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, [Ce ₁₀ O ₈ (acac) ₁₄ (CH ₃ O) ₆ (CH ₃ OH) ₂ ]·10.5MeOH ( Ce-10 ) and [Ce ₁₂ O ₁₂ (OH) ₄ (acac) ₁₆ (CH ₃ COO) ₂ ]·6(CH ₃ CN) ( 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 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 Ce ₁₀ core. Electrospray ionization mass spectrometry data for solutions prepared by dissolving Ce-10 in acetonitrile showed that the major ions could be attributed to Ce ₁₀ 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 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.