title: Covalency in lanthanides. An X-ray absorption spectroscopy and density functional theory study of LnCl6(x-) (x = 3, 2).
abstract: Covalency in Ln-Cl bonds of Oh-LnCl6(x-) (x = 3 for Ln = Ce(III), Nd(III), Sm(III), Eu(III), Gd(III); x = 2 for Ln = Ce(IV)) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L3,2-edge and M5,4-edge XAS were also used to characterize CeCl6(x-) (x = 2, 3). The M5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce(III) and Ce(IV)). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (t2g* and eg*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce(III) to Ce(IV) had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl6(3-) (formally Ln(III)), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce(IV) 4f-orbital mixing (t1u* + t2u*) in CeCl6(2-). This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl6(2-) (M = Ti, Zr, Hf, U).
authors.affiliation: Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Matthias W
authors.initials: MW
authors.lastname: Löble
authors.forename: Jason M
authors.initials: JM
authors.lastname: Keith
authors.forename: Alison B
authors.initials: AB
authors.lastname: Altman
authors.forename: S Chantal E
authors.initials: SC
authors.lastname: Stieber
authors.forename: Enrique R
authors.initials: ER
authors.lastname: Batista
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Boland
authors.forename: Steven D
authors.initials: SD
authors.lastname: Conradson
authors.forename: David L
authors.initials: DL
authors.lastname: Clark
authors.forename: Juan
authors.initials: J
authors.lastname: Lezama Pacheco
authors.forename: Stosh A
authors.initials: SA
authors.lastname: Kozimor
authors.forename: Richard L
authors.initials: RL
authors.lastname: Martin
authors.forename: Stefan G
authors.initials: SG
authors.lastname: Minasian
authors.forename: Angela C
authors.initials: AC
authors.lastname: Olson
authors.forename: Brian L
authors.initials: BL
authors.lastname: Scott
authors.forename: David K
authors.initials: DK
authors.lastname: Shuh
authors.forename: Tolek
authors.initials: T
authors.lastname: Tyliszczak
authors.forename: Marianne P
authors.initials: MP
authors.lastname: Wilkerson
authors.forename: Ralph A
authors.initials: RA
authors.lastname: Zehnder