A Toroidal Zr₇₀ Oxysulfate Cluster and Its Diverse Packing Structures

Abstract

Herein, we report the discovery of a toroidal 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 3 nm across, has an inner cavity of 1 nm and displays a pseudo-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, the rings form various crystalline phases in which the torus units are connected in extended chain and network structures. One phase, in which 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 a functional property for potential use in, for example, adsorption or heterogeneous catalysis.

CeIV70Oxosulfate Rings, Frameworks, Supramolecular Assembly, and Redox Activity**

“…[4] One of the most widely exploited families of metal-oxo clusters is that comprised of the large," hard" tetravalent cations that span transition metals (Zr IV ,H f IV ), lanthanides (Ce IV )and actinides (Th IV ,U IV ,Np IV ,Pu IV ). Themost common acidity of the pores is demonstrated by cation exchange.T he Zr 70 family shows yet again different arrangements, [18] bringing to light that this emerging family of M IV 70 -rings could rival other families of cluster-based materials and isolated clusters in both structural and functional diversity.…”

“…[4b, 17] Following U 70 ,t he Zr 70 analogue was described in multiple frameworks with transition metals,Mg 2+ ,Na + and no countercations. [18] This large toroid, with external and internal diameters of approximately 35 and 17 respectively,y ields pore volumes in its lattices,u pt o6 0%.A dditionally,t hese cluster-frameworks are insoluble in water and mild acid, yet they can be dissolved in short chain amines.T he former insolubility along with high porosity enables applications akin to MOFs,a sd emonstrated for the Ce 38 framework; [16] but without unstable organic components.T he latter provides opportunity to assemble 2-dimensional cluster arrays onto surfaces.Herein, we introduce the Ce 70 -sulfate torus,t he third member of the M 70 family,a nd unveil some distinct differences from the U 70 and Zr 70 families.S pecifically,t he transition metals and Ce-monomers play am ore significant role in framework assembly,l eading to four different framework types (instead of one type for U 70 ). Ther oles are also distinguished upon re-dissolution in amine solution (probed by small angle X-ray scattering,SAXS).…”

“…[4b, 17] Following U 70 ,t he Zr 70 analogue was described in multiple frameworks with transition metals,Mg 2+ ,Na + and no countercations. [18] This large toroid, with external and internal diameters of approximately 35 and 17 respectively,y ields pore volumes in its lattices,u pt o6 0%.A dditionally,t hese cluster-frameworks are insoluble in water and mild acid, yet they can be dissolved in short chain amines.T he former insolubility along with high porosity enables applications akin to MOFs,a sd emonstrated for the Ce 38 framework; [16] but without unstable organic components.T he latter provides opportunity to assemble 2-dimensional cluster arrays onto surfaces.…”

CeIV70Oxosulfate Rings, Frameworks, Supramolecular Assembly, and Redox Activity**

“…Second, frameworks featuring Ce‐monomer linkers exhibit redox activity, while acidity of the pores is demonstrated by cation exchange. The Zr 70 family shows yet again different arrangements, [18] bringing to light that this emerging family of M IV 70 ‐rings could rival other families of cluster‐based materials and isolated clusters in both structural and functional diversity.…”

“…We exploited Ln III and TM II countercations to create a new family of giant U IV ‐oxo clusters including the U 84 “superatom” (with Ln III ) and U 70 wheel (with TM II ) [4b, 17] . Following U 70 , the Zr 70 analogue was described in multiple frameworks with transition metals, Mg 2+ , Na + and no countercations [18] . This large toroid, with external and internal diameters of approximately 35 and 17 Å respectively, yields pore volumes in its lattices, up to 60 %.…”