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

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

1. INTRODUCTION Among the classes of highly porous materials, metalÀorganic frameworks (MOFs) are unparalleled in their degree of tunability and structural diversity as well as their range of chemical and physical properties. MOFs are extended crystalline structures wherein metal cations or clusters of cations (\" nodes \") are connected by multitopic organic \" strut \" or \" linker \" ions or molecules. The variety of metal ions, organic linkers, and structural motifs affords an essentially infinite number of possible combinations. 1 Furthermore, the possibility for postsynthetic modification adds an additional dimension to the synthetic variability. 2 Coupled with the growing library of experimentally determined structures, the potential to computationally predict, with good accuracy, affinities of guests for host frameworks points to the prospect of routinely predesigning frameworks to deliver desired properties. 3,4 MOFs are often compared to zeolites for their large internal surface areas, extensive porosity, and high degree of crystallinity. Correspondingly, MOFs and zeolites have been utilized for many of the same applications

Metal–Organic Framework Materials as Chemical Sensors

Metal–Organic Frameworks for Separations

Kenji Sumida, David L. Rogow, Jarad A. Mason, Thomas M. McDonald, Eric D. Bloch, Zoey R. Herm, Tae-Hyun Bae, Jeffrey R. Long

Carbon Dioxide Capture in Metal–Organic Frameworks

A layered aluminium carboxylate containing the 4,4′-azobenzenedicarboxylate anion (MIL-129) has been hydrothermally synthesized (210 °C, 24 h). Its crystal structure was determined by means of microdiffraction technique using synchrotron radiation. It consists of infinite trans-connected chains of aluminium-centered octahedra, linked to each other through the organic molecules, in order to generate infinite sheets, containing double stacking of organic species. The cohesion of the structure is ensured by the close packing due to π–π interactions between aromatic rings of the ligands and no porosity is observed.

A layered coordination polymer based on an azodibenzoate linker connected to aluminium (MIL-129)

Oxyfluorinated microporous compounds. IX: Synthesis and crystal structure of ULM-8: a new layered fluorinated gallophosphate Ga3(PO4)2(HPO4)(H2O)F2, 5N4C6H19)

Simple hydrothermal treatment of the well-known aluminum polycation varepsilon-Al(13) produces the novel Al(30) structure (see picture), the largest polycation yet observed. Its characterization, by X-ray diffraction and NMR spectroscopy, also solved previously unassigned signals in (27)Al NMR spectra of other Al - O species.

Al30: A Giant Aluminum Polycation.

A new aluminum fluoride, Al2F8·2NC5H6·C6H3(CO2H)3, was synthesized under mild hydrothermal conditions (200 °C, 3 days) in the presence of 1,3,5-benzenetricarboxylic acid (btc) in pyridine/HF (pyr/HF) solvent. Its structure is characterized with single-crystal XRD analysis and high-resolution solid-state NMR. The inorganic framework consists of the corner- and edge-shared connections of AlF6 octahedra. They are linked via a common edge and form a bioctahedral motif which is trans-connected through the corner-shared fluorine. It results in the formation of an original infinite double file of AlF6 octahedra running along the a axis. A high-power decoupled MAS 27Al{19F} Hahn echo NMR spectrum allowed us to distinguish the two crystallographic hexacoordinated Al sites. Four unresolved 19F NMR signals are observed in the MAS spectra to account for the eight crystallographic fluorine atoms. Half of the terminal fluorine sites interact via strong hydrogen bonds with the ammonium groups of the pyridine moieties. T...

A ladderlike chain aluminum fluoride ([Al2F8]2-)n with edge-sharing AlF6 octahedra.

Crystal structure and solid-state nuclear magnetic resonance characterization of an oxyfluorinated three-dimensional framework gallophosphate with ULM-4 structural type. Structural relationships with GaAsO4-2

Thierry Loiseau

Papers

A layered coordination polymer based on an azodibenzoate linker connected to aluminium (MIL-129)

Oxyfluorinated microporous compounds. IX: Synthesis and crystal structure of ULM-8: a new layered fluorinated gallophosphate Ga3(PO4)2(HPO4)(H2O)F2, 5N4C6H19)

Al30: A Giant Aluminum Polycation.

A ladderlike chain aluminum fluoride ([Al2F8]2-)n with edge-sharing AlF6 octahedra.

Crystal structure and solid-state nuclear magnetic resonance characterization of an oxyfluorinated three-dimensional framework gallophosphate with ULM-4 structural type. Structural relationships with GaAsO4-2