The construction of thousands of well-defined, porous, metal–organic framework (MOF) structures, spanning a broad range of topologies and an even broader range of pore sizes and chemical functionalities, has fuelled the exploration of many applications. Accompanying this applied focus has been a recognition of the need to engender MOFs with mechanical, thermal and/or chemical stability. Chemical stability in acidic, basic and neutral aqueous solutions is important. Advances over recent years have made it possible to design MOFs that possess different combinations of mechanical, thermal and chemical stability. Here, we review these advances and the associated design principles and synthesis strategies. We focus on how these advances may render MOFs effective as heterogeneous catalysts, both in chemically harsh condensed phases and in thermally challenging conditions relevant to gas-phase reactions. Finally, we briefly discuss future directions of study for the production of highly stable MOFs. Metal–organic frameworks (MOFs) have shown promise in a broad range of applications, including catalysis. In this Review, the chemical, thermal and mechanical stabilities of MOFs, in particular with catalytic uses in mind, are discussed.

Chemical, thermal and mechanical stabilities of metal–organic frameworks

This review article presents the fundamental and practical aspects of water adsorption in Metal–Organic Frameworks (MOFs). The state of the art of MOF stability in water, a crucial issue to many applications in which MOFs are promising candidates, is discussed here. Stability in both gaseous (such as humid gases) and aqueous media is considered. By considering a non-exhaustive yet representative set of MOFs, the different mechanisms of water adsorption in this class of materials are presented: reversible and continuous pore filling, irreversible and discontinuous pore filling through capillary condensation, and irreversibility arising from the flexibility and possible structural modifications of the host material. Water adsorption properties of more than 60 MOF samples are reported. The applications of MOFs as materials for heat-pumps and adsorbent-based chillers and proton conductors are also reviewed. Some directions for future work are suggested as concluding remarks.

/pdf/water-adsorption-in-mofs-fundamentals-and-applications-25siy6wd87.pdf

Water adsorption in MOFs: fundamentals and applications

This review (over 380 references) summarizes metal–organic frameworks (MOFs), Materials Institute Lavoisier (MILs), iso-reticular metal–organic frameworks (IR-MOFs), porous coordination networks (PCNs), zeolitic metal–organic frameworks (ZMOFs) and porous coordination polymers (PCPs) with selected examples of their structures, concepts for linkers, syntheses, post-synthesis modifications, metal nanoparticle formations in MOFs, porosity and zeolitic behavior for applications in gas storage for hydrogen, carbon dioxide, methane and applications in conductivity, luminescence and catalysis.

MOFs, MILs and more: concepts, properties and applications for porous coordination networks (PCNs)

Triazoles and tetrazoles: Prime ligands to generate remarkable coordination materials

While much attention of the MOF community has been devoted to adsorption and purification of gases, there is now also a vast body of data on the capability of MOFs to separate and purify liquid mixtures. Initial studies focused on separation of petrochemicals in apolar backgrounds, but the attention has moved now to the separation of complex, e.g. chiral compounds, and to the isolation of biobased compounds from aqueous media. We here give an overview of most of the existing literature, with an accent on separation mechanisms and structure–selectivity relationships.

/pdf/adsorptive-separation-on-metal-organic-frameworks-in-the-26c5c11a8w.pdf

Adsorptive separation on metal-organic frameworks in the liquid phase.

The 3D metal−organic framework (MOF) 3∞{[Ni3(μ3-btc)2(μ4-btre)2(μ-H2O)2]·∼22H2O} is found to be a reversibly dehydratable−hydratable water-stable MOF material with a large loading spread of 210 g/kg as a candidate for solid adsorbents in heat transformation cycles for refrigeration, heat pumping, and heat storage.

MOFs as adsorbents for low temperature heating and cooling applications.

The hydrothermal reaction of M(NO3)2·6H2O (M = Ni and Zn) with benzene-1,3,5-tricarboxylic acid (H3btc) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers (MOFs) 3∞{[Ni3(µ3-btc)2(µ4-btre)2(µ-H2O)2]·∼22H2O} (1) and 3∞{[Zn3(µ4-btc)2(µ4-btre)(H2O)2]·2H2O} (3). The compounds, characterized by single-crystal X-ray diffraction, X-ray powder diffraction and thermoanalysis feature trinuclear secondary building units (SBU) within the three-dimensional frameworks. The trinuclear nickel unit in 1 exhibits an intra-trimer together with some weak inter-trimer antiferromagnetic coupling with J = −13.88(8) cm−1 from the magnetic susceptibility measurement between 1.9–300 K. The zinc coordination polymer 3 shows a strong fluorescence at 423 nm upon excitation at 323 nm (not seen in the free btre ligand). Compound 3 is thermally robust until 200 °C (ambient pressure) where loss of the water molecules starts. Careful control of the dehydration procedure (freeze-drying) for 1 and (heating to 280 °C) for 3 allowed for a solid-state reaction with single-crystal-to-single-crystal structural transformations in obtaining the largely dehydrated products 3∞{[Ni3(µ2-btc)2(µ4-btre)2(µ-H2O)2(H2O)2]·4H2O} (2) and 3∞{[Zn3(µ6-btc)2(µ4-btre)2]·∼0.67H2O} (4), respectively. In the transformation from 1 to 2 the unit cell volume is reduced to about 60%. The transition from 3 to 4 involves breakage and formation of new Zn–O bonds.

Mixed-ligand coordination polymers from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzene-1,3,5-tricarboxylate: Trinuclear nickel or zinc secondary building units for three-dimensional networks with crystal-to-crystal transformation upon dehydration

Hydrothermal reactions of 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) with copper(II), zinc(II), and cadmium(II) salts have yielded the dinuclear complexes [Zn2Cl4(μ2-btre)2] (1) and [Zn2Br4(μ2-btre)2] (2), the one-dimensional coordination polymer ∞1[Zn(NCS)2(μ2-btre)] (3), the two-dimensional networks ∞2[Cu2(μ2-Cl)2(μ4-btre)] (4), ∞2[Cu2(μ2-Br)2(μ4-btre)] (5), and ∞2{[Cd6(μ3-OH)2(μ3-SO4)4(μ4-btre)3(H2O)6](SO4)·∼6H2O} (6), and the three-dimensional frameworks ∞3{[Cu(μ4-btre)]ClO4·∼0.25H2O} (7), ∞3{[Zn(μ4-btre)(μ2-btre)](ClO4)2} (8), ∞3{[Cd(μ4-btre)(μ2-btre)](ClO4)2} (9), and ∞3[Cu2(μ2-CN)2(μ4-btre)] (10, 2-fold 3D interpenetrated framework). The copper-containing products 4, 5, 7, and 10 contain the metal in the +1 oxidation state, from a simultaneous redox and self-assembly reaction of the Cu(II) starting materials. The cyanide-containing framework 10 has captured the CN− ions from the oxidative btre decomposition. The perchlorate frameworks 7, 8, or 9 react in an aqueous NH4+PF6− solution with formation of...

Crystal structure solid-state cross polarization magic angle spinning 13C NMR correlation in luminescent d10 metal-organic frameworks constructed with the 1,2-Bis(1,2,4-triazol-4-yl)ethane ligand.

The hydrothermal reaction of M(NO3)2·4H2O (M = Zn and Cd) with benzene-1,4-dicarboxylic acid (H2bdc) or benzene-1,3-dicarboxylic acid (H2ip) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers (MOFs) 3∞{[Zn2(μ2-bdc)2(μ4-btre)]} (1), 3∞{[Cd2(μ4-bdc)(μ4-btre)2](NO3)2·H2O} (2) and 2∞{[Zn2(μ3-ip)2(μ2-btre)(H2O)2]·2H2O} (3). The compounds, characterized by single-crystal X-ray diffraction, X-ray powder diffraction, solid-state cross-polarization (CP) magic-angle-spinning (MAS) 13C NMR and thermoanalysis, feature 3D metal–organic frameworks for 1 and 2 and 2D double layers which are connected through hydrogen bonds from the aqua ligands for 3. The CPMAS 13C NMR spectra picture the symmetry-independent (unique) C atoms and the bdc/ip-to-btre ligand ratio in agreement with the crystal structures. The zinc and cadmium coordination polymers 1–3 show a strong bluish fluorescence upon excitation with UV light (the free btre ligand is non-luminescent).

Crystal structures and solid-state CPMAS 13C NMR correlations in luminescent zinc(II) and cadmium(II) mixed-ligand coordination polymers constructed from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzenedicarboxylate

Magnetic and luminescence properties of Cu(II), Cu(II)4O4 core, and Cd(II) mixed-ligand metal–organic frameworks constructed from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzene-1,3,5-tricarboxylate

Hesham A. Habib

Papers

MOFs as adsorbents for low temperature heating and cooling applications.

Mixed-ligand coordination polymers from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzene-1,3,5-tricarboxylate: Trinuclear nickel or zinc secondary building units for three-dimensional networks with crystal-to-crystal transformation upon dehydration

Crystal structure solid-state cross polarization magic angle spinning 13C NMR correlation in luminescent d10 metal-organic frameworks constructed with the 1,2-Bis(1,2,4-triazol-4-yl)ethane ligand.

Crystal structures and solid-state CPMAS 13C NMR correlations in luminescent zinc(II) and cadmium(II) mixed-ligand coordination polymers constructed from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzenedicarboxylate

Magnetic and luminescence properties of Cu(II), Cu(II)4O4 core, and Cd(II) mixed-ligand metal–organic frameworks constructed from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzene-1,3,5-tricarboxylate