Abstract
Actinide based metal‐organic frameworks (MOFs) are unique not only because compared to the transition metal and lanthanide systems, they are substantially less explored, but also owing to the uniqueness of actinide ions in bonding and coordination. We report here a new 3D thorium‐organic framework (SCU‐11) that contains a series of cages with an effective size of ca. 21~24 Å. Th4+ in SCU‐11 is 10‐coordinate with a new bicapped square pri** coordination geometry, which has never been documented for any metal cation complexes before. The bicapped position is occupied by two coordinated water molecules that can be removed to afford a very unique open Th4+ site, confirmed by X‐ray diffraction, colour change, thermogravimetry, and spectroscopy. The degassed phase (SCU‐11‐A) exhibits a Brunauer‐Emmett‐Teller surface area of 1272 m2 g‐1, one of the highest values among reported actinide materials, enabling it to sufficiently retain water vapor, Kr, and Xe with uptake capacities of 234 cm3 g‐1, 0.77 mmol g‐1, 3.17 mmol g‐1, respectively and a Xe/Kr selectivity of 5.7.