The tetravalent oxidation state is common for many d and f block metal ions. While these metal ions can assemble into identical structural units such as the hexanuclear cluster, [M6(OH)4O4]12+, significant dissimilarities are found to exist in their structural chemistry. For example, Th and Pu adopt different structural units in the presence of the DOTA ligand.1 Further, Ce has been used as an analog to study Pu, yet in the presence of various phosphate and phosphonate ligands, differences in the coordination environments about the tetravalent metal centers are observed.2 These variances in tetravalent metal ion coordination chemistry have been attributed to disparities in the ionic radii, acidity, and/or bonding of the metal ions and are well established in the literature. More recently outer coordination sphere molecules and ions have also been shown to influence metal-ligand coordination chemistry and the composition of the products that form. In an effort to further elucidate the role that the nature of the metal ion and/or the identity of the counter-ions have on the composition, nuclearity, and structural chemistry of the M(IV) compounds that self-assemble in aqueous solution, we have examined the structural chemistry of Ce(IV), Th(IV), and U(IV) complexes that precipitate in the presence of non-coordinating pyridinium cations. Despite their common valence, Ce(IV), Th(IV), U(IV) exhibit divergent structural units under nearly identical reaction conditions adopting complexes that vary significantly in nuclearity, ranging from monomers to discrete clusters. These differences that arise in the structural chemistry of Ce, Th, and U in the presence of pyridinium cations under acidic aqueous conditions will be highlighted.

Structural chemistry of Ce(IV), Th(IV), and U(IV) complexes isolated from acidic aqueous media

255th National Meeting (2018)

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