Fig. 2: Energetic contributions to metal–ligand bonding.
From: Actinide inverse trans influence versus cooperative pushing from below and multi-center bonding
Left: a Natural bond orbital (NBO) representation of dominant non-Lewis delocalization and corresponding ΔE(2) stabilization (kcal mol−1) for \({({{{{{{{{\rm{R}}}}}}}}}^{{{{{{{{\rm{a}}}}}}}}})}_{3}{{{{{{{\rm{N}}}}}}}}{-}{{{{{{{\rm{U}}}}}}}}{-}{{{{{{{\rm{N}}}}}}}}\) shown by the favorable NBO donor–acceptor overlap in each case. Interactions 1 to 3 (circled numbers) correspond to contributions from the semi-core 6s, 6pσ, and 6pπ U orbitals; 4 and 5 correspond to donation from the terminal (N) and trans U−Namine ligand lone pair to formally empty U and NBOs. NBO isosurfaces at ± 0.03 atomic units in red/blue for donor and cyan/orange for acceptor NBOs. The proposed structure (Fig. 1a) for \({({{{{{{{{\rm{R}}}}}}}}}^{{{{{{{{\rm{a}}}}}}}}})}_{3}{{{{{{{\rm{N}}}}}}}}{-}{{{{{{{\rm{U}}}}}}}}{-}{{{{{{{\rm{N}}}}}}}}\) was used as the Lewis reference for the ΔE(2) analysis. Right: Energetic contributions ΔEorb with corresponding natural orbitals for chemical valence (NOCV) analysis (NOCV isosurfaces at ± 0.001 atomic units in red/blue) for the terminal (b) \({({{{{{{{{\rm{R}}}}}}}}}^{{{{{{{{\rm{a}}}}}}}}})}_{3}{{{{{{{\rm{NU}}}}}}}}{-}{{{{{{{\rm{N}}}}}}}}\) and (c) \({{{{{{{\rm{Me}}}}}}}}{({{{{{{{{\rm{R}}}}}}}}}^{{{{{{{{\rm{b}}}}}}}}})}_{3}{{{{{{{\rm{U}}}}}}}}{-}{{{{{{{\rm{O}}}}}}}}\) bonds, and the σ trans \({{{{{{{\rm{O}}}}}}}}{({{{{{{{{\rm{R}}}}}}}}}^{{{{{{{{\rm{b}}}}}}}}})}_{3}{{{{{{{\rm{U}}}}}}}}{-}{{{{{{{\rm{Me}}}}}}}}\) bond (d). Hydrogens are omitted from the structures for clarity. DFT/B3LYP calculations.
