Pentavalent lanthanide nitride-oxides: NPrO and NPrO− complexes with NPr triple bonds

Abstract

The neutral molecule NPrO and its anion NPrO⁻ are produced via co-condensation of laser-ablated praseodymium atoms with nitric oxide in a solid neon matrix. Combined infrared spectroscopy and state-of-the-art quantum chemical calculations confirm that both species are pentavalent praseodymium nitride-oxides with linear structures that contain PrN triple bonds and PrO double bonds. Electronic structure studies show that the neutral NPrO molecule features a 4f⁰ electron configuration and a Pr(V) oxidation state similar to that of the isoelectronic PrO₂⁺ ion, while its NPrO⁻ anion possesses a 4f¹ electron configuration and a Pr(IV) oxidation state. The neutral NPrO molecule is thus a rare lanthanide nitride-oxide species with a Pr(V) oxidation state, which follows the recent identification of the first Pr(V) oxidation state in the PrO₂⁺ and PrO₄ complexes (Angew. Chem. Int. Ed., 2016, 55, 6896). This finding indicates that lanthanide compounds with oxidation states of higher than +IV are richer in chemistry than previously recognized.