Pentavalent lanthanide nitride-oxides: NPrO and NPrO(–) complexes with N[triple bond, length as m-dash]Pr triple bonds

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 Pr[triple bond, length as m-dash]N triple bonds and Pr[double bond, length as m-dash]O double bonds. Electronic structure studies show that the neutral NPrO molecule features a 4f(0) electron configuration and a Pr(v) oxidation state similar to that of the isoelectronic PrO(2)(+) ion, while its NPrO(–) anion possesses a 4f(1) 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 PrO(2)(+) and PrO(4) 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.