Redox-switchable carboranes for uranium capture and release

The uranyl ion (UO₂ ²⁺; U(vi) oxidation state) is the most common form of uranium found in terrestrial and aquatic environments and is a central component in nuclear fuel processing and waste remediation efforts. Uranyl capture from either seawater or nuclear waste has been well studied and typically relies on extremely strong chelating/binding affinities to UO₂ ²⁺ using chelating polymers^1,2, porous inorganic^3–5 or carbon-based^6,7 materials, as well as homogeneous⁸ compounds. By contrast, the controlled release of uranyl after capture is less established and can be difficult, expensive or destructive to the initial material^2,9. Here we show how harnessing the redox-switchable chelating and donating properties of an ortho-substituted closo-carborane (1,2-(Ph₂PO)₂-1,2-C₂B₁₀H₁₀) cluster molecule can lead to the controlled chemical or electrochemical capture and release of UO₂ ²⁺ in monophasic (organic) or biphasic (organic/aqueous) model solvent systems. This is achieved by taking advantage of the increase in the ligand bite angle when the closo-carborane is reduced to the nido-carborane, resulting in C–C bond rupture and cage opening. The use of electrochemical methods for uranyl capture and release may complement existing sorbent and processing systems.