Plutonium and Cerium Perrhenate/Pertechnetate Coordination Polymers and Frameworks.

Spent nuclear fuel (SNF) contains transuranic and lanthanide species, which are sometimes recovered and repurposed. One particularly problematic fission product, TcO, hampers this recovery via coextraction with high valence metals, perhaps by complexation during aqueous reprocessing of SNF. There is limited molecular-level knowledge concerning the coordination chemistry between TcO or its well-known surrogate ReO and transuranic/lanthanide species. In the current study, we investigated the coordination of ReO/TcO with plutonium and cerium cations by structural and chemical characterization of a series of isolated extended solids. In this study, Ce represents both trivalent lanthanides and is considered a surrogate for Pu, respectively, in its common trivalent and tetravalent oxidation states. The structural elucidation of the seven isolated crystalline solids revealed that ReO/TcO directly connects to Pu, PuO, Ce, and Ce in the terminal and bridging coordination modes, leading to 1-, 2-, and 3-dimensional frameworks. For example, ReO coordination to Pu(IV) formed a 1D chain or 2D framework, isostructural with previously isolated Th(IV) compounds. However, PuO alternating with ReO led to a unique 1D chain, different from the prior-reported U(VI)/Np(VI)-ReO/TcO structures. Coordination of ReO/TcO with Ce(III) promotes the assembly of 3D frameworks. Finally, attempted synthesis of a Ce(IV)-ReO compound resulted in a 2D framework with a mixed-valence Ce. The highly acidic reaction conditions supported the reduction of both Ce and Tc, challenging isolation of compounds featuring these species. Only one TcO-containing structure was obtained in this study (Ce-TcO 3D framework), vs the six total Ce/Pu-ReO compounds. Our three Pu-ReO crystal structures are the first reported and translated to atomic-level information about Pu-TcO coordination in nuclear fuel reprocessing scenarios, in addition to broadening our knowledge of bonding trends in the early, high-valence actinides.