Structural and Spectroscopic Comparison of Soft-Se vs. Hard-O Donor Bonding in Trivalent Americium/Neodymium Molecules

Covalency is often considered to be an influential factor in driving An(3+) vs. Ln(3+) selectivity invoked by soft donor ligands. This is intensely debated, particularly the extent to which An(3+)/Ln(3+) covalency differences prevail and manifest as the f-block is traversed, and the effects of periodic breaks beyond Pu. Herein, two Am complexes, [Am{N(E=PPh2)(2)}(3)] (1-Am, E=Se; 2-Am, E=O) are compared to isoradial [Nd{N(E=PPh2)(2)}(3)] (1-Nd, 2-Nd) complexes. Covalent contributions are assessed and compared to U/La and Pu/Ce analogues. Through ab initio calculations grounded in UV-vis-NIR spectroscopy and single-crystal X-ray structures, we observe differences in f orbital involvement between Am-Se and Nd-Se bonds, which are not present in O-donor congeners.

Automated summary

This study compared two Am complexes with Nd complexes, analyzing covalent contributions and comparing them to U/La and Pu/Ce analogues. By using ab initio calculations based on UV-vis-NIR spectroscopy and single-crystal X-ray structures, differences in f orbital involvement between Am-Se and Nd-Se bonds were observed.