Relativistic theoretical studies on hydrogen bonds and the electronic structure of aqueous solvated bis(uranyl) complex: an insight into explicit and/or implicit solvent effects.

To understand the chemical behavior of uranyl complexes in water, a bis-uranyl [(phen)(UO2)(μ2-F)(F)]2 (A; phen = phenanthroline, μ2 = doubly bridged) and its hydrated form A·(H2O)n (n = 2, 4 and 6) were examined using scalar relativistic density functional theory. The addition of water caused the phen ligands to deviate slightly from the U2(μ2-F)2 plane, and red-shifts the U-F-terminal and U = O stretching vibrations. Four types of hydrogen bonds are present in the optimized hydrated A·(H2O)n complexes; their energies were calculated to fall within the range 4.37-6.77 kcal mol(-1), comparable to the typical values of 5.0 kcal mol(-1) reported for hydrogen bonds. An aqueous environment simulated by explicit and/or implicit models lowers and re-arranges the orbitals of the bis-uranyl complex.