title: 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.
abstract: More than a century after its discovery the structure of the Pa(4+) ion in acidic aqueous solution has been investigated for the first time experimentally and by quantum chemistry. The combined results of EXAFS data and quantum chemically optimized structures suggest that the Pa(4+) aqua ion has an average of nine water molecules in its first hydration sphere at a mean Pa-O distance of 2.43 Å. The data available for the early tetravalent actinide (An) elements from Th(4+) to Bk(4+) show that the An-O bonds have a pronounced electrostatic character, with bond distances following the same monotonic decreasing trend as the An(4+) ionic radii, with a decrease of the hydration number from nine to eight for the heaviest ions Cm(4+) and Bk(4+). Being the first open-shell tetravalent actinide, Pa(4+) features a coordination chemistry very similar to its successors. The electronic configuration of all open-shell systems corresponds to occupation of the valence 5f orbitals, without contribution from the 6d orbitals. Our results thus demonstrate that Pa(iv) resembles its early actinide neighbors.
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany. nidhu.banik@kit.edu.
authors.forename: Nidhu lal
authors.initials: Nl
authors.lastname: Banik
authors.affiliation: Laboratoire PhLAM, UMR-CNRS 8523, Université Lille 1 (Sciences et Technologies), F-59655 Villeneuve d'Ascq, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Vallet
authors.affiliation: Laboratoire PhLAM, UMR-CNRS 8523, Université Lille 1 (Sciences et Technologies), F-59655 Villeneuve d'Ascq, France.
authors.forename: Florent
authors.initials: F
authors.lastname: Réal
authors.affiliation: Laboratoire de Thermodynamique et Modélisation Moléculaire, Faculté de Chimie, USTHB BP 32 El-Alia, 16111 Bab-Ezzouar, Algeria.
authors.forename: Réda Mohamed
authors.initials: RM
authors.lastname: Belmecheri
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany. nidhu.banik@kit.edu.
authors.forename: Bernd
authors.initials: B
authors.lastname: Schimmelpfennig
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany. nidhu.banik@kit.edu.
authors.forename: Jörg
authors.initials: J
authors.lastname: Rothe
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany. nidhu.banik@kit.edu.
authors.forename: Rémi
authors.initials: R
authors.lastname: Marsac
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany. nidhu.banik@kit.edu.
authors.forename: Patric
authors.initials: P
authors.lastname: Lindqvist-Reis
authors.affiliation: Institut für Radioökologie und Strahlenschutz, Leibniz Universität Hannover, Hannover, Germany.
authors.forename: Clemens
authors.initials: C
authors.lastname: Walther
authors.affiliation: Dalton Nuclear Institute, The University of Manchester, Manchester, UK.
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Denecke
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany. nidhu.banik@kit.edu.
authors.forename: Christian M
authors.initials: CM
authors.lastname: Marquardt