Homoleptic Cerium(III) and Cerium(IV) Nitroxide Complexes: Significant Stabilization of the 4+ Oxidation State

• DOI: 10.1021/ic401974t
• Publication Date: 2013-09-11T19:23:28Z
• Authors: Justin A. Bogart; Andrew J. Lewis; Scott A. Medling; Nicholas A. Piro; Patrick J. Carroll; Corwin H. Booth; Eric J. Schelter
• Keywords: physical and analytical chemistry; CERIA; GAS SHIFT REACTION; organic; CATALYSTS; 01 natural sciences; 0104 chemical sciences; Inorganic; Inorganic, organic, physical and analytical chemistry; MAGNETIC-PROPERTIES; TRANSITION-METAL; LANTHANIDE CHEMISTRY; NITRIDE; OXIDATION-STATES; LIGAND; OXIDE FUEL-CELLS

Electrochemical experiments performed on the complex Ce(IV)[2-((t)BuNO)py]4, where [2-((t)BuNO)py](-) = N-tert-butyl-N-2-pyridylnitroxide, indicate a 2.51 V stabilization of the 4+ oxidation state of Ce compared to [(n)Bu4N]2[Ce(NO3)6] in acetonitrile and a 2.95 V stabilization compared to the standard potential for the ion under aqueous conditions. Density functional theory calculations suggest that this preference for the higher oxidation state is a result of the tetrakis(nitroxide) ligand framework at the Ce cation, which allows for effective electron donation into, and partial covalent overlap with, vacant 4f orbitals with δ symmetry. The results speak to the behavior of CeO2 and related solid solutions in oxygen uptake and transport applications, in particular an inherent local character of bonding that stabilizes the 4+ oxidation state. The results indicate a cerium(IV) complex that has been stabilized to an unprecedented degree through tuning of its ligand-field environment.