Octacarbonyl Ion Complexes of Actinides [An(CO)8]+/− (An=Th, U) and the Role of f Orbitals in Metal–Ligand Bonding

• Published in: Chemistry : a European journal 2019-09, Vol.25 (50), p.11772-11784
• Main Authors: Chi, Chaoxian, Pan, Sudip, Jin, Jiaye, Meng, Luyan, Luo, Mingbiao, Zhao, Lili, Zhou, Mingfei, Frenking, Gernot
• Format: Article
• Language: English
• Subjects: Actinides; Anions; bonding analysis; Cations; Chemistry; Coordination compounds; Density functional theory; electronic structure; Ground state; Heavy metals; IR spectroscopy; Mass spectroscopy; Mathematical analysis; Metals; octacarbonyl complexes; Orbitals; Organic chemistry; Photodissociation; Quantum chemistry; Thorium; Uranium; Vapor phases
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201902625

The octacarbonyl cation and anion complexes of actinide metals [An(CO)8]+/− (An=Th, U) are prepared in the gas phase and are studied by mass‐selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)8]+ and [Th(CO)8]− complexes have a distorted octahedral (D4h) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)8]+ cation and the [U(CO)8]− anion exhibit cubic structures (Oh) with a 6A1g ground state for the cation and a 4A1g ground state for the anion. The neutral species [Th(CO)8] (Oh; 1A1g) and [U(CO)8] (D4h; 5B1u) have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal–CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium. Electron‐counting rules for the actinide complexes: An energy decomposition analysis of the covalent metal–CO interactions in the actinide octacarbonyl cations and anions [An(CO)8]+/− (An=Th, U) reveals that the major contribution comes from the metal d AOs followed by f‐orbital interactions (see picture).