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.