Theoretical Insights into Halogenated Uranium Cyanide/Isocyanide Compounds.

Two kinds of halogenated uranium cyanide/isocyanide compounds, XUCN and XUNC (X = halogen) formed by the insertion of uranium atom into X-C(N) bonds of XCN (or XNC), were investigated by DFT and ab initio methods. Although XNC is less stable thermodynamically than XCN, XUNC is more stable than XUCN and is expected to be prepared and characterized in matrix isolation experiments. The C-N stretching vibration mode (νC-N) is the primary fingerprint for the identification of these isomers due to its red-shift character with respect to the relevant precursor. Atoms-in-molecule (AIM) analysis illustrates that both X-U and U-C(N) bonds in XUCN and XUNC show closed-shell interaction character, although partial covalent character contributes to them, and can be denoted as X-U2+(CN)- and X-U2+(NC)-, respectively. Charge decomposition analysis (CDA) further reveals that the isocyanide exhibits better donation performance than the cyanide, which should be the root cause of the difference between XUCN and XUNC.