Trends and new directions in the crystal chemistry of actinide oxo-clusters incorporated in polyoxometalates

The present highlight article deals with the incorporation of actinide cations into polyoxometalate (POM) moieties since the first example was structurally characterized and described in the literature at the beginning of the 70s. It illustrates the various structural types of topologies that can arise from the association of different polyoxometalates (molybdates or tungstates, Keggin- or Wells-Dawson-based entities, etc.) with the light actinide elements (mainly thorium and uranium). Nevertheless, some rare investigations have also been reported, performed with transuranium elements such as neptunium, plutonium, americium, curium and californium. The synthetic strategies for obtaining such molecular species, their crystal structure arrangements and their behavior in aqueous solution are discussed. The diverse varieties of actinide-POM assemblies are classified on the basis of the nature of the metal (Mo or W) and the vacancy states occurring in the polyoxometallic precursors, starting with the polyoxomolybdate family. The second series of polyoxotungstates has been intensively studied and is described more widely.