Recent advancement in bimetallic metal organic frameworks (M’MOFs): Synthetic challenges and applications

Metal-organic frameworks (MOFs) is a burgeoning research field and has received increasing interest in recent years due to their inherent advantages of inorganic metal ions, range of organic linkers, tunable...

Structural Variation and Switchable Nonlinear Optical Behavior of Metal-Organic Frameworks

Two europium metal-organic frameworks (MOFs) based on the same ligand, named as ZJU-23-Eu and ZJU-24-Eu, are selectively synthesized by fine-tuning solvent contents to tailor the coordination modes. Eu atoms are eight-coordinated and nine-coordinated in ZJU-23-Eu and ZJU-24-Eu respectively, and their frameworks vary in both spatial connectivity and symmetry. The ligand not only has multiphoton response but also suitable triplet energy level (19 998 cm^-1 ) to sensitize Eu³⁺ . Thus ZJU-23-Eu exhibits characteristic emission of Eu³⁺ peaking at 614 nm via the energy transfer from the two-/three-photon excited ligand to Eu³⁺ , with its bidimensional layered structure benefiting this process. In contrast, the changed spatial connectivity in tridimensional ZJU-24-Eu narrows the distances between adjacent Eu³⁺ ions and reduces the density, resulting in poor two-photon excited fluorescence. Besides, noncentrosymmetric ZJU-24-Eu shows second harmonic generation (SHG) response with an intensity of ≈6.2 times relative to KH₂ PO₄ (KDP) microcrystalline powder while centrosymmetric ZJU-23-Eu cannot. These results have established two nonlinear optical (NLO) models based on MOFs to synchronously analyze the effects of two structural variables on different NLO behaviors, and provide ingenious ways to design MOF-based NLO devices with function on demand.

Influence of counter ions on structure, morphology, thermal stability of lanthanide complexes containing dipicolinic acid ligand

Two kinds of lanthanide coordination polymers formed by dipicolinic acid with lanthanide ions were synthesized by varying the counter ions. And their crystal structures, morphology and thermal stabilities were measured and compared. X-ray single-crystal diffraction analysis reveals that Na₃[Ln(DPA)₃] (Ln = Tb or Eu) stretches to a rigid network by means of bridging Na⁺ ion. Moreover, Na₃[Ln(DPA)]₃ exhibits good thermal stability and luminescent properties, and its optical properties can be remained even after heating at 200 °C more than 3 days. However, when Na⁺ in Na₃[Ln(DPA)₃] was replaced with NH₄⁺, i.e., (NH₄)₃[Ln(DPA)₃] with a supramolecular structure based on π-π stacking and other weak interactions, shows relatively poor thermal stability which leads to deterioration of their luminescence properties after heating treatment. This result confirms that the rigid frame structure of Na₃[Ln(DPA)]₃ plays a crucial role in improving its thermal stability and keeping its highly luminescent quantum efficiency.

Multifunctional Metal-Organic Frameworks Based on Redox-Active Rhenium Octahedral Clusters

The redox-active rhenium octahedral cluster unit [Re₆Se₈(CN)₆]^4- was combined with Gd³⁺ ions and dicarboxylate linkers in novel types of metal-organic frameworks (MOFs) that display a set of functional properties. The hydrolytically stable complexes [{Gd(H₂O)₃}₂(L)Re₆Se₈(CN)₆]·nH₂O (1, L = furan-2,5-dicarboxylate, fdc; 2, L = thiophene-2,5-dicarboxylate, tdc) exhibit a 3D framework of trigonal symmetry where 1D chains of [{Gd(H₂O)₃}₂(L)]⁴⁺ are connected by [Re₆Se₈(CN)₆]^4- clusters. Frameworks contain spacious channels filled with H₂O. Solvent molecules can be easily removed under vacuum to produce permanently porous solids with high volumetric CO₂ uptake and remarkable CO₂/N₂ selectivity at room temperature. The frameworks demonstrate an ability for reversible redox transformations of the cluster fragment. The orange powders of compounds 1 and 2 react with Br₂, yielding dark-green powders of [{Gd(H₂O)₃}₂(L)Re₆Se₈(CN)₆]Br·nH₂O (3, L = fdc; 4, L = tdc). Compounds 3 and 4 are isostructural with 1 and 2 and also have permanently porous frameworks but display different optical, magnetic, and sorption properties. In particular, oxidation of the cluster fragment "switches off" its luminescence in the red region, and the incorporation of Br^- leads to a decrease of the solvent-accessible volume in the channels of 3 and 4. Finally, the green powders of 3 and 4 can be reduced back to the orange powders of 1 and 2 by reaction with hydrazine, thus displaying a rare ability for fully reversible chemical redox transitions. Compounds 1-4 are mentioned as a new class of redox-active cluster-based MOFs with potential usage as multifunctional materials for gas separation and chemical contamination sensors.

A dye-like ligand-based metal–organic framework for efficient photocatalytic hydrogen production from aqueous solution

A dye-like based Gd-MOF exhibits efficient photocatalytic activity for hydrogen generation without a co-catalyst. Depositing Ag further enhances its activity.

Ln-Ag heterometallic coordination polymers

The last few years have seen an increasing interest in the study of lanthanide-silver (Ln-Ag) heterometallic coordination polymers due to their potential applications. It has led to intense activity of chemists to produce Ln-Ag heterometallic coordination polymers and investigate their properties. In this review, we summarize recent research development in the fascinating and challenging field of Ln-Ag heterometallic coordination polymers. This review covers 182 Ln-Ag heterometallic coordination polymers, which are categorized by the kind of ligand as N-heterocyclic carboxylate ligands and others. There are three categories of Ln-Ag coordination polymer based on N-heterocyclic carboxylate ligands: one dimensional (1D), 2D, and 3D. The 3D part was divided into Ln-Ag coordination polymers based on pyridine carboxylate ligands and other N-heterocyclic carboxylate ligands. This perspective illustrates the coordination features of compounds constructed by N-heterocyclic carboxylate ligands. Luminescent properties are also discussed.

Chemical stability and tunable luminescence of Ln(iii)–K(i) coordination polymers featuring a tracery-like architecture

With the help of in situ generation of sulfate anion, three Ln(iii)–K(i) sulfate and oxalate coordination polymers have been synthesized. These compounds display thermal and chemical stability, as well as good temperature and pH sensing ability.

Semidirected versus holodirected coordination and single-component white light luminescence in Pb(ii) complexes

LMCT and MC luminescence due to electron lone pairs in semidirected Pb(ii) complexes results in single-component white light emission.

Photoluminescence and white-light emission in two series of heteronuclear Pb(ii)–Ln(iii) complexes

Tunable photoluminescence and single component white light emission is achieved in Pb(ii)–Eu(iii) heteronuclear complexes.

First tetrazole-bridged d–f heterometallic MOFs with a large magnetic entropy change

The first example of tetrazole-bridged 3d–4f heterometallic MOFs {(H₃O)₃[Gd₃Mn₂(Trz)₄]·12H₂O}_n was obtained, exhibiting a large magnetic entropy change.

Insight into luminescence enhancement of coordinated water-containing lanthanide metal–organic frameworks by guest molecules

The luminescence of novel metal–organic frameworks can be enhanced and reversibly modified by different guest molecules.

Diethyl 2,2′-(ethane-1,2-diyldioxy)dibenzoate

The molecular title compound, C20H22O6, was obtained by the reaction of ethyl 2-hydroxybenzoate with 1,2-dichloroethane. The molecule lies on a twofold rotation axis which passes through the middle of the central ethylene bridge. This group exhibits agaucheconformation with the corresponding O—C—C—O torsion angle being 73.2 (2)°. The C atoms of the carboxyl group, the aryl and the O—CH2group are coplanar, with an r.m.s. deviation of 0.01 Å. The two aryl rings form a dihedral angle of 67.94 (4)°. The ester ethyl group is disordered over two sets of sites with an occupancy ratio of 0.59 (2):0.41 (2). The crystal packing is dominated by van der Waals forces.