Pentavalent Lanthanide Compounds: Formation and Characterization of Praseodymium(V) Oxides

The chemistry of lanthanides (Ln = La-Lu) is dominated by the low-valent +3 or +2 oxidation state because of the chemical inertness of the valence 4f electrons. The highest known oxidation state of the whole lanthanide series is +4 for Ce, Pr, Nd, Tb, and Dy. We report the formation of the lanthanide oxide species PrO4 and PrO2+ complexes in the gas phase and in a solid noble-gas matrix. Combined infrared spectroscopic and advanced quantum chemistry studies show that these species have the unprecedented Pr-V oxidation state, thus demonstrating that the pentavalent state is viable for lanthanide elements in a suitable coordination environment.