Snapshots of Ce70 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 Ce70-torroid formulated [CeIV70(OH)36(O)64(SO4)60(H2O)10] 4- , part of a larger emerging family of MIV70- materials (M=Zr, U, Ce), presents such an opportunity. We have elucidated assembly mechanisms by X-ray scattering (small-angle scattering and total scattering) of solutions and solids, as well as crystallizing and identifying fragments of Ce70 by single-crystal X-ray diffraction. Fragments show evidence for templated growth (Ce5, [Ce5(O)3(SO4)12] 10- ) and modular assembly from hexamer (Ce6) building units (Ce13, [Ce13(OH)6(O)12(SO4)14(Η2Ο)14] 6- and Ce62, [Ce62(OH)30(O)58(SO4)58] 14- ). Ce62, an almost complete ring, precipitates instantaneously in the presence of ammonium cations as two torqued arcs that interlock by hydrogen boding through NH4 +, which can also be replaced by other cations, demonstrated with CeIII. Room temperature rapid assembly of both Ce70 and Ce62, respectively, by addition of Li+ and NH4 +, along with ion?exchange and redox behavior, invite exploitation of this emerging material family in environmental and energy applications.