Supramolecular Assembly of U(IV) Clusters and Superatoms

Abstract

Superatoms are nanometer-sized molecules or particles that can form ordered lattices, mimicking their atomic counterparts. Hierarchical assembly of superatoms gives rise to emergent properties in superlattices 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 countercation. In acid, larger Ln<sup>III</sup> (Ln=La-Ho) link hexamer (U<sub>6</sub>) oxoclusters into body-centered cubic frameworks, while smaller Ln<sup>III</sup> (Ln=Er-Lu &Y) promote linking of fourteen U<sub>6</sub>-clusters into hollow superclusters (U<sub>84</sub> superatoms). U<sub>84</sub> assembles into superlattices including cubic-closest packed, body-centered cubic, and interpenetrating networks, bridged by interstitial countercations, and U<sub>6</sub>-clusters. Divalent transition metals (TM=Mn<sup>II </sup>and Zn<sup>II</sup>), with no added acid, charge-balance and promote the fusion of 10 U<sub>6</sub> and 10 U-monomers into a wheel–shaped cluster (U<sub>70</sub>). Dissolution of U<sub>70</sub> in organic media reveals (by small-angle Xray scattering) that differing supramolecular assemblies are accessed, controlled by TM-linking of U<sub>70</sub>-clusters. <br>

Supramolecular Assembly of CeIV-Oxo Sulfate Torus with Transition Metal Countercations

“…[61][62][63][64] Combining first-row transition metals with Ce IV (SO4)2 and heating at 75 °C (see SI for details) promotes assembly of the Ce70 torus cluster; fully formulated [Ce IV (OH)36(O)64(SO4)60(H2O)10] 4-, isostructural with prior reported U70 (Figure 1a). 26,59 Analogous to U70, the Ce70 cluster can be viewed as alternating Ce6 and Ce1; four sulfates bridge a Ce6 and a Ce1 along the outer rim, and four additional sulfate line the inner rim bridging only between Ce6, see Figure 1b. 59 The Individual TM II bonding behaviors and the synthesis conditions leads to four unique architectural assemblies of the Ce70 plus Ce IV -monomer/TM II -counterions, and addenda sulfates, and will be described in detail later.…”

“…The structure occupancy factor (S.O.F., Table S9) is accounted due to different occupancies of these monomer sites, ranging from 0.25 to 1.0, and different ligation; similar to the prior-reported U70 frameworks. 26 structures, Zn is unique in its strong preference for bonding to water over bonding to sulfate, promoting formation of the isolated framework with extensive incorporation of Ce IV -monomer bonding to Ce70. 26,59 Additionally, for the Ce IV -monomer, tracking of sulfate ligation can also be seen by the coordination mode for the ligands.…”

“…26 structures, Zn is unique in its strong preference for bonding to water over bonding to sulfate, promoting formation of the isolated framework with extensive incorporation of Ce IV -monomer bonding to Ce70. 26,59 Additionally, for the Ce IV -monomer, tracking of sulfate ligation can also be seen by the coordination mode for the ligands. There's a notable shift in the coordination of the monomers, highlighted by the number of monodentate (pink in figure 1d) and the chelating sulfates (turquoise in figure 1d), see also Table 1.…”

“…[12][13][14][15][16][17][18][19][20][21] Supramolecular assembly of metal-oxo clusters creates another level of complexity and emergent properties in fractals, superlattices and nanomaterials. [22][23][24][25][26] Cerium oxide clusters and nanomaterials are of special relevance. Owed to the facile Ce III -Ce IV redox behavior and concomitant oxygen transport, ceria nanoparticles are used as automotive redox catalysts, in oxide fuel cells, and as photoactive solar cell materials.…”

“…Isolating mixed oxidation state or heterometal oxo-clusters represents enormous potential in tuning electronic, structural and chemical properties.Recently we exploited sulfate ligation and high oxidation state counter-cations (lanthanides and transition metals, Ln III and TM II ) to isolate a new family of giant U IV oxo-clusters including the U84 'superatom' (with Ln III ) and U70 wheel structure (with TM III ). 26,59 In addition to…”