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.

The title compound, C9H6O2, contains two moderate C—H⋯O hydrogen bonds. That involving the terminal alkyne gives rise to chains along the b axis. The other hydrogen bond occurs over a centre of symmetry, leading to dimers. The combination of the two interactions gives rise to rings, each comprising six mol­ecules, which are part of infinite sheets in the bc plane.

4-Ethynyl-1,2-methylenedioxybenzene at 150 K.

In the title compound, [Co(C 6 H 12 S 3 ) 2 ](I 3 ) 2 , the cations and anions are linked into infinite sheets through interion S...I contacts of 3.800 (2)-3.989 (2) A.

Bis(1,4,7-trithiacyclononane-S, S', S)-cobalt(II) bis(triiodide)

In the title compound (the ester 2-formyl-3-pyrrolylmethyl acetate, C 8 H 9 NO 3 ), hydrogen bonding between the N-H function in one molecule and the ester carbonyl O atom in a molecule related to the first by the 2 1 screw axis leads to the formation of zigzag chains.

3-Acetoxymethylpyrrole-2-carbaldehyde

A New Cofacial Binucleating Macropolycycle: Segregated versus Encapsulated Complexation.

7-(3-[1-(4-Phenylthiosemicarbazono)ethyl]-bicyclo[2.2.1]hept-2- yl)-5-heptenoic acid, C23H31N3-O2S, Mr = 413.7, monoclinic, P2(1)/a, a = 12.9650 (7), b = 11.2081 (6), c = 16.8941 (12) A, beta = 110.452 (5) degrees, V = 2300.2 A3, Z = 4, Dx = 1.194 g cm-3, Mo K alpha, lambda = 0.71073 A, mu = 1.55 cm-1, F(000) = 888, T = 298 K. Final R = 0.0472 with 2778 independent data. EP 092 is a thromboxane receptor antagonist akin to many other analogues of the thromboxane A2 [Wilson & Jones (1985). Adv. Prostaglandin Thromboxane Leukotriene Res. 14, 393-425].

Alexander J. Blake

Papers

4-Ethynyl-1,2-methylenedioxybenzene at 150 K.

Bis(1,4,7-trithiacyclononane-S, S', S)-cobalt(II) bis(triiodide)

3-Acetoxymethylpyrrole-2-carbaldehyde

A New Cofacial Binucleating Macropolycycle: Segregated versus Encapsulated Complexation.

Structure of the thromboxane receptor antagonist EP 092.