Synthesis and Characterization of Cerium-Oxo Clusters Capped by Acetylacetonate

Cerium-oxo clusters have applications in fields ranging from catalysis to electronics and also hold the potential to inform on aspects of actinide chemistry. Toward this end, a cerium-acetylacetonate (acac^1-) monomeric molecule, Ce(acac)₄ (Ce-1), and two acac^1--decorated cerium-oxo clusters, [Ce₁₀O₈(acac)₁₄(CH₃O)₆(CH₃OH)₂]·10.5MeOH (Ce-10) and [Ce₁₂O₁₂(OH)₄(acac)₁₆(CH₃COO)₂]·6(CH₃CN) (Ce-12), were prepared and structurally characterized. The Ce(acac)₄ monomer contains Ce^IV. Crystallographic data and bond valence summation values for the Ce-10 and Ce-12 clusters are consistent with both clusters having a mixture of Ce^III and Ce^IV cations. Ce L₃-edge X-ray absorption spectroscopy, performed on Ce-10, showed contributions from both Ce^III and Ce^IV. The Ce-10 cluster is built from a hexameric cluster, with six Ce^IV sites, that is capped by two dimeric Ce^III units. By comparison, Ce-12, which formed upon dissolution of Ce-10 in acetonitrile, consists of a central decamer built from edge sharing Ce^IV hexameric units, and two monomeric Ce^III sites that are bound on the outer corners of the inner Ce₁₀ core. Electrospray ionization mass spectrometry data for solutions prepared by dissolving Ce-10 in acetonitrile showed that the major ions could be attributed to Ce₁₀ clusters that differed primarily in the number of acac^1-, OH^1-, MeO^1-, and O^2- ligands. Small angle X-ray scattering measurements for Ce-10 dissolved in acetonitrile showed structural units slightly larger than either Ce₁₀ or Ce₁₂ in solution, likely due to aggregation. Taken together, these results suggest that the acetylacetonate supported clusters can support diverse solution-phase speciation in organic solutions that could lead to stabilization of higher order cerium containing clusters, such as cluster sizes that are greater than the Ce₁₀ and Ce₁₂ reported herein.