Complexes featuring a linear [N≡U≡N] core isoelectronic to the uranyl cation

• Published in: Nature chemistry 2020-10, Vol.12 (10), p.962-967
• Main Authors: Rudel, Stefan S., Deubner, H. Lars, Müller, Matthias, Karttunen, Antti J., Kraus, Florian
• Format: Article
• Language: English
• Subjects: 639/638/263/910; 639/638/263/915; 639/638/911; Ammonia; Analytical Chemistry; Argon; Biochemistry; Cations; Chemical bonds; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Infrared spectroscopy; Inorganic Chemistry; Isotope studies; Ligands; Liquid ammonia; Mathematical analysis; Nitrogen isotopes; Organic Chemistry; Physical Chemistry; Quantum chemistry; Single crystals; Uranium; Uranium dioxide; X-ray diffraction
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/s41557-020-0505-5

The aqueous chemistry of uranium is dominated by the linear uranyl cation [UO 2 ] 2+ , yet the isoelectronic nitrogen-based analogue of this ubiquitous cation, molecular [UN 2 ], has so far only been observed in an argon matrix. Here, we present three different complexes of [UN 2 ] obtained by the reaction of the uranium pentahalides UCl 5 or UBr 5 with anhydrous liquid ammonia. The [UN 2 ] moieties are linear, with the U atoms coordinated by five additional ligands (ammonia, chloride or bromide), resulting in a pentagonal bipyramidal coordination sphere that is also commonly adopted by the uranyl cation [UO 2 (L) 5 ] 2+ (L, ligand). In all three cases, the nitrido ligands are further coordinated through their lone pairs by the Lewis-acidic ligands [U(NH 3 ) 8 ] 4+ to form almost linear, trinuclear complex cations. Those were characterized by single-crystal X-ray diffraction, Raman and infrared spectroscopy, 14 N/ 15 N isotope studies and quantum chemical calculations, which support the presence of two U≡N triple bonds within the [UN 2 ] moieties. Three crystalline complexes comprising a linear [UN 2 ] moiety that is isoelectronic to the ubiquitous uranyl cation [UO 2 ] 2+ have been prepared by reaction of UCl 5 or UBr 5 with liquid ammonia. Quantum chemical calculations showed that the bonding in the [UN 2 ] moieties is best described with two U≡N triple bonds.