Three-Dimensional Polycatenation of a Uranium-Based Metal–Organic Cage: Structural Complexity and Radiation Detection

The potential applications of metal–organic
cages (MOCs)
are mostly achieved through specific host–guest interactions
within their cavities. Electronic applications would require an effective
electron transport pathway, which has been extensively studied in
hybrid organic–inorganic materials with extended structures.
These properties have not been considered for MOCs because cage-to-cage
interactions in these materials have rarely been examined and are
challenging to functionalize. We report here a previously unobserved
actinide-based MOC assembled from four hexagonal-bipyramidal-coordinated
uranyl ions and six bidentate flexible ligands. Remarkably, each isolated
cage is further interlocked with six adjacent ones through mechanical
bonds, resulting in the first case of a 0D → 3D f-element polycatenated
metal–organic cage, SCU-14. Long-range π–π
stacking extending throughout the structure is built via polycatenation,
providing a visible carrier transmission path. SCU-14 is also an extremely rare case of an intrinsically semiconductive
MOC with a wide band gap of 2.61 eV. Combined with the high X-ray
attenuation efficiency, SCU-14 can effectively convert
X-ray photons to electrical current signals and presents a promising
sensitivity of 54.93 μC Gy–1 cm–2.