Alkali Counterion-Dependent Crystallization of Uranium(IV)-Chloro Structural Units.

The synthesis, structural characterization, and spectroscopic properties of five tetravalent uranium (U) phases including Li[U(μ-O)Cl(HO)]·10HO (), [U(HO)Cl] (), [U(HO)Cl]·KCl (), RbUCl (), and CsUCl () are reported. Notably, a change in the U solid-state structural unit was observed based on the identity of the alkali counterion used in the synthesis. Li yielded a tetranuclear oxo-bridged cluster, [U(μ-O)Cl(HO)], Na and K yielded two structurally distinct [U(HO)Cl] complexes, and Rb and Cs resulted in [UCl] as the dominant phases. The spectroscopic properties of the compounds were analyzed using Raman and UV-vis-NIR absorption spectroscopy. The UV-vis-NIR spectra of compounds - exhibited transitions consistent with uranium in the +4 oxidation state. Clear differences in the absorption band splitting were observed and are likely attributed to differences in metal ion coordination, crystal field effects, and outer sphere interactions Overall, this work demonstrates the utility of noncovalent interactions in tuning the crystallization of various metal complexes from otherwise identical reaction solutions and provides further evidence that counterions impact the composition and structure of actinide complexes isolated in the solid state. In this way, this work affords important insight into directing and controlling the structure of actinide complexes and clusters.