First structural characterization of Pa(IV) in aqueous solution and quantum chemical investigations of the tetravalent actinides up to Bk(IV): the evidence of a curium break
Résumé
While for the tetravalent An Th, U, Np, and Pu, an understanding of their chemistry in aquatic solution was achieved recently, this is not the case for the Pa(IV). Its simple 5f1 ground-state electronic configuration enables speciation by complementary spectroscopic methods, such as XAFS, TRLFS and UV-Vis, and is also of interest for quantum chemical (QC) studies to probe the nature of the An-water bonds across the An series. The combined results of EXAFS and QC data suggest that the Pa4+ aqua ion binds on the average 9 water molecules in its first hydration sphere. The An-O bond distances follow the monotonic decreasing trend of the An4+ ionic radii, with a decrease of the hydration number from 9 to 8 for the heaviest ions Cm4+ and Bk4+, marking a “Curium break” [1].
[1] N. L. Banik, V. Vallet, F. Réal, R. M. Belmécheri, B. Schimmelpfennig, J. Rothe, R. Marsac, P. Lindqvist-Reis, C. Walther, M. A. Denecke and C. M. Marquardt, Dalton Trans. 45, 453–457 (2016).