Solvent‐Mediated Transformation from Achiral to Chiral Nickel(II) Metal–Organic Frameworks and Reassembly in Solution

Structural Comparisons, Fluorescence Properties, and Glass-to-Crystal Transformations of Heat-Cooled and Melt-Quenched Zeolitic Imidazolate Framework Glass

As a representative of zeolitic imidazolate framework glass, agZIF-62 has been reported to be synthesized using a melt-quenching method in which the ZIF-62 crystal is heated to a temperature above the melting point. Interestingly, we unexpectedly found that agZIF-62 can also be synthesized by simple heating at temperatures lower than the melting point, which may be assisted by the release of encapsulated solvent molecules. The structural differences between melt-quenched agZIF-62 (MQ-agZIF-62) and heat-cooled agZIF-62 (HC-agZIF-62) were investigated. The results indicated that MQ-agZIF-62 is closer to the liquid state, while HC-agZIF-62 is closer to the crystal state. Interestingly, their luminescent emissions exhibit significant differences. Compared with the ZIF-62 crystal, MQ-agZIF-62 showed a blue-shift of 14 nm, whereas HC-agZIF-62 showed a red-shift of 9 nm. The emission intensity of agZIF-62 is also significantly stronger than that of ZIF-62; thus, rapid semiquantitative detection of the content of the MOF glass in glass and crystal mixtures can be achieved. In addition, HC-agZIF-62 and MQ-agZIF-62 can transform into ZIF-62 crystals via a solvent-media mechanism. This study provides new insights into ZIF-62 glass.

Recent progress in the design, synthesis and applications of chiral metal-organic frameworks

Chiral Metal-Organic Frameworks (CMOFs) are unique crystalline and porous class of materials which is composed of organic linkers and metal ions. CMOFs surpass traditional organic and inorganic porous materials because of their tunable shape, size, functional diversity, and selectivity. Specific applications of CMOFs may be exploited by introducing desired functional groups. CMOFs have chiral recognition abilities, making them unique for chiral compound synthesis and separation. The CMOFs can be synthesized through different approaches. Two main approaches have been discussed, i.e., direct and indirect synthesis. Synthetic strategies play an essential role in getting desired properties in MOFs. CMOFs find potential applications in adsorption, asymmetric catalysis, luminescence, degradation, and enantioselective separation. The MOFs' porosity, stability, and reusability make them an attractive material for these applications. The plethora of applications of CMOFs have motivated chemists to synthesize novel MOFs and number of MOFs have been ever-escalating. Herein, the synthetic methods of CMOFs and their various applications have been discussed.

Structural Transformation of Copper Coordination Complexes with Inducing Supramolecular Chirality

Four copper coordination complexes [CuL(CH3OH)]n (1), [CuL(C2H5OH)]n (2), [(CuL)·0.5H2O]n (3), and [CuL(H2O)·0.5H2O]n (4) with a tridentated Schiff base ligand (H2L = (E)-2-((4-fluoro-2-hydroxybenzylidene)amino)acetate) were obtained in different solvents and reaction times....

Light actuated stable radicals of the 9-anthracene carboxylic acid for designing new photochromic complexes

The photogeneration of stable radicals is important but still challenging in the field of optical switching, displays, and other devices. Herein, crystalline 9-anthracene carboxylic acid (9-AC) and a mononuclear complex constructed from this ligand were for the first time discovered to show radical-induced photochromism and photomagnetism after Xe lamp light irradiation. This study finds a simple radical-actuated photochromic molecule for constructing a novel system of photochromic materials.

A reversible photochemical solid-state transformation in an interpenetrated 3D metal-organic framework with mechanical softness

We synthesized a two-fold interpenetrated 3D MOF with two crystallographically distinct C[double bond, length as m-dash]C bonds, which undergoes [2+2] photo-cycloaddition and thermal reversible reaction, in a single-crystal-to-single-crystal (SCSC) manner. The softer nature and comparable mechanical properties of the crystals of the parent and cyclized MOFs revealed by nanoindentation allowed rationalizing their structural softness and SCSC transformation behaviour.

Three helical chain-based 3D coordination polymers: solvent-induced syntheses, tunable structures and catalytic properties for the Strecker reaction

Three 3D Sc-CPs with different helical chains have been synthesized from isophthalic acid derivatives by solvent induced methods. Among them, 3 is optically active. Furthermore, 1 exhibits good catalytic activity for the Strecker reactions.

Irreversible solvent-assisted structural transformation in 3D metal-organic frameworks: Structural modification and enhanced iodine-adsorption properties

In this work, we demonstrate a solvent-assisted structural transformation between two 3D metal-organic frameworks (MOFs) ([Zn₄(α-bptc)₂(H₂O)₃]_n (1) → {[Zn₂(α-bptc)(H₂O)₄]·(pra)}_n (2)) (α-H₄bptc = 2,3,3',4'-biphenyl tetra-carboxylic acid and pra = pyridin-2-amine) at room temperature by immersing complex 1 in a mother solution. The structural transformation involves not only solvent exchange but also the cleavage and formation of coordination bonds, which is confirmed by infrared spectroscopy, single-crystal X-ray diffraction analysis, powder X-ray diffraction patterns, and thermogravimetric analysis. Structural analyses revealed that significant modifications occurred during the transformation including the changes in lattice parameters, unit cell volume, space group, coordination number, secondary building units, and topological type. In the case of drastic structural transitions, significant changes in properties were also observed. Complex 2 displayed the interesting uptake and release of iodine with the changes in visible color, UV and fluorescence spectra, and fully reversible I2 uptake of 8.5 mg g-1, which further suggested about its future application as iodine absorbing material.

Mechanisms of Solvent-Mediated Structural Transformations for Dynamic Crystals of Supramolecular Coordination Systems

Thus far, reports about the transformations for dynamic crystals of supramolecular coordination systems mainly include single-crystal-to-single-crystal reactions, and solvent-mediated processes. This Concept focuses on the mechanisms for solvent-mediated structural transformations of dynamic crystals, which can be classified into two categories, that is, core-on-shell and core-to-core. The core-on-shell mechanism means that the core of the new crystal is generated from the shell of original crystal, being concomitant with the dissolution of the mother crystal. In contrast, for the core-to-core case, the growth of new crystal core and the dissolution of original crystal core will proceed simultaneously, but they are physically separated. Herein, the two mechanisms are elucidated in detail, with some typical examples from recent advances.

Long-range magnetic ordering in a metal-organic framework based on octanuclear nickel(ii) clusters

A novel three-dimensional metal-organic framework [Ni₃(BTC)₂(bpp)₂(H₂O)]·3H₂O (1) based on mixed ligands H₃BTC (1,2,4-benzenetricarboxylic acid) and bpp (1,3-bis(4-pyridyl)propane) was obtained under hydrothermal conditions. Crystal structure analysis reveals that 1 is a framework based on cage-like Ni₈(COO)₁₂ units. Furthermore, long-range magnetic ordering is observed at low temperature.

Solvent-mediated preparation of a heterometallic [2 × 2] grid via a 1D metal–organic template with extraordinary acid/base-resistance

Here, we have demonstrated that a metal–organic chain can serve as a template to prepare a heterometallic [2 × 2] grid through a solvent-mediated strategy.

A new strategy to obtain tetranuclear cobalt(ii) metal–organic frameworks based on the [Co4(μ3-OH)2] cluster: synthesis, structures and properties

Three MOFs based on [Co₄(μ₃-OH)₂] with 4-, 6- and 8-connected frameworks exhibit antiferromagnetic interactions and are good photocatalysts.