Highly stable actinide(iii) complexes supported by doubly aromatic ligands

Abstract

Owing to the electron-deficient nature of boron atoms, the structures and properties of boron clusters can be enriched by doping various metal atoms, including lanthanide metal atoms. Nevertheless, the viability of actinide analogues has not been fully elucidated up to now. Here we demonstrate a series of highly stable low-valent actinide(III) boron clusters AnB₇ (An = Pa, U, Np, and Pu) using first-principles calculations. The predicted global minimum structures of all the AnB₇ complexes possess half-sandwich geometries with C_6v symmetry and belong to M^III[B₇]³⁻-type species. In each AnB₇ species, the B₇³⁻ ligand possesses double aromaticity features with six delocalized π electrons and six delocalized σ electrons. Bonding analysis shows that although there is a substantial contribution of electrostatic interaction in each cluster, covalent interaction is responsible for the stability of AnB₇. All the AnB₇ species show significantly high formation energies, especially for NpB₇, which is in line with the stronger Np-B covalent bonds. In addition, the simulated photoelectron spectroscopy analysis confirms the high electronic stability of neutral AnB₇. These results imply that these ultrastable actinide(III) complexes are accessible in the gas phase at room temperature. This work may provide a theoretical basis for the design of highly stable boron-based nanomaterials as well as preparation of low-valent actinide complexes.