Bisactinyl halogenated complexes: relativistic density functional theory calculation and experimental synthesis

Abstract

Relativistic density functional theory was used to explore a series of bisactinyl complexes, [(phen)(An^VIO₂)(μ₂-F)(F)]₂ (An = U (1), Np (2) and Pu (3); phen = phenanthroline; μ₂ = doubly bridged), [(phen)(U^VO₂)(μ₂-F)(F)]₂²⁻ (4), [(phen)(U^VIO₂)(μ₂-X)(X)]₂ (X = Cl (5), Br (6) and I (7)), [(L)(U^VIO₂)(μ₂-F)(F)]₂ (L = bpy (8), 2NH₃ (9) and 2F (10); bpy = 2,2′-bipyridine) and [NH₄]₄[(F)₂(U^VIO₂)(μ₂-F)(F)]₂ (11). The effects of varying actinyl ions (UO₂²⁺, NpO₂²⁺ and PuO₂²⁺), oxidation states of uranium (VI and V) and equatorial ligands (phen → bpy → 2NH₃ → 2F and F → Cl → Br → I) on the structures and electronic properties of complexes were examined. The calculated distances and bond orders of AnO indicate the partial triple bonding character, and agree with the trends in the AnO stretching vibrational frequencies. The free energies of formation reactions of 1–11 calculated in the aqueous solution demonstrate that 1, 8 and 11 are thermodynamically stable. In this work, we have successfully synthesized 1 and [Me₂NH₂]₄[(F)₂(U^VIO₂)(μ₂-F)(F)]₂ (12), which is represented by theoretical model complex 11. Their characterizations of the single crystal X-ray diffraction and infrared are consistent with the calculated results; the measured fine-structured fluorescent emissions were assigned as transitions from the UO bonding to the U (f) orbital by analyzing the electronic structure and absorption spectra.