Gas Adsorption Sites in a Large-Pore Metal-Organic Framework

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.

Supramolecular-jack-like guest in ultramicroporous crystal for exceptional thermal expansion behaviour

The dynamic behaviours of host frameworks and guest molecules have received much attention for their great relevance with smart materials, but little has been developed to control or understand the host-guest interplay. Here we show that the confined guest can utilize not only molecular static effects but also bulk dynamic properties to control the host dynamics. By virtue of the three-dimensional hinge-like framework and quasi-discrete ultramicropores, a flexible porous coordination polymer exhibits not only drastic guest-modulation effect of the thermal expansion magnitude (up to 422 × 10(-6) K(-1)) and even the anisotropy but also records positive/negative thermal expansion coefficients of +482/-218 × 10(-6) K(-1). Moreover, single-crystal X-ray diffraction analyses demonstrate that the jack-like motion of the guest supramolecular dimers, being analogous to the anisotropic thermal expansion of bulk van der Waals solids, is crucial for changing the flexibility mode and thermal expansion behaviour of the crystal.

Zero-strain reductive intercalation in a molecular framework

Reductive intercalation of potassium within the molecular framework Ag3[Fe(CN)6] gives rise to a volume strain that is an order of magnitude smaller than is typical for common ion-storage materials. We suggest that framework flexibility might be exploited as a general strategy for reducing cycling strain in battery and ion-storage materials.

Construction of sole benzene ring porous aromatic frameworks and their high adsorption properties

Porous organic frameworks (POFs), with their excellent performance in catalysis, electricity, sensor, gas storage, and separation, have attracted a great deal of attention from researchers all over the world. Generally, the monomers of POF materials require a rigid three-dimensional molecule configuration together with special functional groups, as well as being triggered by noble metal catalysts. Here we report a low-cost and easy-construction strategy for synthesizing PAF materials. A series of flat multi-benzene compounds are selected as building units, and those phenyl rings could couple together to form polymeric skeletons. The BET surface areas of resulting PAFs are moderate, ranging from 777 to 972 m(2) g(-1). However, they unexpectedly exhibit superior gas sorption capacities. At 1.0 bar and 77 K, the H2 uptake of PAF-48 reaches 215 cm(3) g(-1). In addition, PAF-49 shows excellent performance in carbon dioxide and methane sorption, with values of 104 and 35 cm(3) g(-1), respectively. With those adsorption properties, these PAF materials could be considered as potential candidates for energetic gas adsorbents.

One-step synthesis of a copper-based metal–organic framework–graphene nanocomposite with enhanced electrocatalytic activity

A facile one-step method to prepare a Cu-MOF–graphene composite and its electrochemical application.

Formation of a quasi-solid structure by intercalated noble gas atoms in pores of CuI-MFU-4l metal–organic framework

Ten crystallographically different positions for Xe and eight positions for Kr form a quasi-solid structures within the large-pore metal–organic framework Cu^I-MFU-4l.

Predicting and creating 7-connected Zn4O vertices for the construction of an exceptional metal–organic framework with nanoscale cages

A 7-connected Zn₄O unit has been theoretically predicted based on basic zinc acetate [Zn₄O(CH₃COO)₆], which was then experimentally extended into a three-dimensional structure featuring three kinds of nanocage in a unit cell.

Amide functionalized metal–organic frameworks for diastereoselective nitroaldol (Henry) reaction in aqueous medium

The metal–organic frameworks [Zn₂(L)₂(1,4-BDC)]_n·2n(DMF) (L = 4-(pyridin-4-ylcarbamoyl)benzoate; BDC = benzenedicarboxylate) and [Cu(L)₂]_n·4n(DMF)·n(H₂O) work as catalysts for the diastereoselective nitroaldol reaction in aqueous medium.

Structural diversification and photocatalytic properties of zinc(ii) polymers modified by auxiliary N-containing ligands

Four zinc coordination polymers with different architectures based on 5-(1H-benzoimidazol-2-ylsulfanylmethyl)-isophthalic acid have been prepared. Their photoluminescence and photocatalytic properties were also investigated.

Critical factors influencing the structures and properties of metal–organic frameworks

This article highlights the recent advances in the different factors influencing the structures of MOFs.

Solvent modulated assembly of two Zn metal–organic frameworks: syntheses, luminescence, and gas adsorption properties

Two new MOFs based on H₂btca and zinc – [Zn(btca)(2,2′-bipy)]_n (1) and [Zn₂(btca)₂(bpy)(H₂O)]_n·n(DMA) (2) – have been designed and synthesized by modulating the solvent.

A robust microporous metal–organic framework as a highly selective and sensitive, instantaneous and colorimetric sensor for Eu3+ ions

A highly thermostable Mg-MOF with nanoscale pores acts as a highly selective, sensitive and instantaneous sensor for Eu³⁺ in a water solution.

Tuning the topology structures of polymolybdate-based hybrids from interpenetrated framework to interdigitated architecture via changing polymolybdate clusters

Three distinct hybrids were synthesized by modulating polyoxomolybdates, which suggests that both the size and the charge of polyoxometalates play a key role in the assembling.

Crystallography of metal-organic frameworks

Metal-organic frameworks (MOFs) are one of the most intensely studied material types in recent times. Their networks, resulting from the formation of strong bonds between inorganic and organic building units, offer unparalled chemical diversity and pore environments of growing complexity. Therefore, advances in single-crystal X-ray diffraction equipment and techniques are required to characterize materials with increasingly larger surface areas, and more complex linkers. In addition, whilst structure solution from powder diffraction data is possible, the area is much less populated and we detail the current efforts going on here. We also review the growing number of reports on diffraction under non-ambient conditions, including the response of MOF structures to very high pressures. Such experiments are important due to the expected presence of stresses in proposed applications of MOFs - evidence suggesting rich and complex behaviour. Given the entwined and inseparable nature of their structure, properties and applications, it is essential that the field of structural elucidation is able to continue growing and advancing, so as not to provide a rate-limiting step on characterization of their properties and incorporation into devices and applications. This review has been prepared with this in mind.

Capturing snapshots of post-synthetic metallation chemistry in metal-organic frameworks

Post-synthetic metallation is employed strategically to imbue metal-organic frameworks (MOFs) with enhanced performance characteristics. However, obtaining precise structural information for metal-centred reactions that take place within the pores of these materials has remained an elusive goal, because of issues with high symmetry in certain MOFs, lower initial crystallinity for some chemically robust MOFs, and the reduction in crystallinity that can result from carrying out post-synthetic reactions on parent crystals. Here, we report a new three-dimensional MOF possessing pore cavities that are lined with vacant di-pyrazole groups poised for post-synthetic metallation. These metallations occur quantitatively without appreciable loss of crystallinity, thereby enabling examination of the products by single-crystal X-ray diffraction. To illustrate the potential of this platform to garner fundamental insight into metal-catalysed reactions in porous solids we use single-crystal X-ray diffraction studies to structurally elucidate the reaction products of consecutive oxidative addition and methyl migration steps that occur within the pores of the Rh-metallated MOF, 1·[Rh(CO)2][Rh(CO)2Cl2].

Gate-opening gas adsorption and host-guest interacting gas trapping behavior of porous coordination polymers under applied AC electric fields

The gate-opening adsorption behavior of the one-dimensional chain compound [Ru2(4-Cl-2-OMePhCO2)4(phz)] (1; 4-Cl-2-OMePhCO2(-) = 4-chloro-o-anisate; phz = phenazine) for various gases (O2, NO, and CO2) was electronically monitored in situ by applying ac electric fields to pelletized samples attached to a cryostat, which was used to accurately control the temperature and gas pressure. The gate-opening and -closing transitions induced by gas adsorption/desorption, respectively, were accurately monitored by a sudden change in the real part of permittivity (ε'). The transition temperature (TGO) was also found to be dependent on the applied temperature and gas pressure according to the Clausius-Clapeyron equation. This behavior was also observed in the isostructural compound [Rh2(4-Cl-2-OMePhCO2)4(phz)] (2), which exhibited similar gate-opening adsorption properties, but was not detected in the nonporous gate-inactive compound [Ru2(o-OMePhCO2)4(phz)] (3). Furthermore, the imaginary part of permittivity (ε″) effectively captured the electronic perturbations of the samples induced by the introduced guest molecules. Only the introduction of NO resulted in the increase of the sample's electronic conductivity for 1 and 3, but not for 2. This behavior indicates that electronic host-guest interactions were present, albeit very weak, at the surface of sample 1 and 3, i.e., through grain boundaries of the sample, which resulted in perturbation of the conduction band of this material's framework. This technique involving the in situ application of ac electric fields is useful not only for rapidly monitoring gas sorption responses accompanied by gate-opening/-closing structural transitions but also potentially for the development of molecular framework materials as chemically driven electronic devices.

Crystallographic studies of gas sorption in metal-organic frameworks

Metal-organic frameworks (MOFs) are a class of porous crystalline materials of modular design. One of the primary applications of these materials is in the adsorption and separation of gases, with potential benefits to the energy, transport and medical sectors. In situ crystallography of MOFs under gas atmospheres has enabled the behaviour of the frameworks under gas loading to be investigated and has established the precise location of adsorbed gas molecules in a significant number of MOFs. This article reviews progress in such crystallographic studies, which has taken place over the past decade, but has its origins in earlier studies of zeolites, clathrates etc. The review considers studies by single-crystal or powder diffraction using either X-rays or neutrons. Features of MOFs that strongly affect gas sorption behaviour are discussed in the context of in situ crystallographic studies, specifically framework flexibility, and the presence of (organic) functional groups and unsaturated (open) metal sites within pores that can form specific interactions with gas molecules.

Towards imaging electron density inside metal-organic framework structures

Herein, we present electron density maps of three MOFs with different guests or post-synthetic modifications produced using single crystal X-ray data from laboratory diffractometers. Analysis of the electron density maps reveals possible differences inside the pores indicating that this approach may be used to explore frameworks using inexpensively gained X-ray data.

Crystal growth of MOF-5 using secondary building units studied by in situ atomic force microscopy

Crystal growth of the metal–organic framework, MOF-5, using basic zinc benzoate, [Zn₄O(O₂CC₆H₅)₆], was studied in real time using atomic force microscopy.

Synthesis of a series of coordination polymers based on mixed ligands to tune the structural dimension

Schematic illustrating the 2D network of complex 1. Color code: yellow, Mn; cob²⁻ ligand, red.

Molecular simulation of gas adsorption and diffusion in a breathing MOF using a rigid force field

Gas adsorption and diffusion of CO₂ and CH₄ in NH₂-MIL-53(Al) using a linear combination of two crystallographic rigid structures.

Force field for ZIF-8 flexible frameworks: atomistic simulation of adsorption, diffusion of pure gases as CH4, H2, CO2 and N2

A full set of flexible force field parameters for ZIF-8, applied for its gas adsorption and diffusion, has been presented.

Toughening of epoxy resin using Zn4O (1,4-benzenedicarboxylate)3 metal–organic frameworks

The potential of metal–organic frameworks (MOF 5) towards toughening of brittle cycloaliphatic epoxy thermosetting resin has been demonstrated.

Tuning the dimension of POM-based inorganic–organic hybrids from 3D self-penetrating framework to 1D poly-pendant chain via changing POM clusters and introducing secondary spacers

The four compounds show distinct structure motifs, which illustrate that the POMs and the secondary spacers are key factors to tune the dimension of the POM-based hybrids.

An Efficient synthesis of Weinreb amides and ketones via palladium nanoparticles on ZIF-8 catalysed carbonylative coupling

Palladium nanoparticles on ZIF-8 as a robust and recyclable catalyst for Weinreb amide and ketone synthesis through carbonylative coupling.

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.

An unusual cobalt(ii)-based single-walled metal–organic nanotube

Self-adaption to the formation of an unusual cobalt(ii)-based single-walled metal–organic nanotube is reported. In addition, a pseudo-merohedral twinning problem encountered in the X-ray diffraction analysis was solved, which significantly improves the crystallographic results.

Structure of organic solids at low temperature and high pressure

This tutorial review summarises the current state of the art in low temperature and high pressure crystallography of molecular organic and coordination compounds.

Hydrogen and halogen bonding in a concerted act of anion recognition: F− induced atmospheric CO2 uptake by an iodophenyl functionalized simple urea receptor

Halogen bonding plays a key role in the fixation of atmospheric CO₂ because air-stable crystals of HCO₃⁻ dimer by a simple urea based para-iodo substituted acyclic receptor in the presence of n-TBA salt of F⁻ in MeCN solution.