Reduction of Pentavalent Uranyl to U(IV) Facilitated by Oxo Functionalization

Schnaars, David D.; Hayton, Trevor W.

doi:10.1021/ja906880d

Cited by 73 publications

(84 citation statements)

References 22 publications

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“…In general, charge reduction is a well known process associated with the formation of gas-phase ions. Reduction of UO 2 2ϩ to UO 2 ϩ (U VI ¡U V ) is also known from solution chemistry [16,17] and was also observed upon ESI mass spectrometric studies [18].…”

Section: Methodsmentioning

confidence: 86%

Unusual ion UO₄⁻ formed upon collision induced dissociation of [UO₂(NO₃)₃]⁻, [UO₂(ClO₄)₃]⁻, [UO₂(CH₃COO)₃]⁻ ions

Sokalska

Prussakowska

Hoffmann

et al. 2010

J. Am. Soc. Mass Spectrom.

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The following ions [UO 2 (NO 3 Ϫ were generated from respective salts (UO 2 (NO 3 ) 2 , UO 2 (ClO 4 ) 3 , UO 2 (CH 3 COO) 2 ) by laser desorption/ionization (LDI). Collision induced dissociation of the ions has led, among others, to the formation of UO 4 Ϫ ion (m/z 302). The undertaken quantum mechanical calculations showed this ion is most likely to possess square planar geometry as suggested by MP2 results or strongly deformed geometry in between tetrahedral and square planar as indicated by DFT results. Interestingly, geometrical parameters and analysis of electron density suggest it is an U VI compound, in which oxygen atoms bear unpaired electron and negative charge. In the laboratory, the most common uranium compounds are the salts of uranyl (UO 2 2ϩ -U VI -containing cation), e.g., UO 2 (NO 3 ) 2 , UO 2 (CH 3 COO) 2 . Uranium compounds with this element at other oxidation states (other than IV and VI) are also known, however, they are less stable, e.g., the U V species in solutions easily undergo disproportionation reaction to U(IV) and U(VI) [2]. In nature, there are also uranyl peroxides UO 2 (O 2 ), but the respective minerals UO 2 (O 2 )(H 2 O) 2 and UO 2 (O 2 )(H 2 O) 4 do not exist in high abundances [3]. A number of more developed uranyl peroxides were obtained in labs [4 -7].Mass spectrometric studies of uranyl salts (mainly UO 2 (NO 3 ) 2 ) have been reported, first by using FAB (fast atom bombardment) as ionization method [8], and then by electrospray ionization [9 -15]. Most of the studies were performed in the positive ion mode; only Pasilis et al. have performed the ESI analysis in both positive and negative ion modes [10]. In this very excellent paper, the authors have systematically investigated the gasphase uranyl-containing ions and they have examined ligand association/exchange and H/D exchange reactions of the species, using FT-ICR mass spectrometry to obtain accurate mass measurements. In this communication, the collision induced dissociation (CID) of the ions [UO 2 (NOϪ is discussed. The ions were generated from respective salts (UO 2 (NO 3 ) 2 , UO 2 (ClO 4 ) 3 , UO 2 (CH 3 COO) 2 ) by laser desorption/ionization (LDI). As described further, the unusual formation of ion UO 4 Ϫ was detected upon decomposition of the ions subjected to CID. ExperimentalThe LDI mass spectra and LDI MS/MS spectra were obtained on a Waters/Micromass (Manchester, UK) Q-TOF Premier mass spectrometer (software MassLynx ver. 4.1; Manchester, UK) fitted with a 200 Hz repetition rate Nd/YAG laser ( ϭ 355 nm, power density 10 7 W/cm 2 ). For MS/MS experiments, argon was used as a collision gas at the flow-rate 0.5 mL/min in the collision cell. Collision energy (CE -the most important parameter for MS/MS experiments) is indicated in each MS/MS spectrum presented further.To prepare the target spots, 1 L of methanol solution containing uranyl salts was used (the concentration was of about 0.1 mol/dm [3]. After a few min at room temperature, the spot was dry and LDI mass spectra could be recorded. If the concentra...

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Section: Methodsmentioning

confidence: 86%

Unusual ion UO₄⁻ formed upon collision induced dissociation of [UO₂(NO₃)₃]⁻, [UO₂(ClO₄)₃]⁻, [UO₂(CH₃COO)₃]⁻ ions

Sokalska

Prussakowska

Hoffmann

et al. 2010

J. Am. Soc. Mass Spectrom.

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“…We have used the organic Pacman ligand as well as THF solvent in order to bypass the formation of U(H 2 O) 8 4+ in aqueous solutions and the relative "ambiguity" of the reactions: 2 ], (where Ar is 3,5-t Bu 2 C 6 H 3 ), to the tetravalent state. 82 They postulated that the B(C 6 F 5 ) 3 axial group actually shifts the reduction process to a point where it is chemically accessible (against the ferrocene/ferrocenium electrode). A similar effect has been observed for the U(VI)/U(V) reduction of an hexavalent complex, UO 2 ( Ar acnac) 2 , and its axially oxof u n c t i o n a l i z e d h e x a v a l e n t c o u n t e r p a r t , O U O B -(C 6 F 5 ) 3 ( Ar acnac) 2 .…”

Section: +mentioning

confidence: 99%

DFT Study of Oxo-Functionalized Pentavalent Dioxouranium Complexes: Structure, Bonding, Ligand Exchange, Dimerization, and U(V)/U(IV) Reduction of OUOH and OUOSiH₃ Complexes

Odoh

Schreckenbach

2012

Inorg. Chem.

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The structural and electronic properties of model oxo-functionalized pentavalent dioxouranium complexes have been studied using scalar relativistic density functional theory (DFT) calculations. The electronic structures of these complexes are compared to those of their hexavalent and pentavalent counterparts with free axial oxo groups while paying particular emphasis on the effect of oxo-functionalization on the formation of binuclear complexes, the U(V)/U(IV) redox potentials, as well as ligand exchange between the axial and equatorial regions of the dioxouranium moiety. The stabilization of the σ(d) orbitals of the UO(2) moiety is one of the major effects of oxo-functionalization. The origin of this effect is the mixing of the σ(d) orbital of the uranyl group with the σ(OH)/σ(OSiH(3)) orbitals of the axial OH/OSiH(3) group. The 6p atomic orbitals of the uranium center are mixed to a greater extent with the σ(d) orbital after stabilization caused by oxo-functionalization. The asymmetric nature of the oxo-functionalization has dramatic effects not only on the U-O bond lengths (elongation by up to 0.24 Å) and U-O bond orders (loss of a full bond order) but also on the formation and type of U(2)O(4) core found in binuclear complexes. The loss of a full bond order upon oxo-functionalization means the axial U-OH/U-OSiH(3) bonds are only slightly stronger than they would be if they were found in the equatorial region of the uranyl moiety. This raises the possibility of ligand exchange between the axial and equatorial regions as well as increasing the stability of the binuclear complexes with butterfly-shaped U(2)O(4) cores relative to those with diamond U(2)O(4) cores. Reductive oxo-functionalization results in complexes with lower electron density at their U(V) centers in comparison to UO(2)(+) complexes. This has dramatic effects on the calculated U(V)/U(IV) redox potentials.

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“…This feature is 0.63 V higher than that observed for [Cp* 2 Co]-[U(OB{C 6 F 5 } 3 ) 2 ( Ar acnac) 2 ], which exhibits a U V /U IV redox potential at E 1/2 = À1.21 V (vs Fc/Fc þ ). 33 We attribute the less negative reduction potential in 1 to the replacement of a neutral B(C 6 F 5 ) 3 substituent with the cationic Ph 3 Si þ fragment. In addition, complex 1 exhibits an irreversible oxidation feature at 0.96 V (vs Fc/Fc þ , 200 mV/s).…”

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confidence: 94%

Borane-Mediated Silylation of a Metal–Oxo Ligand

Schnaars

Hayton

2011

Inorg. Chem.

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The addition of 1 equiv of HSiPh(3) to UO(2)((Ar)acnac)(2) ((Ar)acnac = ArNC(Ph)CHC(Ph)O; Ar = 3,5-(t)Bu(2)C(6)H(3)), in the presence of 1 equiv of B(C(6)F(5))(3), results in the formation of U(OSiPh(3))(OB{C(6)F(5)}(3))((Ar)acnac)(2) (1), via silylation of an oxo ligand and reduction of the uranium center. The addition of 1 equiv of Cp(2)Co to 1 results in a reduction to uranium(IV) and the formation of [Cp(2)Co][U(OSiPh(3))(OB{C(6)F(5)}(3))((Ar)acnac)(2)] (2) in 78% yield. Complexes 1 and 2 have been characterized by X-ray crystallography, while the solution-phase redox properties of 1 have been measured with cyclic voltammetry.

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Reduction of Pentavalent Uranyl to U(IV) Facilitated by Oxo Functionalization

Cited by 73 publications

References 22 publications

Unusual ion UO₄⁻ formed upon collision induced dissociation of [UO₂(NO₃)₃]⁻, [UO₂(ClO₄)₃]⁻, [UO₂(CH₃COO)₃]⁻ ions

Unusual ion UO₄⁻ formed upon collision induced dissociation of [UO₂(NO₃)₃]⁻, [UO₂(ClO₄)₃]⁻, [UO₂(CH₃COO)₃]⁻ ions

DFT Study of Oxo-Functionalized Pentavalent Dioxouranium Complexes: Structure, Bonding, Ligand Exchange, Dimerization, and U(V)/U(IV) Reduction of OUOH and OUOSiH₃ Complexes

Borane-Mediated Silylation of a Metal–Oxo Ligand

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Reduction of Pentavalent Uranyl to U(IV) Facilitated by Oxo Functionalization

Cited by 73 publications

References 22 publications

Unusual ion UO4− formed upon collision induced dissociation of [UO2(NO3)3]−, [UO2(ClO4)3]−, [UO2(CH3COO)3]− ions

Unusual ion UO4− formed upon collision induced dissociation of [UO2(NO3)3]−, [UO2(ClO4)3]−, [UO2(CH3COO)3]− ions

DFT Study of Oxo-Functionalized Pentavalent Dioxouranium Complexes: Structure, Bonding, Ligand Exchange, Dimerization, and U(V)/U(IV) Reduction of OUOH and OUOSiH3 Complexes

Borane-Mediated Silylation of a Metal–Oxo Ligand

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Unusual ion UO₄⁻ formed upon collision induced dissociation of [UO₂(NO₃)₃]⁻, [UO₂(ClO₄)₃]⁻, [UO₂(CH₃COO)₃]⁻ ions

Unusual ion UO₄⁻ formed upon collision induced dissociation of [UO₂(NO₃)₃]⁻, [UO₂(ClO₄)₃]⁻, [UO₂(CH₃COO)₃]⁻ ions

DFT Study of Oxo-Functionalized Pentavalent Dioxouranium Complexes: Structure, Bonding, Ligand Exchange, Dimerization, and U(V)/U(IV) Reduction of OUOH and OUOSiH₃ Complexes