Infrared spectra and electronic structure calculations for NN complexes with U, UN, and NUN in solid argon, neon, and nitrogen

Reactions of laser-ablated U atoms with N₂molecules upon codeposition in excess argon or neon at 4 K gave intense NUN and weak UN absorptions. Annealing produced progressions of new absorptions for the UN ₂(N₂)_1,2,3,4,5and UN(N₂) _1,2,3,4,5,6complexes. The neon-to-argon matrix shift decreases with increasing NN ligation and therefore the number of noble gas atoms left in the primary coordination sphere around the NUN molecule. Small matrix shifts are observed when the secondary coordination layers around the primary UN ₂(N₂)_1,2,3,4,5and UN(N₂) _1,2,3,4,5,6complexes are changed from neon-to-argon to nitrogen. Electronic structure, energy, and frequency calculations provide support for the identification of these complexes and the characterization of the N≡U≡N and U≡N core molecules as terminal uranium nitrides. Codeposition of U with pure nitrogen produced the saturated U(NN) ₇complex, which UV irradiation converted to the NUN(NN) ₅complex with slightly lower frequencies than found in solid argon.