Porosity Properties of the Conformers of Sodalite-like Zeolitic Imidazolate Frameworks.

The conformational isomers of zeolitic imidazolate frameworks (ZIFs) can have their own unique porosity and structural stability. We report that a new sodalite-like ZIF (termed ß-ZIF-65(Zn)) is polymorphous with as the existing ZIF-65(Zn) (Zn(nIm)2, nIm = 2-nitroimidazolate) but has a different linker conformation in the six-membered rings of sodalite cages. This conformational isomerism leads to distinctive permanent porosity for each conformer, which has been verified by gas adsorption measurements. In addition, variable-temperature X-ray diffraction analyses indicate that ß-ZIF-65(Zn) is more resistant to displacive phase transitions than ZIF-65(Zn). The activated ß-ZIF-65(Zn) conformer adsorbs 2.8 times more benzene than the activated ZIF-65(Zn) at P/ P0 = 0.3 and 298 K. This work suggests that other types of ZIF conformers can be discovered.

Separation of Acetylene from Carbon Dioxide and Ethylene by a Water-Stable Microporous Metal-Organic Framework with Aligned Imidazolium Groups inside the Channels.

Separation of acetylene from carbon dioxide and ethylene is challenging in view of their similar sizes and physical properties. Metal-organic frameworks (MOFs) in general are strong candidates for these separations owing to the presence of functional pore surfaces that can selectively capture a specific target molecule. Here, we report a novel 3D microporous cationic framework named JCM-1. This structure possesses imidazolium functional groups on the pore surfaces and pyrazolate as a metal binding group, which is well known to form strong metal-to-ligand bonds. The selective sorption of acetylene over carbon dioxide and ethylene in JCM-1 was successfully demonstrated by equilibrium gas adsorption analysis as well as dynamic breakthrough measurement. Furthermore, its excellent hydrolytic stability makes the separation processes highly recyclable without a substantial loss in acetylene uptake capacity.

High-Pressure Chemistry of a Zeolitic Imidazolate Framework Compound in the Presence of Different Fluids.

Pressure-dependent structural and chemical changes of the zeolitic imidazolate framework compound ZIF-8 have been investigated using different pressure transmitting media (PTM) up to 4 GPa. The unit cell of ZIF-8 expands and contracts under hydrostatic pressure depending on the solvent molecules used as PTM. When pressurized in water up to 2.2(1) GPa, the unit cell of ZIF-8 reveals a gradual contraction. In contrast, when alcohols are used as PTM, the ZIF-8 unit cell volume initially expands by 1.2% up to 0.3(1) GPa in methanol, and by 1.7% up to 0.6(1) GPa in ethanol. Further pressure increase then leads to a discontinuous second volume expansion by 1.9% at 1.4(1) GPa in methanol and by 0.3% at 2.3(1) GPa in ethanol. The continuous uptake of molecules under pressure, modeled by the residual electron density derived from Rietveld refinements of X-ray powder diffraction, reveals a saturation pressure near 2 GPa. In non-penetrating PTM (silicone oil), ZIF-8 becomes amorphous at 0.9(1) GPa. The structural changes observed in the ZIF-8-PTM system under pressure point to distinct molecular interactions within the pores.

Mixed-Metal Zeolitic Imidazolate Frameworks and their Selective Capture of Wet Carbon Dioxide over Methane.

A presynthesized, square planar copper imidazole complex, [Cu(imidazole)4](NO3)2, was utilized as a precursor in the synthesis of a new series of zeolitic imidazolate frameworks, termed ZIF-202, -203, and -204. The structures of all three members were solved by single-crystal X-ray diffraction analysis, which revealed ZIF-203 and -204 having successfully integrated square planar units within the backbones of their respective frameworks. As a result of this unit, the structures of both ZIF-203 and -204 were found to adopt unprecedented three-dimensional nets, namely, ntn and thl, respectively. One member of this series, ZIF-204, was demonstrated to be highly porous, exhibit exceptional stability in water, and selectively capture CO2 over CH4 under both dry and wet conditions without any loss in performance over three cycles. Remarkably, the regeneration of ZIF-204 was performed under the mild conditions of flowing a pure N2 gas through the material at ambient temperature.

Introduction of functionality, selection of topology, and enhancement of gas adsorption in multivariate metal-organic framework-177.

Metal-organic framework-177 (MOF-177) is one of the most porous materials whose structure is composed of octahedral Zn4O(-COO)6 and triangular 1,3,5-benzenetribenzoate (BTB) units to make a three-dimensional extended network based on the qom topology. This topology violates a long-standing thesis where highly symmetric building units are expected to yield highly symmetric networks. In the case of octahedron and triangle combinations, MOFs based on pyrite (pyr) and rutile (rtl) nets were expected instead of qom. In this study, we have made 24 MOF-177 structures with different functional groups on the triangular BTB linker, having one or more functionalities. We find that the position of the functional groups on the BTB unit allows the selection for a specific net (qom, pyr, and rtl), and that mixing of functionalities (-H, -NH2, and -C4H4) is an important strategy for the incorporation of a specific functionality (-NO2) into MOF-177 where otherwise incorporation of such functionality would be difficult. Such mixing of functionalities to make multivariate MOF-177 structures leads to enhancement of hydrogen uptake by 25%.

Synthesis and Selective CO2 Capture Properties of a Series of Hexatopic Linker-Based Metal-Organic Frameworks.

Four crystalline, porous metal-organic frameworks (MOFs), based on a new hexatopic linker, 1',2',3',4',5',6'-hexakis(4-carboxyphenyl)benzene (H6CPB), were synthesized and fully characterized. Interestingly, two members of this series exhibited new topologies, namely, htp and hhp, which were previously unseen in MOF chemistry. Gas adsorption measurements revealed that all members exhibited high CO2 selectivity over N2 and CH4. Accordingly, breakthrough measurements were performed on a representative example, in which the effective separation of CO2 from binary mixtures containing either N2 or CH4 was demonstrated without any loss in performance over three consecutive cycles.

Poly[(µ3-5-tert-butyl-benzene-1,3-di-carboxyl-ato)di-pyridine-cobalt(II)].

In the title compound, [Co(C12H12O4)(C5H5N)2] n , the Co(II) cation is coordinated by four O atoms from three 5-tert-butyl-benzene-1,3-di-carboxyl-ate anions and two N atoms from pyridine mol-ecules in a distorted octa-hedral geometry. One carboxyl-ate group of the anionic ligand chelates a Co(II) cation while another carboxyl-ate group bridges two Co(II) cations, resulting in a polymeric layer parallel to (101). Weak C-H⋯O hydrogen bonds occur between adjacent polymeric layers. In the crystal, one of pyridine mol-ecules is equally disordered over two positions.

Poly[bis-(ethanol)(µ4-2,3,5,6-tetra-fluoro-benzene-1,4-di-carboxyl-ato)cadmium].

In the title compound, [Cd(C8F4O4)(C2H5OH)2] n , the Cd(II) cation sits on an inversion centre and is coordinated by six O atoms from four tetra-fluoro-benzene-1,4-di-carboxyl-ate anions and two ethanol mol-ecules in a distorted octa-hedral geometry. The anionic ligand is also located on an inversion centre, and connects four Cd(II) cations, generating a two-dimensional polymeric layer parallel to the ab plane. Within the layer, the ethanol mol-ecule links F and O atoms of the nearest anionic ligands via O-H⋯O and O-H⋯F hydrogen bonds. The ethyl group of the ethanol mol-ecule is disordered over two positions with an occupancy ratio of 0.567 (10):0.433 (10).

Porous zeolitic imidazolate frameworks assembled with highly-flattened tetrahedral copper(II) centres and 2-nitroimidazolates.

Cu(II)-based zeolitic imidazolates (Cu-ZIFs), Cu-ZIF-gis and -rho, formulated as Cu(nIm)2 (nIm = 2-nitroimidazolate) have highly-flattened tetrahedral coordination geometry. Cu-ZIF-gis has 2.4 Å cylindrical pores that can adsorb H2 gas, and Cu-ZIF-rho has 19.8 Å cages with a BET surface area of 1320 m2 g-1.

Interplay of metalloligand and organic ligand to tune micropores within isostructural mixed-metal organic frameworks (M'MOFs) for their highly selective separation of chiral and achiral small molecules.

Four porous isostructural mixed-metal-organic frameworks (M'MOFs) have been synthesized and structurally characterized. The pores within these M'MOFs are systematically tuned by the interplay of both the metalloligands and organic ligands which have enabled us not only to direct their highly selective separation of chiral alcohols 1-phenylethanol (PEA), 2-butanol (BUT), and 2-pentanol (2-PEN) with the highest ee up to 82.4% but also to lead highly selective separation of achiral C(2)H(2)/C(2)H(4) separation. The potential application of these M'MOFs for the fixed bed pressure swing adsorption (PSA) separation of C(2)H(2)/C(2)H(4) has been further examined and compared by the transient breakthrough simulations in which the purity requirement of 40 ppm in the outlet gas can be readily fulfilled by the fixed bed M'MOF-4a adsorber at ambient conditions.

Metal imidazolate sulphate frameworks as a variation of zeolitic imidazolate frameworks.

Sulphate ions can be incorporated into zinc imidazolate frameworks to give rise to zinc imidazolate sulphate frameworks, that is, a square-grid network, a zeolite-like GIS framework, or a porous pillar-layered structure where interlayer octahedral Zn2+ ions connect honeycomb-like layers.

Reversible ammonia uptake at room temperature in a robust and tunable metal-organic framework.

Ammonia is useful for the production of fertilizers and chemicals for modern technology, but its high toxicity and corrosiveness are harmful to the environment and human health. Here, we report the recyclable and tunable ammonia adsorption using a robust imidazolium-based MOF (JCM-1) that uptakes 5.7 mmol g-1 of NH3 at 298 K reversibly without structural deformation. Furthermore, a simple substitution of NO3 - with Cl- in a post-synthetic manner leads to an increase in the NH3 uptake capacity of JCM-1(Cl-) up to 7.2 mmol g-1.

Isoreticular expansion of metal-organic frameworks with triangular and square building units and the lowest calculated density for porous crystals.

The concept and occurrence of isoreticular (same topology) series of metal-organic frameworks (MOFs) is reviewed. We describe the preparation, characterization, and crystal structures of three new MOFs that are isoreticular expansions of known materials with the tbo (Cu(3)(4,4',4''-(benzene-1,3,5-triyl-tris(benzene-4,1-diyl))tribenzoate)(2), MOF-399) and pto topologies (Cu(3)(4,4',4''-(benzene-1,3,5-triyl-tribenzoate)(2), MOF-143; Cu(3)(4,4',4''-(triazine-2,4,6-triyl-tris(benzene-4,1-diyl))tribenzoate)(2), MOF-388). One of these materials (MOF-399) has a unit cell volume 17 times larger than that of the first reported material isoreticular to it, and has the highest porosity (94%) and lowest density (0.126 g cm(-3)) of any MOFs reported to date.

Nucleophilicity and accessibility calculations of alkanolamines: applications to carbon dioxide absorption reactions.

Both nucleophilicities and accessibilities of three alkanolamines [monoethanolamine (MEA), (2-(methylamino)ethanol (MAE), and 2-amino-2-methyl-1-propanol (AMP)] were calculated to predict their reactivities with CO(2). After DFT geometry-optimization calculations, the global, group, and atomic nucleophilicities of each amine were obtained using MP2 quantum mechanical calculations. Only global nucleophilicity matched an experimental pK(a) order (MAE > AMP > MEA). However, it failed to predict the slow rate of the sterically hindered AMP and the order of rate constants, MAE > MEA > AMP. The accessibilities of amines to CO(2) have been calculated by MD simulations by monitoring collisions at the reaction centers: N atoms in amines and C in CO(2). The accessibility results indicate that global nucleophilicity needs quantitative correction for steric effects to predict better reactivities of amines with CO(2).

A route to high surface area, porosity and inclusion of large molecules in crystals.

One of the outstanding challenges in the field of porous materials is the design and synthesis of chemical structures with exceptionally high surface areas. Such materials are of critical importance to many applications involving catalysis, separation and gas storage. The claim for the highest surface area of a disordered structure is for carbon, at 2,030 m2 g(-1) (ref. 2). Until recently, the largest surface area of an ordered structure was that of zeolite Y, recorded at 904 m2 g(-1) (ref. 3). But with the introduction of metal-organic framework materials, this has been exceeded, with values up to 3,000 m2 g(-1) (refs 4-7). Despite this, no method of determining the upper limit in surface area for a material has yet been found. Here we present a general strategy that has allowed us to realize a structure having by far the highest surface area reported to date. We report the design, synthesis and properties of crystalline Zn4O(1,3,5-benzenetribenzoate)2, a new metal-organic framework with a surface area estimated at 4,500 m2 g(-1). This framework, which we name MOF-177, combines this exceptional level of surface area with an ordered structure that has extra-large pores capable of binding polycyclic organic guest molecules--attributes not previously combined in one material.

Solvothermal synthesis of Fe-MOF-74 and its catalytic properties in phenol hydroxylation.

A Fe-containing metal-organic framework, Fe-MOF-74, was solvothermally synthesized using FeCl2.4H2O and 2,5-di-hydroxy-1,4-benzenedicarboxylic acid. Characterization was conducted by XRD, BET surface area measurement, FT-IR spectroscopy, TGA, and elemental analysis, which confirmed successful preparation of Fe-MOF-74 having an identical framework structure to that reported for MOF-74. Fe-MOF-74 was found to be an effective heterogeneous catalyst for the hydroxylation of phenol using H2O2 as an oxidant; 60% phenol conversion was achieved at 20 degrees C in water with 68 and 32% selectivity to catechol and hydroquinone, respectively. The effect of temperature, phenol/H2O2 mole ratio, catalyst quantity, and solvent on catalytic performance was discussed, and a reaction mechanism is proposed based upon the experimental results.

Two-step gas adsorption induced by the transmetallation in a two-dimensional metal-organic framework.

Transmetallation or replacement of Zn2+ ions with Cu2+ ions in a two-dimensional metal-organic framework, Zn3(TCPB)2(H2O)2 (H3TCPB = 1,3,5-tri(4-carboxyphenoxy)benzene), gives rise to additional gas adsorption, where the additional adsorption amount linearly depends on the degree of the transmetallation.

Poly[bis-(N,N-dimethyl-formamide)(µ-formato)(µ(5)-4-oxidoisophthalato)dizinc(II)].

The title compound, [Zn(2)(CHO(2))(C(8)H(3)O(5))(C(3)H(7)NO)(2)](n), is a three-dimensional metal-organic framework, of which two independent Zn(II) atoms (denoted Zn1 and Zn2) are linked by both 4-oxidoisophthalate and formate bridging ligands. The 4-oxidoisophthalate ligands link two Zn1-type and three Zn2-type atoms, forming a corrugated sheet roughly parallel to the ac plane. The formate ions join two neighboring sheets along the b axis, forming a three-dimensional network. Two independent dimethylformamide ligands are coordinated to separate Zn(II) atoms and fill the voids provided by the framework. Both types of Zn(II) atoms have a distorted trigonal-bipyramidal coordination geometry.

Formation and Encapsulation of All-Inorganic Lead Halide Perovskites at Room Temperature in Metal-Organic Frameworks.

Improving the stability and tuning the optical properties of semiconducting perovskites are vital for their applications in advanced optoelectronic devices. We present a facile synthetic method for hybrid composites of perovskites and metal-organic frameworks (MOFs). A simple two-step solution-based method without organic surfactants was employed to make all-inorganic lead-halide perovskites (CsPbX3; X = Cl, Br, I, or mixed halide compositions) form directly in the pores of MIL-101 MOF. That is, a polar organic solution of lead halide (PbX2) was impregnated into the MOF pores to give PbX2@MIL-101, which was then subjected to a perovskite-formation reaction with cesium halide (CsX) dissolved in methanol. The compositions of the halogen anions in the perovskites can be modulated with various halide precursors, leading to CsPbX3@MIL-101 composites with X3 = Cl3, Cl2Br, Br2Cl, Br3, Br2I, I2Br, and I3 that exhibit gradual variation of band gap energies and tuned emission wavelengths from 417 to 698 nm.

Control of vertex geometry, structure dimensionality, functionality, and pore metrics in the reticular synthesis of crystalline metal-organic frameworks and polyhedra.

Metal-organic polyhedra and frameworks (MOPs and MOFs) were prepared by linking square units M2(CO2)4 (M = Cu and Zn) with a variety of organic linkers designed to control the dimensionality (periodicity) and topology of the resulting structures. We describe the preparation, characterization, and crystal structures of 5 new MOPs and 11 new MOFs (termed MOP-14, -15, -17, -23, -24 and MOF-114, -115, -116, -117, -118, -119, -222, -601, -602, -603, -604) and show how their structures are related to the shape and functionality of the building blocks. The gas uptake behaviors of MOP-23 and MOF-601 to -603 are also presented as evidence that these structures have permanent porosity and rigid architectures.