Abstract
The role of the 5f and 6d orbitals in the chemistry of the actinide elements has been of considerable interest since their discovery and synthesis. Relativistic effects cause the energetics of the 5f and 6d orbitals to change as the actinide series is traversed left to right imparting a rich and complex chemistry. The 5f and 6d atomic states cross in energy at protactinium (Pa), making it a potential intersection between transition metal and actinide chemistries. Herein, we report the synthesis of a Pa-peroxo cluster, A6(Pa4O(O2)6F12) [A = Rb, Cs, (CH3)4N], formed in pursuit of an actinide polyoxometalate. Quantum chemical calculations at the density functional theory level demonstrate equal 5f and 6d orbital participation in the chemistry of Pa and increasing 5f orbital participation for the heavier actinides. Periodic changes in orbital character to the bonding in the early actinides highlights the influence of the 5f orbitals in their reactivity and chemical structure.
Highlights
The role of the 5f and 6d orbitals in the chemistry of the actinide elements has been of considerable interest since their discovery and synthesis
The complex chemistry encountered in the early actinide series is a result of the changing relative energetics of the 5f and 6d electronic states across the actinide series, the energetics of which change with increasing Z, a consequence of relativistic effects and the incomplete shielding of the 5f orbitals from the positive nuclear charge[2]
Using an approach combining synthetic inorganic chemistry and quantum chemical calculations to explore the chemistry of the Group V hexametalates, M6O198− as exemplars of classic transition metal chemistry, and applying this approach to their 5f counterparts in Pa and U chemistry, we demonstrate that Pa represents an intersection between transition metal and actinide chemistry
Summary
The role of the 5f and 6d orbitals in the chemistry of the actinide elements has been of considerable interest since their discovery and synthesis. The proximity in energy of the d- and f-states at Pa and its geometric preference for a mono-oxo bond like that of the transition metals leads us to hypothesize that protactinium may be a candidate for forming a hexametalate complex of the Lindqvist type, M6O198−, providing insight into the roles of the 5f and 6d orbitals at Pa, protactinium’s differences from its transition metal homologues, and further insight into the influence of the f-orbitals and electrons in the chemistry of the actinide elements To this end, we undertook an experimental and computational study of the synthesis of a protactinium polyoxometalate
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