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

A strategy based on reticulating metal ions and organic carboxylate links into extended networks has been advanced to a point that allowed the design of porous structures in which pore size and functionality could be varied systematically. Metal-organic framework (MOF-5), a prototype of a new class of porous materials and one that is constructed from octahedral Zn-O-C clusters and benzene links, was used to demonstrate that its three-dimensional porous system can be functionalized with the organic groups –Br, –NH2, –OC3H7, –OC5H11, –C2H4, and –C4H4 and that its pore size can be expanded with the long molecular struts biphenyl, tetrahydropyrene, pyrene, and terphenyl. We synthesized an isoreticular series (one that has the same framework topology) of 16 highly crystalline materials whose open space represented up to 91.1% of the crystal volume, as well as homogeneous periodic pores that can be incrementally varied from 3.8 to 28.8 angstroms. One member of this series exhibited a high capacity for methane storage (240 cubic centimeters at standard temperature and pressure per gram at 36 atmospheres and ambient temperature), and others the lowest densities (0.41 to 0.21 gram per cubic centimeter) for a crystalline material at room temperature.

http://science.sciencemag.org/content/sci/295/5554/469.full.pdf

Systematic Design of Pore Size and Functionality in Isoreticular MOFs and Their Application in Methane Storage

This critical review will be of interest to the experts in porous solids (including catalysis), but also solid state chemists and physicists. It presents the state-of-the-art on hybrid porous solids, their advantages, their new routes of synthesis, the structural concepts useful for their ‘design’, aiming at reaching very large pores. Their dynamic properties and the possibility of predicting their structure are described. The large tunability of the pore size leads to unprecedented properties and applications. They concern adsorption of species, storage and delivery and the physical properties of the dense phases. (323 references)

Hybrid porous solids: past, present, future

Secondary building units (SBUs) are molecular complexes and cluster entities in which ligand coordination modes and metal coordination environments can be utilized in the transformation of these fragments into extended porous networks using polytopic linkers (1,4-benzenedicarboxylate, 1,3,5,7-adamantanetetracarboxylate, etc.). Consideration of the geometric and chemical attributes of the SBUs and linkers leads to prediction of the framework topology, and in turn to the design and synthesis of a new class of porous materials with robust structures and high porosity.

/pdf/modular-chemistry-secondary-building-units-as-a-basis-for-1s30wd1erl.pdf

Modular chemistry: secondary building units as a basis for the design of highly porous and robust metal-organic carboxylate frameworks.

"Space—the final frontier." This preamble to a well-known television series captures the challenge encountered not only in space travel adventures, but also in the field of porous materials, which aims to control the size, shape and uniformity of the porous space and the atoms and molecules that define it. The past decade has seen significant advances in the ability to fabricate new porous solids with ordered structures from a wide range of different materials. This has resulted in materials with unusual properties and broadened their application range beyond the traditional use as catalysts and adsorbents. In fact, porous materials now seem set to contribute to developments in areas ranging from microelectronics to medical diagnosis.

Ordered porous materials for emerging applications

We review the various kinds of symbols used to characterize the topology of vertices in 3-periodic nets, tiles and polyhedra, and symbols for tilings, making a recommendation for uniform nomenclature where there is some confusion and misapplication of terminology.

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Vertex-, face-, point-, Schläfli-, and Delaney-symbols in nets, polyhedra and tilings: recommended terminology

Stable zeolite-like microporosity, even in the absence of guest molecules, is exhibited by a lanthanide-benzenedicarboxylate (BDC) framework, which was synthesized by the copolymerization of Tb(III) and 1,4-benzenedicarboxylic acid. The open Tb-BDC framework adopts an expanded PtS network structure (see diagram; Tb: open circles; C: full circles; lines connecting Tb to C represent O atoms, and those connecting C atoms are benzene rings) and is capable of reversible gas and liquid sorption.

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A Microporous Lanthanide-Organic Framework.

The rapid growth in the area of metal-organic frameworks (MOFs) continues to provide open structures with interesting compositions, architectures and properties. 2,3 However, this progress, although significant, has not witnessed many discussions on the relationship between porosity and interpenetration of open frameworks; a topic addressed here. We have recently used a synthetic strategy utilizing secondary building units (SBUs) for achieving stable, highly porous, and functionalized open networks.4-6 Here, the extended 3-D framework of crystalline MOF9, Tb2(ADB)3[(CH3)2SO]4‚16[(CH3)2SO], illustrates another aspect of SBUs: namely, their ability to support the existence of large free volume in interpenetrating structures, which thus far have had the propensity to form assemblies containing very little or no free volume. 2

Large free volume in maximally interpenetrating networks: The role of secondary building units exemplified by TB2(ADB)3[(CH3)2SO]4·16[(CH3)2SO]

Self-assembly of a trigonal building subunit with diaminotriazines (DAT) functional groups leads to a unique rod-packing 3D microporous hydrogen-bonded organic framework (HOF-3). This material shows permanent porosity and demonstrates highly selective separation of C2H2/CO2 at ambient temperature and pressure.

/pdf/a-rod-packing-microporous-hydrogen-bonded-organic-framework-3xbabte69k.pdf

M. O'Keeffe

Papers

Vertex-, face-, point-, Schläfli-, and Delaney-symbols in nets, polyhedra and tilings: recommended terminology

A Microporous Lanthanide-Organic Framework.

Large free volume in maximally interpenetrating networks: The role of secondary building units exemplified by TB2(ADB)3[(CH3)2SO]4·16[(CH3)2SO]

A Rod-Packing Microporous Hydrogen-Bonded Organic Framework for Highly Selective Separation of C2H2/CO2 at Room Temperature†

The Crystal Structures of Mg3N2and Zn3N2