Cis - and trans-binding influences in [NUO center dot N-2)(n)](+)

Uranium nitride-oxide cations [NUO](+) and their complexes with equatorial N-2 ligands, [NUO center dot(N-2)n](+) (n = 1-7), were synthesized in the gas phase. Mass-selected infrared photodissociation spectroscopy and quantum chemical calculations confirm [NUO center dot(N-2)(5)](+) to be a sterically fully coordinated cation, with electronic singlet ground state of (1)A(1), linear [NUO](+) core, and C-5v structure. The presence of short N-U bond distances and high stretching modes, with slightly elongated U-O bond distances and lowered stretching modes, is rationalized by attributing them to cooperative covalent and dative [vertical bar N equivalent to U equivalent to O vertical bar](+) triple bonds. The mutual trans-interaction through flexible electronic U-5f6d7sp valence shell and the linearly increasing perturbation with increase in the number of equatorial dative N2 ligands has also been explained, highlighting the bonding characteristics and distinct features of uranium chemistry. Published under an exclusive license by AIP Publishing.