Prediction of high bond-order metal–metal multiple-bonds in heterobimetallic 3d–4f/5f complexes [TM–M{N(o-[NCH2P(CH3)2]C6H4)3}] (TM = Cr, Mn, Fe; M = U, Np, Pu, and Nd)

Abstract

Despite continuing and burgeoning interest in f-block complexes and their bonding chemistry in recent years, investigations of the electronic structures and oxidation states of heterobimetallic complexes, and their bonding features between transition-metals (TMs) and f-elements remain relatively less explored. Here, we report a quantum chemical computational study on the series of TM–actinide and –neodymium complexes [TMAn(L)] and [TMNd(L)] [An = U, Np, Pu; TM = Cr, Mn, Fe; L = {N(o-[NCH₂P(CH₃)₂]C₆H₄)₃}³⁻] in order to explore periodic trend, generalities and differences in the electronic structure and metal–metal bonding between f-block and d-block elements. Based on the calculations, we find up to five-fold covalent multiple bonding between actinide and transition metal ions, which is in sharp contrast with a single bond between neodymium and transition metals. From a comparative study, a general trend of strength of the An–TM interaction emerges in accordance with the atomic number of the actinide metal, which relates to the nature, energy level, and spatial arrangement of their frontier orbitals. The trend presents a valuable insight for future experimental endeavour searching for isolable complexes with strong and multiple An–TM bonding interactions, especially for the experimentally challenging transuranic elements that require targeted research due to their radioactive nature.