Pronounced Pressure Dependence of Electronic Transitions for Americium Compared to Isomorphous Neodymium and Samarium Mellitates.

The mellitate ion is relevant in spent nuclear fuel processing and is utilized as a surrogate for studying the interactions of f elements with humic acids. A wealth of different coordination modes gives the potential for diverse structural chemistry across the actinide series. In this study, an americium mellitate, Am[(C(COO)](HO)·2HO (), has been synthesized and characterized using structural analysis and spectroscopy at ambient and elevated pressures. was then compared to isomorphous neodymium () and samarium () mellitates via bond-length analysis and pressure dependence of their Laporte-forbidden f → f transitions. Results show that the pressure dependence of the f → f transitions of is significantly greater than that observed in and , with average shifts of 21.4, 4.7, and 3.6 cm/GPa, respectively. This greater shift found in shows further evidence that the 5f orbitals are more affected than the 4f orbitals when pressure is applied to isostructural compounds.