84-Nuclearity Lanthanide-Aluminum Cyclic Clusters: Promising Materials for Iodine Capture and Storage.

Developing high-performance adsorbents for iodine uptake and storage has become an urgent priority for safe disposal and long-term storage of nuclear waste. In this work, two cyclic lanthanide-aluminum clusters with the formula [Ln₁₂Al₇₂(hmp)₆₀(C₂H₅O₂)₆(μ₂-OH)₁₂₀(μ₃-OH)₁₈(H₂O)₃₀]Cl₂₄·(NO₃)₂₄·(H₂O)_x (Ln = Tb, x ≈ 80, Tb₁₂Al₇₂; Ln = Gd, x ≈ 100, Gd₁₂Al₇₂; Hhmp = 2-(hydroxymethyl)pyridine and C₂H₆O₂ = ethylene glycol) are reported. Single-crystal analysis reveals that its inner diameter is approximately 1.1 nm, with an outer diameter of 4.1 nm and a thickness of 3.1 nm. The packing of cyclic clusters through intermolecular interactions generates a 3D supramolecular structure with one-dimensional channels. Investigation of the iodine adsorption performance of the cluster indicates an uptake capacity of 3.14 g g^-1 for Tb₁₂Al₇₂ and 3.1 g g^-1 for Gd₁₂Al₇₂. The effectiveness of iodine adsorption is largely due to the accessible micropore structure along with the high density of pyridine rings and abundant hydroxyl oxygen atoms. Consistently, DFT calculations indicate that the [Al(μ-OH)_n] clusters and pyridine ring regions synergistically facilitate iodine adsorption, effectively promoting the dissociation of I₂ into I^- anions. This unique micropore environment enhances the electrostatic stabilization of polyiodide anions through a strong Coulombic attraction, significantly boosting the capture of iodine.