The Ammonolysis of Uranium Compounds and Theoretical Considerations on Fluorides in High Oxidation States
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Philipps-Universität Marburg
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Abstract
This work combines the chemistry of two closely entangled elements,
fluorine and uranium, whereby the specialty lies in the approach. The
chemistry of uranium was studied experimentally, while the investigation
of the chemistry of fluorine was mainly of computational nature.
In context of the ammonolysis reaction of uranium compounds, ten novel
compounds are presented in this work. Furthermore, theoretical methods
have successfully been established to characterize the nature of bonding of
uranium in ammine compounds, by the use of Intrinsic Bonding Orbitals
(IBOs). It was shown that the IBO analysis produces reasonable results
for orbital contributions in comparison to other localization methods.
The numerous analyzed ions of this work represent a set of references
for future uranium ammine compounds or can be used for comparison of
other related ammine compounds like of thorium or of group 6 metals.
For the Th atom a reference basis set for the IBO procedure was already
designed as part of this work. Furthermore, the first fluoride ion affinities
(FIAs) for uranyl(VI) species are presented, which enable further insights
into the complex chemistry of such compounds. Additionally, the crystal
structure of α-ThBr4 was rerefined and the novel γ-ThBr4 polymorph
was observed from a chemical vapor transport reaction.
On the theoretical considerations of fluorine compounds in high
oxidation states, the electronic structures and anharmonic vibrational
frequencies of the closed-shell binary molecular hexafluorides MF6,
M = S – Po, Xe, Rn, Cr – W, U, are presented, which have been
studied with DFT-PBE0 and coupled-cluster methods. This allowed the
exact assignment of combination modes observed in the experimentally
recorded infrared spectra. For the first time the NdF6 molecule and its
harmonic vibrational frequencies along with the nature of the bonding is reported. The FIAs of RuF5 and its dimer [Ru2F10] are presented, which
were computed with coupled-cluster methods. Further theoretical studies
are presented in the field of BrF5 chemistry. BrF5 was reinvestigated
and its follow-up chemistry studied. The nature of the bonding of the
central F atom in the experimentally observed anions [(μx-F)(BrF5)x]– ,
with x = 3, 4 is presented. As a theoretical product of oxidation of
BrF5, a computational study on the electronic structure, along with
spectroscopic properties for the BrOF5 molecule is introduced. Lastly,
the electronic structure of the P2F8 molecule is presented.
A few highlights of both projects are shortly summarized in the
following:
The ammonolysis of uranium compounds can be divided into the
respective oxidation states of starting material. From the reaction of
UBr3 and UI3 with AgCN in liquid aNH3 at +40 ◦C, novel uranium
cyanide compounds, 1∞
[(μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]X4 · 2NH3,
with X = Br, I, were observed. A special feature is the polymeric
structure of the 1
∞[(μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]4+ cation. These
novel compounds represent two of the very few known uranium(IV)
cyanides, as of today. Furthermore, the bonding situation within the
{(H3N)5U(μ-NH2)3U(NH3)5} unit of the cation, shows the expected σ-
type bond between U– (μ-NH2), but additionally, a π-type interaction
towards the second U atom is observed.
Similar observations were found for the
[U(NH3)3({U(NH3)6}(μ-NH2)3)2]6+ cation in the compound
[U(NH3)3({U(NH3)6}(μ-NH2)3)2]Br6 · 8NH3.
From the reaction of UO2F2 with MF compounds, with M =
Rb, Cs, Tl, two different anions were observed, [UO2F3(NH3)2]–
and [{UO2F2(NH3)}2(μ-F)2]2– . In case of M = Rb, Cs the anion [UO2F3(NH3)2]– was observed in the compounds M[UO2F3(NH3)2] at
−40 ◦C, while for M = Tl the anion [{UO2F2(NH3)}2(μ-F)2]2– was observed
in the compound [Tl2(NH3)6][{UO2F2(NH3)}2(μ-F)2] at +40 ◦C.
Quantum-chemical considerations suggest that the [UO2F3(NH3)2]–
anion represents the thermodynamically favored product, formed at lower
temperatures, while the dinuclear anion [{UO2F2(NH3)}2(μ-F)2]2– is
the kinetically favored product.
Furthermore, the FIAs for the species [UO2Fx]2–x and
[UO2Fx(NH3)5–x]2–x were studied with the CCSD(T) method.
It was found that for the [UO2Fx(NH3)5–x]2–x complexes with
x = 0 to 2, the FIAs are in the range of medium to strong acceptors
in comparison to SbF5, with values of −216, −193, and
−169 kJ mol−1, respectively. A further special feature of the compound
[Tl2(NH3)6][{UO2F2(NH3)}2(μ-F)2] is the [Tl2(NH3)6]2+ cation,
where a thallophilic interaction was observed, and investigated with
coupled-cluster methods.
Theoretical considerations on the nature of the bonding
in the mixed-valent uranyl(V,VI) cations for the composition
[(U(VI)O2)2(U(V)O2)2(μ3-O)2(NH3)12]2+ and
[(U(VI)O2)4(U(V)O2)4(μ3-O)4(NH3)22]4+ are presented, which
both feature μ3-O bridges. The latter cation additionally shows a novel
bonding motif in the field of mixed-valent uranyl(V,VI) compounds, were
an O atom of an uranyl(V) moiety μ3-O bridges towards two uranyl(VI)
units. Moreover, the calculated bond length and angles were used to
distinguish between N and O atom within the crystal structure. The
electronic structure of the [(NH3)8U(μ-N)U(NH3)5(μ-N)UO2(NH3)4]6+
cation was studied, as the cation features a UN2 unit next to a UO2 unit,
which is the first example of its kind.
For the closed-shell binary molecular hexafluorides MF6 molecules in the
gasphase, with M = S – Po, Xe, Rn, Cr – W, U, anharmonic vibrational frequencies were calculated at the CCSD(T)/cc-pVZT(-PP) level of theory.
It was shown that for the experimentally known MF6 compounds, M = S –
Te, Xe, Mo, W, U, the calculated frequencies and intensities are in overall
agreement. In addition to the experimentally known MF6 molecules,
anharmonic vibrational frequencies were calculated for the unknown ones,
with M = Cr, Po, Rn. Furthermore, the combination modes ν1+ν3 and
ν2+ν3, were identified to be a typical fingerprint in the infrared spectra
of these compounds. This work presents the first report of the NdF6
molecule, along with an analysis of the potential energy surface (PES).
The NdF6 molecule was calculated to be true local minimum on it. The
bonding situation is presented by means of IBOs, for which a Nd reference
basis set was designed.
For the molecules RuF5 and Ru2F10 the FIAs are presented, which
were calculated with the CCSD(T) method. The FIAs range in the area
of strong acceptors with values of 602 and 494 kJ mol−1, respectively.
For the BrF5 molecule anharmonic frequencies along with 19F NMR
shifts were calculated and compared to the experimental findings. The FIA
for the BrF5 molecule in the gasphase was calculated to be 276 kJ mol−1.
The electronic structure, and the bonding situation of the central F
atom in particular of interhalogen ions [(μx-F)(BrF5)x]– , with x = 3, 4
are presented. These findings are compared to the related chlorine and
iodine compounds. Furthermore, the hypothetical product of oxidation
of BrF5, BrOF5, was quantum-chemically investigated. It was shown
to be a true local minimum on the PES. Harmonic frequencies were
calculated with DFT-PBE0 and coupled-cluster methods and the bonding
situation studied by means of IBOs. Additionally, the 19F NMR shifts
were predicted.
As a side project the electronic structure of the P2F8 molecule is
presented along with an analysis of the bonding situation.
Review
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Contributors
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Dates
Created: 2024Issued: 2025-01-08Updated: 2025-01-08
Faculty
Fachbereich Chemie
Publisher
Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
Keywords
Fluorchemieammonia chemistryUranium chemistryAmmoniakchemieFluorine chemistryQuantum-chemical calculationsUranchemieQuantenchemie
DFG-subjects
UranFluorQuantenchemieAmmoniak
DDC-Numbers
540
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Graubner, Tim: The Ammonolysis of Uranium Compounds and Theoretical Considerations on Fluorides in High Oxidation States. : Philipps-Universität Marburg 2025-01-08. DOI: https://doi.org/10.17192/z2024.0396.
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This item has been published with the following license: In Copyright