The need to discover unique bonding tendencies in the heavier actinides (Pu-Cf) grows more urgently every day, as this knowledge is necessary for separating these elements in spent nuclear fuel. One way our group investigates this is to employ different inorganic ligand systems in synthesis that can potentially access the 5f-orbitals. Ligands with high hyperpolarizabilities are attractive in this regard due to their flexible electron cloud; it is important that the bonds of the ligand are strongly polarizable in order to induce a more covalent interaction with the actinide metal. Based on second-harmonic generation measurements as well as second hyperpolarizability calculations, the Group VI transition metal-oxygen bonds have significant bond polarization suitable for our investigation of inorganic actinide compounds. CsPu3Mo6O24(H2O), CsAm(CrO4)2, and their lanthanide analogues have been prepared. The former actinide compounds are black or dark red semiconductors, whereas the latter are gold or orange insulators. The trivalent americium compound deviates from the structural and spectroscopic trends observed across the 4f chromates; there is a shift from monoclinic structure types in the lanthanide compounds to triclinic for Am, and the charge-transfer features in the lanthanide UV-Vis-NIR spectra are not nearly as broad as that of the americium compound. Band structure calculations give further information on how the 5f and 6d electrons are participating in bonding with the chromate ligand in CsAm(CrO4)2.

Semiconductivity in plutonium and americium chromates and molybdates: Evidence for energy-degeneracy-driven covalency

253rd National Meeting (2017)

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