Putting an ultrahigh concentration of amine groups into a metal-organic framework for CO2 capture at low pressures

Hydrazine can be grafted in CPO-27-Mg/MOF-74-Mg to provide an ultrahigh concentration of amine groups on the pore surface, giving an exceptionally high CO₂ capture performance, especially at extremely low pressures.

Tremendous efforts have been devoted to increasing the CO₂ capture performance of porous materials, especially for low CO₂ concentration environments. Here, we report that hydrazine can be used as a diamine short enough to functionalize the small-pore metal–organic framework [Mg₂(dobdc)] (H₄dobdc = 2,5-dihydroxyl-1,4-benzenedicarboxylic acid). By virtue of the ultrahigh concentration of free amine groups (6.01 mmol g^–1 or 7.08 mmol cm^–3) capable of reversible carbamic acid formation, the new material [Mg₂(dobdc)(N₂H₄)_1.8] achieves a series of new records for CO₂ capture, such as single-component isotherm uptakes of 3.89 mmol g^–1 or 4.58 mmol cm^–3 at the atmospheric CO₂ concentration of 0.4 mbar at 298 K and 1.04 mmol g^–1 or 1.22 mmol cm^–3 at 328 K, as well as more than a 4.2 mmol g^–1 or 4.9 mmol cm^–3 adsorption/desorption working capacity under dynamic mixed-gas conditions with CO₂ concentrations similar to those in flue gases and ambient air.

A Metal-Organic Framework with a Pore Size/Shape Suitable for Strong Binding and Close Packing of Methane

Much effort has been devoted to develop new porous structures for methane storage. We report a new porous coordination framework showing exceptional methane uptakes (e.g. 263 v/v at 298 K and 65 bar) and adsorption enthalpies (21.6 kJ mol(-1)) as high as current record holders functionalized by open metal sites. Computational simulations demonstrated that the hierarchical pore structure consisting of single-wall nanocages has suitable sizes/shapes and organic binding sites to enforce not only strong host-methane and methane-methane interactions but also dense packing of methane molecules.

Synthesis and stabilization of a hypothetical porous framework based on a classic flexible metal carboxylate cluster

A hypothetical porous network isomeric to MIL-88/MIL-101 has been realized by the introduction of terminal ligands and further stabilized by crosslinking.

Coordination templated [2+2+2] cyclotrimerization in a porous coordination framework

Controlling chemical reactions by the supramolecular confinement effects of nanopores has attracted great attention. Here we show that open metal sites in porous coordination frameworks can constitute more powerful and strict templates for precision syntheses. A Fe(III) dicarboxylate framework functionalized with triangularly arranged metal sites is used to accomplish [2+2+2] cyclotrimerization reactions for organonitrile, alkyne and alkene monomers bearing a geometrically suitable pyridyl group. In situ single-crystal X-ray diffraction facilitates the direct observation of such a coordination templated reaction, before cylcotrimerization, the monomer coordinates at the Fe(III) centre by its pyridyl donor, which forces three unsaturated groups to gather around a position very similar with that of the desired covalent cyclic trimer. After the reaction, the trimers serve as tripodal ligands to perfectly fix the Fe(III) ions and the whole crystal to generate an exceptionally rigid and porous material with large surface area coupled with guest-proof zero thermal expansion.

Structural, energetic, and dynamic insights into the abnormal xylene separation behavior of hierarchical porous crystal

Separation of highly similar molecules and understanding the underlying mechanism are of paramount theoretical and practical importance, but visualization of the host-guest structure, energy, or dynamism is very difficult and many details have been overlooked. Here, we report a new porous coordination polymer featuring hierarchical porosity and delicate flexibility, in which the three structural isomers of xylene (also similar disubstituted benzene derivatives) can be efficiently separated with an elution sequence inversed with those for conventional mechanisms. More importantly, the separation mechanism is comprehensively and quantitatively visualized by single-crystal X-ray crystallography coupled with multiple computational simulation methods, in which the small apertures not only fit best the smallest para-isomer like molecular sieves, but also show seemingly trivial yet crucial structural alterations to distinguish the meta- and ortho-isomers via a gating mechanism, while the large channels allow fast guest diffusion and enable the structural/energetic effects to be accumulated in the macroscopic level.

Syntheses, structures and gas sorption properties of two coordination polymers with a unique type of supramolecular isomerism

Two genuine supramolecular isomers with a unique type of structural difference and completely different porous properties have been synthesized and characterized.

Controlling the flexibility and single-crystal to single-crystal interpenetration reconstitution of metal–organic frameworks

By controlling the guest accessibility to open metal sites, MOFs can select interpenetration reconstitution or not.

Single-crystal X-ray diffraction studies on structural transformations of porous coordination polymers

This review gives a brief overview of single-crystal X-ray diffraction studies and single-crystal to single-crystal transformations of porous coordination polymers.