Local Structure in Americium and Californium Hexacyanoferrates – Comparison with Their Lanthanide Analogues

Abstract

Metal hexacyanoferrates are well known molecular solids for a large variety of cations, although very little has been described for actinide adducts. Two new members of actinide(III) hexacyanoferrates were synthesized with the cations americium and californium. They were structurally characterized by infrared and X-ray absorption spectroscopy. Combined EXAFS data at the iron K edge and actinide L3 edge provide evidence for a three-dimensional model for these two new compounds. Structural data in terms of bond lengths were compared to those reported for the parent lanthanide(III) compounds, neodymium and gadolinium hexacyanoferrates, respectively: the americium compound with KNdIIIFeII(CN)6*4H2O and the californium compound with KGdIIIFeII(CN)6*3.5H2O and KGdIIIFeII(CN)6*3H2O. This comparison between actinide and lanthanide homologues has been carried out on the basis of ionic radii considerations. The americium and neodymium environments appear to be very similar and are arranged in a tricapped trigonal prism polyhedron of coordination number 9 (CN: 9), in which the americium atom is bonded to six nitrogen atoms and to three water molecules. For the californium adduct, a similar comparison and bond length and angle values derived fromEXAFS studies suggest that the californium cation sits in a bicapped trigonal prism (CN: 8) as in KGdIIIFeII(CN)6*3H2O. This arrangement differs from that in the structure of KGdIIIFeII(CN)6*3.5H2O, in which the gadolinium atom is surrounded by 9 atoms. This is one of the rare pieces of information revealed by EXAFS spectroscopy for americium and californium in comparison to lanthanide atoms in molecular solid compounds. A discussion on the decrease in bond length and coordination number from americium to californium is also provided, on the basis of crystallographic results reported in the literature for actinide(III) and lanthanide(III) hydrate series

Polarizable interaction potential for molecular dynamics simulations of actinoids(III) in liquid water

“…5). This similarity between Ln 3+ and An 3+ globally holds, confirming what was suggested by Apostolidis et al 46 and Dupouy et al, 89 for which also the light An 3+ ions behave similarly to Ln 3+ reflecting mainly the electrostatic nature of the An-O and Ln-O interaction in liquid water. By inspecting simulation details, we can notice a shift in hydration properties between Ln and corresponding An ions that is not constant across the series from one row position to the other.…”

Pillared metal(IV) phosphate-phosphonate extraction of actinides

“…Neodymium(III), plutonium(IV), neptunium(V), and plutonium(VI) were chosen as representatives for the different valencies of this series. Nd 3+ having very similar ionic radius and charge is often used as an analog for Am 3+ and Pu 3+ [22,23]. The Nd 3+ extractions were observed as a function of acid concentration, the results are presented in Fig.…”

Molecular solids of actinide hexacyanoferrate: Structure and bonding

“…Details about sample preparation and description of the EXAFS data fitting procedure will be given in a coming article [11]. Details about the study of aqueous californium cation by a combination of EXAFS data and theoretical calculations will also be provided in a future article [12].…”