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 acac1--decorated cerium-oxo clusters, [Ce10O8(acac)(14)(CH3O)(6)(CH3OH)(2)]center dot 10.5MeOH (Ce-10) and [Ce12O12(OH)(4)(acac)(16)(CH3COO)(2)]center dot (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 L-3-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 CeIV 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 CeIV hexameric units, and two monomeric CeIII 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-), OH1-, MeO1-, and O2- ligands. Small angle X-ray scattering measurements for Ce-10 dissolved in acetonitrile showed structural units slightly larger than either Ce-10 or Ce-12 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 Ce-10 and Ce-12 reported herein.