Flexible Microporous Framework for One-Step Acquisition of Ethylene from Ternary C2 Hydrocarbons

One-step purification of ethylene (C2H4) from ternary C2 hydrocarbon mixtures is a crucial task and an enduring challenge because of their similar molecular size and physical properties. Owing to their intriguing structural dynamics, flexible MOFs have attracted more attention for gas adsorption and separation. Herein, we report a flexible MOF FJI-W-66 that exhibits rarely seen "breathing" behaviors for C2 hydrocarbons. Upon activation, the channels of guest-free FJI-W-66a significantly contract to a nearly closed-pore state. FJI-W-66a shows the stepwise adsorption isotherms for C2 hydrocarbons, which suggests the occurrence of structural transformation between less open and more open phases. Breakthrough experiments provide evidence that FJI-W-66a can selectively separate C2H4 from C2H2/C2H4/C2H6 mixtures with different ratios under ambient conditions, realizing the one-step acquisition of C2H4 from ternary C2 hydrocarbons.

Design of a MOF based on octa-nuclear zinc clusters realizing both thermal stability and structural flexibility

An octa-nuclear zinc (Zn₈) cluster-based two-fold interpenetrated metal-organic framework (MOF) of [(CH₃)₂NH₂]₂[Zn₈O₃(FDC)₆]·7DMF (denoted as Zn8-as; H₂FDC = 9H-fluorene-2,7-dicarboxylic acid; DMF = N,N-dimethylformamide) was synthesized by the reaction of a hard base of a curved dicarboxylate ligand (H₂FDC) with the borderline acid of Zn(II) under solvothermal conditions. Zn8-as shows significant crystal volume shrinkage upon heating, yielding a solvate-free framework of [(CH₃)₂NH₂]₂[Zn₈O₃(FDC)₆] (Zn8-de). Zn8-de displays gated adsorption for C₂H₂ and type-I adsorption for CO₂, attributed to the framework flexibility and the different interactions between the gas molecules and the host framework.

Single-crystal superprotonic conductivity in an interpenetrated hydrogen-bonded quadruplex framework

A proton-transporting pathway is crucial to the conduction mechanism in fuel cells and biological systems. Here, we report a novel 5-fold interpenetrated three-dimensional (3D) hydrogen-bonded quadruplex framework, which exhibits an ultrahigh single-crystal proton conductivity of 1.2(1) × 10^-2 S cm^-1 at 95 °C and 98% relative humidity, benefitting from the spiral H₃O⁺/H₂O chains in 1D pore channels studded with COOH/COO^- groups.

Precise regulating synergistic effect in metal–organic framework for stepwise-controlled adsorption

MAC-20 shows a unique two-step pore-shape change and executes a stepwise-controlled adsorption of dyes mixture in order of their sizes.

Metal Halide Perovskite@Metal-Organic Framework Hybrids: Synthesis, Design, Properties, and Applications

Metal halide perovskites (MHPs) have excellent optoelectronic and photovoltaic applications because of their cost-effectiveness, tunable emission, high photoluminescence quantum yields, and excellent charge carrier properties. However, the potential applications of the entire MHP family are facing a major challenge arising from its weak resistance to moisture, polar solvents, temperature, and light exposure. A viable strategy to enhance the stability of MHPs could lie in their incorporation into a porous template. Metal-organic frameworks (MOFs) have outstanding properties, with a unique network of ordered/functional pores, which render them promising for functioning as such a template, accommodating a wide range of MHPs to the nanosized region, alongside minimizing particle aggregation and enhancing the stability of the entrapped species. This review highlights recent advances in design strategies, synthesis, characterization, and properties of various hybrids of MOFs with MHPs. Particular attention is paid to a critical review of the emergence of MHP@MOF for comprehensive studies of next-generation materials for various technological applications including sensors, photocatalysis, encryption/decryption, light-emitting diodes, and solar cells. Finally, by summarizing the state-of-the-art, some promising future applications of reported hybrids are proposed. Considering the inherent correlation and synergic functionalities of MHPs and MOFs, further advancement; new functional materials; and applications can be achieved through designing MHP@MOF hybrids.

Topological polymorphism and temperature-driven topotactic transitions of metal–organic coordination polymers

A facile crystal-to-crystal solid-state phase transition between a low-temperature phase and a high temperature phase changes the MOF topology and involves a significant rearrangement of bulky organic ligands.

Photochemical cycloaddition and temperature-dependent breathing in pillared-layer metal-organic frameworks

Single crystallinity of metal-organic frameworks (MOFs) enables the studies of their flexible behaviors with atomic precision. Here, we investigated the structural transformations triggered by photochemical cycloaddition and with temperature-dependent breathing in a series of pillared-layer MOF structures using a variety of pyrazolecarboxylate linkers for the layers and bipyridyl linkers as the pillars. The ethylenic double bonds from the pillars in close proximity undergo quantitative and seteroselective photochemical [2 + 2] cycloaddition upon UV irradiation, transforming the MOFs into structures with cyclobutane-based pillars. Furthermore, reversible breathing of the new pillared-layer MOF was evidenced by the 10.8% unit cell parameter change along c axis upon temperature change between 298 and 173 K. As revealed by single crystal X-ray diffraction, this transformation originates from the relative flattening of the wavy layers upon cooling. These two different types of characteristic structural transformations responding to inherent reactions and external stimuli happen at single crystalline state, providing a well-defined robust system with controlled flexibility.

Rational Construction of Breathing Metal-Organic Frameworks through Synergy of a Stretchy Ligand and Highly Variable π-π Interaction

The synergy of a stretchy ligand and highly variable π-π interaction has been proposed as a rational strategy for the construction of breathing metal-organic frameworks (MOFs). Based on this strategy, a breathing MOF, {[Cd₂(AzDC)₂(TPT)₂](DMF)₃} _n, was successfully constructed with stretchy 4,4'-diazene-1,2-diyldibenzoate acid (H₂AzDC) and 2,4,6-tris(4-pyridyl)triazine (TPT) as a source of the π-π interaction. The MOF features structure transformation upon stimulation with solvent guests and varied temperatures, which is straightforwardly characterized by single-crystal structures. Moreover, the solvent-free framework shows breathing behaviors in response to light hydrocarbon (C₂H₄, C₂H₆, C₃H₆, and C₃H₈) sorption, which was verified by stepwise sorption isotherms and in situ powder X-ray diffraction. Additional investigation of the sorption selectivity of C3/C2 systems indicated that the selectivity can be regulated by the modulation of the dynamic breathing behaviors, which can be used for the selective separation of C3/C2 light hydrocarbons.

Single-side and double-side swing behaviours of a flexible porous coordination polymer with a rhombic-lattice structure

A rhombic porous coordination polymer can show special reversible–irreversible structural transformations with single-side and double-side swing, as well as sophisticated bond reconstitution behaviours.

Controlling Thermal Expansion Behaviors of Fence-Like Metal-Organic Frameworks by Varying/Mixing Metal Ions

Solvothermal reactions of 3-(4-pyridyl)-benzoic acid (Hpba) with a series of transition metal ions yielded isostructral metal-organic frameworks [M(pba)2]·2DMA (MCF-52; M = Ni2+, Co2+, Zn2+, Cd2+, or mixed Zn2+/Cd2+; DMA = N,N-dimethylacetamide) possessing two-dimensional fence-like coordination networks based on mononuclear 4-connected metal nodes and 2-connected organic ligands. Variable-temperature single-crystal X-ray diffraction studies of these materials revealed huge positive and negative thermal expansions with |α| > 150 × 10-6 K-1, in which the larger metal ions give the larger thermal expansion coefficients, because the increased space not only enhance the ligand vibrational motion and hinged-fence effect, but also allow larger changes of steric hindrance between the layers. In addition, the solid-solution crystal with mixed metal ions further validates the abundant thermal expansion mechanisms of these metal-organic layers.

Vapour-driven crystal-to-crystal transformation showing an interlocking switch of the coordination polymer chains between 1D and 3D

A rare crystal-to-crystal transformation occurs between 1D coordination polymer chains and 3D mechanically interlocked structures via reversible opening and closing of the homogeneous chains without any change in the coordination mode and composition.

Tailoring the structure, pH sensitivity and catalytic performance in Suzuki–Miyaura cross-couplings of Ln/Pd MOFs based on the 1,1′-di(p-carboxybenzyl)-2,2′-diimidazole linker

Four Pd/Ln MOFs have been synthesized and tested as catalysts in Suzuki–Miyaura reactions in neat water, neat ethanol as well as water–ethanol mixtures.

Liquid-free single-crystal to single-crystal transformations in coordination polymers

Single-crystal to single-crystal (SCSC) transformations not only can create new materials, but also provide an opportunity to explore the process of forming a chemical bond. SCSC transformations discussed in this paper are confined to transformationsviaan absolutely liquid-free mode and involve the breakage and formation of new chemical bonds.

MOF the beaten track: unusual structures and uncommon applications of metal-organic frameworks

Over the past few decades, metal-organic frameworks (MOFs) have proved themselves as strong contenders in the world of porous materials, standing alongside established classes of compounds such as zeolites and activated carbons. Following extensive investigation into the porosity of these materials and their gas uptake properties, the MOF community are now branching away from these heavily researched areas, and venturing into unexplored avenues. Ranging from novel synthetic routes to post-synthetic functionalisation of frameworks, host-guest properties to sensing abilities, this review takes a sidestep away from increasingly 'traditional' approaches in the field, and details some of the more curious qualities of this relatively young family of materials.

Pre-design and synthesis of a five-fold interpenetrated pcu-type porous coordination polymer and its CO2/CO separation

The first five-fold interpenetrated PCP with pcu topology and high porosity was rationally designed and prepared, which showed high separation potential of CO₂/CO mixtures.

A nanoporous Ag(i) coordination polymer for selective adsorption of carcinogenic dye Acid Red 26

This work presents a unique Ag(i) nanoporous coordination polymer, showing selective and complete removal of carcinogenic dye Acid Red 26 from aqueous solution upon the size-exclusion and charge-matching effect.

Highly efficient Cr2O72−removal of a 3D metal-organic framework fabricated by tandem single-crystal to single-crystal transformations from a 1D coordination array

Tandem single-crystal to single-crystal (SC–SC) transformation of a 1D neutral chain affords a 3D cationic framework, showing highly efficient Cr₂O₇²⁻captureviaSC–SC anion-exchange.

Dual structure evolution of a Ag(i) supramolecular framework triggered by anion-exchange: replacement of terminal ligand and switching of network interpenetration degree

Dual single-crystal to single-crystal transformations triggered by different anion-exchanges are achieved for a Ag(i) coordination framework, where switching of network interpenetration degree is observed.

Isoreticular synthesis of 2D MOFs with rotating aryl rings

A series of isoreticular two-dimensional metal–organic frameworks (MOFs) was synthesized with group 11 metals and semirigid ligands that bind in a syn conformation.