Relativistic DFT Probe for Reaction Energies and Electronic/Bonding Properties of Polypyrrolic Hetero-Bimetallic Actinide Complexes: Effects of Uranyl -Oxo Functionalization.

A series of hetero-bimetallic actinide complexes of the Schiff-base polypyrrolic macrocycle (L), featuring cation-cation interactions (CCIs), were systematically investigated using relativistic density functional theory (DFT). The tetrahydrofuran (THF) solvated complex [(THF)(OUOU)(THF)(L)] has high reaction free energy (Δ), and its replacement with electron-donating iodine promotes the reaction thermodynamics to obtain uranyl iodide [(I)(OUOU)(I)(L)] (-). Retaining this coordination geometry, calculations have been extended to other An(IV) (An = Th, Pa, Np, Pu), i.e., for the substitution of U(IV) to obtain -. As a consequence, the reaction free energy is appreciably lowered, suggesting the thermodynamic feasibility for the experimental synthesis of these bimetallic complexes. Among all -, the electron-spin density and high-lying occupied orbitals of - show a large extent of electron transfer from electron-rich Pa(IV) to electron-deficient U(VI), leading to a more stable - oxidation state. Additionally, the shortest bond distance and the comparatively negative of the Pa-O bond suggest more positive and negative charges () of Pa and -oxo atoms, respectively. As a result of the enhanced Pa-O bond and strong CCI in - along with the corresponding lowest reaction free energy among all of the optimized complexes, uranyl species is a better candidate for the experimental synthesis in the ultimate context of environmental remediation.