| Abstract
| - Elucidation of the crystal structure of the dianionic complex [Na(18-crown-6)(thf)2]2[U(COT)(dddt)2](COT = η8-C8H8, dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate), complementing that of [Na(18-crown-6)(thf)][U(COT)(dddt)2], allowed the first structural comparison of analogous uranium(IV) and -(V)compounds with anionic sulfur ligands. The distinct conformations of the dithiolene ligands, exo−exoand exo−endo in the uranium (IV) and -(V) complexes, respectively, are the observable manifestation ofthe differences in the metal−ligand bonding according to the oxidation state of the metal. The relationshipbetween electronic structure, bonding, and conformational changes in these dianionic uranium(IV) andanionic uranium(V) species and the hypothetical neutral uranium(VI) counterpart has been investigatedin the framework of relativistic density functional theory. The calculations reveal the occurrence in theuranium(V) anionic species of a significant intramolecular interaction involving the 5f metal orbitals andthe CC double bond of the endo dithiolene ligand, which stabilizes its peculiar exo−endo conformation.Such an interaction does not exist in the uranium(IV) complex.
- The distinct conformations of the dithiolene ligands in the X-ray structure of the [Na(18-crown-6)(thf)2]2[U(IV)(COT)(dddt)2] and [Na(18-crown-6)(thf)][U(V)(COT)(dddt)2] complexes are the observable manifestation of the differences in the metal−ligand bonding, according to the metal oxidation state. Relativistic DFT calculations confirm the occurrence in the U(V) species of an intramolecular interaction involving the 5f metal orbitals and the CC bond of the endo dithiolene, stabilizing its peculiar exo−endo conformation. Such an interaction does not exist in the U(IV) complex but should occur in the hypothetical neutral uranium(VI) complex [U(COT)(dddt)2].
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