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

Metal–Organic Frameworks for Separations

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

Luminescent Functional Metal–Organic Frameworks

Metal–organic frameworks (MOFs) display a wide range of luminescent behaviors resulting from the multifaceted nature of their structure. In this critical review we discuss the origins of MOF luminosity, which include the linker, the coordinated metal ions, antenna effects, excimer and exciplex formation, and guest molecules. The literature describing these effects is comprehensively surveyed, including a categorization of each report according to the type of luminescence observed. Finally, we discuss potential applications of luminescent MOFs. This review will be of interest to researchers and synthetic chemists attempting to design luminescent MOFs, and those engaged in the extension of MOFs to applications such as chemical, biological, and radiation detection, medical imaging, and electro-optical devices (141 references).

Luminescent Metal–Organic Frameworks

When Robson introduced for the first time the design of coordination polymers (CPs) in 1989, nobody could imagine that this concept would open a fascinating new world in the field of chemistry, materials science, and nanotechnology. Although based on the very simple concept that “multifunctional organic molecules can connect metal ions through the space,” this synthetic strategy has become an invaluable source of new materials with exceptional structures, properties and applications. In fact, since 1989, the progress made on the design, synthesis, and characterization of CPs as well as on the study of their properties and applications has been spectacular. Today, chemists seem to do magic when they use coordination chemistry to connect metal ions through bridging organic ligands, allowing the continuous discovery of novel CPs. In addition, the coordination chemistry has not walked alone! The development of CPs has also been closely accompanied by the rapid evolution and sophistication of the supramolecular chemistry and the crystal engineering. Today, a CP cannot be considered as an isolated object. Their structures, shapes, and properties depend not only on the metal-organic association but also on the supramolecular interaction, such as hydrogen bonds and π–π interactions, existing between each coordination entity. Among the highly diverse family of CPs, the one-dimensional (1D) systems represent the simplest and undoubtedly one of the most abundant topologies in the literature. The simplicity of these topologies confers to these systems high degrees of freedom, and consequently, a large panel of interchains interactions and self-association leading to original architectures with a variety of properties. Thus, in the last years, a large number of novel materials, such as chains and helices, based on the self-assembly of 1D CPs have been reported. In this section, we attempt to give not an exhaustive but a representative overview of self-assembled coordination chains and helices.


Keywords:

self-assembly;
coordination polymer;
nanomaterials;
chains;
helices

Self‐Assembly of Coordination Chains and Helices

Review: [recently developed synthetic strategies to control the one-, two- and three-dimensional organisation of MOF crystals; 53 refs.

Metal-Organic Frameworks: From Molecules/Metal Ions to Crystals to Superstructures

Abstract Water pollution threatens human and environmental health worldwide. Thus, there is a pressing need for new approaches to water purification. Herein, we report a novel supramolecular strategy based on the use of a metal‐organic polyhedron (MOP) as a capture agent to remove nitrogenous organic micropollutants from water, even at very low concentrations (ppm), based exclusively on coordination chemistry at the external surface of the MOP. Specifically, we exploit the exohedral coordination positions of RhII‐MOP to coordinatively sequester pollutants bearing N‐donor atoms in aqueous solution, and then harness their exposed surface carboxyl groups to control their aqueous solubility through acid/base reactions. We validated this approach for removal of benzotriazole, benzothiazole, isoquinoline, and 1‐napthylamine from water.

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pH‐Triggered Removal of Nitrogenous Organic Micropollutants from Water by Using Metal‐Organic Polyhedra

Ammonia (NH3) is among the world’s most widely produced bulk chemicals, given its extensive use in diverse sectors such as agriculture; however, it poses environmental and health risks at low concentrations. Therefore, there is a need for developing new technologies and materials to capture and store ammonia safely. Herein, we report for the first time the use of metal–organic polyhedra (MOPs) as ammonia adsorbents. We evaluated three different rhodium-based MOPs: [Rh2(bdc)2]12 (where bdc is 1,3-benzene dicarboxylate); one functionalized with hydroxyl groups at its outer surface [Rh2(OH-bdc)2]12 (where OH-bdc is 5-hydroxy-1,3-benzene dicarboxylate); and one decorated with aliphatic alkoxide chains at its outer surface [Rh2(C12O-bdc)2]12 (where C12O-bdc is 5-dodecoxybenzene-1,3-benzene dicarboxylate). Ammonia-adsorption experiments revealed that all three Rh-MOPs strongly interact with ammonia, with uptake capacities exceeding 10 mmol/gMOP. Furthermore, computational and experimental data showed that the mechanism of the interaction between Rh-MOPs and ammonia proceeds through a first step of coordination of NH3 to the axial site of the Rh(II) paddlewheel cluster, which triggers the adsorption of additional NH3 molecules through H-bonding interaction. This unique mechanism creates H-bonded clusters of NH3 on each Rh(II) axial site, which accounts for the high NH3 uptake capacity of Rh-MOPs. Rh-MOPs can be regenerated through their immersion in acidic water, and upon activation, their ammonia uptake can be recovered for at least three cycles. Our findings demonstrate that MOPs can be used as porous hosts to capture corrosive molecules like ammonia, and that their surface functionalization can enhance the ammonia uptake performance.

Ammonia Capture in Rhodium(II)-Based Metal–Organic Polyhedra via Synergistic Coordinative and H-Bonding Interactions

Vapor-phase film deposition of metal–organic frameworks (MOFs) would facilitate the integration of these materials into electronic devices. We studied the vapor-phase layer-by-layer deposition of zeolitic imidazolate framework 8 (ZIF-8) by consecutive, self-saturating reactions of diethyl zinc, water, and 2-methylimidazole on a substrate. Two approaches were compared: (1) Direct ZIF-8 “molecular layer deposition” (MLD), which enables a nanometer-resolution thickness control and employs only self-saturating reactions, resulting in smooth films that are crystalline as-deposited, and (2) two-step ZIF-8 MLD, in which crystallization occurs during a postdeposition treatment with additional linker vapor. The latter approach resulted in a reduced deposition time and an improved MOF quality, i.e., increased crystallinity and probe molecule uptake, although the smoothness and thickness control were partially lost. Both approaches were developed in a modified atomic layer deposition reactor to ensure cleanroom compatibility. 

Daniel Maspoch

Papers

Self‐Assembly of Coordination Chains and Helices

Metal-Organic Frameworks: From Molecules/Metal Ions to Crystals to Superstructures

pH‐Triggered Removal of Nitrogenous Organic Micropollutants from Water by Using Metal‐Organic Polyhedra

Ammonia Capture in Rhodium(II)-Based Metal–Organic Polyhedra via Synergistic Coordinative and H-Bonding Interactions

Molecular Layer Deposition of Zeolitic Imidazolate Framework-8 Films