title: Tetrahalide complexes of the [U(NR)2]2+ ion: synthesis, theory, and chlorine K-edge X-ray absorption spectroscopy.
abstract: Synthetic routes to salts containing uranium bis-imido tetrahalide anions [U(NR)(2)X(4)](2-) (X = Cl(-), Br(-)) and non-coordinating NEt(4)(+) and PPh(4)(+) countercations are reported. In general, these compounds can be prepared from U(NR)(2)I(2)(THF)(x) (x = 2 and R = (t)Bu, Ph; x = 3 and R = Me) upon addition of excess halide. In addition to providing stable coordination complexes with Cl(-), the [U(NMe)(2)](2+) cation also reacts with Br(-) to form stable [NEt(4)](2)[U(NMe)(2)Br(4)] complexes. These materials were used as a platform to compare electronic structure and bonding in [U(NR)(2)](2+) with [UO(2)](2+). Specifically, Cl K-edge X-ray absorption spectroscopy (XAS) and both ground-state and time-dependent hybrid density functional theory (DFT and TDDFT) were used to probe U-Cl bonding interactions in [PPh(4)](2)[U(N(t)Bu)(2)Cl(4)] and [PPh(4)](2)[UO(2)Cl(4)]. The DFT and XAS results show the total amount of Cl 3p character mixed with the U 5f orbitals was roughly 7-10% per U-Cl bond for both compounds, which shows that moving from oxo to imido has little effect on orbital mixing between the U 5f and equatorial Cl 3p orbitals. The results are presented in the context of recent Cl K-edge XAS and DFT studies on other hexavalent uranium chloride systems with fewer oxo or imido ligands.
authors: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors: Liam P
authors: LP
authors: Spencer
authors: Ping
authors: P
authors: Yang
authors: Stefan G
authors: SG
authors: Minasian
authors: Robert E
authors: RE
authors: Jilek
authors: Enrique R
authors: ER
authors: Batista
authors: Kevin S
authors: KS
authors: Boland
authors: James M
authors: JM
authors: Boncella
authors: Steven D
authors: SD
authors: Conradson
authors: David L
authors: DL
authors: Clark
authors: Trevor W
authors: TW
authors: Hayton
authors: Stosh A
authors: SA
authors: Kozimor
authors: Richard L
authors: RL
authors: Martin
authors: Molly M
authors: MM
authors: MacInnes
authors: Angela C
authors: AC
authors: Olson
authors: Brian L
authors: BL
authors: Scott
authors: David K
authors: DK
authors: Shuh
authors: Marianne P
authors: MP
authors: Wilkerson
mesh_terms: D002713:Chlorine / Q000737:chemistry*; D007094:Imides / Q000737:chemistry*; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D014501:Uranium / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D007094:Imides; D009942:Organometallic Compounds; D014501:Uranium; D002713:Chlorine