A relativistic DFT study of small-molecule activation facilitated by actinocenes (An(η8-C8H8)2)

Abstract

The scarcity and radioactivity of actinides have made it very difficult to study actinocene and other actinide-containing complexes experimentally. Hence, theoretical studies of these complexes can offer significant direction in the enlightenment of difficult-to-obtain experimental data. Keeping in mind, actinocene (An(COT)2, An = Th, Pa, U, Np, Pu, Am, Cm) with D8h symmetry has been investigated in the present study. Under D8h symmetry, the structural parameters of optimized sandwich compounds are found to be in concurrence with the experimental data. This study extensively examines the experimentally characterized actinocene for their capability to activate small molecules (Y = CO, and N2) through relativistic density functional theory (DFT) analysis. After forming a complex with CO, and N2, D8h symmetry of An(COT)2 gets distorted resulting in the bending of both the COT rings. In all the [An(COT)2Y] complexes, a covalent bond was realized between An and Y except [U(COT)2N2], [Np(COT)2N2], and [Pu(COT)2N2], where an ionic bond was observed between An and Y. Furthermore, the experimental inaccessible [An(COT)2Y] complexes were elucidated through thermodynamic computations along with the analyses of geometric, electronic properties and bonding analysis. [Pu(COT)2N2] adducts have the largest contribution of ΔEorb to total ΔEint among all the complexes suggesting that the Pu-N bond is dominated by orbital attractions and shows significant covalency.