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 [Ce IV 70(OH)36(O)64(SO4)60(H2O)10] 4-, part of a larger emerging family of M IV 70materials (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] 6and 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 Ce III . Room temperature rapid assembly of both Ce70 and Ce62, respectively, by addition of Li + and NH4 + , along with ionexchange and redox behavior, invite exploitation of this emerging material family in environmental and energy applications. Ce70, [Ce IV 70(OH)36(O)64(SO4)60] 4-, was described prior, and is also isostructural with Zr70 and U70. [49][50][51][52] Briefly, the Ce70 cluster can be viewed as ten Ce6-hexamers that alternate with ten Ce1-monomers. Four sulfates bridge each Ce6 and Ce1 along the outer rim, and four additional sulfates bridge only Ce6 units along the inner rim. Each fragment discussed later can be viewed in the same context. The Ce62, [Ce62(OH)30(O)58(SO4)58] 14-, consisting of ~90% of the ring, contains nine Ce6 and eight Ce1. Ce13, [Ce13(OH)6(O)12(SO4)14(Η2Ο)14] 6-, consists of two Ce6 and Ce1, and is approximately 20% of the ring. Ce5 [Ce5(O)3(SO4)12] 10-, resembles half of the Ce6 plus two flanking monomers. These clusters and their intrinsic relation to the Ce70, summarized in figure 1, serve as crystallographic snapshots of mechanistic pathways for ring formation.

The promise of polyhydroxamic acid ligands for the selective chelation of the f-elements is becoming increasingly more apparent. The initial studies of polyhydroxamic acid siderophores showed the formation of highly stable complexes with Pu(IV), but a higher preference for Fe(III) hindered effective applications. The development of synthetic routes toward highly pure and customizable ligands containing multiple hydroxamic acids allowed for the growth of new classes of compounds. While the first round of these ligands focused on the incorporation of siderophore-like frameworks, the new synthetic strategies led to small molecules of various frameworks and even resins for applications in the field of f-element separations and biological desorption. Unfortunately, a lack of consistent stability constant data makes direct comparisons across this body of work difficult. More studies into the stability constants and separations of the f-elements in a variety of pH ranges is necessary to truly realize the potential for polyhydroxamic acid ligands.

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.

Plutonium(IV) oxalate hexahydrate (Pu(C 2 O 4 ) 2 • 6 H 2 O; PuOx) is an important intermediate in the recovery of plutonium from used nuclear fuel. Its formation by precipitation is well studied, yet its crystal structure remains unknown. Instead, the crystal structure of PuOx is assumed to be isostructural with neptunium(IV) oxalate hexahydrate (Np-(C 2 O 4 ) 2 • 6 H 2 O; NpOx) and uranium(IV) oxalate hexahydrate (U(C 2 O 4 ) 2 • 6 H 2 O; UOx) despite the high degree of unresolved disorder that exists when determining water positions in the crystal structures of the latter two compounds. Such assumptions regarding the isostructural behavior of the actinide elements have been used to predict the structure of PuOx for use in a wide range of studies. Herein, we report the first crystal structures for PuOx and Th(C 2 O 4 ) 2 • 6 H 2 O (ThOx). These data, along with new characterization of UOx and NpOx, have resulted in the full determination of the structures and resolution of the disorder around the water molecules. Specifically, we have identified the coordination of two water molecules with each metal center, which necessitates a change in oxalate coordination mode from axial to equatorial that has not been reported in the literature. The results of this work exemplify the need to revisit previous assumptions regarding fundamental actinide chemistry, which are heavily relied upon within the current nuclear field.

Old, limited data in the nuclear field is relied upon, but often requires revisiting for clarity. Like cracked glasses, flaws in old data can lead to missing information. Structural assumptions about PuIV oxalate hexahydrate have existed for decades, but only now has the structure been reported. These data have led to the identification of previously unreported coordination of water and changing oxalate positions across the isostructural AnIV series. More information can be found in the Research Article by A. K. Sockwell, A. E. Hixon and co‐workers (DOI: 10.1002/chem.202301164).