Sang Beom Choi

Ultrahigh Porosity in Metal-Organic Frameworks

Network Approaches to Highly Porous Materials Metal-organic frameworks (MOFs), in which inorganic centers are bridged by organic linkers, can achieve very high porosity for gas absorption. However, as the materials develop larger void spaces, there is also more room for growing interpenetrating networks—filling the open spaces not with gas molecules but with more MOFs. Furukawa et al. (p. 424, published online 1 July) describe the synthesis of a MOF in which zinc centers are bridged with long, highly conjugated organic linkers, but in which the overall symmetry of the networks created prevents formation of interpenetrating networks. Extremely high surface areas and storage capacities for hydrogen, carbon dioxide, and methane were observed. The large surface areas of these materials would correspond to that of dispersed nanocubes just 3 to 6 nanometers wide. Crystalline solids with extended non-interpenetrating three-dimensional crystal structures were synthesized that support well-defined pores with internal diameters of up to 48 angstroms. The Zn4O(CO2)6 unit was joined with either one or two kinds of organic link, 4,4′,4″-[benzene-1,3,5-triyl-tris(ethyne-2,1-diyl)]tribenzoate (BTE), 4,4′,44″-[benzene-1,3,5-triyl-tris(benzene-4,1-diyl)]tribenzoate (BBC), 4,4′,44″-benzene-1,3,5-triyl-tribenzoate (BTB)/2,6-naphthalenedicarboxylate (NDC), and BTE/biphenyl-4,4′-dicarboxylate (BPDC), to give four metal-organic frameworks (MOFs), MOF-180, -200, -205, and -210, respectively. Members of this series of MOFs show exceptional porosities and gas (hydrogen, methane, and carbon dioxide) uptake capacities. For example, MOF-210 has Brunauer-Emmett-Teller and Langmuir surface areas of 6240 and 10,400 square meters per gram, respectively, and a total carbon dioxide storage capacity of 2870 milligrams per gram. The volume-specific internal surface area of MOF-210 (2060 square meters per cubic centimeter) is equivalent to the outer surface of nanoparticles (3-nanometer cubes) and near the ultimate adsorption limit for solid materials.

Catalytic nickel nanoparticles embedded in a mesoporous metal–organic framework

Ni nanoparticles embedded in the pores of a mesoporous MOF (MesMOF-1) act as a catalyst for hydrogenolysis of nitrobenzene or hydrogenation of styrene.

Reversible Interpenetration in a Metal-Organic Framework Triggered by Ligand Removal and Addition

Interpenetration is known for the structures of many minerals and ice; most notably for ice, it exists in doubly interpenetrating (VI, VII, and VIII) and non-interpenetrating (Ih) forms with the latter being porous and having nearly half of the density of the former. In synthetic materials, specifically in metal–organic frameworks (MOFs), interpenetration is generally considered undesirable because it reduces porosity. However, on the contrary, many advantageous properties also arise when MOFs are interpenetrated, such as selective guest capture, stepwise gas adsorption, enhanced framework robustness, photoluminescence control, and guest-responsive porosity. Therefore, various strategies have been suggested to control interpenetration during synthesis. However, once these extended network materials are prepared as interpenetrating or non-interpenetrating structures, the degree of interpenetration generally remains unchanged, because numerous chemical bonds must be broken and subsequently reformed in a very concerted way during the process unlike some interlocked coordination compounds in solution (Figure 1a).

Control of catenation in CuTATB-n metal–organic frameworks by sonochemical synthesis and its effect on CO2 adsorption

The metal–organic frameworks CuTATB-n (TATB = 4,4′,4″-s-triazine-2,4,6-triyltribenzoate; n = power level) having either catenated (CuTATB-60) or non-catenated (CuTATB-30) structure were synthesized in 1 h via a novel sonochemical route. The control of catenation was achieved by simple adjustment of the ultrasonic power levels. The X-ray diffraction patterns, BET surface areas (3778 and 2477 m2 g−1, respectively) and pore volumes, and TGA patterns of the individual product obtained were in agreement with the published literature data of the corresponding materials known as PCN-6 (catenated) and PCN-6′ (non-catenated). Catenation of the two identical networks within large pores resulted in both high surface area and enhanced stability of the network. Such control of catenation was additionally demonstrated by successful synthesis of IRMOF-9 (catenated) and IRMOF-10 (non-catenated) pair by the same sonochemical method. CO2 adsorption properties of the CuTATB-n were measured at 273 and 298 K, which indicated the contribution of catenation in CuTATB-n for CO2 capture. The adsorption isotherms for CO2 and N2 show high adsorption capacity for CO2 (189 mg g−1 and 156 mg g−1, respectively for CuTATB-60 and -30 at 298 K) and excellent selectivity over N2 (>20 : 1). Five consecutive adsorption–desorption runs performed using high purity CO2 in a flow system established no deterioration in the adsorption capacity of CuTATB-60, which showed reversible adsorbent regeneration at 75 °C under He flow and excellent stability for a total duration of 800 min. CuTATB-60 has also demonstrated high gas adsorption capacity (1171 mgCO2 g−1adsorbent) at 30 bar and 298 K.

Crystal structure and electronic properties of 2-amino-2-methyl-1-propanol (AMP) carbamate

A crystal structure of a carbamate of 2-amino-2-methyl-1-propanol (AMP-carbamate) has been elucidated and its structural and electronic properties investigated by density functional theory calculations and natural bond orbital analyses.

Near achiral metal–organic frameworks from conformationally flexible homochiral ligands resulted by the preferential formation of pseudo-inversion center in asymmetric unit

A near identical MOF from the reaction between a homochiral ligand and LaIII ion to that from racemic ligand was obtained due to the preferential formation of the pseudo-centrosymmetric arrangement in asymmetric units.

Poly[bis­(μ4-2,3,5,6-tetra­fluoro­benzene-1,4-di­carboxyl­ato-κ4O1:O1′:O4:O4′)bis­(tetra­hydro­furan-κO)dizinc]

The title compound, [Zn2(C8F4O4)2(C4H8O)2]n, has a three-dimensional metal-organic framework structure. The asymmetric unit consists of two ZnII atoms, two tetrahydrofuran ligands, one 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylate ligand and two half 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylate ligands, which are completed by inversion symmetry. One ZnII atom has a distorted trigonal–bipyramidal coordination geometry, while the other has a distorted octahedral geometry. Two independent tetrahydrofuran ligands are each disordered over two sets of sites with occupancy ratios of 0.48 (4):0.52 (4) and 0.469 (17):0.531 (17).

Quantitative Structure-Uptake Relationship of Metal-Organic Frameworks as Hydrogen Storage Material

We reported the relationship between the structure of metal-organic frameworks (MOFs) and the capability of hydrogen uptake. The QSPR (quantitative structure-property relationship) method was used to find out the factor which affects the adsorption amount of hydrogen molecule on the MOFs. The derivatives which were substituted by functionalized aromatic rings showed the effect of polarization within the identical topology of the frame and similar lattice constants. And the typical series of MOFs with different topology of the frames were investigated to examine the influence of topological change. For the consideration of saturation of hydrogen adsorption amounts, the result of fitting the adsorption curve with Langmuir-Freundlich equation was used to the QSPR approach additionally. We found out that the polar surface area plays a key role on the adsorption amount of hydrogen molecule into the MOFs and the specific value of electrostatic potential surface was calculated to indicate the interaction between hydrogen molecule and MOF.