligned nanochannel can selectively transport xylene isomers, and the flux (J) values of o, m, and p-xylene were 9.2, 11.6, and 171.3 nM m-2 h-1, resp. Finally, the sepn. and purifn. of mixed samples have been achieved. This method provides a strategy for constructing ordered nanochannels.
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  • Abstract

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    Figure 1

    Figure 1. Synthesis of TPBD-αI via solid-state synthesis.

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    Figure 2

    Figure 2. (a) Solvent and temperature-mediated conformational polymorphism of TPBD. (a) Illustration of the formation of TPBD-αII from the recrystallization of TPBD-αI in DMF or DCM and subsequent recovery of TPBD-αI by heating. (b) VT-PXRD indicates that conversion of TPBD-αII to TPBD-αI occurs after heating to temperatures ≥200 °C and that this structure is maintained when cooled to 25 °C.

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    Figure 3

    Figure 3. (a) Interconversion of TPBD-αI, TPBD-αII, and TPBD-PX; (b) VT-PXRD study of TPBD-PX reveals transformation to TPBD-αI upon heating.

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    Figure 4

    Figure 4. (a) Comparison of nonporous (●) and porous (⧫) absorbents for PX separation from ternary and quaternary mixtures. The experimental conditions may vary, like temperature and composition (E: equimolar, NE: nonequimolar mixture). (b) Gas chromatograms used to quantify the composition of TPBD crystals exposed to pure C8 isomers or approximately equimolar mixtures of C8 isomers at RT.

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    Figure 5

    Figure 5. (a, b) Separation performance of TPBD-αI and TPBD-αII upon exposure to equimolar ternary and quaternary mixture of C8 isomers at 293 K. (c) TPBD-αI recyclability after 11 consecutive cycles of PX enclathration/release. (d) Asymmetric unit and crystal packing of TPBD-PX.

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    Figure 6

    Figure 6. Illustration depicting the arrangement of PX molecules in TPBD-PX, highlighting that multiple C–H···π interactions occur in the yellow area, along with CH···O interactions (PX guest molecules are purple).

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      Nicolau, M. P. M.; Bárcia, P. S.; Gallegos, J. M.; Silva, J. A. C.; Rodrigues, A. E.; Chen, B. Single- and Multicomponent Vapor-Phase Adsorption of Xylene Isomers and Ethylbenzene in a Microporous Metal–Organic Framework. J. Phys. Chem. C 2009, 113 (30), 13173– 13179,  DOI: 10.1021/jp9006747
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      Single- and Multicomponent Vapor-Phase Adsorption of Xylene Isomers and Ethylbenzene in a Microporous Metal-Organic Framework
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      Vapor-phase adsorption of the C8 alkylarom. components p-xylene (p-x), m-xylene (m-x), o-xylene (o-x), and ethylbenzene (eb) on the three-dimensional microporous metal-org. framework (MOF) Zn(BDC)(Dabco)0.5 (BDC = 1,4-benzenedicarboxylate, Dabco = 1,4-diazabicyclo[2.2.2]octane) was studied. Single- and multicomponent fixed-bed expts. were carried out at 125-175° and total hydrocarbon pressures up to 0.10 bar. At high pressure, the adsorption capacity for all the components varies from 35 to 26 g/100 gads at 125 and 175°. Henry's consts. are slightly different for all C8 alkylaroms., except for o-xylene, which is significantly higher. The adsorption enthalpies at zero coverage for the different isomers ranges from 77.40 (eb) to 79.84 kJ/mol (o-x), indicating that the C8 alkylaroms. have comparable interactions with the framework at the low coverage. From binary and quaternary breakthrough expts. performed at different hydrocarbon pressures and temps., MOF Zn(BDC)(Dabco)0.5 was realized for the efficient and feasible sepn. of o-xylene from other C8 alkylarom. components with the selectivity up to 1.88 because of the stronger interactions between o-xylene mols. and the framework and their differential pore-filling and mol.-packing effects confined within nanopores of MOFs.
      >> More from SciFinder ®
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    12. 12
      Kim, S.-I.; Lee, S.; Chung, Y. G.; Bae, Y.-S. The Origin of p-Xylene Selectivity in a DABCO Pillar-Layered Metal–Organic Framework: A Combined Experimental and Computational Investigation. ACS Appl. Mater. Interfaces 2019, 11 (34), 31227– 31236,  DOI: 10.1021/acsami.9b11343
      12
      Origin of p-xylene selectivity in a DABCO pillar-layered metal-organic framework: Combined experimental and computational investigation
      Kim, Seung-Ik; Lee, Seulchan; Chung, Yongchul G.; Bae, Youn-Sang
      ACS Applied Materials & Interfaces (2019), 11 (34), 31227-31236CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      We report high exptl. p-xylene (pX) selectivity in a pillar-layered metal-org. framework, DUT-8(Cu). Vapor- and liq.-phase adsorption expts. were carried out to confirm high pX selectivity and large pX uptakes in DUT-8(Cu). Grand canonical Monte Carlo simulation results show that the presence of DABCO ligands allows for the packing of pX mols. and is responsible for the pX selective nature of the material. The simulation also suggests that the presence of isooctane solvents in the liq.-phase expts. plays an essential role by lowering the adsorption of other xylene isomers, and leads to increased pX selectivity in the liq.-phase as compared to the vapor phase. D. functional theory simulations show that the preferential arrangement is due to the preferential adsorption of pX on the DABCO ligand and the preferential adsorption of isooctane over other xylene isomers.
      >> More from SciFinder ®
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    13. 13
      Bae, H. J.; Kim, S.-I.; Choi, Y.; Kim, K.-M.; Bae, Y.-S. High p-xylene selectivity in aluminum-based metal–organic framework with 1-D channels. J. Ind. Eng. Chem. 2023, 117, 333– 341,  DOI: 10.1016/j.jiec.2022.10.021
      13
      High p-xylene selectivity in aluminum-based metal-organic framework with 1-D channels
      Bae, Hyun Jin; Kim, Seung-Ik; Choi, Yujin; Kim, Kyung-Min; Bae, Youn-Sang
      Journal of Industrial and Engineering Chemistry (Amsterdam, Netherlands) (2023), 117 (), 333-341CODEN: JIECFI; ISSN:1226-086X. (Elsevier B.V.)
      The sepn. of highly pure p-xylene (pX) from xylene isomers is an industrially important and challenging issue. Although simulated moving bed (SMB) processes using faujasite zeolites are currently used for pX sepn., developing novel adsorbents with improved pX sepn. performances is strongly needed. In this study, an aluminum-based metal-org. framework (MOF), MIL-120(Al) with 1-D channels of approx. 7 Å , exhibited considerably high pX selectivities compared to xylene isomers (αpX/oX: 31; αpX/mX: 17; αpX/EB: 7.5; αpX/OME: 11), which are superior to reported values for other MOFs and zeolites under similar conditions. Such high selectivities may originate from the proper pore shape and size of MIL-120(Al). MIL-120(Al) also showed good cyclic adsorption properties as well as superior hydrothermal and chem. stabilities. Finally, a dynamic simulation showed that MIL-120(Al) could achieve approx. complete sepn. of pX from a xylene isomer mixt. using an SMB process.
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    14. 14
      Cui, W.-G.; Hu, T.-L.; Bu, X.-H. Metal–Organic Framework Materials for the Separation and Purification of Light Hydrocarbons. Adv. Mater. 2020, 32 (3), 1806445  DOI: 10.1002/adma.201806445
      14
      Metal-Organic Framework Materials for the Separation and Purification of Light Hydrocarbons
      Cui, Wen-Gang; Hu, Tong-Liang; Bu, Xian-He
      Advanced Materials (Weinheim, Germany) (2020), 32 (3), 1806445CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. The sepn. and purifn. of light hydrocarbons (LHs) mixts. is one of the most significantly important but energy demanding processes in the petrochem. industry. As an alternative technol. to energy intensive traditional sepn. methods, such as distn., absorption, extn., etc., adsorptive sepn. using selective solid adsorbents could potentially not only lower energy cost but also offer higher efficiency. The need to develop solid materials for the efficiently selective adsorption of LHs mols., under mild conditions, is therefore of paramount importance and urgency. Metal-org. frameworks (MOFs), emerging as a relatively new class of porous org.-inorg. hybrid materials, have shown promise for addressing this challenging task due to their unparalleled features. Herein, recent advances of using MOFs as sepg. agents for the sepn. and purifn. of LHs, including the purifn. of CH4, and the sepns. of alkynes/alkenes, alkanes/alkenes, C5-C6-C7 normal/isoalkanes, and C8 alkylaroms., are summarized. The relationships among the structural and compositional features of the newly synthesized MOF materials and their sepn. properties and mechanisms are highlighted. Finally, the existing challenges and possible research directions related to the further exploration of porous MOFs in this very active field are also discussed.
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    15. 15
      Wang, S.-Q.; Mukherjee, S.; Zaworotko, M. J. Spiers Memorial Lecture: Coordination networks that switch between nonporous and porous structures: an emerging class of soft porous crystals. Faraday Discuss. 2021, 231, 9– 50,  DOI: 10.1039/D1FD00037C
      15
      Spiers Memorial Lecture: Coordination networks that switch between nonporous and porous structures: an emerging class of soft porous crystals
      Wang, Shi-Qiang; Mukherjee, Soumya; Zaworotko, Michael J.
      Faraday Discussions (2021), 231 (MOFs for Energy and the Environment), 9-50CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
      Coordination networks (CNs) are a class of (usually) cryst. solids typically comprised of metal ions or cluster nodes linked into 2 or 3 dimensions by org. and/or inorg. linker ligands. Whereas CNs tend to exhibit rigid structures and permanent porosity as exemplified by most metal-org. frameworks, MOFs, there exists a small but growing class of CNs that can undergo extreme, reversible structural transformation(s) when exposed to gases, vapors or liqs. These "soft" or "stimuli-responsive" CNs were introduced two decades ago and are attracting increasing attention thanks to two features: the amenability of CNs to design from first principles, thereby enabling crystal engineering of families of related CNs; and the potential utility of soft CNs for adsorptive storage and sepn. A small but growing subset of soft CNs exhibit reversible phase transformations between nonporous (closed) and porous (open) structures. These "switching CNs" are distinguished by stepped sorption isotherms coincident with phase transformation and, perhaps counterintuitively, they can exhibit benchmark properties with respect to working capacity (storage) and selectivity (sepn.). This review addresses fundamental and applied aspects of switching CNs through surveying their sorption properties, analyzing the structural transformations that enable switching, discussing structure-function relationships and presenting design principles for crystal engineering of the next generation of switching CNs.
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    16. 16
      Schneemann, A.; Bon, V.; Schwedler, I.; Senkovska, I.; Kaskel, S.; Fischer, R. A. Flexible metal–organic frameworks. Chem. Soc. Rev. 2014, 43 (16), 6062– 6096,  DOI: 10.1039/C4CS00101J
      16
      Flexible metal-organic frameworks
      Schneemann, A.; Bon, V.; Schwedler, I.; Senkovska, I.; Kaskel, S.; Fischer, R. A.
      Chemical Society Reviews (2014), 43 (16), 6062-6096CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Advances in flexible and functional metal-org. frameworks (MOFs), also called soft porous crystals, are reviewed by covering the literature of the five years period 2009-2013 with ref. to the early pertinent work since the late 1990s. Flexible MOFs combine the cryst. order of the underlying coordination network with cooperative structural transformability. These materials can respond to phys. and chem. stimuli of various kinds in a tunable fashion by mol. design, which does not exist for other known solid-state materials. Among the fascinating properties are so-called breathing and swelling phenomena as a function of host-guest interactions. Phase transitions are triggered by guest adsorption/desorption, photochem., thermal, and mech. stimuli. Other important flexible properties of MOFs, such as linker rotation and sub-net sliding, which are not necessarily accompanied by crystallog. phase transitions, are briefly mentioned as well. Emphasis is given on reviewing the recent progress in application of in situ characterization techniques and the results of theor. approaches to characterize and understand the breathing mechanisms and phase transitions. The flexible MOF systems, which are discussed, are categorized by the type of metal-nodes involved and how their coordination chem. with the linker mols. controls the framework dynamics. Aspects of tailoring the flexible and responsive properties by the mixed component solid-soln. concept are included, and as well examples of possible applications of flexible metal-org. frameworks for sepn., catalysis, sensing, and biomedicine.
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    17. 17
      Chang, Z.; Yang, D.-H.; Xu, J.; Hu, T.-L.; Bu, X.-H. Flexible Metal–Organic Frameworks: Recent Advances and Potential Applications. Adv. Mater. 2015, 27 (36), 5432– 5441,  DOI: 10.1002/adma.201501523
      17
      Flexible Metal-Organic Frameworks: Recent Advances and Potential Applications
      Chang, Ze; Yang, Dong-Hui; Xu, Jian; Hu, Tong-Liang; Bu, Xian-He
      Advanced Materials (Weinheim, Germany) (2015), 27 (36), 5432-5441CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Flexible metal-org. frameworks (MOFs) receive much attention owing to their attractive properties that originate from their flexibility and dynamic behavior, and show great potential applications in many fields. Here, recent progress in the discovery, understanding, and property studies of flexible MOFs are reviewed, and the examples of their potential applications in storage and sepn., sensing, and guest capture and release are presented to highlight the developing trends in flexible MOFs.
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    18. 18
      Mukherjee, S.; Joarder, B.; Manna, B.; Desai, A. V.; Chaudhari, A. K.; Ghosh, S. K. Framework-Flexibility Driven Selective Sorption of p-Xylene over Other Isomers by a Dynamic Metal-Organic Framework. Sci. Rep. 2014, 4 (1), 5761  DOI: 10.1038/srep05761
      18
      Framework-Flexibility Driven Selective Sorption of p-Xylene over Other Isomers by a Dynamic Metal-Organic Framework
      Mukherjee, Soumya; Joarder, Biplab; Manna, Biplab; Desai, Aamod V.; Chaudhari, Abhijeet K.; Ghosh, Sujit K.
      Scientific Reports (2014), 4 (), 5761CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      Chem. sepn. has great importance in industrial applications. Sepn. of xylene isomers still prevails to be one of the most important challenges in chem. industry, due to the large amt. of com. use of p-xylene in the prodn. of beverage bottles, fibers and films. A novel Zn(II)-based dynamic coordination framework based on flexible ether-linkage, exhibiting selective adsorption of p-Xylene over its congener C8-alkyl arom. isomers at ambient conditions is reported. Notably, no dynamic structure based MOF compd. is known in the literature which shows clear preference of p-xylene over other isomers. This type of framework-breathing and guest-induced reversible solid-state structural transformations with unique adsorption selectivity can be exploited purposefully to develop smart functional host materials capable of industrially important chem. sepns.
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    19. 19
      Yang, X.; Zhou, H.-L.; He, C.-T.; Mo, Z.-W.; Ye, J.-W.; Chen, X.-M.; Zhang, J.-P. Flexibility of Metal-Organic Framework Tunable by Crystal Size at the Micrometer to Submillimeter Scale for Efficient Xylene Isomer Separation. Research 2019, 2019, 9463719  DOI: 10.34133/2019/9463719
      19
      Flexibility of metal-organic framework tunable by crystal size at the micrometer to submillimeter scale for efficient xylene isomer separation
      Yang, Xiao; Zhou, Hao-Long; He, Chun-Ting; Mo, Zong-Wen; Ye, Jia-Wen; Chen, Xiao-Ming; Zhang, Jie-Peng
      Research (Washington, DC, United States) (2019), 2019 (), 9463719CODEN: RESECF; ISSN:2639-5274. (American Association for the Advancement of Science)
      Understanding, controlling, and utilizing the flexibility of adsorbents are of great importance and difficulty. Analogous with conventional solid materials, downsizing to the nanoscale is emerging as a possible strategy for controlling the flexibility of porous coordination polymers (or metal-org. frameworks). We report a unique flexibility controllable by crystal size at the micrometer to submillimeter scale. Template removal transforms [Cu2(pypz)2] ·0.5p-xylene (MAF-36, Hpypz=4-(1H-pyrazol-4-yl)pyridine) with one-dimensional channels to α-[Cu2(pypz)2] with discrete small cavities, and further heating gives a nonporous isomer β-[Cu2(pypz)2]. Both isomers can adsorb p-xylene to give [Cu2(pypz)2] ·0.5p-xylene, meaning the coexistence of guest-driven flexibility and shape-memory behavior. The phase transition temp. from α-[Cu2(pypz)2] to β-[Cu2(pypz)2] decreased from ~ 270 °C to ~ 150°C by increasing the crystal size from the micrometer to the submillimeter scale, ca. 2-3 orders larger than those of other size-dependent behaviors. Single-crystal X-ray diffraction showed coordination bond reconstitution and chirality inversion mechanisms for the phase transition, which provides a sufficiently high energy barrier to stabilize the metastable phase without the need of downsizing to the nanoscale. By virtue of the cryst. mol. imprinting and gate-opening effects, α-[Cu2(pypz)2] and β-[Cu2(pypz)2] show unprecedentedly high p-xylene selectivities of 16 and 51, resp., as well as ultrafast adsorption kinetics (<2minutes), for xylene isomers.
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    20. 20
      Ye, Z.-M.; Zhang, X.-F.; Liu, D.-X.; Xu, Y.-T.; Wang, C.; Zheng, K.; Zhou, D.-D.; He, C.-T.; Zhang, J.-P. A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation. Sci. China Chem. 2022, 65 (8), 1552– 1558,  DOI: 10.1007/s11426-022-1304-1
      20
      A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation
      Ye, Zi-Ming; Zhang, Xue-Feng; Liu, De-Xuan; Xu, Yan-Tong; Wang, Chao; Zheng, Kai; Zhou, Dong-Dong; He, Chun-Ting; Zhang, Jie-Peng
      Science China: Chemistry (2022), 65 (8), 1552-1558CODEN: SCCCCS; ISSN:1869-1870. (Springer International Publishing AG)
      Adsorptive sepn. of p-xylene (pX) from xylene isomers is a key process in chem. industry, but known adsorbents cannot simultaneously achieve high adsorption selectivity, capacity, and rate. Here, we demonstrate gating ultramicropore as a soln. for this challenge. Slight modification of the synthetic condition gives rise to isomeric metal-org. frameworks α-[Zn(pba)] (MAF-88, H2pba = 4-(1H-pyrazol-4-yl)benzoic acid) and β-[Zn(pba)] (MAF-89) possessing similar pillared-column structures, porosities, and high pX capacities of 2.0 mmol g-1, but very different framework/pore topologies, pore sizes, and pX selectivities. For binary and ternary mixts. of liq. xylene isomers, MAF-88 with narrow one-dimensional (1D) channels shows pX selectivity of 11 and 1.6, while MAF-89 with 3D-connected quasi-discrete pores shows pX selectivity up to 221 and 46, resp. Thermogravimetry, differential scanning calorimetry, and time-dependent sepn. expts. reveal that the kinetic effects of the gating pores play more important roles than the thermodn. effects, which is further confirmed by single-crystal X-ray diffraction and computational simulations.
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    21. 21
      Sapianik, A. A.; Dudko, E. R.; Kovalenko, K. A.; Barsukova, M. O.; Samsonenko, D. G.; Dybtsev, D. N.; Fedin, V. P. Metal–Organic Frameworks for Highly Selective Separation of Xylene Isomers and Single-Crystal X-ray Study of Aromatic Guest–Host Inclusion Compounds. ACS Appl. Mater. Interfaces 2021, 13 (12), 14768– 14777,  DOI: 10.1021/acsami.1c02812
      21
      Metal-Organic Frameworks for Highly Selective Separation of Xylene Isomers and Single-Crystal X-ray Study of Aromatic Guest-Host Inclusion Compounds
      Sapianik, Aleksandr A.; Dudko, Evgeny R.; Kovalenko, Konstantin A.; Barsukova, Marina O.; Samsonenko, Denis G.; Dybtsev, Danil N.; Fedin, Vladimir P.
      ACS Applied Materials & Interfaces (2021), 13 (12), 14768-14777CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Sepn. of hydrocarbon mols., such as benzene/cyclohexane and o-xylene/m-xylene/p-xylene, is relevant due to their widespread application as chem. feedstock but challenging because of their similar b.ps. and close mol. sizes. Physisorption sepn. could offer an energy-efficient soln. to this problem, but the design and synthesis of sorbents that exhibit high selectivity for one of the hydrocarbons remain a largely unmet challenge. Herein, we report a new heterometallic MOF with a unique tortuous shape of channels decorated with arom. sorption sites [Li2Zn2(bpy)(ndc)3] (NIIC-30(Ph), bpy = 4,4'-bipyridine, ndc2- = naphthalene-1,4-dicarboxylate) and study of its benzene/cyclohexane and xylene vapor and liq. sepn. For an equimolar benzene/cyclohexane mixt., it is possible to achieve a 10-fold excess of benzene in the adsorbed phase. In the case of xylenes, microporous framework NIIC-30(Ph) demonstrates outstanding selective sorption properties and becomes a new benchmark for m-/o-xylene sepn. In addn., NIIC-30(Ph) is stable enough to carry out at least three sepn. cycles of benzene/cyclohexane mixts. or ternary o-xylene/m-xylene/p-xylene mixts. both in the liq. and in the vapor phase. Insights into the performance of NIIC-30(Ph) are gained from X-ray structural studies of each arom. guest inclusion compd.
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    22. 22
      Polyukhov, D. M.; Poryvaev, A. S.; Sukhikh, A. S.; Gromilov, S. A.; Fedin, M. V. Fine-Tuning Window Apertures in ZIF-8/67 Frameworks by Metal Ions and Temperature for High-Efficiency Molecular Sieving of Xylenes. ACS Appl. Mater. Interfaces 2021, 13 (34), 40830– 40836,  DOI: 10.1021/acsami.1c12166
      22
      Fine-Tuning Window Apertures in ZIF-8/67 Frameworks by Metal Ions and Temperature for High-Efficiency Molecular Sieving of Xylenes
      Polyukhov, Daniil M.; Poryvaev, Artem S.; Sukhikh, Aleksandr S.; Gromilov, Sergey A.; Fedin, Matvey V.
      ACS Applied Materials & Interfaces (2021), 13 (34), 40830-40836CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Sepn. of structurally similar components from their mixts. is one of the most promising applications of metal-org. frameworks (MOFs). A high efficiency of such mol. sieving requires fine tuning of the MOF structure. In this work, we investigate subtle metal- and temp.-induced changes in window dimensions of zeolitic imidazolate frameworks (ZIF-8(Zn) and ZIF-67(Co)) and apply such structural tuning for efficient sepn. of xylene isomers (p-, m-, and o-xylenes). The use of Co instead of Zn favorably modifies window geometry: it accelerates the diffusion of all components by a factor of 2-3 while maintaining closely the same sepn. efficiency as that of ZIF-8(Zn). Outstanding selectivity above 18:1 and faster isolation of demanded p-xylene from the ternary mixt. using ZIF-67(Co) have been demonstrated at room temp., opening new horizons for its energy-efficient xylene sepn. More generally, our findings suggest the prospective ways to tune various MOFs for target liq.-state sepns.
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    23. 23
      Polyukhov, D. M.; Poryvaev, A. S.; Gromilov, S. A.; Fedin, M. V. Precise Measurement and Controlled Tuning of Effective Window Sizes in ZIF-8 Framework for Efficient Separation of Xylenes. Nano Lett. 2019, 19 (9), 6506– 6510,  DOI: 10.1021/acs.nanolett.9b02730
      23
      Precise Measurement and Controlled Tuning of Effective Window Sizes in ZIF-8 Framework for Efficient Separation of Xylenes
      Polyukhov, Daniil M.; Poryvaev, Artem S.; Gromilov, Sergey A.; Fedin, Matvey V.
      Nano Letters (2019), 19 (9), 6506-6510CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Metal-org. frameworks (MOFs) are the promising nanomaterials for sepn. of mols. with close dimensions and structures, such as various types of isomers. The efficiency of sepn. can be greatly enhanced if the apertures of the nanosized windows, controlling the diffusion of a particular mol. inside the cavities, are fine-tuned by external stimuli. The authors report the new approach for precise measurement of window sizes in ZIF-8 MOF and employ it in efficient sepn. of xylenes, which is of high practical importance. For this sake, the authors synthesized ZIF-8 with embedded stable nitroxides in the pores and applied ESR spectroscopy for in situ kinetic measurement of the diffusion of various guest mols. through the material. Slight variation of temp. within 298-333 K allowed tuning of the windows and reaching optimum conditions for sepn. of p-, m-, and o-xylenes with the efficiency up to 92-95%. The developed methodol. provides deeper understanding of steric and kinetic aspects of mol. diffusion in ZIF-8 and paves the way to rational optimization of other MOF-based sepn. applications.
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    24. 24
      Mukherjee, S.; Desai, A. V.; Ghosh, S. K. Potential of metal–organic frameworks for adsorptive separation of industrially and environmentally relevant liquid mixtures. Coord. Chem. Rev. 2018, 367, 82– 126,  DOI: 10.1016/j.ccr.2018.04.001
      24
      Potential of metal-organic frameworks for adsorptive separation of industrially and environmentally relevant liquid mixtures
      Mukherjee, Soumya; Desai, Aamod V.; Ghosh, Sujit K.
      Coordination Chemistry Reviews (2018), 367 (), 82-126CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
      Metal-org. frameworks (MOFs) or porous coordination polymers (PCPs) are defined as cryst., open, coordination network architectures with potential voids. They have drawn momentous attention across several crossroads of material chem. since their discovery, owing to an exciting plethora of application-oriented footprints left by this class of supramol. network solids. The unmatched aspect of tunable coordination nanospace arising from the countless choice of pre-functionalized org. struts pertaining to varying lengths alongside multivariate coordination geometries/oxidn. states of the metal nodes, bestows a distinct chem. tailorability facet to this class of porous materials. Amidst the two-decade long attention dedicated to the adsorption-governed purifn. of gases, the MOF literature has substantially expanded its horizon into the manifestation of industrially relevant liq. mixts.' adsorptive sepn.-driven purifn. Such chem. sepn. phenomena categorically encompasses high importance to the manufg. and processing industry sectors, apart from the fundamental scientific pursuit of discovering novel physicochem. principles. Aimed at the energy-economic prepn. of pure industrial feedstocks and their consequent usage as end products, structure-property correlations pursued in the alleys of coordination chem. has led to major advancements in a no. of crit. sepn. frontiers, inclusive of biofuels (alc./water), diverse hydrocarbon mixts., and chiral species. This comprehensive review summarizes the topical developments accrued in the field of MOF based liq. mixts.' adsorptive sepn. phenomena, structure-selectivity relationships as well as the assocd. plausible mechanisms substantiating such behavior.
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    25. 25
      Vermoortele, F.; Maes, M.; Moghadam, P. Z.; Lennox, M. J.; Ragon, F.; Boulhout, M.; Biswas, S.; Laurier, K. G. M.; Beurroies, I.; Denoyel, R.; Roeffaers, M.; Stock, N.; Düren, T.; Serre, C.; De Vos, D. E. p-Xylene-Selective Metal–Organic Frameworks: A Case of Topology-Directed Selectivity. J. Am. Chem. Soc. 2011, 133 (46), 18526– 18529,  DOI: 10.1021/ja207287h
      25
      p-Xylene-Selective Metal-Organic Frameworks: A Case of Topology-Directed Selectivity
      Vermoortele, Frederik; Maes, Michael; Moghadam, Peyman Z.; Lennox, Matthew J.; Ragon, Florence; Boulhout, Mohammed; Biswas, Shyam; Laurier, Katrien G. M.; Beurroies, Isabelle; Deboyel, Renaud; Roeffaers, Maarten; Stock, Norbert; Duren, Tina; Serre, Christian; De Vos, Dirk E.
      Journal of the American Chemical Society (2011), 133 (46), 18526-18529CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Para-disubstituted alkylaroms. such as p-xylene are preferentially adsorbed from an isomer mixt. on three isostructural metal-org. frameworks: MIL-125(Ti) ([Ti8O8(OH)4(BDC)6]), MIL-125(Ti)-NH2 ([Ti8O8(OH)4(BDC-NH2)6]), and CAU-1(Al)-NH2 ([Al8(OH)4(OMe)8(BDC-NH2)6]) (BDC = 1,4-benzenedicarboxylate). Their unique structure contains octahedral cages, which can sep. mols. from differences in packing and interaction with the pore walls, as well as smaller tetrahedral cages, which are capable of sepg. mols. by mol. sieving. These exptl. data are in line with predictions by mol. simulations. Addnl. adsorption and microcalorimetric expts. provide insight in the complementary role of the two cage types in providing the para selectivity.
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    26. 26
      Gonzalez, M. I.; Kapelewski, M. T.; Bloch, E. D.; Milner, P. J.; Reed, D. A.; Hudson, M. R.; Mason, J. A.; Barin, G.; Brown, C. M.; Long, J. R. Separation of Xylene Isomers through Multiple Metal Site Interactions in Metal–Organic Frameworks. J. Am. Chem. Soc. 2018, 140 (9), 3412– 3422,  DOI: 10.1021/jacs.7b13825
      26
      Separation of xylene isomers through multiple metal site interactions in metal-organic frameworks
      Gonzalez, Miguel I.; Kapelewski, Matthew T.; Bloch, Eric D.; Milner, Phillip J.; Reed, Douglas A.; Hudson, Matthew R.; Mason, Jarad A.; Barin, Gokhan; Brown, Craig M.; Long, Jeffrey R.
      Journal of the American Chemical Society (2018), 140 (9), 3412-3422CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Purifn. of the C8 alkylaroms. o-xylene, m-xylene, p-xylene, and ethylbenzene remains among the most challenging industrial sepns., due to the similar shapes, b.ps., and polarities of these mols. Herein, we report the evaluation of the metal-org. frameworks Co2(dobdc) (dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate) and Co2(m-dobdc) (m-dobdc4- = 4,6-dioxido-1,3-benzenedicarboxylate) for the sepn. of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co2(dobdc) distinguishes among all four mols., with binding affinities that follow the trend o-xylene > ethylbenzene > m-xylene > p-xylene. Multicomponent liq.-phase adsorption measurements further demonstrate that Co2(dobdc) maintains this selectivity over a wide range of concns. Structural characterization by single-crystal X-ray diffraction reveals that both frameworks facilitate the sepn. through the extent of interaction between each C8 guest mol. with two adjacent cobalt(II) centers, as well as the ability of each isomer to pack within the framework pores. Moreover, counter to the presumed rigidity of the M2(dobdc) structure, Co2(dobdc) exhibits an unexpected structural distortion in the presence of either o-xylene or ethylbenzene that enables the accommodation of addnl. guest mols.
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    27. 27
      Peng, B.; Wang, S. Separation of p-xylene and m-xylene by simulated moving bed chromatography with MIL-53(Fe) as stationary phase. J. Chromatogr. A 2022, 1673, 463091  DOI: 10.1016/j.chroma.2022.463091
      27
      Separation of p-xylene and m-xylene by simulated moving bed chromatography with MIL-53(Fe) as stationary phase
      Peng, Bo; Wang, Shaoyan
      Journal of Chromatography A (2022), 1673 (), 463091CODEN: JCRAEY; ISSN:0021-9673. (Elsevier B.V.)
      The sepn. of p-xylene (PX) and m-xylene (MX) isomers with near b.ps. is a worldwide problem. The metal-org. framework material is an ideal stationary phase for chromatog. sepn. because of its high porosity, homogeneous pore diam. and good chem. stability. In this paper, a simulated moving bed (SMB) chromatog. system with MIL-53(Fe) as the stationary phase and petroleum ether-dichloromethane as the mobile phase was designed to sep. PX and MX at ambient temp. Firstly, according to the elution curves of a single column, nonlinear competitive Langmuir adsorption isotherm equation was confirmed by equil. dispersive chromatog. model. Then, the SMB sepn. zone was detd. based on triangle theory, and the SMB operating conditions were optimized. Finally, the purity, recovery and productivity of PX reached 100.0%, 99.1% and 93.1 g/L/h, resp.; the purity, recovery and productivity of MX reached 96.4%, 100.0% and 23.5 g/L/h, resp.; the solvent consumption was 0.42 L/g.
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    28. 28
      Kumar, N.; Wang, S.-Q.; Mukherjee, S.; Bezrukov, A. A.; Patyk-Kaźmierczak, E.; O’Nolan, D.; Kumar, A.; Yu, M.-H.; Chang, Z.; Bu, X.-H.; Zaworotko, M. J. Crystal engineering of a rectangular sql coordination network to enable xylenes selectivity over ethylbenzene. Chem. Sci. 2020, 11 (26), 6889– 6895,  DOI: 10.1039/D0SC02123G
      28
      Crystal engineering of a rectangular sql coordination network to enable xylenes selectivity over ethylbenzene
      Kumar, Naveen; Wang, Shi-Qiang; Mukherjee, Soumya; Bezrukov, Andrey A.; Patyk-Kazmierczak, Ewa; O'Nolan, Daniel; Kumar, Amrit; Yu, Mei-Hui; Chang, Ze; Bu, Xian-He; Zaworotko, Michael J.
      Chemical Science (2020), 11 (26), 6889-6895CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Sepn. of the C8 arom. isomers, p-xylene (PX), m-xylene (MX), o-xylene (OX) and ethylbenzene (EB), is relevant thanks to their widespread application as chem. feedstocks but challenging because of their similar b.ps. and close mol. dimensions. Physisorptive sepn. could offer an energy-efficient soln. to this challenge but sorbents which exhibit strong selectivity for one of the isomers remain a largely unmet challenge despite recent reports of OX or PX selective sorbents with high uptake capacity. For example, the square lattice, sql, topol. coordination network [Co(bipy)2(NCS)2]n (sql-1-Co-NCS) exhibits the rare combination of high OX selectivity and high uptake capacity. Herein we report that a crystal engineering approach enabled isolation of the mixed-linker sql coordination network [Co(bipy)(bptz)(NCS)2]n (sql-1,3-Co-NCS, bipy = 4,4'-bipyridine, bptz = 4,4'-bis(4-pyridyl)tetrazine) and study of its C8 vapor and liq. sorption properties. sql-1,3-Co-NCS was found to exhibit high adsorption capacity from liq. xylenes (~ 37 wt%) and is to our knowledge the first sorbent to exhibit high selectivity for each of xylene isomer over EB (SOX/EB, SMX/EB, SPX/EB > 5). Insights into the performance of sql-1,3-Co-NCS are gained from structural studies which reveal stacking interactions between electron-deficient bptz linkers and the resp. xylenes. sql-1,3-Co-NCS is the first N-donor mixed-linker sql coordination network studied for its gas/vapor sorption properties and represents a large and diverse class of understudied coordination networks.
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    29. 29
      Wang, S.-Q.; Mukherjee, S.; Patyk-Kaźmierczak, E.; Darwish, S.; Bajpai, A.; Yang, Q.-Y.; Zaworotko, M. J. Highly Selective, High-Capacity Separation of o-Xylene from C8 Aromatics by a Switching Adsorbent Layered Material. Angew. Chem., Int. Ed. 2019, 58 (20), 6630– 6634,  DOI: 10.1002/anie.201901198
      29
      Highly selective, high-capacity separation of o-xylene from C8 aromatics by a switching adsorbent layered material
      Wang, Shi-Qiang; Mukherjee, Soumya; Patyk-Kazmierczak, Ewa; Darwish, Shaza; Bajpai, Alankriti; Yang, Qing-Yuan; Zaworotko, Michael J.
      Angewandte Chemie, International Edition (2019), 58 (20), 6630-6634CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Purifn. of the C8 aroms. (xylenes and ethylbenzene) is particularly challenging because of their similar phys. properties. It is also relevant because of their industrial utility. Physisorptive sepn. of C8 aroms. has long been suggested as an energy efficient soln. but no physisorbent has yet combined high selectivity (>5) with high adsorption capacity (>50 wt %). Now a counterintuitive approach to the adsorptive sepn. of o-xylene from other C8 aroms. involves the study of a known nonporous layered material, [Co(bipy)2(NCS)2]n (sql-1-Co-NCS), which can reversibly switch to C8 aroms. loaded phases with different switching pressures and kinetics, manifesting benchmark o-xylene selectivity (SOX/EB≈60) and high satn. capacity (>80 wt %). Structural insight into the obsd. selectivity and capacity is gained by anal. of the crystal structures of C8 aroms. loaded phases.
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    30. 30
      Wright, J. S.; Vitórica-Yrezábal, I. J.; Thompson, S. P.; Brammer, L. Arene Selectivity by a Flexible Coordination Polymer Host. Chem. - Eur. J. 2016, 22 (37), 13120– 13126,  DOI: 10.1002/chem.201601870
      30
      Arene Selectivity by a Flexible Coordination Polymer Host
      Wright, James S.; Vitorica-Yrezabal, Inigo J.; Thompson, Stephen P.; Brammer, Lee
      Chemistry - A European Journal (2016), 22 (37), 13120-13126CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The coordination polymers [Ag4(O2CCF3)4(phen)3]·phen·arene (1·phen·arene) (phen = phenazine; arene = toluene, p-xylene or benzene) were prepd. from the soln. phase in arene solvents and crystallog. characterized. By contrast, analogous syntheses from o-xylene and m-xylene as solvent yield the solvent-free coordination polymer [Ag4(O2CCF3)4(phen)2] (2). Toluene, p-xylene and benzene were successfully used in mixed-arene syntheses to template the formation of coordination polymers 1·phen·arene, which incorporate o- or m-xylene. The selectivity of 1·phen·arene for arene guests was detd. through pairwise competition expts. to be p-xylene > toluene ≈ benzene o-xylene m-xylene. The largest selectivity coeff. was 14.2 for p-xylene:m-xylene and the smallest was 1.0 for toluene:benzene.
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    31. 31
      Li, L.; Guo, L.; Olson, D. H.; Xian, S.; Zhang, Z.; Yang, Q.; Wu, K.; Yang, Y.; Bao, Z.; Ren, Q.; Li, J. Discrimination of xylene isomers in a stacked coordination polymer. Science 2022, 377 (6603), 335– 339,  DOI: 10.1126/science.abj7659
      31
      Discrimination of xylene isomers in a stacked coordination polymer
      Li, Liangying; Guo, Lidong; Olson, David H.; Xian, Shikai; Zhang, Zhiguo; Yang, Qiwei; Wu, Kaiyi; Yang, Yiwen; Bao, Zongbi; Ren, Qilong; Li, Jing
      Science (Washington, DC, United States) (2022), 377 (6603), 335-339CODEN: SCIEAS; ISSN:1095-9203. (American Association for the Advancement of Science)
      The sepn. and purifn. of xylene isomers is an industrially important but challenging process. Developing highly efficient adsorbents is crucial for the implementation of simulated moving bed technol. for industrial sepn. of these isomers. Herein, we report a stacked one-dimensional coordination polymer {[Mn(dhbq)(H2O)2], H2dhbq = 2,5-dihydroxy-1,4-benzoquinone} that exhibits an ideal mol. recognition and sieving of xylene isomers. Its distinct temp.-adsorbate-dependent adsorption behavior enables full sepn. of p-, m-, and o-xylene isomers in both vapor and liq. phases. The delicate stimuli-responsive swelling of the structure imparts this porous material with exceptionally high flexibility and stability, well-balanced adsorption capacity, high selectivity, and fast kinetics at conditions mimicking industrial settings. This study may offer an alternative approach for energy-efficient and adsorption-based industrial xylene sepn. and purifn. processes.
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    32. 32
      Kałuża, A. M.; Mukherjee, S.; Wang, S.-Q.; O’Hearn, D. J.; Zaworotko, M. J. [Cu(4-phenylpyridine)4(trifluoromethanesulfonate)2], a Werner complex that exhibits high selectivity for o-xylene. Chem. Commun. 2020, 56 (13), 1940– 1943,  DOI: 10.1039/C9CC09525J
      32
      [Cu(4-phenylpyridine)4(trifluoromethanesulfonate)2], a Werner complex that exhibits high selectivity for o-xylene
      Kaluza, Adrianna M.; Mukherjee, Soumya; Wang, Shi-Qiang; O'Hearn, Daniel J.; Zaworotko, Michael J.
      Chemical Communications (Cambridge, United Kingdom) (2020), 56 (13), 1940-1943CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      [Cu(4-phenylpyridine)4(trifluoromethanesulfonate)2] is a new Werner complex that exhibits switching behavior between non-porous (apohost) and porous (guest-loaded) phases upon exposure to o-xylene but not when exposed to other C8 isomers. High o-xylene selectivity (>6) vs. the other C8 isomers was obsd. from binary mixts., only the third occurrence across all sorbent types.
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    33. 33
      Lusi, M.; Barbour, L. J. Solid–Vapor Sorption of Xylenes: Prioritized Selectivity as a Means of Separating All Three Isomers Using a Single Substrate. Angew. Chem., Int. Ed. 2012, 51 (16), 3928– 3931,  DOI: 10.1002/anie.201109084
      33
      Solid-Vapor Sorption of Xylenes: Prioritized Selectivity as a Means of Separating All Three Isomers Using a Single Substrate
      Lusi, Matteo; Barbour, Leonard J.
      Angewandte Chemie, International Edition (2012), 51 (16), 3928-3931, S3928/1-S3928/7CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Soln.-state and solid-vapor prepns. of the xylene clathrates of [Ni(NCS)2(ppp)4] (I) (ppp = p-phenylpyridine) are reported. The previously unknown structure of [Ni(NCS)2(ppp)4]·3p-xylene was detd. Significant selectivity of 1 for ortho- over meta- and para-xylene from a ternary mixt., and then similar selectivity for meta- over para-xylene from a binary mixt. were obsd. The reason for such selectivity is discussed.
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    34. 34
      Lusi, M.; Barbour, L. J. Solid–vapour reactions as a post-synthetic modification tool for molecular crystals: the enclathration of benzene and toluene by Werner complexes. Chem. Commun. 2013, 49 (26), 2634– 2636,  DOI: 10.1039/c3cc40521d
      34
      Solid-vapour reactions as a post-synthetic modification tool for molecular crystals: the enclathration of benzene and toluene by Werner complexes
      Lusi, Matteo; Barbour, Leonard J.
      Chemical Communications (Cambridge, United Kingdom) (2013), 49 (26), 2634-2636CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      The enclathration of benzene and toluene by Werner complexes has been described. In the case of toluene, time-lapse PXRD anal. reveals that solid-liq. and solid-vapor reactions proceed according to different pathways. These preliminary results suggest that solid-liq. reactions destroy the host structure, whereas the solid-vapor reactions allow post-synthetic modification.
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    35. 35
      Sun, N.; Wang, S.-Q.; Zou, R.; Cui, W.-G.; Zhang, A.; Zhang, T.; Li, Q.; Zhuang, Z.-Z.; Zhang, Y.-H.; Xu, J.; Zaworotko, M. J.; Bu, X.-H. Benchmark selectivity p-xylene separation by a non-porous molecular solid through liquid or vapor extraction. Chem. Sci. 2019, 10 (38), 8850– 8854,  DOI: 10.1039/C9SC02621E
      35
      Benchmark selectivity p-xylene separation by a non-porous molecular solid through liquid or vapor extraction
      Sun, Na; Wang, Shi-Qiang; Zou, Ruqiang; Cui, Wen-Gang; Zhang, Anqi; Zhang, Tianzhen; Li, Qi; Zhuang, Zhan-Zhong; Zhang, Ying-Hui; Xu, Jialiang; Zaworotko, Michael J.; Bu, Xian-He
      Chemical Science (2019), 10 (38), 8850-8854CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Solid-liq. sepn. of similarly sized org. mols. utilizing sorbents offers the potential for new energy-efficient approaches to a no. of important industrial sepns. such as xylenes (C8) sepns. Research on selective C8 sorption has tended to focus upon rigid porous materials such as zeolites and MOFs but has revealed generally weak selectivity that is inconsistent across the range of C8 mols. Nevertheless, there are a few recent examples of non-porous mol. materials that exhibit relatively high selectivity for p-xylene (pX) from pX/oX, approaching that of the current benchmark pX sorbent, the zeolite H/ZSM-5. Herein, we report that a L-shaped Ag(I) complex, AgLClO4 (M), which crystallizes as a non-porous mol. solid material, offering exceptional performance for pX selectivity across the range of C8 isomers with liq. extn. selectivity values of 24.0, 10.4 and 6.2 vs. oX, eB and mX, resp. The pX selectivities over oX and eB are among the highest yet reported. Moreover, M also exhibits strong vapor extn. selectivity and can be regenerated by exposure to vacuum drying.
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    36. 36
      Nassimbeni, L. R. Physicochemical Aspects of Host–Guest Compounds. Acc. Chem. Res. 2003, 36 (8), 631– 637,  DOI: 10.1021/ar0201153
      36
      Physicochemical Aspects of Host-Guest Compounds
      Nassimbeni, Luigi R.
      Accounts of Chemical Research (2003), 36 (8), 631-637CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. The macro properties of cryst. inclusion compds. depend on their structures. Their thermal stabilities are a function of the strength and the directionality of the various nonbonded interactions occurring in the host-guest assembly. Their lattice energies, as measured by the method of atom-atom potentials, correlate with the thermodn. of the guest-release reactions and the selectivity that a given host displays for a particular guest. The kinetics of solid-host:vapor-guest reactions and of guest exchange are important in our understanding of catalytic processes. Crystal engineering, in which materials of predetd. properties may be synthesized, is still at the empirical stage.
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    37. 37
      Barbour, L. J. Crystal porosity and the burden of proof. Chem. Commun. 2006, (11), 1163– 1168,  DOI: 10.1039/b515612m
      37
      Crystal porosity and the burden of proof
      Barbour, Leonard J.
      Chemical Communications (Cambridge, United Kingdom) (2006), (11), 1163-1168CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A review. The study of porosity in the context of crystal engineering is rapidly growing in intensity. However, claims of porosity are often highly subjective and use of the term porous is susceptible to abuse. This contribution discusses some of the criteria to be considered when stating that a particular crystal structure is porous.
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    38. 38
      Wang, Z.; Sikdar, N.; Wang, S.-Q.; Li, X.; Yu, M.; Bu, X.-H.; Chang, Z.; Zou, X.; Chen, Y.; Cheng, P.; Yu, K.; Zaworotko, M. J.; Zhang, Z. Soft Porous Crystal Based upon Organic Cages That Exhibit Guest-Induced Breathing and Selective Gas Separation. J. Am. Chem. Soc. 2019, 141 (23), 9408– 9414,  DOI: 10.1021/jacs.9b04319
      38
      Soft Porous Crystal Based upon Organic Cages That Exhibit Guest-Induced Breathing and Selective Gas Separation
      Wang, Zhifang; Sikdar, Nivedita; Wang, Shi-Qiang; Li, Xia; Yu, Meihui; Bu, Xian-He; Chang, Ze; Zou, Xiaolong; Chen, Yao; Cheng, Peng; Yu, Kuang; Zaworotko, Michael J.; Zhang, Zhenjie
      Journal of the American Chemical Society (2019), 141 (23), 9408-9414CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Soft porous crystals (SPCs) that exhibit stimuli-responsive dynamic sorption behavior are attracting interest for gas storage/sepn. applications. However, the design and synthesis of SPCs is challenging. Herein, we report a new type of SPC based on a [2 + 3] imide-based org. cage (NKPOC-1) and find that it exhibits guest-induced breathing behavior. Various gases were found to induce activated NKPOC-1 crystals to reversibly switch from a "closed" nonporous phase (α) to two porous "open" phases (β and γ). The net effect is gate-opening behavior induced by CO2 and C3 hydrocarbons. Interestingly, NKPOC-1-α selectively adsorbs propyne over propylene and propane under ambient conditions. Thus, NKPOC-1-α has the potential to sep. binary and ternary C3 hydrocarbon mixts., and the performance was subsequently verified by fixed bed column breakthrough expts. In addn., mol. dynamics calcns. and in situ X-ray diffraction expts. indicate that the gate-opening effect is accompanied by reversible structural transformations. The adsorption energies from mol. dynamics simulations aid are consistent with the exptl. obsd. selective adsorption phenomena. The understanding gained from this study of NKPOC-1 supports the further development of SPCs for applications in gas sepn./storage because SPCs do not inherently suffer from the recyclability problems often encountered with rigid materials.
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    39. 39
      Jie, K.; Zhou, Y.; Li, E.; Huang, F. Nonporous Adaptive Crystals of Pillararenes. Acc. Chem. Res. 2018, 51 (9), 2064– 2072,  DOI: 10.1021/acs.accounts.8b00255
      39
      Nonporous Adaptive Crystals of Pillararenes
      Jie, Kecheng; Zhou, Yujuan; Li, Errui; Huang, Feihe
      Accounts of Chemical Research (2018), 51 (9), 2064-2072CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. The authors focus on the discussion of pillararene-based nonporous adaptive crystals (NACs) for adsorption and sepn. and the crystal structure transformations from the initial nonporous cryst. state to new guest-loaded structures during the adsorption and sepn. processes. Single-crystal X-ray diffraction, powder X-ray diffraction, gas chromatog., and soln. NMR spectroscopy are the main techniques to verify the adsorption and sepn. processes and the structural transformations. Compared with traditional porous materials, NACs of pillararenes have several advantages. First, their prepn. is simple and cheap, and they can be synthesized on a large scale to meet practical demands. Second, pillararenes have better chem., moisture, and thermal stability than cryst. MOFs, COFs, and POCs, which are usually constructed on the basis of reversible chem. bonds. Third, pillararenes are sol. in many common org. solvents, which means that they can be easily processed in soln. Fourth, their regeneration is simple and they can be reused many times with no decrease in performance. It is expected that this class of materials will not only exert a significant influence on scientific research but also show practical applications in chem. industry.
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    40. 40
      Jie, K.; Zhou, Y.; Li, E.; Zhao, R.; Liu, M.; Huang, F. Linear Positional Isomer Sorting in Nonporous Adaptive Crystals of a Pillar[5]arene. J. Am. Chem. Soc. 2018, 140 (9), 3190– 3193,  DOI: 10.1021/jacs.7b13156
      40
      Linear Positional Isomer Sorting in Nonporous Adaptive Crystals of a Pillar[5]arene
      Jie, Kecheng; Zhou, Yujuan; Li, Errui; Zhao, Run; Liu, Ming; Huang, Feihe
      Journal of the American Chemical Society (2018), 140 (9), 3190-3193CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Here we show a new adsorptive sepn. approach using nonporous adaptive crystals of a pillar[5]arene. Desolvated perethylated pillar[5]arene crystals (EtP5α) with a nonporous character selectively adsorb 1-pentene (1-Pe) over its positional isomer 2-pentene (2-Pe), leading to a structural change from EtP5α to 1-Pe loaded structure (1-Pe@EtP5). The purity of 1-Pe reaches 98.7% in just one cycle and EtP5α can be reused without losing sepn. performance.
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    41. 41
      Zhang, G.; Hua, B.; Dey, A.; Ghosh, M.; Moosa, B. A.; Khashab, N. M. Intrinsically Porous Molecular Materials (IPMs) for Natural Gas and Benzene Derivatives Separations. Acc. Chem. Res. 2021, 54 (1), 155– 168,  DOI: 10.1021/acs.accounts.0c00582
      41
      Intrinsically Porous Molecular Materials (IPMs) for Natural Gas and Benzene Derivatives Separations
      Zhang, Gengwu; Hua, Bin; Dey, Avishek; Ghosh, Munmun; Moosa, Basem A.; Khashab, Niveen M.
      Accounts of Chemical Research (2021), 54 (1), 155-168CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. Conspectus: Sepg. and purifying chems. without heat would go a long way toward reducing the overall energy consumption and the harmful environmental footprint of the process. Mol. sepn. processes are crit. for the prodn. of raw materials, commodity chems., and specialty fuels. Over 50% of the energy used in the prodn. of these materials is spent on sepn. and purifn. processes, which primarily includes vacuum and cryogenic distns. Chem. manufacturers are now investigating modest thermal approaches, such as membranes and adsorbent materials, as they are more cognizant than ever of the need to save energy and prevent pollution. Porous materials, such as zeolites, metal-org. frameworks (MOFs), and covalent org. frameworks (COFs), have dominated the field of industrial sepns. as their high surface areas and robust pores make them ideal candidates for mol. sepns. of gases and hydrocarbons. Sepn. processes involving porous materials can save 70%-90% of energy costs compared to that of thermally driven distns. However, most porous materials have low thermal, chem., and moisture stability, in addn. to limited soln. processability, which tremendously constrain their broad industrial translation. Intrinsically porous mol. materials (IPMs) are a subclass of porous mol. materials that are comprised of mol. host macrocycles or cages that absorb guests in or around their intrinsic cavity. IPMs range from discrete porous mols. to assemblies with amorphous or highly cryst. structures that are held together by weak supramol. interactions. Compared to the coordination or dynamic covalent bond-constructed porous frameworks, IPMs possess high thermal, chem., and moisture stability and maintain their porosity under crit. conditions. Moreover, the intrinsic porosity endows IPMs with excellent host-guest properties in solid, liq. (org. or aq.), and gas states, which can be further utilized to construct diverse sepn. strategies, such as solid-gas adsorption, solid-liq. absorption, and liq.-liq. extn. The diversity of host-guest interactions in the engineered IPMs affords a plethora of possibilities for the development of the ideal "mol. sieves". Herein, we present a different take on the applicability of intrinsically porous materials such as cyclodextrin (CD), cucurbiturils (CB), pillararene (P), trianglamines (T), and porous org. cages (POCs) that showed an impressive performance in gas purifn. and benzene derivs. sepn. IPMs can be easily scaled up and are quite stable and soln. processable that consequently facilitates a favorable technol. transformation from the traditional energy-intensive sepns. We will account for the main advances in mol. host-guest chem. to design "on-demand" sepn. processes and also outline future challenges and opportunities for this promising technol.
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    42. 42
      Moosa, B.; Alimi, L. O.; Shkurenko, A.; Fakim, A.; Bhatt, P. M.; Zhang, G.; Eddaoudi, M.; Khashab, N. M. A Polymorphic Azobenzene Cage for Energy-Efficient and Highly Selective p-Xylene Separation. Angew. Chem., Int. Ed. 2020, 59 (48), 21367– 21371,  DOI: 10.1002/anie.202007782
      42
      A Polymorphic Azobenzene Cage for Energy-Efficient and Highly Selective p-Xylene Separation
      Moosa, Basem; Alimi, Lukman O.; Shkurenko, Aleksander; Fakim, Aliyah; Bhatt, Prashant M.; Zhang, Gengwu; Eddaoudi, Mohamed; Khashab, Niveen M.
      Angewandte Chemie, International Edition (2020), 59 (48), 21367-21371CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Developing the competence of mol. sorbents for energy-saving applications, such as C8 sepns., requires efficient, stable, scalable, and easily recyclable materials that can readily transition to com. implementation. Herein, we report an azobenzene-based cage for the selective sepn. of p-xylene isomer across a range of C8 isomers in both vapor and liq. states with selectivity that is higher than the reported all-org. sorbents. The crystal structure shows non-porous cages that are sepd. by p-xylene mols. through selective CH-π interactions between the azo bonds and the Me hydrogen atoms of the xylene mols. This cage is stable in soln. and can be regenerated directly under vacuum to be used in multiple cycles. We envisage that this work will promote the investigation of the azo bond as well as guest-induced crystal-to-crystal phase transition in non-porous org. solids for energy-intensive sepns.
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    43. 43
      Jie, K.; Liu, M.; Zhou, Y.; Little, M. A.; Pulido, A.; Chong, S. Y.; Stephenson, A.; Hughes, A. R.; Sakakibara, F.; Ogoshi, T.; Blanc, F.; Day, G. M.; Huang, F.; Cooper, A. I. Near-Ideal Xylene Selectivity in Adaptive Molecular Pillar[n]arene Crystals. J. Am. Chem. Soc. 2018, 140 (22), 6921– 6930,  DOI: 10.1021/jacs.8b02621
      43
      Near-ideal xylene selectivity in adaptive molecular pillar[n]arene crystals
      Jie, Kecheng; Liu, Ming; Zhou, Yujuan; Little, Marc A.; Pulido, Angeles; Chong, Samantha Y.; Stephenson, Andrew; Hughes, Ashlea R.; Sakakibara, Fumiyasu; Ogoshi, Tomoki; Blanc, Frederic; Day, Graeme M.; Huang, Feihe; Cooper, Andrew I.
      Journal of the American Chemical Society (2018), 140 (22), 6921-6930CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The energy-efficient sepn. of alkylarom. compds. is a major industrial sustainability challenge. The use of selectively porous extended frameworks, such as zeolites or metal-org. frameworks, is one soln. to this problem. Here, we studied a flexible mol. material, perethylated pillar[n]arene crystals (n = 5, 6), which can be used to sep. C8 alkylarom. compds. Pillar[6]arene is shown to sep. para-xylene from its structural isomers, meta-xylene and ortho-xylene, with 90% specificity in the solid state. Selectivity is an intrinsic property of the pillar[6]arene host, with the flexible pillar[6]arene cavities adapting during adsorption thus enabling preferential adsorption of para-xylene in the solid state. The flexibility of pillar[6]arene as a solid sorbent is rationalized using mol. conformer searches and crystal structure prediction (CSP) combined with comprehensive characterization by X-ray diffraction and 13C solid-state NMR spectroscopy. The CSP study, which takes into account the structural variability of pillar[6]arene, breaks new ground in its own right and showcases the feasibility of applying CSP methods to understand and ultimately to predict the behavior of soft, adaptive mol. crystals.
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    44. 44
      du Plessis, M.; Nikolayenko, V. I.; Barbour, L. J. Record-Setting Selectivity for p-Xylene by an Intrinsically Porous Zero-Dimensional Metallocycle. J. Am. Chem. Soc. 2020, 142 (10), 4529– 4533,  DOI: 10.1021/jacs.9b11314
      44
      Record-Setting Selectivity for p-Xylene by an Intrinsically Porous Zero-Dimensional Metallocycle
      du Plessis, Marike; Nikolayenko, Varvara I.; Barbour, Leonard J.
      Journal of the American Chemical Society (2020), 142 (10), 4529-4533CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      In its cryst. state, a dinuclear Cu-based metallocycle discriminates between the three isomers of xylene with liq.-phase selectivity in the order p-xylene » m-xylene » o-xylene. This selectivity holds over a wide concn. range, with p-xylene concns. as low as 5%. Single-crystal X-ray diffraction and gas chromatog. further indicate that the metallocyclic host exts. trace amts. of p-xylene from com. pure o-xylene (≥99%); using NMR spectroscopy, we show that the metallocycle exhibits exclusive selectivity for p-xylene. Crystallog. studies show that the selectivity is based on the size and shape of the guest in combination with the flexibility of the host.
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    45. 45
      Barton, B.; Caira, M. R.; de Jager, L.; Hosten, E. C. N,N′-Bis(9-phenyl-9-thioxanthenyl)ethylenediamine: Highly Selective Host Behavior in the Presence of Xylene and Ethylbenzene Guest Mixtures. Cryst. Growth Des. 2017, 17 (12), 6660– 6667,  DOI: 10.1021/acs.cgd.7b01284
      45
      N,N'-Bis(9-phenyl-9-thioxanthenyl)ethylenediamine: Highly Selective Host Behavior in the Presence of Xylene and Ethylbenzene Guest Mixtures
      Barton, Benita; Caira, Mino R.; de Jager, Lize; Hosten, Eric C.
      Crystal Growth & Design (2017), 17 (12), 6660-6667CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      Host compd. N,N'-bis(9-phenyl-9-thioxanthenyl)ethylenediamine formed 1:1 host:guest complexes with o- and p-xylene, and ethylbenzene, when recrystd. from them. The meta-isomer was not included. Competition expts. using equimolar binary and ternary mixts. of the three xylenes demonstrated that this host is markedly selective for p-xylene (≥94% on both a milligram- and gram-scale), while 68% of this guest was extd. from an equimolar quaternary mixt. of the three xylenes and ethylbenzene. This selectivity was also evident when guest ratios in binary mixts. contg. p-xylene were varied. The obsd. high affinity for the para-isomer was explained using single crystal X-ray diffraction, Hirshfeld surface anal. and thermoanal. expts. Furthermore, the host was subjected to gas phase guests in order to establish whether the ability existed for complexation of these guests from the solid state.
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    46. 46
      Barton, B.; Senekal, U.; Hosten, E. C. trans-α,α,α′,α′-Tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol and its tetra(p-chlorophenyl) derivative: roof-shaped host compounds for the purification of aromatic C8H10 isomeric guest mixtures. J. Inclusion Phenom. Macrocyclic Chem. 2022, 102 (1), 77– 87,  DOI: 10.1007/s10847-021-01102-5
      46
      trans-α,α,α',α'-Tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol and its tetra(p-chlorophenyl) derivative: roof-shaped host compounds for the purification of aromatic C8H10 isomeric guest mixtures
      Barton, Benita; Senekal, Ulrich; Hosten, Eric C.
      Journal of Inclusion Phenomena and Macrocyclic Chemistry (2022), 102 (1-2), 77-87CODEN: JIPCF5; ISSN:1388-3127. (Springer)
      Roof-shaped host compds. trans-α,α,α',α'-tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12sda-dimethanol H3 and trans-α,α,α',α'-tetra(p-chlorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol H6 were assessed for their host potential and selectivity behavior when presented with single or mixed guest solvents comprising o-xylene, m-xylene, p-xylene and ethylbenzene (o-Xy, m-Xy, p-Xy and EB). H3 included each solvent with 3:1 host:guest ratios, while the ratios preferred by H6 were more varied (4:3, 1:1 and 3:2). More importantly, the selectivity behavior of these two host compds. was obsd. to be entirely different: H3 possessed only a very modest preference for o-Xy (37.9-68.2%) when recrystd. from various equimolar binary, ternary and quaternary guest mixts., while H6 was considerably more selective, preferring m-Xy (the least favored guest of H3) with selectivities ranging from 57.7 to 91.4% in analogous conditions. The latter result was obtained in o-Xy/m-Xy mixts. and demonstrates that H6 may be employed as a purifn. tool for mixts. of these two xylenes via host-guest chem. protocols. A single crystal diffraction expt. on 3(H3)·o-Xy (contg. the preferred guest of H3) revealed that the guest was retained in the host crystal by means of a singular (host)m-Ar-H···π(guest) interaction that measured 2.73 Å (148°) as well as numerous other host···guest interactions involving only the arom. protons of the free host Ph groups and the guest Me protons or arom. carbons and protons (2.20-2.54 Å, 121-125°). Thermal analyses explained the preference of H3 for o-Xy, while these were less informative for the complexes of H6.
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    47. 47
      Little, M. A.; Cooper, A. I. The Chemistry of Porous Organic Molecular Materials. Adv. Funct. Mater. 2020, 30 (41), 1909842  DOI: 10.1002/adfm.201909842
      47
      The Chemistry of Porous Organic Molecular Materials
      Little, Marc A.; Cooper, Andrew I.
      Advanced Functional Materials (2020), 30 (41), 1909842CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Porous org. mol. materials are a subclass of porous solids that are defined by their modular, mol. structures, and the absence of extended covalent or coordination bonding in the solid-state. As a result, porous mol. materials are sol. and they can be processed into different forms, such as mixed matrix membranes. The structure of the porous modules can be fine-tuned for specific applications, such as gas isotope sepns., and in some cases the solid-state properties of these materials can be defined by the structure of the porous mol. as viewed in isolation. In this review, the authors focus on the design of porous org. mol. materials and how their properties can be tuned for specific applications by using crystal engineering techniques. The authors distinguish between strategies where porosity is defined largely by the mol. itself, for example, in porous org. cages, and cases where porosity is generated by the solid-state cryst. assembly. They emphasize the importance of computational techniques in the de novo design of functional, porous org. mol. materials, and how mol. modeling is applied to understand the properties of these materials.
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    48. 48
      Mitra, T.; Jelfs, K. E.; Schmidtmann, M.; Ahmed, A.; Chong, S. Y.; Adams, D. J.; Cooper, A. I. Molecular shape sorting using molecular organic cages. Nat. Chem. 2013, 5 (4), 276– 281,  DOI: 10.1038/nchem.1550
      48
      Molecular shape sorting using molecular organic cages
      Mitra, Tamoghna; Jelfs, Kim E.; Schmidtmann, Marc; Ahmed, Adham; Chong, Samantha Y.; Adams, Dave J.; Cooper, Andrew I.
      Nature Chemistry (2013), 5 (4), 276-281CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
      The energy-efficient sepn. of chem. feedstocks is a major sustainability challenge. Porous extended frameworks such as zeolites or metal-org. frameworks are one potential soln. to this problem. Here, we show that org. mols., rather than frameworks, can sep. other org. mols. by size and shape. A mol. org. cage is shown to sep. a common arom. feedstock (mesitylene) from its structural isomer (4-ethyltoluene) with an unprecedented perfect specificity for the latter. This specificity stems from the structure of the intrinsically porous cage mol., which is itself synthesized from a deriv. of mesitylene. In other words, cryst. org. mols. are used to sep. other org. mols. The specificity is defined by the cage structure alone, so this solid-state 'shape sorting' is, uniquely, mirrored for cage mols. in soln. The behavior can be understood from a combination of atomistic simulations for individual cage mols. and solid-state mol. dynamics simulations.
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    49. 49
      Ye, J.; du Plessis, M.; Loots, L.; van Wyk, L. M.; Barbour, L. J. Solid–Liquid Separation of Xylene Isomers Using a Cu-Based Metallocycle. Cryst. Growth Des. 2022, 22 (4), 2654– 2661,  DOI: 10.1021/acs.cgd.2c00082
      49
      Solid-Liquid Separation of Xylene Isomers Using a Cu-Based Metallocycle
      Ye, Jiajia; du Plessis, Marike; Loots, Leigh; van Wyk, Lisa Mercene; Barbour, Leonard J.
      Crystal Growth & Design (2022), 22 (4), 2654-2661CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      Industrial sepn. of xylene isomers is a challenge due to their similarity in size, shape, d., b.p. and polarity. Xylene isomers have been sepd. using zero-dimensionally porous crystals composed of a Cu-based metallocycle, with selectivity in the order p-xylene » m-xylene > o-xylene. The selectivity trend follows that of increasing kinetic diams. of the xylenes. Crystallog. studies show that the flexible host transforms from one phase to another to adapt to the inclusion of xylenes.
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    50. 50
      Atwood, J. L.; Barbour, L. J.; Jerga, A.; Schottel, B. L. Guest Transport in a Nonporous Organic Solid via Dynamic van der Waals Cooperativity. Science 2002, 298 (5595), 1000– 1002,  DOI: 10.1126/science.1077591
      50
      Guest Transport in a Nonporous Organic Solid via Dynamic van der Waals Cooperativity
      Atwood, Jerry L.; Barbour, Leonard J.; Jerga, Agoston; Schottel, Brandi L.
      Science (Washington, DC, United States) (2002), 298 (5595), 1000-1002CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      A well-known org. host compd. undergoes single-crystal-to-single-crystal phase transitions upon guest uptake and release. Despite a lack of porosity of the material, guest transport through the solid occurs readily until a thermodynamically stable structure is achieved. In order to actively facilitate this dynamic process, the host mols. undergo significant positional and/or orientational rearrangement. This transformation of the host lattice is triggered by weak van der Waals interactions between the mol. components. In order for the material to maintain its macroscopic integrity, extensive cooperativity must exist between the mols. throughout the crystal, such that rearrangement can occur in a well-orchestrated fashion. We demonstrate here that even weak dispersive forces can exert a profound influence over solid-state dynamics.
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    51. 51
      Barrer, R. M.; Shanson, V. H. Dianin’s compound as a zeolitic sorbent. J. Chem. Soc., Chem. Commun. 1976, (9), 333– 334,  DOI: 10.1039/c39760000333
      51
      Dianin's compound as a zeolitic sorbent
      Barrer, Richard M.; Shanson, Vivien H.
      Journal of the Chemical Society, Chemical Communications (1976), (9), 333-4CODEN: JCCCAT; ISSN:0022-4936.
      Dianin's compd., suitably agitated, sorbed freely Ar, Kr, Xe, CO2, CH4, C2H6, C3H8, C4H10, iso-C4H10, and neo-C5H12, and behaved in some respects like an org. zeolite because of the permanent character of its porous host lattice. The nos. of mols. filling each cavity in the host lattice varied from 6 for Ar at -196° and CH4 at -183° to 2 for iso-C4H10 and neo-C5H12 at 0°, and satn. nos. depended on the size and shape of the guest mols., as for zeolites.
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    52. 52
      Enright, G. D.; Ratcliffe, C. I.; Ripmeester, J. A. Crystal structure and 13C CP/MAS NMR of the p-xylene clathrate of Dianin’s compound. Mol. Phys. 1999, 97 (11), 1193– 1196,  DOI: 10.1080/00268979909482920
      52
      Crystal structure and 13C CP/MAS NMR of the p-xylene clathrate of Dianin's compound
      Enright, G. D.; Ratcliffe, C. I.; Ripmeester, J. A.
      Molecular Physics (1999), 97 (11), 1193-1196CODEN: MOPHAM; ISSN:0026-8976. (Taylor & Francis Ltd.)
      Single-crystal x-ray diffraction and 13C solid-state NMR spectroscopy were used to characterize the structure and dynamics of the p-xylene clathrate of Dianin's compd. In contrast to conclusions obtained from single-crystal 2H NMR and modeling, the diffraction results suggest there is a single (symmetry disordered) guest site without any significant distortion of the host framework. S single xylene guest statistically disordered over 6 overlapping equiv. positions can account for the 13C NMR spectrum at room temp. The high crystallog. symmetry arises from space averaging. At high temps. the 13C spectrum is consistent with the onset of dynamic processes that result in higher effective symmetry.
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    53. 53
      Harris, K. D. M. Meldola Lecture: understanding the properties of urea and thiourea inclusion compounds. Chem. Soc. Rev. 1997, 26 (4), 279– 289,  DOI: 10.1039/cs9972600279
      53
      Meldola lecture: understanding the properties of urea and thiourea inclusion compounds
      Harris, Kenneth D. M.
      Chemical Society Reviews (1997), 26 (4), 279-290CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review with 49 refs.; much of the intrinsic appeal of structural science arises from the fact that structural behavior at the mol. level often resembles macroscopic structures that we can see in the world around us. In the same way that we perceive beauty in the symmetries and forms of macroscopic objects, there is an equally enthralling beauty in the way that nature fashions symmetry and diversity within the architectures of cryst. solids. In the field of inclusion chem., for example, many direct analogies can be drawn between the concepts of inclusion in the microscopic and macroscopic worlds, but the scientific interest and importance of inclusion chem. extends far beyond such structural comparisons. As this article demonstrates, solid org. inclusion compds. can exhibit a diversity of interesting and important fundamental properties, which can form the basis of a range of important applications.
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    54. 54
      Palin, D. E.; Powell, H. M. 50. The structure of molecular compounds. Part III. Crystal structure of addition complexes of quinol with certain volatile compounds. J. Chem. Soc. (Resumed) 1947, 0, 208– 221,  DOI: 10.1039/jr9470000208
      There is no corresponding record for this reference.
    55. 55
      Terres, E.; Vollmer, W. Solubility of Mineral Oil and tar constituents in liquid Hydrogen Sulphide. Petroleum 1935, 31, 1– 12
      55
      The solubility of petroleum and tar constituents in liquid hydrogen sulfide
      Terres, Ernst; Vollmer, Walter
      (1935), 31 (No. 19), 1-12 ISSN:.
      Development of solvent extn. methods and the early works on the behavior of liquid H2S with org. substances are reviewed. Binary systems of the following constituents of petroleum and tar and H2S were investigated: benzene, toluene, phenol, o-cresol, naphthalene, β-methylnaphthalene, anthracene,phenanthrene, octadecane, hexahydrobenzene and quinoline. Benzene, toluene, hexahydrobenzene and quinoline, and the paraffin hydrocarbons are miscible in all proportions at 0° with liquid H2S. The soly. of phenol, o-cresol, naphthalene and β-methyl-naphthalene is very high. The f.-p. curve of anthracene and phenanthrene cuts the crit. line of H2S. All the org. substances investigated form only 1 liquid phase with liquid H2S; in no case was a miscibility gap present. Toluene, phenol, β-methylnaphthalene and quinoline form intermediate compds.: 2C6H5CH3.H2S, 2C6H5OH.H2S, 4C10H7CH3.H2S and C8H7N.H2S. Octadecane and hexahydrobenzene form solid solns. with H2S.
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    56. 56
      Dwivedi, B.; Kumar, S.; Das, D. Selective inclusion of p-xylene by bis-hydrazone compounds. CrystEngComm 2022, 24 (6), 1161– 1165,  DOI: 10.1039/D1CE01569A
      56
      Selective inclusion of p-xylene by bis-hydrazone compounds
      Dwivedi, Bhavna; Kumar, Sunil; Das, Dinabandhu
      CrystEngComm (2022), 24 (6), 1161-1165CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
      The sepn. of xylene isomers from their mixt. is a challenging task. The present study describes the highly selective inclusion of p-xylene (p-XY) from a mixt. of xylene isomers by three novel org. bis-hydrazone compds., ethanedial-1,2-bis(4,4'-dichlorobenzophenone hydrazone) (1), ethanedial-1,2-bis(4,4'-dibromobenzophenone hydrazone) (2) and ethanedial-1,2-bis(4,4'-diiodobenzophenone hydrazone) (3). These van der Waals host compds. specifically enclathrate p-XY from a mixt. of xylene isomers. Crystn. of the host compds. in all possible mixts. of xylene isomers, X-ray diffraction (both single-crystal and powder) and thermogravimetric anal. (TGA) confirm the selective inclusion property of the bis-hydrazone compds. Compds. 1, 2 and 3 might be suitable candidates for the sepn. of p-XY from a mixt. of xylene isomers.
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    57. 57
      Pivovar, A. M.; Holman, K. T.; Ward, M. D. Shape-Selective Separation of Molecular Isomers with Tunable Hydrogen-Bonded Host Frameworks. Chem. Mater. 2001, 13 (9), 3018– 3031,  DOI: 10.1021/cm0104452
      57
      Shape-Selective Separation of Molecular Isomers with Tunable Hydrogen-Bonded Host Frameworks
      Pivovar, Adam M.; Holman, K. Travis; Ward, Michael D.
      Chemistry of Materials (2001), 13 (9), 3018-3031CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      The propensity of H-bonded guanidinium (G) organodisulfonates (S) to form cryst. inclusion compds. was studied in the context of sepg. isomeric mixts. of xylenes and dimethylnaphthalenes via selective inclusion. Pairwise competition expts., in which inclusion compds. are grown from solns. contg. an isomeric mixt. of guests, map the inclusion selectivity of a particular host as a function of guest content in soln. Whereas the G2[4,4'-biphenyldisulfonate] host is minimally selective with respect to inclusion of o-, m-, or p-xylene, the homologous G2[2,6-naphthalenedisulfonate] is highly selective toward the inclusion of p-xylene, by a factor of 36 and 160 vs. o-xylene and m-xylene, resp. Similarly, the hosts of the homologous series G2[2,6-naphthalenedisulfonate], G2[4,4'-biphenyldisulfonate], G2[2,6-anthracenedisulfonate], and G2[4,4'-azobenzenedisulfonate] display different selectivity for the 10 isomers of dimethylnaphthalene. The details of the selectivity behavior are highly dependent on the mol. structure of the GS host and the solid-state structures of the corresponding inclusion compds. Single crystal structure detns. reveal that isomer selectivity is most pronounced when the structures of corresponding inclusion compds. are significantly different, i.e., when the isomeric guests template different architectural isomers of the host. also, selectivity appears to be a consequence of size and shape compatibility between the host and guest. The observation of selective inclusion demonstrates the feasibility of a crystn.-based sepn. process based on these host compds.
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    58. 58
      Matos, C. R. M. O.; Sanii, R.; Wang, S.-Q.; Ronconi, C. M.; Zaworotko, M. J. Reversible single-crystal to single-crystal phase transformation between a new Werner clathrate and its apohost. Dalton Trans. 2021, 50 (37), 12923– 12930,  DOI: 10.1039/D1DT01839F
      58
      Reversible single-crystal to single-crystal phase transformation between a new Werner clathrate and its apohost
      Matos, Catiucia R. M. O.; Sanii, Rana; Wang, Shi-Qiang; Ronconi, Celia M.; Zaworotko, Michael J.
      Dalton Transactions (2021), 50 (37), 12923-12930CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      The authors report the synthesis and structural characterization of the ligand 2-(pyridin-3-yl)-benzo[de]isoquinoline-1,3(2H)-dione, 5, its isostructural Werner complexes ML4(NCS)2 (L = 5; M = Co(II) and Ni(II)), and five clathrates with three arom. guests, ML4(NCS)2·2G (M = Co(II) and Ni(II), G = nitrobenzene (NB); M = Co, G = 1,2-dichlorobenzene (1,2-DCB); M = Co(II) and Ni(II), G = o-xylene (OX)). 5 was prepd. in high yield by condensation in the solid-state (C3S3, Cocrystal Controlled Solid-State Synthesis). The Werner complexes ML4(NCS)2 (M = Co(II) and Ni(II)) (apohosts) were prepd. by reacting M(NCS)2 (M = Co(II) and Ni(II)) and 5 in 1-butanol at 60° for 24 h. The Werner clathrates were prepd. by reacting M(NCS)2 (M = Co(II) and Ni(II)), G and 5 in 1-butanol at 60° for 48-96 h. The clathrates transform to the apohost ML4(NCS)2 upon heating. CoL4(NCS)2·2NB was subsequently regenerated by exposing CoL4(NCS)2 to liq. NB at 60° for 48 h. This phase change occurred as a single-crystal to single-crystal phase transformation and was studied by single crystal X-ray diffraction, powder X-ray diffraction and thermal analyses. Structural analyses of the apohost CoL4(NCS)2 and its Werner clathrate CoL4(NCS)2·2NB indicated that rotational freedom of the Co-N bonds together with torsional flexibility of the ligand between the imide bond and the pyridine moiety are key to enabling the structural switching induced by exposure to NB or its removal.
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    59. 59
      Cheney, M. L.; McManus, G. J.; Perman, J. A.; Wang, Z.; Zaworotko, M. J. The Role of Cocrystals in Solid-State Synthesis: Cocrystal-Controlled Solid-State Synthesis of Imides. Cryst. Growth Des. 2007, 7 (4), 616– 617,  DOI: 10.1021/cg0701729
      59
      The Role of Cocrystals in Solid-State Synthesis: Cocrystal-Controlled Solid-State Synthesis of Imides
      Cheney, Miranda L.; McManus, Gregory J.; Perman, Jason A.; Wang, Zhenqiang; Zaworotko, Michael J.
      Crystal Growth & Design (2007), 7 (4), 616-617CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      1,4,5,8-Naphthalenetetracarboxylic dianhydride (I) and arylamines such as 2-methyl-4-nitroaniline and 3-aminobenzoic acid form cocrystals upon grinding of the solids in the presence of a small amt. of solvent; the cocrystals undergo cyclocondensation reactions [cocrystal-controlled solid-state synthesis (C3S3)] upon heating in the solid state to yield imides II (R = Me; R1 = H; R2 = O2N) and II (R = R2 = H; R1 = HO2C) in 75% and 99% yields, resp. The effect of solvent on the formation of either imides or cocrystals of I with arylamines is studied by both IR spectroscopy and by X-ray powder diffraction. Phase transitions of the cocrystals are studied by differential scanning calorimetry. Charge transfer bands are obsd. in the UV/visible spectra of the cocrystals of I with 2-methyl-4-nitroaniline and 3-aminobenzoic acid. Structures for the 1:2 cocrystal of I and 2-methyl-4-nitroaniline, the 1:2:1 cocrystal of I, 3-aminobenzoic acid, and 1,4-dioxane, the mono-DMF solvate of II (R = Me; R1 = H; R2 = O2N), and the 2:5 solvate of II (R = R2 = H; R1 = HO2C) with pyridine are detd. by X-ray crystallog.
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    60. 60
      Sanii, R.; Bajpai, A.; Patyk-Kaźmierczak, E.; Zaworotko, M. J. High Yield, Low-Waste Synthesis of a Family of Pyridyl and Imidazolyl-Substituted Schiff Base Linker Ligands. ACS Sustainable Chem. Eng. 2018, 6 (11), 14589– 14598,  DOI: 10.1021/acssuschemeng.8b03204
      60
      High Yield, Low-Waste Synthesis of a Family of Pyridyl and Imidazolyl-Substituted Schiff Base Linker Ligands
      Sanii, Rana; Bajpai, Alankriti; Patyk-Kazmierczak, Ewa; Zaworotko, Michael J.
      ACS Sustainable Chemistry & Engineering (2018), 6 (11), 14589-14598CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
      Solid-state synthesis (S3) is an attractive approach to org. synthesis as in principle it offers minimal solvent waste and high yield. However, many functional groups are ill-suited for S3 reactions, which tend to only proceed when substrates are aligned in the solid-state according to the topochem. principle. The aim of this work is to use high yield, low-waste synthetic methods to develop a library of novel Schiff bases that can be used as linker ligands to prep. coordination networks. Herein, the authors report that eight pyridyl- and/or imidazolyl-substituted Schiff bases, five of which are new chem. entities, can be prepd. via reaction of an amine and an aldehyde without the use of solvent. All eight compds. were prepd. via solvent-drop grinding (SDG) in multigram scale in >95% yield and each was characterized by FTIR, 1H and 13C NMR spectroscopies and single crystal x-ray diffraction. One of the aldehydes used is a liq. under ambient conditions so its reactions to form the corresponding Schiff bases are not classified as S3 reactions whereas the other aldehydes are solids and the other four Schiff bases are therefore obtained by S3. The SDG solvents were selected in accordance with guidelines used by industry. Four Schiff bases were also prepd. quant. via addn. of the liq. aldehyde (4-pyridinecarboxaldehyde) to a soln. of the corresponding amine. That the Schiff bases contain functional groups suitable for coordinating with metal cations will enable them to serve as linker ligands in coordination networks as exemplified by one nickel complex, which forms a parallel interpenetrated coordination network with square lattice, sql, topol.
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    61. 61
      Friščić, T.; Trask, A. V.; Jones, W.; Motherwell, W. S. Screening for inclusion compounds and systematic construction of three-component solids by liquid-assisted grinding. Angew. Chem. 2006, 118 (45), 7708– 7712,  DOI: 10.1002/ange.200603235
      There is no corresponding record for this reference.
    62. 62
      Shan, N.; Toda, F.; Jones, W. Mechanochemistry and co-crystal formation: effect of solvent on reaction kinetics. Chem. Commun. 2002, (20), 2372– 2373,  DOI: 10.1039/b207369m
      62
      Mechanochemistry and co-crystal formation: effect of solvent on reaction kinetics
      Shan, Ning; Toda, Fumio; Jones, William
      Chemical Communications (Cambridge, United Kingdom) (2002), (20), 2372-2373CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Significant improvements in kinetics of co-crystal formation by grinding can be achieved by the addn. of minor amts. of appropriate solvent.
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    63. 63
      Bowmaker, G. A. Solvent-assisted mechanochemistry. Chem. Commun. 2013, 49 (4), 334– 348,  DOI: 10.1039/C2CC35694E
      63
      Solvent-assisted mechanochemistry
      Bowmaker, Graham A.
      Chemical Communications (Cambridge, United Kingdom) (2013), 49 (4), 334-348CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A review. The literature on solvent-assisted mechanochem. is reviewed with a view to linking observations concerning the applicability of the technique to theories of its mechanism, and summarizing the advantages and limitations of the technique when applied to a variety of different reaction types. Previously unnoticed links between "solvent-free" and solvent-assisted reaction mechanisms are presented, and reasons why the method should be considered more widely by synthetic chemists are given.
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    64. 64
      Cheney, M. L.; Zaworotko, M. J.; Beaton, S.; Singer, R. D. Cocrystal Controlled Solid-State Synthesis. A Green Chemistry Experiment for Undergraduate Organic Chemistry. J. Chem. Educ. 2008, 85 (12), 1649  DOI: 10.1021/ed085p1649
      64
      Cocrystal controlled solid-state synthesis. A green chemistry experiment for undergraduate organic chemistry
      Cheney, Miranda L.; Zaworotko, Michael J.; Beaton, Steve; Singer, Robert D.
      Journal of Chemical Education (2008), 85 (12), 1649-1651CODEN: JCEDA8; ISSN:0021-9584. (Journal of Chemical Education, Dept. of Chemistry)
      The article presents expts. that can be adapted to a typical undergraduate org. chem. course easily and are inexpensive, relatively safe, require no solvent (or extremely small quantities of solvent), have high atom economy, make use of non-toxic or low toxicity compds., and generate negligible quantities of waste. The expts. can be accomplished through the use of a new technique known as cocrystal controlled solid-state synthesis, C3S3.
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    65. 65
      Burger, A.; Ramberger, R. On the polymorphism of pharmaceuticals and other molecular crystals. I. Microchim. Acta 1979, 72 (3), 259– 271,  DOI: 10.1007/BF01197379
      There is no corresponding record for this reference.
    66. 66
      Burger, A.; Ramberger, R. On the polymorphism of pharmaceuticals and other molecular crystals. II. Microchim. Acta 1979, 72 (3), 273– 316,  DOI: 10.1007/BF01197380
      There is no corresponding record for this reference.
    67. 67
      Burtch, N. C.; Jasuja, H.; Walton, K. S. Water Stability and Adsorption in Metal–Organic Frameworks. Chem. Rev. 2014, 114 (20), 10575– 10612,  DOI: 10.1021/cr5002589
      67
      Water Stability and Adsorption in Metal-Organic Frameworks
      Burtch, Nicholas C.; Jasuja, Himanshu; Walton, Krista S.
      Chemical Reviews (Washington, DC, United States) (2014), 114 (20), 10575-10612CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review; water stability and adsorption in metal-org. frameworks are discussed.
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    68. 68
      Waterman, K. C.; Huynh-Ba, K. Understanding and Predicting Pharmaceutical Product Shelf-Life. In Handbook of Stability Testing in Pharmaceutical Development: Regulations, Methodologies, and Best Practices; Springer New York: New York, NY, 2009; pp 115– 135.
      There is no corresponding record for this reference.
    69. 69
      Brouwers, J.; Brewster, M. E.; Augustijns, P. Supersaturating drug delivery systems: the answer to solubility-limited oral bioavailability?. J. Pharm. Sci. 2009, 98 (8), 2549– 2572,  DOI: 10.1002/jps.21650
      69
      Supersaturating drug delivery systems: The answer to solubility-limited oral bioavailability?
      Brouwers, Joachim; Brewster, Marcus E.; Augustijns, Patrick
      Journal of Pharmaceutical Sciences (2009), 98 (8), 2549-2572CODEN: JPMSAE; ISSN:0022-3549. (Wiley-Liss, Inc.)
      A review. Contemporary pharmaceutical pipelines are often highly populated with poorly water-sol. drug candidates necessitating novel formulation technologies to provide dosage forms with appropriate biopharmaceutical properties. The configuration of supersaturating drug delivery systems (SDDS) is a promising concept to obtain adequate oral bioavailability. SDDS contain the drug in a high energy or otherwise rapidly dissolving form such that intraluminal concns. above the satn. soly. of the drug are generated. For the strategy to be useful, the formed supersatd. soln. must then be stabilized to allow for significant absorption and eventually sufficient bioavailability. The stabilization of a supersatd. soln. can be accomplished by adding pptn. inhibitors which may act through a variety of mechanisms. The goal of this review is to assess methods and excipients assocd. with the development of SDDS and provide some context for their use. In addn., the future directions and factors likely to contribute to or detract from optimal dosage form selection are assessed. This includes a discussion on the potential effect of the gastrointestinal physiol. on the ability to attain and maintain supersatn. as this information is essential in designing useful formulations based on the supersaturating concept. © 2009 Wiley-Liss, Inc. and the American Pharmacists Assocn. J Pharm Sci 98:2549-2572, 2009.
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    70. 70
      Peralta, D.; Chaplais, G.; Paillaud, J.-L.; Simon-Masseron, A.; Barthelet, K.; Pirngruber, G. D. The separation of xylene isomers by ZIF-8: A demonstration of the extraordinary flexibility of the ZIF-8 framework. Microporous Mesoporous Mater. 2013, 173, 1– 5,  DOI: 10.1016/j.micromeso.2013.01.012
      70
      The separation of xylene isomers by ZIF-8: A demonstration of the extraordinary flexibility of the ZIF-8 framework
      Peralta, David; Chaplais, Gerald; Paillaud, Jean-Louis; Simon-Masseron, Angelique; Barthelet, Karin; Pirngruber, Gerhard D.
      Microporous and Mesoporous Materials (2013), 173 (), 1-5CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Inc.)
      The present work describes the adsorption and sepn. of xylene isomers by ZIF-8. Although the formal pore diam. of ZIF-8 is much smaller than the mol. diam. of the xylene isomers, ZIF-8 is able to sep. the isomers by mol. sieving. A structural study indicates that the diffusion of the xylenes into the pore structure of ZIF-8 happens via a transitory deformation of the pore aperture which is based on a tilt of the imidazolate linkers, followed by a return to the initial conformation. The rate of adsorption depends on the size of the isomer, i.e. it decreases from para- to meta- and to ortho-xylene. The sepn. of the xylene isomers is good in the gas phase. In liq. phase breakthrough expts., the quality of the sepn. is deteriorated. Moreover, as expected for a sepn. based on mol. sieving, para-xylene cannot be well sepd. from ethyl-benzene.
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    71. 71
      Barton, B.; de Jager, L.; Hosten, E. C. Minor modifications afford improved host selectivities in xanthenyl-type host systems. CrystEngComm 2019, 21 (19), 3000– 3013,  DOI: 10.1039/C9CE00265K
      71
      Minor modifications afford improved host selectivities in xanthenyl-type host systems
      Barton, Benita; de Jager, Lize; Hosten, Eric C.
      CrystEngComm (2019), 21 (19), 3000-3013CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
      In this work, we examine the selectivity of host N,N'-bis(9-phenyl-9-xanthenyl)ethylenediamine in the presence of two different guest series', namely the C8 arom. fraction of crude oil (i.e., ethylbenzene, and o-, m- and p-xylene) and anisoles (anisole, and o-, m- and p-methylanisole). Of the four alkyl aroms., only p-xylene formed a complex with this host when it was recrystd. from each one, while both anisole and p-methylanisole from the second guest series were clathrated in this way. Host : guest ratios were consistently 1 : 1. When this host was recrystd. from various mixts. of the solvents from the two guest groups, an unequivocal bias towards p-xylene and p-methylanisole, resp., was obsd., with the other competing guests essentially being excluded from the host crystal in these expts. Furthermore, this host displayed significantly enhanced selectivities relative to the structurally-related compd., N,N'-bis(9-phenyl-9-thioxanthenyl)ethylenediamine, in the presence of the xylenes and ethylbenzene, when considering a previous report. The latter compd. was also assessed for inclusion behavior in the presence of the anisoles and, once more, its inferior selectivity compared with the oxo-host counterpart was strikingly evident. Both single crystal X-ray diffraction and thermal expts. were conducted in order to investigate the noted selectivity differences.
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    72. 72
      Gee, J. A.; Zhang, K.; Bhattacharyya, S.; Bentley, J.; Rungta, M.; Abichandani, J. S.; Sholl, D. S.; Nair, S. Computational Identification and Experimental Evaluation of Metal–Organic Frameworks for Xylene Enrichment. J. Phys. Chem. C 2016, 120 (22), 12075– 12082,  DOI: 10.1021/acs.jpcc.6b03349
      72
      Computational Identification and Experimental Evaluation of Metal-Organic Frameworks for Xylene Enrichment
      Gee, Jason A.; Zhang, Ke; Bhattacharyya, Souryadeep; Bentley, Jason; Rungta, Meha; Abichandani, Jeevan S.; Sholl, David S.; Nair, Sankar
      Journal of Physical Chemistry C (2016), 120 (22), 12075-12082CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      We report the computational discovery and exptl. evaluation of nanoporous materials targeted at the adsorptive sepn. of p-xylene from a C8 aroms. mixt. We first introduce a computational method that is capable of efficiently predicting the p-xylene selectivities and capacities for a large database of porous materials. We then demonstrate the application of this method to screen a database of several thousand metal-org. framework (MOF) structures. Our computational screening methodol. predicted that two MOFs with good solvothermal stability and com. available linkers give comparable performance to the state-of-the-art zeolite BaX currently used in industrial p-xylene sepns. The best-performing MOFs are then synthesized, and their xylene sepn. characteristics are evaluated in detail through breakthrough adsorption expts. and modeling. We find that the selectivities obtained in these materials are higher than that of any MOF previously reported in the literature and in some cases exceed the measured performance of zeolite BaX. In the case of the p-xylene selective material MOF-48, we use calcd. free energy profiles to show how the presence of Me substituents on the linkers allows the inversion of selectivity from the equiv. MOF with no Me substituents (MIL-47, which is o-xylene selective). This combined computational and exptl. methodol. is a useful step in the development of MOFs for sepn. of arom. hydrocarbons and can also be applied to other chem. sepns. and other classes of porous materials as long as the appropriate intermol. force fields are available.
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    73. 73
      Wang, J.-Y.; Mangano, E.; Brandani, S.; Ruthven, D. M. A review of common practices in gravimetric and volumetric adsorption kinetic experiments. Adsorption 2021, 27 (3), 295– 318,  DOI: 10.1007/s10450-020-00276-7
      73
      A review of common practices in gravimetric and volumetric adsorption kinetic experiments
      Wang, Jin-Yu; Mangano, Enzo; Brandani, Stefano; Ruthven, Douglas M.
      Adsorption (2021), 27 (3), 295-318CODEN: ADSOFO; ISSN:0929-5607. (Springer)
      Abstr.: The availability of com. gravimetric and volumetric systems for the measurement of adsorption equil. has seen also a growth of the use of these instruments to measure adsorption kinetics. A review of publications from the past 20 years has been used to assess common practice in 180 cases. There are worrying trends obsd., such as lack of information on the actual conditions used in the expt. and the fact that the anal. of the data is often based on models that do not apply to the exptl. systems used. To provide guidance to users of these techniques this contribution is divided into two parts: a discussion of the appropriate models to describe diffusion in porous materials is presented for different gravimetric and volumetric systems, followed by a structured discussion of the main trends in common practice uncovered reviewing a large no. of recent publications. We conclude with recommendations for best practice to avoid incorrect interpretation of these expts.
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    74. 74
      Bezrukov, A. A.; O’Hearn, D. J.; Gascón-Pérez, V.; Darwish, S.; Kumar, A.; Sanda, S.; Kumar, N.; Francis, K.; Zaworotko, M. J. Metal-organic frameworks as regeneration optimized sorbents for atmospheric water harvesting. Cell Rep. Phys. Sci. 2023, 4 (2), 101252  DOI: 10.1016/j.xcrp.2023.101252
      74
      Metal-organic frameworks as regeneration optimized sorbents for atmospheric water harvesting
      Bezrukov, Andrey A.; O'Hearn, Daniel J.; Gascon-Perez, Victoria; Darwish, Shaza; Kumar, Amrit; Sanda, Suresh; Kumar, Naveen; Francis, Kurt; Zaworotko, Michael J.
      Cell Reports Physical Science (2023), 4 (2), 101252CODEN: CRPSF5; ISSN:2666-3864. (Elsevier Inc.)
      As the freshwater crisis looms, metal-org. frameworks (MOFs) with stepped isotherms lie at the forefront of desiccant development for atm. water harvesting (AWH). Despite numerous studies on water sorption kinetics in MOF desiccants, the kinetics of AWH sorbents are a challenge to quantify. Here, we report that the AWH kinetics of seven known MOFs and the industry-std. desiccant Syloid are limited by diffusion to the sorbent bed surface. A quant. model that exploits isotherm shape enables simulation of sorption cycling to evaluate sorbent performance through productivity contour plots ("heatmaps"). These heatmaps reveal two key findings: steady-state oscillation around partial loading optimizes productivity, and dense ultramicroporous MOFs with a step at low relative humidity afford superior volumetric performance under practically relevant temp. swing conditions (27°C, 30% relative humidity [RH] - 60°C, 5.4% RH). Cellulose-desiccant composites of two such regeneration optimized sorbents retain the kinetics of powders, producing up to 7.3 L/kg/day of water under these conditions.
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    75. 75
      Snurr, R. Q.; Bell, A. T.; Theodorou, D. N. Prediction of adsorption of aromatic hydrocarbons in silicalite from grand canonical Monte Carlo simulations with biased insertions. J. Phys. Chem. A 1993, 97 (51), 13742– 13752,  DOI: 10.1021/j100153a051
      75
      Prediction of adsorption of aromatic hydrocarbons in silicalite from grand canonical Monte Carlo simulations with biased insertions
      Snurr, Randall Q.; Bell, Alexis T.; Theodorou, Doros N.
      Journal of Physical Chemistry (1993), 97 (51), 13742-52CODEN: JPCHAX; ISSN:0022-3654.
      Adsorption isotherms and isosteric heats of adsorption for benzene and p-xylene in silicalite have been calcd. from mol. simulations. The simulations were performed using newly developed grand canonical ensemble Monte Carlo (GCMC) techniques in which insertion attempts are biased toward the most favorable regions of the zeolite pore space. The new techniques result in a substantial improvement in the efficiency of the simulations compared to traditional GCMC. The adsorption thermodn. and mol.-level structure were studied for benzene and p-xylene in silicate with Pnma symmetry (ORTHO) and P212121 symmetry (PARA). The subtle differences between ORTHO and PARA silicate result in qual. different sorption behavior. An explanation of the exptl. obsd. step in the adsorption isotherm is presented, based on the results of the simulations and the ORTHO to PARA framework transformation that is obsd. exptl. Prediction of the adsorption isotherms, isosteric heats, and siting locations of the adsorbates are in good agreement with expt.
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    76. 76
      Torres-Knoop, A.; Krishna, R.; Dubbeldam, D. Separating Xylene Isomers by Commensurate Stacking of p-Xylene within Channels of MAF-X8. Angew. Chem., Int. Ed. 2014, 53 (30), 7774– 7778,  DOI: 10.1002/anie.201402894
      76
      Separating Xylene Isomers by Commensurate Stacking of p-Xylene within Channels of MAF-X8
      Torres-Knoop, Ariana; Krishna, Rajamani; Dubbeldam, David
      Angewandte Chemie, International Edition (2014), 53 (30), 7774-7778CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The development of energy-efficient processes for selective sepn. of p-xylene from mixts. with its isomers is of vital importance in the petrochem. industries. Current industrial practice uses BaX zeolite that has high adsorption selectivity for p-xylene. Finding para-selective structures is challenging. With state-of-the-art simulation methodologies the authors systematically screened a wide variety of zeolites and metal-org. frameworks (MOFs). The authors' studies highlight the crucial importance of the channel dimension on the sepn. MAF-X8 is particularly noteworthy because the channel dimensions and geometry allow commensurate stacking which the authors exploit as a sepn. mechanism at satn. conditions. Due to a significantly improved capacity compared to BaX, the cycle times for p-xylene with MAF-X8 are about a factor of 4.5 longer. This is expected to result in significant process improvements.
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    77. 77
      Yan, H.; Quan, J.; Qu, H.; Zhu, F.; Wang, Y.; Dhinakaran, M. K.; Han, T.; Li, H. Membranes with Nanochannels Based on Pillar[6]arenes to Separate Xylenes. ACS Appl. Nano Mater. 2022, 5 (12), 18637– 18644,  DOI: 10.1021/acsanm.2c04408
      77
      Membranes with Nanochannels Based on Pillar[6]arenes to Separate Xylenes
      Yan, Hewei; Quan, Jiaxin; Qu, Haonan; Zhu, Fei; Wang, Yingqian; Dhinakaran, Manivannan Kalavathi; Han, Ting; Li, Haibing
      ACS Applied Nano Materials (2022), 5 (12), 18637-18644CODEN: AANMF6; ISSN:2574-0970. (American Chemical Society)
      Membrane sepn. technol. has been widely applied in material sepn. fields. However, it still has the disadvantage of poor selectivity at nanometer and sub-nanometer scales. Here, two kinds of pillar[6]arene with opposite charges were prepd. by modification, and the aligned nanochannel composite membrane was successfully constructed by directional assembly on a neg. charged silicon interface. The precise sieving properties of aligned channels were studied using the xylene isomer as a model mol. It has been proved that the aligned channel can better maintain the pore size close to the macrocyclic mols., which is beneficial to realize the customized construction of the through-ordered nanochannel. The exptl. results show that the aligned nanochannel can selectively transport xylene isomers, and the flux (J) values of o, m, and p-xylene were 9.2, 11.6, and 171.3 nM m-2 h-1, resp. Finally, the sepn. and purifn. of mixed samples have been achieved. This method provides a strategy for constructing ordered nanochannels.
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