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Establishing new energy-saving systems for gas separation using porous materials is indispensable for ensuring a sustainable future. Herein, we show that ELM-11 ([Cu(BF4)2(4, 4′-bipyridine)2]n), a member of flexible metal–organic frameworks (MOFs), exhibits rapid responsiveness to a gas feed and an ‘intrinsic thermal management’ capability originating from a structural deformation upon gas adsorption (gate-opening). These two characteristics are suitable for developing a pressure vacuum swing adsorption (PVSA) system with rapid operations. A combined experimental and theoretical study reveals that ELM-11 enables the high-throughput separation of CO2 from a CO2/CH4 gas mixture through adiabatic operations, which are extreme conditions in rapid pressure vacuum swing adsorption. We also propose an operational solution to the ‘slipping-off’ problem, which is that the flexible MOFs cannot adsorb target molecules when the partial pressure of the target gas decreases below the gate-opening pressure. Furthermore, the superiority of our proposed system over conventional systems is demonstrated., ゲート型吸着剤を活用した二酸化炭素の高効率分離システムを提案 --二酸化炭素の分離回収技術の開発に貢献--. 京都大学プレスリリース. 2020-08-04.

Flexible porous materials have great potential for adsorption/separation of small molecules. In this study, a highly CO2-selective two-dimensional (2D) layered metal-organic framework (MOF) showing gate-type adsorption properties was synthesized and fully characterized by single-crystal X-ray diffraction (XRD), in situ powder XRD, thermogravimetric analysis, inductively coupled plasma atomic emission spectroscopy, and gas adsorption/separation analyses. The MOF named ELM-13 is a 2D layered material functionalized with (trifluoromethyl)trifluoroborate to control interlayer interactions and exhibits dynamic guest accommodation/removal properties. In a gas adsorption study, the MOF showed no adsorption at low pressure followed by abrupt uptake and sudden desorption at a pressure lower than that of adsorption, i.e., gate adsorption, in the N2, O2, Ar, NO, and CO2 isotherms at the boiling/sublimation temperature of each gas. The structure of the MOF in the CO2 adsorption was influenced by both the amount adsorbed and the adsorption process. High-pressure adsorption experiments at 273 K indicated that, out of N2, O2, Ar, and CO2, only CO2 was adsorbed on the MOF below 900 kPa. The CO2 selectivity from an equimolar CO2/N2 mixture with a total gas pressure of 1 MPa at 273 K was experimentally evaluated and compared with the CO2 selectivities of other selected porous materials theoretically, suggesting that ELM-13 is a good candidate for CO2 separation.

A double-step CO2 sorption by [Cu(4,4'-bpy)2(BF4)2] (ELM-11) was observed during isothermal measurements at 195, 253, 273, and 298 K and was accompanied by interlayer expansion in the layered structure of ELM-11. The first step occurred in the range of the relative pressure (P/P0) from 10(-3) to 10(-2). The second step was observed at P/P0 ≈ 0.3 at the four temperatures. Structural changes in ELM-11 during the CO2 sorption process were examined by X-ray diffraction (XRD) measurements. The structural change for the first step was well understood from a detailed structural analysis, as reported previously. The XRD results showed further expansion of the layers during the second step as compared to the already expanded structure in the first step, and both steps were found to be caused by the gate phenomenon. The energy for the expansion of the layer structure was estimated from experimental and simulated data.

The gate adsorption mechanism and kinetics of an elastic layer-structured metal–organic framework (ELM), [Cu(bpy)2(BF4)2]n (ELM-11), that shows typical single-step CO2 gate adsorption/desorption isotherms accompanied with dynamic structural transformation in a wide temperature range were investigated. Adsorption of quite a small amount of CO2 on the external surface of ELM-11 crystals was observed at the pressure just below a gate adsorption pressure and induced a slight structural change in ELM-11. The structural change should start occurring at the outer parts of ELM-11 and transmit to more inner parts with rising pressure. The adsorption provides the stabilization of the framework through the interaction between fluid–solid and fluid–fluid and enables the framework to expand largely along the stacking direction. The CO2 adsorption rate of ELM-11 is almost comparable to that of Zeolite 5A at around ambient temperatures and shows temperature dependence with an anti-Arrhenius trend: higher adsorption rate...

Selective synthetic routes to coordination polymers [Cu(bpy)(2)(OTf)(2)](n) (bpy = 4,4'-bipyridine, OTf = trifluoromethanesulfonate) with 2- and 3-dimensionalities of the frameworks were established by properly choosing each different solvent-solution system. They show a quite similar local coordination environment around the Cu(II) centers, but these assemble in a different way leading to the 2D and 3D building-up structures. Although the two kinds of porous coordination polymers (PCPs) both have flexible frameworks, the 2D shows more marked flexibility than the 3D, giving rise to different flexibility-associated gas adsorption behaviors. All adsorption isotherms for N(2), CO(2), and Ar on the 3D PCP are of type I, whereas the 2D PCP has stepwise gas adsorption isotherms, also for CH(4) and water, in addition to these gases. The 3D structure, having hydrophilic and hydrophobic pores, shows the size-selective and quadrupole-surface electrical field interaction dependent adsorption. Remarkably, the 2D structure can accommodate greater amounts of gas molecules than that corresponding to the inherent crystallographic void volume through framework structural changes. In alcohol adsorption isotherms, however, the 2D PCP changes its framework structure through the guest accommodation, leading to no stepwise adsorption isotherms. The structural diversity of the 2D PCP stems from the breathing phenomenon and expansion/shrinkage modulation.

A two-dimensional flexible porous coordination polymer (2D-PCP) that shows expansion/shrinkage structural transformation accompanied by molecular accommodation was synthesized by control of dimensionality in zero-dimensional and one-dimensional PCPs: The dynamic structural transformation cooperatively proceeds in the solid state with a drastic molecular rearrangement. Kinetics of the structural transformation was investigated.

Coordination polymers (CPs) or metal-organic frameworks (MOFs) have attracted considerable attention because of the tunable diversity of structures and functions. A 4,4'-bipyridine molecule, which is a simple, linear, exobidentate, and rigid ligand molecule, can construct two-dimensional (2D) square grid type CPs. Only the 2D-CPs with appropriate metal cations and counter anions exhibit flexibility and adsorb gas with a gate mechanism and these 2D-CPs are called elastic layer-structured metal-organic frameworks (ELMs). Such a unique property can make it possible to overcome the dilemma of strong adsorption and easy desorption, which is one of the ideal properties for practical adsorbents.

Elastic layer-structured metal organic frameworks (ELMs) having flexible two-dimensional structure show a gate phenomenon in sorption/desorption of simple gas molecules. The gate phenomenon is accompanied by expansion/shrinkage of the layers. The gas sorption/desorption is not based on a physical adsorption, but on a chemical reaction, which includes high cooperativity. The cooperative reaction could be analyzed thermodynamically. The gate phenomenon showed advantages in separation of CO2 from mixed gases and in storage of CH4 owing to easy release of absorbed molecules.

It is important to study the interaction between water molecules and a host structure for understanding the adsorption mechanism of metal-organic framework (MOF) materials. The evolution of the structure of a flexible Cu-MOF, {[Cu(bpy)(H2O)2(BF4)2](bpy)} (bpy=4,4'-bipyridine), upon dehydration and rehydration was studied by thermogravimetric analysis (TGA), infrared (IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and water adsorption. A nearly reversible structural change was observed upon rehydration. More importantly, a unique CO2 "gate adsorption" phenomenon was observed despite the exposure of the Cu-MOF to water. This shows that the Cu-MOF has relatively good stability after exposure to water.

The crystal structure of [Cu(4,4'-bipyridine) 2(CF 3SO 3) 2] n metal-organic framework (CuBOTf) of one-dimensional pore networks after pre-evacuation at 383 K was determined with synchrotron X-ray powder diffraction measurement. Effective nanoporosity of the pre-evacuated CuBOTf was determined with N 2 adsorption at 77 K. The experimental H 2 and D 2 adsorption isotherms of CuBOTf at 40 and 77 K were measured and then compared with GCMC-simulated isotherms using the effective nanoporosity. The quantum-simulated H 2 and D 2 isotherms at 77 K using the Feynman-Hibbs effective potential coincided with the experimental ones, giving a direct evidence on the quantum molecular sieving effect for adsorption of H 2 and D 2 on CuBOTf. However, the selectivity for the 1:1 mixed gas of H 2 and D 2 was 1.2. On the contrary, experimental H 2 and D 2 isotherms at 40 K had an explicit adsorption hysteresis, originating from the marked pore blocking effect on measuring the adsorption branch. The blocking effect for quantum H 2 is more prominent than that for quantum D 2; the selectivity for D 2 over H 2 at 40 K was in the range of 2.6 to 5.8. The possibility of the quantum molecular sieving effect for H 2 and D 2 adsorption on [Cu 3(benzene-1,3,5-tricarboxylate) 2(H 2O) 3] n of three-dimensional pore networks was also shown at 77 K.

The supercritical N2, O2, and CH4 adsorption isotherms on a Cu-based metal−organic framework, [Cu(4,4‘-bipyridine)2(BF4)2]n, over the temperature range of 196−303 K were measured by a gravimetric method. The N2 and O2 adsorption isotherms at 196 K showed a vertical adsorption accompanied by a rectangular hysteresis loop. A method of evaluating the absolute adsorption amount of these gases was developed taking into account the intermolecular interactions for the buoyancy-mediated method. The isotherms of the absolute adsorption amount were obviously different from the isotherms of the surface-excess mass adsorption at 196 K. We also obtained isotherms of the absolute adsorption amount of CH4 at different temperatures. The isosteric heat of adsorption from the isotherms of the absolute adsorption amount of CH4 is larger than the liquefaction heat of CH4 at its boiling point by more than 3 kJ mol-1.

N2 adsorption on Cu–organic crystals [Cu(bpy)2(BF4)2] (bpy = bipyridine) at 77 K begins suddenly at P/P 0 = 0.1. This unique adsorption is named gate adsorption. Gate adsorption is associated with the change of crystal structure from GCMC and dynamic GCMC simulations. An expansion of 10% opens internal pore spaces in the crystal, giving rise to gate adsorption. The complete filling of the internal spaces with N2 molecules induces an expansion of 30%.

The development of “LAMINELIGHT®” laminated stainless steel foil for the packaging of lithium-ion batteries is now complete. As a result of simulation, the degree of the deformation of battery packaging made from laminated stainless steel foil caused by rising inner pressure is less than that made from laminated aluminum foil. The simulation also shows that stainless steel foil packaging has a high level of stability and can withstand stress as the laminated resin film is smaller than that of laminated aluminum foil. In addition, the result of laminated stainless steel foil’s critical piercing load is about four times higher than that of laminated aluminum foil. These results show that laminated stainless steel foil can make packaging tougher and more durable than laminated aluminum foil.

Scandium trifluoromethanesulfonate is found to be a Lewis acid catalyst for selective cleavage of esters containing a coordinative group adjacent to an ester moiety. The reaction proceeds under weak acidic conditions at room temperature; the catalyst can be recovered and reused. Even α-acyloxy ketones are deacetylated without racemization. Selective monodeacetylation at C-10 of paclitaxel has been achieved.

A synthesis of (1S,2R)-1-amino-2-indanol (1), a key component of an HIV protease inhibitor, was accomplished through (R)-2-hydroxy-1-indanone ((R)-3), which was prepared by an intramolecular Friedel–Crafts acylation of (R)-2-acetoxy-3-phenylpropanoic acid readily available from D-(R)-phenylalanine. Alternatively, (R)-3 was obtained by an enzymatic resolution of (±)-2-acetoxy-1-indanone. Ketone (R)-3 was converted into 1 through an oxime formation and diastereoselective hydrogenation.

Reduction of several α,β-unsaturated ketones with dimethylphenylsilane and 10–100 mol% of CuF(PPh3)3·2EtOH or CuCl/PPh3/Bu4NF proceeds in a 1,4-selective manner to give the corresponding saturated ketones in up to >99% yield.

Scandium trifluoromethanesulfonate is a useful Lewis acid catalyst for cleavage of acetates containing coordinative groups adjacent to the acetyl carbonyl. The reaction proceeds under weak acidic conditions at room temperature. Racemizable α-keto acyloxy compounds are deacetylated without racemization. Selective mono-deacetylation at the 10-position of paclitaxel has been achieved.

Enantiomerically pure ( R )- or ( S )-2-hydroxy-1-indanone was synthesized by enzymatic kinetic resolution of racemic 2-acetoxy-1-indanone through hydrolysis or transesterification.

It is important to tune the sorption behavior of metal-organic framework (MOF) materials. Ethanol treatment on the hydrated form of [Cu(bpy)(2)(BF(4))(2)], which is a representative flexible MOF showing the fascinating gate phenomenon on CO(2) sorption, induces an easier dehydration and a significant decrease in the CO(2) gate pressure. The results of IR, X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) measurements indicated that water molecules in the lattice of the hydrated form can be removed even at room temperature after the ethanol treatment and the basic 2D layered structure remains with a slight interlayer expansion. The results of thermogravimetric (TG) and gas chromatograph/mass spectrometry (GC/MS) analyses and of CO(2) sorptions indicated that the change of the gate phenomenon was caused by a trace of residual ethanol molecules included in the structure. Similar phenomena were observed on alcohols with different polarity and molecular size.

Coordination polymers (CPs) or metal-organic frameworks (MOFs) have attracted considerable attention because of the tunable diversity of structures and functions. A 4,4'-bipyridine molecule, which is a simple, linear, exobidentate, and rigid ligand molecule, can construct two-dimensional (2D) square grid type CPs. Only the 2D-CPs with appropriate metal cations and counter anions exhibit flexibility and adsorb gas with a gate mechanism and these 2D-CPs are called elastic layer-structured metal-organic frameworks (ELMs). Such a unique property can make it possible to overcome the dilemma of strong adsorption and easy desorption, which is one of the ideal properties for practical adsorbents.

Enantiomerically pure ( R )- or ( S )-2-hydroxy-1-indanone was synthesized by enzymatic kinetic resolution of racemic 2-acetoxy-1-indanone through hydrolysis or transesterification.

Both (E)- and (Z)-alkenylsilanes are synthesized by the reaction of hydrosilanes and 1-alkynes catalyzed by RhCl(PPh3)3/NaI or RhI(PPh3)3 highly selectively.

Scandium trifluoromethanesulfonate is a useful Lewis acid catalyst for cleavage of acetates containing coordinative groups adjacent to the acetyl carbonyl. The reaction proceeds under weak acidic conditions at room temperature. Racemizable α-keto acyloxy compounds are deacetylated without racemization. Selective mono-deacetylation at the 10-position of paclitaxel has been achieved.

The scandium trifluoromethanesulfonate-catalyzed cleavage of acetate bearing two or three fluorine atoms at a position β to an acetoxy group proceeds exceptionally rapidly. The high efficiency of the hydrolysis is caused by a chelating effect of scandium with the fluorine atoms and an acetate moiety.

Reduction of several α,β-unsaturated ketones with dimethylphenylsilane and 10–100 mol% of CuF(PPh3)3·2EtOH or CuCl/PPh3/Bu4NF proceeds in a 1,4-selective manner to give the corresponding saturated ketones in up to >99% yield.

Scandium trifluoromethanesulfonate is found to be a Lewis acid catalyst for selective cleavage of esters containing a coordinative group adjacent to an ester moiety. The reaction proceeds under weak acidic conditions at room temperature; the catalyst can be recovered and reused. Even α-acyloxy ketones are deacetylated without racemization. Selective monodeacetylation at C-10 of paclitaxel has been achieved.

We synthesized a discrete type of organic-inorganic hybrid crystal [Cu(ina)2(NH3)2(H2O)2] (ina = isonicotinate). The monomer units connect to each other with hydrogen bonds and pi-pi interactions, forming a three-dimensional network. Removal of ammonia and water molecules by vacuum heating treatment induced a substantial change from nonporous to porous crystals. The resultant porous crystals can predominantly adsorb supercritical hydrogen rather than nitrogen vapor at 77 K.

One-dimensional metal-organic compounds with cis, trans symmetry-controlled counter anions were synthesized (cis compound {[Cu(azpy)(H2O)2(OTs)2]*2H2O*(acetone)} (1) and trans compound {[Cu(H2O)4Cu(azpy)2(OTs)2(H2O)2]*2(OTs)*2H2O*2EtOH} (2)). Only 2, having trans conformation, exhibited a complete structure-restoration effect with a mechanism involving layering of molecular "bricks" of water and solvent molecules.

Crystal-to-crystal transformation from a 3D interpenetrated-type MOF {[Cu(BF(4))(2)(bpy)(H(2)O)(2)] (bpy)} (1) to a 2D square-grid-type [Cu(BF(4))(2)(bpy)(2)] (2) (bpy = 4,4'-bipyridine) was observed. It was derived from dehydration and confirmed by in situ FT-IR, TG, and elemental analysis. Moreover, we elucidate the novel expansion/shrinkage dynamic modulation of 2 triggered by clathrate formation with gas molecules.

Accurate particle densities of the Cu-based metal organic framework [Cu(4,4'-bipyridine) 2 (BF 4 ) 2 ] for He, N 2 and CH 4 molecules using the high-pressure buoyancy method have been determined. A smaller probe molecule gave a larger particle density (1.70 g/ml from He, 1.66 g/ml from N 2 , 1.60 g/ml from CH 4 ). The effect of particle density on the evaluation of the surface excess mass for supercritical gas adsorption was examined; the above particle density difference gave rise to a 2–4% difference in the surface excess mass.

We measured adsorption and desorption isotherms of methane on [Cu(4, 4'-bipyridine)2(BF4)2] (LPC) at 258, 273, and 303 K. Adsorption proceeds almost vertically at a definite pressure, which is named gate pressure. The lower the measurement temperature, the smaller the gate pressure. The temperature dependence of the gate pressure is expressed by the Clapeyron-Clausius equation, giving a thermodynamic evidence on the clathrate formation between the Cu complex and methane.

A perfluorobutyl-functionalized two-dimensional porous coordination polymer (PCP), {[Cu(bpbtp)(L)(DMF)]·(DMF)}n (H2bpbtp = 2,5-bis(perfluorobutyl)terephthalic acid, L = 2,5-bis(perfluorobutyl)-1,4-bis(4-pyridyl)benzene, DMF = N,N-dimethylformamide) has been synthesized and structurally characterized. The pore surface of the PCP is decorated with pendant perfluorobutyl groups which fabricate a densely fluorinated nanospace resulting in unique gas sorption properties.

The synthesis, structural changes, and nitrogen gas sorption isotherm of a porous metal−organic framework (PMOF) comprising stacked two-dimensional sheets are reported. This compound easily loses guest molecules and shrinks its interlayer distance. The guest-free species show a unique double-step sorption isotherm. Sorption and X-ray structural analyses have clarified that the first uptake is a micropore filling, while the second uptake originates from a clathrate formation. This explains the total sorption amount corresponding to about the double of the original void volume of the crystals.

Hydrosilylation of 1-alkynes catalyzed by RhI(PPh3)3 gives (E)- and (Z)-alkenylsilanes in a stereodivergent manner by switching the reaction conditions and the order of the addition of the reagents. The reaction is also applied to the synthesis of silicon-containing polymers with (E) and (Z) main-chain structures via polyaddition.

The scandium trifluoromethanesulfonate-catalyzed cleavage of acetate bearing two or three fluorine atoms at a position β to an acetoxy group proceeds exceptionally rapidly. The high efficiency of the hydrolysis is caused by a chelating effect of scandium with the fluorine atoms and an acetate moiety.

Both (E)- and (Z)-alkenylsilanes are synthesized by the reaction of hydrosilanes and 1-alkynes catalyzed by RhCl(PPh3)3/NaI or RhI(PPh3)3 highly selectively.