Computational Study of Reduction Potentials of Th Compounds and Hydrolysis of ThO(HO), n = 1, 2, 4.

The stability of Th to reduction in water is studied by DFT methods. The standard reduction potential (SRP) of homoleptic complexes including Th(HO), Th(HO), Th(NO), Th(NO), Th(NO), Th(COT), Th(acac), ThCp, ThF, and ThCl have been investigated. The values vary widely (from -3.50 V for Th(OH) to -0.62 V for Th(NO) depending on whether the ligands are redox active (noninnocent) or not. Several additional topics of thorium chemistry are explored, including the hydrolysis mechanism of ThO(HO), n = 1, 2, 4, and the solution phase nonzero dipole moment of ThCp. Dinuclear complexes are also characterized, including ThO, ThO(OH), ThO(HO), Th(OH)(HO), and Th(OH)(NO)(HO) and condensed thorium complexes as [Th(OH)(HO)] and [Th(OH)(HO)]. For the Th(OH)(NO)(HO) dinuclear complex, the first SRP is -0.82 V and the second is 1.59 V. The first SRP corresponds to the reduction of the ligand NO, and the second SRP corresponds to dissociative electron transfer to the NO ligand. The calculated formation constant of Th(EDTA)(HO) is in reasonable agreement with experiment. The different stereochemistries of the bidentate ligands NO, NO, and acetylacetonate (acac) around the thorium center have very similar stabilities.