A Flexible Porous MOF Exhibiting Reversible Breathing Behavior through Single‐Crystal to Single‐Crystal Transformation

Abstract

A two dimensional (2D) flexible Zn(II) MOF (1) with intra-layer channels has been synthesized using a mixed ligand strategy. Interestingly, 1 exhibits reversible breathing behavior upon desolvation/resolvation in crystal state, causing responsive luminescence together with visible color changes. Furthermore, the above-mentioned process even occurred when 1 exposed to humid atmosphere or immersed in various organic solvents.In recent two decades, metal À organic frameworks (MOFs) have received considerable scientific attention for their fascinating structures and potential applications in gas storage and separation, sensor, proton conduction, magnetism, and catalysis, etc. [1][2][3][4][5] Remarkably, single-crystal-to-single-crystal (SC-SC) transformation has recently attracted great attention in the area of MOFs, because the interesting dynamic solid-state structural transformation progress always lead to enhanced functional materials with special properties. [6] Since MOFs with porous and flexible frameworks maintain their single crystallinity throughout the transformation progress, the changes in structure can be precisely and straightforwardly characterized by single-crystal X-ray diffraction, this makes SC-SC transformation an excellent opportunity to study the structureproperty relationships of this kind of functional materials. [7] Moreover, some physical properties of the materials triggered by external stimuli could be changed during the SC-SC transformation process, which may be taken advantage of for potential applications. For example, colour changes could potentially lead to their use in sensing devices. [8] Generally, SC-SC transformation can be mostly caused by chemical changes, including guest molecules, counterions, coordinated metal ions, host À guest interactions, bond rearrangement, and topochemical reactions. [9][10][11][12][13][14] In addition, it can also be triggered by some physical stimuli, such as light, temperature or pressure. [15][16][17] In MOFs, there exist guest molecules in the void spaces provided by suitable organic ligands and metal nodes. The interactions between guest and the framework often play a key role in the stabilization of materials. For these materials, it will be interesting if the framework integrity is maintained upon the removal of guest molecules, which provides a direct and accurate platform for the host-guest chemistry of adsorption and ion exchange. Such a direct insight could help to understand the subtle interaction between the guest molecule and the host framework. [18] Although structure transformations trigged by the removal of guest molecules in MOFs have been reported widely, the research on two dimensional (2D) porous MOFs exhibiting SC-SC transformation are still rare. [19] Herein, we report a 2D flexible cationic MOF with 1D channels, [ZnL(Hatz)]·NO 3 ·2H 2 O (1, H 2 LCl = 1,3-bis(4-carboxyphenyl) imidazolium chloride, Hatz = 5-amino-1H-tetrazole), which exhibits reversible SC-SC transformation process upon desolvation/resolvation, accompanying...

The 50-Fold Enhanced Proton Conductivity Brought by Aqueous-Phase Single-Crystal-to-Single-Crystal Central Metal Exchange

“…(ii) Positive charge of pyridinium salts may contribute to charge transfer. (iii) The flexible structure provides the possibility for the distortion of the skeleton during central metal exchange. , The coordination polymer {[Co 3 L 2 (H 2 O) 6 ]·2H 2 O} n ( 1 ) and the aqueous-phase SC-SC central metal exchange product {[Cu 3 L 2 (H 2 O) 6 ]·2H 2 O} n ( 2 ) were prepared. As expected, the proton conductivity of 2 reached 0.004 S cm –1 , which is 50 times higher than that of 1 at 100% RH and 95 °C.…”

X‐Ray Triggered Coordination‐Bond Breakage in Dysprosium‐Organic Framework and its Impact on Magnetic Properties

“…The X-ray induced water release is very different from thermally induced dehydration. [29] Thermogravimetric (TG) analysis revealed a two-step weight loss below 170 °C for MDAF-5 (Figure S8), corresponding to the removal of six water molecules at 30-130 °C (obs. 4.9 %, calcd.…”

Simultaneous Control of Flexibility and Rigidity in Pore-Space-Partitioned Metal–Organic Frameworks

“…Few porous materials are capable of retaining X-ray-quality single crystallinity after degassing and such large axial change (Table S10). − ,− Clearly, the simultaneous control of flexibility with L1 and rigidity with L2 plays an important role in maintaining single crystallinity and porosity.…”