Multifunctional Two-Dimensional Metal-Organic Frameworks for Radionuclide Sequestration and Detection

Influence of Node-Linker Connectivity on Radiolytic Stability of Thorium-Terephthalate Coordination Polymers

Metal-organic frameworks (MOFs) are promising candidates for applications in the nuclear fuel cycle due to their high porosity and tunable properties. However, for effective use in this context, these materials must be stable under ionizing radiation conditions. While previous studies have explored variations in metal node identities, topologies, and linker types, this study focuses on maintaining consistent metal and linker components to identify structural features that enhance radiation stability. We investigated the radiation resistance of three thorium-terephthalate hybrid materials─Th(BDC)2(DMF)2 (1,4-benzenedicarboxylic acid, dimethylformamide), Th(BDC)2, and Th-UiO-66─irradiated with He-ions up to a dose of 227 MGy. Structural stability was assessed through powder X-ray diffraction (PXRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and density functional theory (DFT) calculations. The radiation stability thresholds were identified for Th(BDC)2(DMF)2 and Th-UiO-66, with Th(BDC)2 demonstrating exceptional stability even at the highest radiation dose. The observed stability trend is Th(BDC)2 > Th(BDC)2(DMF)2 > Th-UiO-66. Notably, the inclusion of DMF in Th(BDC)2(DMF)2 enhanced its radiation tolerance, likely due to DMF acting as a sacrificial ligand, preserving linker integrity at higher doses. Additionally, more unique node-linker connections and shorter interligand distances contributed to the improved radiolytic stability of these materials.

A Luminescent Proton Conductor Based on Dy2 SMM

Multifunctional materials bearing photoluminescence, single-molecule magnet (SMM) behavior, and proton conduction have been particularly attractive for various promising applications in optics, molecular spintronics, high-density data storage, and fuel cells. However, these kinds of multifunctional systems have rarely been reported. Herein, a DyIII-SMM together with luminescent and proton-conducting properties, [Dy2(1-tza)4(phen)4]∙(ClO4)2∙(H2O)2 (1, 1-tza = 2-(1H-tetrazol-1-yl)acetic, phen = 1,10-phenanthroline), was prepared and structurally characterized. Complex 1 features a dinuclear structure bridged by carboxylate oxygen atoms of the 1-tza- ligands, and its supramolecular network contains a 1D stacking channel. Complex 1 exhibits strong room-temperature DyIII characteristic emissions and SMM behaviors. In addition, complex 1 shows a moderate proton conductivity with 4.00 × 10-6 S cm-1 at 37 °C and 100% R.H. (R.H. = Relative Humidity), which may be ascribed to the 1D-extended H-bonds in the 1D stacking channel of 1.

Quest for a Desolvated Structure Unveils Breathing Phenomena in a MOF Leading to Greener Catalysis in a Solventless Setup: Insights from Combined Experimental and Computational Studies

The crystal structure of the metal-organic framework (MOF), {Mn2(1,4-bdc)2(DMF)2}n (1) (1,4-bdcH2, 1,4-benzenedicarboxylic acid; DMF, N,N-dimethylformamide), is known for a long time; however, its desolvated structure, {Mn2(1,4-bdc)2}n (1'), is not yet known. The first-principles-based computational simulation was used to unveil the structure of 1' that shows the expansion in the framework, leading to pore opening after the removal of coordinated DMF molecules. We have used 1' that contains open metal sites (OMSs) in the structure in cyanosilylation and CO2 cycloaddition reactions and recorded complete conversions in a solventless setup. The pore opening in 1' allows the facile diffusion of small aldehyde molecules into the channels, leading to complete conversion. The reactions with larger aldehydes, 2-naphthaldehyde and 9-anthracenecarboxaldehyde, also show 99.9% conversions, which are the highest reported until date in solventless conditions. The in silico simulations illustrate that larger aldehydes interact with Mn(II) OMSs on the surfaces, enabling a closer interaction and facilitating complete conversions. The catalyst shows high recyclability, exhibiting 99.9% conversions in the successive reaction cycles with negligible change in the structure. Our investigations illustrate that the catalyst 1' is economical, efficient, and robust and allows reactions in a solventless greener setup, and therefore the catalysis with 1' can be regarded as "green catalysis".

Robust Carbazole-Based Rare-Earth MOFs: Tunable White-Light Emission for Temperature and DMF Sensing

Rare-earth metal-organic frameworks (RE-MOFs) are an attractive platform to construct luminescent materials for practical applications in lighting, optoelectronics, and sensing. By adjusting the metal composition in mixed RE-MOFs, one can not only realize tunable emission but also construct ratiometric luminescent sensors. As such, it is highly desirable to prepare robust RE-MOFs that display efficient, multifunctional sensing capability. In this work, we designed and synthesized a series of RE-MOFs that exhibit both excellent thermal and chemical stability due to the incorporation of a bulky tert-butyl group on a new carbazole-based ligand. By rationally tuning the molar ratio of Eu³⁺/Tb³⁺/Y³⁺, a white-light-emitting MOF was developed as an excellent thermal sensor that exhibits a temperature-induced ratiometric luminescence response between 278 and 378 K. After removing the coordinated solvent molecules via thermal treatment, the desolvated MOF materials exhibit excellent turn-on or color change sensitivity to recognize dimethylformamide (DMF) molecules. Such high sensitivity is attributed to the DMF coordination that induces the framework structure change and shifts the ligand's excited-state energy level to facilitate the ligand-to-metal energy transfer process. Taking together, NPF-700-RE represents a new class of robust, tunable luminescent materials that have great potential in white-light emission and thermal- and DMF-sensing applications.