Probing Sm(II) and U(V) bonding properties by high resolution X-ray spectroscopy

Deep understanding of the electronic structure and chemical bonding properties of the lanthanide (Ln) and actinide (An) elements poses a great challenge [1-3]. The Ln L2,3 and An M4,5 absorption edges core-to-core and valence band resonant inelastic X-ray scattering (CC/VB-RIXS) and high energy resolution X-ray absorption near edge structure (HR-XANES) techniques probe the occupied and unoccupied parts of the valence band of the Ln and An elements with extraordinary energy resolution. In combination with computational quantum chemistry, detailed information on the chemical bonding can be obtained [1-6]. Two examples of applications of high-resolution X-ray spectroscopic tools will be discussed.
It will be demonstrated that the ionic bond of Sm(II) with (cyclononatetraenyl =CNT) in [Sm(CNT2)] can be modulated and becomes covalent by photon induced transfer of Sm f electrons to Sm d/s orbitals. This photon induced change of bonding properties can potentially activate the rather chemically inert [Sm(CNT2)] and can be applied for further lanthanide molecular materials [5].
The stabilization of uranyl(V) (UO2 1+) by Fe(II) in natural systems remains an open question in uranium chemistry. ... mehrStabilization of U(V)O2 1+ by Fe(II) against disproportionation was also demonstrated in molecular complexes. However, the relation between the Fe(II) induced stability and the change of the bonding properties have not been elucidated up to date. It will be shown that U(V)–O axial bond covalency decreases upon binding to Fe(II) inducing redirection of electron density from the U(V)–O axial bond towards the U(V)– equatorial bonds thereby increasing bond covalency. Our results indicate that such increased covalent interaction of U(V) with the equatorial ligands resulting from iron binding lead to higher stability of uranyl(V) [6].
References
[1] T. Vitova; et al. Nat. Commun.; 2017; 8; 16053.
[2] T. Vitova; et al. Commun. Chem.; 2022; 5 (1); 1-4.
[3] T. Prüßmann; et al. J. Synchrotron Radiat.; 2022; 29 (1); 53-66.
[4] B. Schacherl; et al. J. Synchrotron Radiat.; 2022; 29 (1); 80-88.
[5] T. Vitova; et al., submitted.
[6} T. Vitova; et al., Chem. Sci.; 2022; 13 (37); 11038-1104.