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 Ce-70-torroid formulated [Ce-70(IV)(OH)(36)(O)(64)(SO4)(60)(H2O)(10)](4-), part of a larger emerging family of M-70(IV)-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)(SO4)(12)](10-)) and modular assembly from hexamer (Ce-6) building units (Ce-13, [Ce-13(OH)(6)(O)(12)(SO4)(14)(H2O)(14)](6-) and Ce-62, [Ce-62(OH)(30)(O)(58)(SO4)(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 NH4+, 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 NH4+, along with ion-exchange and redox behavior, invite exploitation of this emerging material family in environmental and energy applications.