375 Additionally, the very large difference in vibrational frequencies observed on changing the matrix from argon to neon suggested that a reordering of the electronic states had occurred. While the results did not support this interpretation, it was concluded that UO 2 exhibits ‘unusually strong interactions with argon.’ Coupled-cluster and DFT calculations suggested that the most likely complex observed under the conditions described above was UO 2(Ar 5).
It was anticipated that, as for CUO (see above), the presence of argon atoms may result in reordering of the low-lying electronic states of UO 2. 374 The electronic ground state of UO 2 in solid argon was determined by near-UV spectroscopy. Laser ablation of uranium in the presence of O 2 resulted in UO 2, which was co-condensed with argon. 373 A singlet ground state was observed for CUO(Ne) x(Ng) y complexes for y = 0–2, and a triplet spin state was observed for y = 3, 4, or when neon was absent. When uranium atoms were isolated in inert and CO-doped matrices using dilute Ar, Kr, or Xe in an excess of neon, CUO(Ar), CUO(Kr), and CUO(Xe) were identified which also contained neon atoms in the uranium coordination sphere. 371,372 In solid argon, triplet states are formed for the different compounds but linear, singlet states are formed in neon. This chemistry has been extended to krypton, resulting in species of the type CUO(Ar) 4 − n(Kr) n. 370, 371 Four noble-gas atoms are coordinated to uranium, representing the first neutral compound involving four noble-gas atoms around a single metal center. Laser ablation of an uranium target produces uranium atoms that, when co-condensed with carbon monoxide, argon, and xenon, yield CUO(Ar) 4 − n(Xe) n ( n = 1–4).
Žemva, in Comprehensive Inorganic Chemistry II (Second Edition), 2013 1.25.9.2 Coordination of Noble Gases to Transition Metal Oxides
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