Covalency involving the 5f orbitals is regularly invoked to explain the reactivity, structure and spectroscopic properties of the actinides, but the ionic versus covalent nature of metal-ligand bonding in actinide complexes remains controversial. The tetrakis 2,6-di-tert-butylphenoxide complexes of Th, U and Np form an isostructural series of crystal structures containing approximately tetrahedral MO4 cores. We show that up to 3 GPa the Th and U crystal structures show negative linear compressibility as the OMO angles distort. At 3 GPa the angles snap back to their original values, reverting to a tetrahedral geometry with an abrupt shortening of the M-O distances by up to 0.1 Å. The Np complex shows similar but smaller effects, transforming above 2.4 GPa. Electronic structure calculations associate the M-O bond shortening with a change in covalency resulting from increased contributions to the M-O bonding by the metal 6d and 5f orbitals, the combination promoting MO4 flexibility at little cost in energy.
SHEPARD Jacob J.;
BERRYMAN Victoria E. J.;
OCHIAI Tatsumi;
WALTER Olaf;
PRICE Amy N.;
WARREN Mark R.;
ARNOLD Polly L.;
KALTSOYANNIS Nikolas;
PARSONS Simon;
2023-01-30
NATURE PORTFOLIO
JRC124929
2041-1723 (online),
https://www.nature.com/articles/s41467-022-33459-7,
https://publications.jrc.ec.europa.eu/repository/handle/JRC124929,
10.1038/s41467-022-33459-7 (online),
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