Ce^IV₇₀Oxosulfate Rings, Frameworks, Supramolecular Assembly, and Redox Activity**

Abstract

M IV molecular oxo-clusters (M = Zr,Hf, Ce,T h, U, Np,P u) are prolific in bottoms-up material design, catalysis, and elucidating reaction pathwaysi nn ature and in synthesis. Here we introduce Ce 70 ,awheel-shaped oxo-cluster,[ Ce IV 70-(OH) 36 (O) 64 (SO 4) 60 (H 2 O) 10 ] 4À .C e 70 crystallizes into intricate high pore volume frameworks with divalent transition metals and Ce-monomer linkers.Eight crystal-structures feature four framework types in which the Ce 70-rings are linked as propellers,i no ffset-stacks,i natartan pattern, and as isolated rings.S mall-angle X-ray scattering of Ce 70 dissolved in butylamine,w ith and without added cations (Ce IV ,a lkaline earths, Mn II), shows the metals differentiating roles in ring linking, leading to supramolecular assemblies.T he large acidic pores and abundant terminal sulfates provideion-exchange behavior, demonstrated with U IV and Nd III .Frameworks featuring Ce III/IVmonomer linkers demonstrate both oxidation and reduction. This study opens the door to mixed-metal, highly porous framework catalysts,a nd new clusters for metal-organic framework design topology of M IV-oxo clusters is the hexamer (M 6 , [M IV 6 (OH,O) 8 ]), [5] which structurally resembles the M IV O 2 fluorite-type lattice.T his molecular oxide fragment has been stabilized and isolated with carboxylate,n itrate,s ulfate,a nd polyoxometalate ligands. [6] Combining rigid bicarboxylate linkers with Zr IV 6 led to the discovery of the metal-organic framework (MOF) known as UiO-66. [5a] This compound and its derivatives comprise an extensive MOF family known for high stability and functionalizabilty,exploited in separations, storage and catalysis. [8] Not suprising,U iO-66 analogues of Hf IV , [7] Ce IV , [8] Th IV , [9] U IV , [10] Np IV , [5f] and Pu IV [11] have all been discovered. Beyond the hexamer,l arger M IV-oxo clusters are built symmetrically around the M 6 core,a nd by extension, are larger fragments of the fluorite lattice.T he largest is M 38 , synthesized from Ce IV , [12] Pu IV , [2c] U IV [13] and Np IV. [14] Ceriumoxo clusters and nanomaterials are of special relevance. [6e, 12] Owed to facile Ce III-Ce IV redox behavior and concomitant oxygen transport, ceria nanoparticles are used as automotive redox catalysts,i no xide fuel cells,a nd as photoactive solar cell materials. [15] Atomically precise cerium-oxo clusters are valuable to understand form-function relationships;and Ce 10 , Ce 20 ,C e 22 ,C e 24 ,C e 38 and Ce 40 have been isolated, some of which have distinct Ce III and Ce IV sites. [6e,12] Farha and coworkers recently demonstrated catalytic activity of Ce 38 ,owed to the high porosity and redox activity of the solid material. [16] We exploited Ln III and TM II countercations to create an ew family of giant U IV-oxo clusters including the U 84 "superatom" (with Ln III)a nd U 70 wheel (with TM II). [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...

Snapshots of Ce70 Toroid Assembly from Solids and Solution

“…, 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.…”

“…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 the prior study of TM-linked Ce70 (TM=transition metal) frameworks, we observed a general trend of increasing TM concentration in reaction solutions yielded frameworks with more incorporation of Ce-monomers, instead of the TM-linkers. 51 This result was initially counterintuitive, but attributable to the TMs inhibiting or slowing Ce70 formation. The Ce-monomers are important in these frameworks because they are either mixed Ce III/IV or purely Ce III oxidation state, where both oxidation states were shown to be redox active in the monomer form.…”

“…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).…”

One-Pot Synthesis of CeO2 Modified SBA-15 With No Pore Clogging for NO Reduction by CO

“…This is probably due to the outstanding oxygen storage capacity (OSC) and ease of the Ce(III)-Ce(IV) redox cycle of ceria (Fan et al, 2013). Possessing these unique properties, ceria can greatly improve the redox properties of CuO (Luo et al, 1997;Colliard and Nyman, 2021). Hence, the reducibility of CuO is improved and the corresponding peaks shift to lower values.…”