Unprecedented neptunyl(V) cation-directed structural variations in Np2Ox compounds

Distinguishing the Geometric and Electronic Structures of Actinide Carbides AnxC8 (An = Th, U; x = 2, 3) through Exchange Interactions

Global-minimum optimizations combined with relativistic quantum chemistry calculations have been performed to characterize the ground-state stable structures of four titled compounds and to analyze the bonding properties. Th2C8 was identified as being a ThC4-Th(C2)2 structure, U2C8 has been found to favor the U-U(C8) structure, and both Th3C8 and U3C8 adopt the (AnC3)2-(AnC2) structure. Then, the wave function analyses reveal that the interactions between the Th 7s-based orbital and the σg molecular orbital of the C2 unit compensate for the excitation energy of 7s16d1 → 6d2 and lead to the stabilization of two Th(IV)s in the ThC4-Th(C2)2 structure. It also reveals that the U species exhibit magnetic exchange coupling behavior in UxC8, for instance, as seen in the direct interaction of U2C8 and the superexchange pathway of U3C8, which effectively stabilizes their low-spin states. This interpretation indicates that the geometric and electronic structures of AnxC8 species are largely influenced by the local magnetic moment and spin correlation.

Electronic Structures and Properties of Bimetallic Plutonium Group 13 Carbonyl Compounds [XPuCO] (X = B, Al, and Ga)

Bonding features of heterobimetallic complexes containing f-block elements are fundamental content in actinide chemistry. In order to account for the structural periodicity of the X-Pu carbonyls and the formation of chemical bonds between bimetallic plutonium and group 13 carbonyl compounds, we report a comprehensively quantum-chemical study of the electronic structure and properties of XPuCO (X = B, Al, and Ga). With increasing atomic radii of the group 13 elements, the XPuCO structure alternates from cyclic [PuCBO] to linear [AlCPuO] and [GaCPuO]. The bonding analysis indicates that the donor-acceptor model is the best description for bonding interactions of metal and ligands with different donation patterns of CBO → Pu and XC → PuO (X = Al and Ga). The apparent XC ← PuO backdonation increases the C-Pu bond strength markedly and stabilizes the linear geometry of [AlCPuO] and [GaCPuO], while spin-orbit coupling is found to be significant in the stabilization of [PuCBO]. The ground electron configurations and natural orbital analysis indicate that cyclic [PuCBO] and linear [XCPuO] (X = Al and Ga) are considered as complexes of Pu(III) and Pu(V), respectively. The trend presents a valuable insight for the 5f/6d-np bonding interactions, especially for the fundamental understanding of transuranic elements.