Spin-Polarization-Induced Preedge Transitions in the Sulfur K-Edge XAS Spectra of Open-Shell Transition-Metal Sulfates: Spectroscopic Validation of σ-Bond Electron Transfer

Symmetry Breaking in Solution-Phase [Cu(tsc)2(H2O)2]2+: Emergent Asymmetry in Cu-S Distances and in Covalence

The structure of aqueous Cu(II)-bis-thiosemicarbazide, [Cu(tsc)₂]²⁺, is reported following EXAFS and MXAN analyses of the copper K-edge X-ray absorption (XAS) spectrum. The rising K-edge feature at 8987.1 eV is higher energy than those of crystalline models, implying unique electronic and structural solution states. EXAFS analysis (k = 2-13 Å^-1; 2 × Cu-N = 2.02 ± 0.01 Å; 2 × Cu-S = 2.27 ± 0.01 Å; Cu-O_ax = 2.41 ± 0.04 Å) could not resolve 5- versus 6-coordinate models. However, MXAN fits converged to an asymmetric broken symmetry 6-coordinate model with cis-disposed TSC ligands (Cu-O_ax = 2.07 and 2.54 Å; Cu-N = 1.94 Å, 1.98 Å; Cu-S = 2.20 Å, 2.41 Å). Transition dipole integral evaluation of the sulfur K-edge XAS 1s → 3p valence transition feature at 2470.7 eV yielded a Cu-S covalence of 0.66 e^-, indicating Cu^1.34+. The high Cu-S covalence and short Cu-S bond in aqueous [Cu(tsc)₂(H₂O)₂]²⁺ again contradict the need for a protein rack to explain the unique structure of the blue copper active site. MXAN models of dissolved Cu(II) complex ions have invariably featured broken centrosymmetry. The potential energy ground state for dissolved Cu(II) evidently includes the extended solvation field, providing a target for improved physical theory. A revised solvation model for aqueous Cu(II), |[Cu(H₂O)₅]·14H₂O|²⁺, is presented.

CeIV 70 Oxosulfate Rings, Frameworks, Supramolecular Assembly, and Redox Activity*

M^IV molecular oxo-clusters (M=Zr, Hf, Ce, Th, U, Np, Pu) are prolific in bottoms-up material design, catalysis, and elucidating reaction pathways in nature and in synthesis. Here we introduce Ce₇₀ , a wheel-shaped oxo-cluster, [Ce^IV ₇₀ (OH)₃₆ (O)₆₄ (SO₄ )₆₀ (H₂ O)₁₀ ]^4- . Ce₇₀ 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 Ce₇₀ -rings are linked as propellers, in offset-stacks, in a tartan pattern, and as isolated rings. Small-angle X-ray scattering of Ce₇₀ dissolved in butylamine, with and without added cations (Ce^IV , alkaline earths, Mn^II ), shows the metals' differentiating roles in ring linking, leading to supramolecular assemblies. The large acidic pores and abundant terminal sulfates provide ion-exchange behavior, demonstrated with U^IV and Nd^III . Frameworks featuring Ce^III/IV -monomer linkers demonstrate both oxidation and reduction. This study opens the door to mixed-metal, highly porous framework catalysts, and new clusters for metal-organic framework design.

Insights into sulfur poisoning and regeneration of Cu-SSZ-13 catalysts: in situ Cu and S K-edge XAS studies

The temperature during sulfur poisoning affects the relation between total sulfur content and the fraction of sulfur-free copper in poisoned and regenerated Cu-SSZ-13 catalysts.

Building [UIV 70 (OH)36 (O)64 ]4- Oxocluster Frameworks with Sulfate, Transition Metals, and UV

Uranium(IV) oxide clusters, colloids, and materials are designed and studied for 1) nuclear materials applications, 2) understanding the environmental fate and transport of actinides, and 3) exploring the complex bonding behavior of open-shell f-elements. U^IV -oxyhydroxsulfate clusters are particularly relevant in industrial processes and in nature. Recent studies have shown that counter-cations to these polynuclear anions differentiate rich structural topologies in the solid-state. Herein, we present nine different structures with wheel-shaped [U₇₀ (OH)₃₆ (O)₆₄ (SO₄ )₆₀ ]^4- (U₇₀ ) linked into one- and two-dimensional frameworks with sulfate, divalent transition metals (Cr^II , Fe^II , Co^II , Ni^II ) and U^V . Small-angle X-ray scattering of these phases dissolved in butylamine reveals differing supramolecular assembly of U₇₀ clusters, controlled primarily by sulfates. However, observed trends in transition metal linking guide future design of U₇₀ materials with different topologies. Finally, U₇₀ linking via U^IV -O-U^V -O-U^IV bridges presents a rare example of mixed-oxidation-state uranium oxides without disorder.

Supramolecular Assembly of U(IV) Clusters and Superatoms with Unconventional Countercations

Superatoms are nanometer-sized molecules or particles that form ordered lattices, mimicking their atomic counterparts. Hierarchical assembly of superatoms gives rise to emergent properties in lattices of quantum dots, p-block clusters, and fullerenes. Here, we introduce a family of uranium-oxysulfate cluster anions whose hierarchical assembly in water is controlled by two parameters: acidity and the lanthanide or transition-metal countercation. In acid, larger Ln^III (Ln = La-Ho) link hexamer (U₆) oxoclusters into body-centered cubic frameworks, while smaller Ln^III (Ln = Er-Lu and Y) promote linking of 14 U₆ clusters into hollow superclusters (U₈₄ superatoms). U₈₄ assembles into superlattices including cubic-closest packed, body-centered cubic, and interpenetrating networks, bridged by interstitial countercations and U₆ clusters. Divalent transition metals (TM = Mn^II and Zn^II) charge-balance and promote the fusion of 10 U₆ and 10 U monomers into a wheel-shaped cluster (U₇₀). Dissolution of U₇₀ in organic media reveals (by small-angle X-ray scattering) that differing supramolecular assemblies are accessed, controlled by TM^II-linking of U₇₀ clusters. Magnetic measurements of these assemblies reveal Curie-Weiss behavior at high temperatures, without pairing of the 5f²-electrons down to 2 K.