A Toroidal Zr₇₀ Oxysulfate Cluster and Its Diverse Packing Structures

Abstract

Herein, we report the discovery of at oroidal inorganic cluster of zirconium(IV) oxysulfate of unprecedented size with the formula Zr 70 (SO 4) 58 (O/OH) 146 •x(H 2 O) (Zr 70), which displays different packing of ring units and thus several polymorphic crystal structures.The ring measures over 3nmacross,has an inner cavity of 1nmand displays apseudo-10-fold rotational symmetry of Zr 6 octahedra bridged by an additional Zr in the outer rim of the ring. Depending on the cocrystallizing species,t he rings form various crystalline phases in which the torus units are connected in extended chain and network structures.O ne phase,i nw hich the ring units are arranged in layers and form one-dimensional channels, displays high permanent porosity (BET surface area: 241 m 2 g À1), and thus demonstrates af unctional property for potential use in, for example,a dsorption or heterogeneous catalysis.

Snapshots of Ce70 Toroid Assembly from Solids and Solution

“…The transition metals and lanthanides that serve as counter-cations and also link the rings into intricate frameworks probably necessitate the heating to promote complete dissolution. [49][50][51] In fact, Zr70 has been isolated at room temperature, as either a neutral form with no counter-cations or as a Na-salt, 52 supporting this hypothesis. The neutral cluster also challenges our understanding of the role of the counter-cations.…”

“…In addition, distinctive features indicative of the Ce70 shape and size is seen by the pair of peaks at high q (1.9 Å -1 and 2.1 Å -1 ), and by the growth of the oscillation around q = 0.3 Å -1 . [49][50][51][52] To differentiate the effects of increasing pH with increasing counterions, the experiment was repeated using LiNO3 instead of LiOH, and was found to be virtually identical. The LiNO3-Ce(SO4)2 series is shown in figure 6a.…”

“…The increase in size is substantial for the Ce70 population, ~25%. This could represent a minor amount of offset ring-stacking (figure S12) seen in many M70 crystal structures, [49][50][51][52] as a pre-nucleation process, 50 or ring fragments (Ce6, Ce13, etc.) assembling neighboring rings from the Ce70 'scaffold'.…”

“…The Ce III/IV redox activity distinguishes this family of metal-oxo clusters: Ce10, Ce22, and Ce40 oxoclusters have distinct Ce III and Ce IV sites, 44,47 while Ce38 reports mixed Ce III/IV -sites. 48 The M IV 70 sulfate ring structure, originally described for U IV 70, followed by Ce IV 70 and Zr70, [49][50][51][52] is the only M IV -topology besides M6 that spans transition metals, lanthanides, and actinides, and is also the largest. The hexamer units are distinct in M70, alternating with monomers around the ring (figure 1a).…”

“…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.…”