Uranyl Nanotubules and Nanospheres: Inspired by Curvature in Phosphonates and Arsonates

This review aims to highlight over three decades of research on the use of phosphonate and arsonate ligands in designing uranyl nanotubules and nanospheres. It discusses the synthesis, structures, properties, as well as how earlier compounds provide valuable insights into the formation of subsequent ones. In general, phosphonate and arsonate derivatives exhibit flexibility, which enhances the curvature of the structural units within uranyl polyhedra. Notably, earlier uranyl phosphonate nanotubules feature a nearly circular cross-section, whereas some recent examples display highly elliptical shapes. The emergence of structurally dynamic polymorphs capable of reversible phase transformations reflects a growing sophistication in synthetic design. Ion-exchange studies further underscore the robustness and reusability of these materials, marking a shift from esthetic curiosity to functional utility. A synergistic interplay between peroxo and phosphonate ligands is key to the stabilization of unique uranyl topologies. While some uranyl cage assemblies arise serendipitously through the use of bulky ligands, a more intentional design approach is achieved through in situ ligand condensation reactions.