Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

J. Appl. Cryst.の発刊に際して

The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.

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Reticular synthesis and the design of new materials

Adsorptive separation is very important in industry. Generally, the process uses porous solid materials such as zeolites, activated carbons, or silica gels as adsorbents. With an ever increasing need for a more efficient, energy-saving, and environmentally benign procedure for gas separation, adsorbents with tailored structures and tunable surface properties must be found. Metal–organic frameworks (MOFs), constructed by metal-containing nodes connected by organic bridges, are such a new type of porous materials. They are promising candidates as adsorbents for gas separations due to their large surface areas, adjustable pore sizes and controllable properties, as well as acceptable thermal stability. This critical review starts with a brief introduction to gas separation and purification based on selective adsorption, followed by a review of gas selective adsorption in rigid and flexible MOFs. Based on possible mechanisms, selective adsorptions observed in MOFs are classified, and primary relationships between adsorption properties and framework features are analyzed. As a specific example of tailor-made MOFs, mesh-adjustable molecular sieves are emphasized and the underlying working mechanism elucidated. In addition to the experimental aspect, theoretical investigations from adsorption equilibrium to diffusion dynamics via molecular simulations are also briefly reviewed. Furthermore, gas separations in MOFs, including the molecular sieving effect, kinetic separation, the quantum sieving effect for H2/D2 separation, and MOF-based membranes are also summarized (227 references).

Selective gas adsorption and separation in metal–organic frameworks

From molecules to crystal engineering: supramolecular isomerism and polymorphism in network solids.

Both 1,4,7-trioxa-10,13-dithiacyclopentadecane, C 10 H 20 O 3 S 2 , and 1,4,7,10-tetraoxa-13,16-dithiacyclooctadecane, C 12 H 24 O 4 S 2 , show exo-oriented S and endo-oriented O atoms. The torsion angle of the SCH 2 CH 2 S moiety is anti [-165.93 (8)°] in the former and gauche [60.0 (2)°] in the latter. The latter exhibits C 2 symmetry through the midpoints of the C3-C3' and C11-C11' bonds.

Redetermination of the Structures of 1,4,7-Trioxa-10,13-dithiacyclopentadecane and 1,4,7,10-Tetraoxa-13,16-dithiacyclooctadecane

The structures of four simple pyridazin-3(2H)-ones, the isomeric 4-methylpyridazin-3(2H)-one [C5H6N2O (5)], 5-methylpyridazin-3(2H)-one monohydrate and 6-methylpyridazin-3(2H)-one monohydrate [C5H6N2O.H2O, (6).H2O and (7).H2O] and 2-(p-tolyl)pyridazin-3(2H-one [C11H10N2O (8)], have been determined. Compounds (6)–(7), which crystallize as monohydrates, show extensive bonding while molecules of (5) form hydrogen-bonded dimers. In (8) there are no strong hydrogen bonds as in compounds (5) and (7), the closest intermolecular contacts being pairwise C—H⋯O interactions.

Four Simple Pyridazin‐3(2H)‐ones

Structure of silyl fluoride, SiH3F, at 96 K

The reaction of [Ru3(CO)9(µ3-η2 : η2 : η2-C16H16)]1 with 2.2 molar equivalents of Me3NO in dichloromethane containing cyclohexa-1,3-diene afforded the new tetrahedral complex [Ru4(CO)9(η4-C6H8)(µ3-C16H16)]2 in modest yield. The thermolysis of [Ru4(CO)12(µ4-C6H8)]3 in octane containing an excess of [2,2]paracyclophane (C16H16) and Me3NO afforded the two new butterfly isomers [Ru4(CO)9(µ4-C6H8)(η6-C16H16)]4 and [Ru4(CO)9(µ4-C6H8)(µ3-η2 : η2 : η2-C16H16)]5. Heating compound 4 results in its irreversible conversion to 5. Compounds 2 and 4 have been characterised in the solid state by single-crystal X-ray diffraction and in 2 the [2,2]paracyclophane ring bonds to the cluster via an unusual µ3-η1 : η2 : η2 bonding mode unseen before for an arene ring.

Alexander J. Blake

Papers

Redetermination of the Structures of 1,4,7-Trioxa-10,13-dithiacyclopentadecane and 1,4,7,10-Tetraoxa-13,16-dithiacyclooctadecane

Four Simple Pyridazin‐3(2H)‐ones

Structure of silyl fluoride, SiH3F, at 96 K

Tetraruthenium cluster isomers containing both C6H8 and [2.2]paracyclophane ligands: a new face-bridging co-ordination mode for a C6 aromatic ring

Supramolecular Design of One-Dimensional Coordination Polymers Based on Silver(I) Complexes of Aromatic Nitrogen-Donor Ligands