Theoretical Study of Complexes of Tetravalent Actinides with DOTA

Abstract

1,4,7,10-Tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (H4DOTA) is a prominent chelating ligand with potential applications in various fields, from radiotherapy to the separation of fission products. The present study explores the stability, structure, and bonding properties of its complexes with tetravalent actinides (An = Th, U, Np, Pu) using density functional theory and relativistic multireference calculations. Neutral complexes prefer to form symmetric (C4) structures with DOTA. The first coordination sphere of the actinide ions is readily saturated by a weakly bonded H2O ligand. The latter ligand reduces the molecular symmetry while exerting only marginal effects on the properties of the parent complex. An-ligand bonding is mainly electrostatic, but there are also significant charge-transfer contributions from DOTA to the An 6d/5f orbitals. The charge-transfer interactions and the covalent character of bonding increase gradually in the order of Th < U < Np < Pu, as indicated by analysis of the electron density distribution using the Quantum Theory of Atoms in Molecules.