Theoretical Investigation on Multiple Bonds in Terminal Actinide Nitride Complexes

A series of actinide (An) species of L-An-N compounds [An = Pa–Pu, L = [N­(CH₂CH₂NSiPrⁱ₃)₃]^3–, Prⁱ = CH­(CH₃)₂] have been investigated using scalar relativistic density functional theory (DFT) without considering spin–orbit coupling effects. The ground state geometric and electronic structures and natural bond orbital (NBO) analysis of actinide compounds were studied systematically in neutral and anionic forms. It was found that with increasing actinide atomic number, the bond length of terminal multiple An–N1 bond decreases, in accordance with the actinide contraction. The Mayer bond order of An–N1 decreases gradually from An = Pa to Pu, which indicates a decrease in bond strength. The terminal multiple bond for L–An–N compounds contains one σ and two π molecular orbitals, and the contributions of the 6d orbital to covalency are larger in magnitude than the 5f orbital based on NBO analysis and topological analysis of electron density. This work may help in understanding of the bonding nature of An–N multiple bonds and elucidating the trends and electronic structure changes across the actinide series. It can also shed light on the construction of novel An–N multiple bonds.