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

Abstract

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, 243Am2[(C6(COO–)6]­(H2O)8·2H2O (1-Am), has been synthesized and characterized using structural analysis and spectroscopy at ambient and elevated pressures. 1-Am was then compared to isomorphous neodymium (1-Nd) and samarium (1-Sm) 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 1-Am is significantly greater than that observed in 1-Nd and 1-Sm, with average shifts of 21.4, 4.7, and 3.6 cm–1/GPa, respectively. This greater shift found in 1-Am shows further evidence that the 5f orbitals are more affected than the 4f orbitals when pressure is applied to isostructural compounds.

Cyclopentadienyl coordination induces unexpected ionic Am−N bonding in an americium bipyridyl complex

“…10,823–8921 cm −1 ) ( J = 4), and 1274–1450 nm (ca. 7849–6897 cm −1 ) ( J = 3) typically not observed in Am 3+ absorption spectroscopy 41 , 51 .…”

Synthesis, characterization, and high-pressure studies of a 3D berkelium(iii) carboxylate framework material

“…The feature extends into lower energy at 3.90 GPa in Bk1 than at over 10 GPa in the americium mellitate. 18 The intense feature is also reversible and therefore is not a result of degradation of the compound since the spectra of before and after the application of pressure are nearly identical (Fig. S14, ESI †).…”

“…14,15 The formation of trivalent f-element mellitate crystals can also occur in short time frames suitable for high activity actinide isotopes. 16 Recently, our group has studied a series of trivalent actinide mellitates for plutonium, 17 americium, 18 curium, 19 and californium. 20 The Bk(III) mellitate, Bk 2 [C 6 (CO 2 ) 6 ](H 2 O) 8 Á2H 2 O (Bk1), was obtained by layering a green aqueous solution of BkBr 3 ÁnH 2 O (3.5 mg, 14 mmol 249 Bk 3+ content) and mellitic acid with ethanol.…”

“…S4-S7, ESI †) and were found by single crystal X-ray diffraction to be isostructural with An 2 [C 6 (CO 2 ) 6 ](H 2 O) 8 Á2H 2 O (An = b-Pu, Am, and Cm). [17][18][19] Bk1 crystallizes in the monoclinic space group P2 1 /n (#14) with a three-dimensional framework as shown in Fig. 1.…”

“…5). Compared to the americium, 18 curium, 19 and californium 20 mellitate, it appears that the average shift of a transition is hypsochromic (blue shifting) as opposed to bathochromic (red shifting) (Fig. S11, ESI †).…”