Theoretical Insights into the Actinide–Silicon Bonding Nature and Stability of a Series of Actinide Complexes with Different Oxidation States

The electronic structures of a series of complexes (CpSiMe3)3AnSi­(NCHMes)2 ([An–Si], An = Th–Am) with different oxidation states (OS = II, III, and IV) of actinides were investigated using the relativistic density functional theory to explore the actinide–silicon bonding, which was evaluated based on the analyses of quantum theory of atoms in molecules (QTAIM) and electron localization function (ELF). The An–Si bond length variation for a series of [An–Si] with different oxidation states may be attributed to the synergistic effect of the steric hindrance and the ability of the actinide atom to accept electrons. The value of An–Si Mayer bond order (MBO) decreases across the actinide series with the same oxidation state. The values of An–Si MBO for the [AnII–Si]− (An = Th–Pu) are the largest in general among the complexes with three actinide oxidation states, except that for the Am–Si MBO of [AmIV–Si]+ is the largest because of more covalent Am–Si bond in the [AmIV–Si]+ complex. The An–Si bonds are highly polarized due to lone pair electrons located on the Si 3s orbital. Moreover, the An–Si bonds possess donor–acceptor interactions according to the analyses of QTAIM and ELF. In addition, the binding energies suggest that the tetravalent complexes [AnIV–Si]+ are thermodynamically accessible, of which [UIV–Si]+ and [PuIV–Si]+ are the most preferable. The electron affinity analysis suggests that the reduction reaction of [AnIII–Si] → [AnII–Si]− should become increasingly facile across the actinide series from Th to Am. This work expands the knowledge on the An–Si bonding, especially for the transuranium–silicon bonding, and guides synthesis of the actinide silicon complexes with different oxidation states.