Snapshots of Ce ₇₀ Toroid Assembly from Solids and Solution

Crystallization at the solid–liquid interface is difficult to spectroscopically observe and therefore challenging to understand and ultimately control at the molecular level. The Ce 70 -torroid formulated [Ce IV 70 (OH) 36 (O) 64 (SO 4 ) 60 (H 2 O) 10 ] 4–, part of a larger emerging family of M IV 70 -materials (M = Zr, U, Ce), presents such an opportunity. We elucidated assembly mechanisms by the X-ray scattering (small-angle scattering and total scattering) of solutions and solids as well as crystallizing and identifying fragments of Ce 70 by single-crystal X-ray diffraction. Fragments show evidence for templated growth (Ce 5, [Ce 5 (O) 3 (SO 4 ) 12 ] 10- ) and modular assembly from hexamer (Ce 6 ) building units (Ce 13, [Ce 13 (OH) 6 (O) 12 (SO 4 ) 14 (H 2 O) 14 ] 6– and Ce 62, [Ce 62 (OH) 30 (O) 58 (SO 4 ) 58 ] 14- ). Ce 62, an almost complete ring, precipitates instantaneously in the presence of ammonium cations as two torqued arcs that interlock by hydrogen boding through NH 4 +, a structural motif not observed before in inorganic systems. The room temperature rapid assemblies of both Ce 70 and Ce 62, respectively, by the addition of Li + and NH 4 +, along with ion-exchange and redox behavior, invite exploitation of this emerging material family in environmental and energy applications.