Fluorescent and Catalytic Properties of a 2D Lamellar Zn Metal-Organic Framework with sql Network Structure

A two-dimensional (2D) lamellar Zn metal-organic framework (Zn-MOF, 1) with a fluorescent 1,6-di(pyridin-3-yl)pyrene (3-DPPy) and 1,4-benzenedicarboxylate (BDC2-) bridging linkers was prepared and structurally characterized. The chemical formula of 1 is [Zn(μ-3-DPPy)(μ-BDC)]n. The mononuclear Zn(II) ion, acting as a node, is tetrahedrally coordinated with two 3-DPPy and two BDC linkers. The coordination environment of Zn(II) is a distorted tetrahedral geometry. The Zn-MOF is the sql network structure based on topology analysis. The undulated 2D sheets of 1 tightly pack together to form a lamellar structure. The pyrene moieties are parallelly oriented to each other. The Zn-MOF is not porous, possibly because the mononuclear Zn(II) node did not form cluster-based secondary building units due to the less symmetric 3-DPPy. The steady-state fluorescence measurements indicate that the fluorescence signal of the 1 is slightly blue-shifted compared to the free 3-DPPy in the solid state. The excimer emission band at 463 nm for crystalline 3-DPPy is shifted to 447 nm for 1. The value of 447 nm is also a blue-shift value compared to nonsubstituted pyrene crystals (470 nm). Despite its nonporosity, the surface Lewis acidic sites of 1 could catalyze the transesterification of esters. Surface defect sites are responsible for this catalytic activity.

Novel Lanthanide-Based Metal-Organic Framework Isomer as a Double Ratiometric Fluorescent Probe for Vanillymandelic Acid

The concentration of vanillymandelic acid (VMA) in urine is closely related with pheochromocytoma diagnosis. Thus, it is essential to develop more accurate and convenient fluorescence sensing strategies toward VMA. Until now, the design of double ratiometric detection methods for VMA was still in the unexplored stage. In this work, novel Ln³⁺-based metal-organic frameworks (QBA-Eu and QBA-Gd_0.875Eu_0.125) possessing dual emission peaks was fabricated successfully, which served as isomers of YNU-1 and exhibited more excellent water stability in fluorescence and structure than the ones of YNU-1. The formation of the complex between QBA ligands and VMA molecules via hydrogen bonds within QBA-Eu frameworks produced a new emission band centered at 450 nm and resulted in the decline of monomer emission intensity for QBA at 390 nm. Owing to the reduced energy gap [ΔE (S₁ - T₁)], the antenna effect was hampered and luminescence of Eu³⁺ ions also decreased. The developed double ratiometric (I_615nm/I_475nm, I_390nm/I_475nm) fluorescence sensors based on QBA-Eu and QBA-Gd_0.875Eu_0.125 possessed the advantages of fast response (4 min), low detection limits (0.58 and 0.51; 0.22 and 0.31 μM), and wide linear ranges (2-100 and 2-80 μM), which met the requirements of pheochromocytoma diagnosis. We also applied them to determine VMA in an artificial urine sample and diluted human urine sample and obtained satisfactory results. They will become prospective fluorescence sensing platforms for VMA.

Highly Sensitive Adsorption and Detection of Iodide in Aqueous Solution by a Post-Synthesized Zirconium-Organic Framework

Effective methods of detection and removal of iodide ions (I^-) from radioactive wastewater are urgently needed and developing them remains a great challenge. In this work, an Ag⁺ decorated stable nano-MOF UiO-66-(COOH)₂ was developed for the I^- to simultaneously capture and sense in aqueous solution. Due to the uncoordinated carboxylate groups on the UiO-66-(COOH)₂ framework, Ag⁺ was successfully incorporated into the MOF and enhanced the intrinsic fluorescence of MOF. After adding iodide ions, Ag⁺ would be produced, following the formation of AgI. As a result, Ag⁺@UiO-66-(COOH)₂ can be utilized for the removal of I^- in aqueous solution, even in the presence of other common ionic ions (NO₂^-, NO₃^-, F^-, SO₄^2-). The removal capacity as high as 235.5 mg/g was calculated by Langmuir model; moreover, the fluorescence of Ag⁺@UiO-66-(COOH)₂ gradually decreases with the deposition of AgI, which can be quantitatively depicted by a linear equation. The limit of detection toward I^- is calculated to be 0.58 ppm.

A rare 4-fold interpenetrated metal-organic framework constructed from an anionic indium-based node and a cationic dicopper linker

A unique 4-fold interpenetrated metal-organic framework, TIF-1, was synthesized by combining an anionic indium node with a cationic linker. This framework shows a rare type of 4-fold interpenetrated dia network, constructed from tessellation of biangular and tetragonal type metal-organic micropores. The porosity of TIF-1 is moderate due to four-fold interpenetration and charge-balancing anions. The cationic feature of this MOF may give good efficiency for selective small anion exchange or separation. In addition, the thermal stability and moderate CO2 adsorption property of the complex were studied.

Structural Isomerism of Two Ce-BTC for Fabricating Pt/CeO2 Nanorods toward Low-Temperature CO Oxidation

Metal-organic frameworks (MOFs) have attracted enormous research interest as precursors/templates to prepare catalytic materials. However, the effect of structural isomerism of MOFs on the catalytic performance has rarely been studied. In this contribution, two topologically different Ce-benzene tricarboxylate (Ce-BTC) based on the same ligands and metal centers (viz., "MOF isomers") are prepared and used as porous supports to load Pt nanoparticles (NPs), which shows distinct differences in porosities and loading behaviors of Pt. Strikingly, an irreversible framework transformation from tetragonal Ce-BTC to monoclinic isomer is observed during water soaking treatment. The results give clear evidence that Pt/CeO₂ derived from tetragonal Ce-BTC inclines to produce more Pt⁰ and smaller Pt NPs, which eventually improve the catalytic performance for CO oxidation (T₁₀₀ = 80 °C). In situ diffuse reflectance infrared Fourier transform spectroscopy analyses demonstrate that the adsorbed CO-Pt⁰ is the dominant intermediate for CO oxidation, rather than CO-Pt^{σ +} at the low temperature. Furthermore, MOF isomers based on the same structural units are also found in other Ln-MOFs, such as Er-BTC, Eu-BTC, Y-BTC, and Ce/Y-BTC. Overall, this study affords a fundamental understanding of the effect of MOF structural isomers on the catalytic performance of the derived composites.

Photophysical properties of cationic dyes captured in the mesoscale channels of micron-sized metal-organic framework crystals

The optical properties of dye molecules in confined spaces can differ from the solution phase due to confinement effects. Pre-organized mesoscale channels of metal-organic frameworks (MOFs) are very suited for hosting various dyes, and the robust frameworks often render the encapsulated dyes with certain preferential geometries, which are different from those found in solution. Furthermore, pre-organized open channels can efficiently guide the uniform and unique spatial distribution of dye molecules in a controlled manner, which are otherwise difficult to achieve. Thus, sufficiently large dye molecules can avoid the formation of complex aggregates when captured inside open channels. In contrast, small dye molecules can form well-defined dimers or aggregates. The resulting dye-encapsulated MOFs can display unusual photophysical properties of the captured dyes. An anionic framework of In-BTB with mesoscale 3D channels is utilized for the efficient encapsulation of various cationic dyes through cation-exchange processes. Six different cationic dyes are encapsulated in the anionic framework of In-BTB, and their crystal structures are completely solved. Novel photophysical properties of these spatially distributed dye molecules in dye@In-BTBs are investigated.

A dual-emission probe to detect moisture and water in organic solvents based on green-Tb3+ post-coordinated metal–organic frameworks with red carbon dots

A new dual-emission Tb³⁺@p-CDs/MOF (red carbon dots, green Tb³⁺) serves as a luminescent sensor for water and humidity, due to the agglomeration effect of p-CDs in different solvents.

Encapsulation of an organometallic cationic catalyst by direct exchange into an anionic MOF

Metal-Organic Frameworks (MOFs) are porous crystalline materials that have emerged as promising hosts for the heterogenization of homogeneous organometallic catalysts, forming hybrid materials which combine the benefits of both classes of catalysts. Herein, we report the encapsulation of the organometallic cationic Lewis acidic catalyst [CpFe(CO)2(L)]+ ([Fp-L]+, Cp = η5-C5H5, L = weakly bound solvent) inside the pores of the anionic [Et4N]3[In3(BTC)4] MOF (H3BTC = benzenetricarboxylic acid) via a direct one-step cation exchange process. To conclusively validate this methodology, initially [Cp2Co]+ was used as an inert spatial probe to (i) test the stability of the selected host; (ii) monitor the stoichiometry of the cation exchange process and (iii) assess pore dimensions, spatial location of the cationic species and guest-accessible space by single crystal X-ray crystallography. Subsequently, the quasi-isosteric [Fp-L]+ was encapsulated inside the pores via partial cation exchange to form [(Fp-L)0.6(Et4N)2.4][In3(BTC)4]. The latter was rigorously characterized and benchmarked as a heterogeneous catalyst in a simple Diels-Alder reaction, thus verifying the integrity and reactivity of the encapsulated molecular catalyst. These results provide a platform for the development of heterogeneous catalysts with chemically and spatially well-defined catalytic sites by direct exchange of cationic catalysts into anionic MOFs.

A robust indium–porphyrin framework for CO2 capture and chemical transformation

A robust indium–porphyrin framework based on amido-decorated porphyrin ligands is used for CO₂ capture and chemical fixation, showing good catalytic activity and recyclability.

Cuboctahedron-based indium–organic frameworks for gas sorption and selective cation exchange

InOF-9is an anionic indium–organic framework, which exhibits excellent gas sorption capacity through supercritical carbon dioxide activation process and selectively encapsulates guest methylene blue cations.

Heterometallic cluster-based indium-organic frameworks

With the help of the ligand-oriented method, we have successfully embedded independent copper-based units into the indium-organic framework system for the first time, in which the Cu4I4 clusters and In3O(CO2)6 clusters coexist. This heterometallic cluster-based framework has a large porosity with extra-open channels along the c-axis, and its sorption capacity has also been investigated.

Template-directed construction of conformational supramolecular isomers for bilayer porous metal–organic frameworks with distinct gas sorption behaviors

Two conformationally isomeric Co(ii)-based bilayer porous coordination frameworks can be prepared using different solvent templates, which show distinct gas sorption behaviors.