Solid-state
uranyl hybrid structures are often formed through unique
intermolecular interactions occurring between a molecular uranyl anion
and a charge-balancing cation. In this work, solid-state structures
of the uranyl tetrachloride anion engaged in uranyl–cation
and uranyl–hydrogen interactions were studied using density
functional theory (DFT). As most first-principles methods used for
systems of this type focus primarily on the molecular structure, we
present an extensive benchmarking study to understand the methods
needed to accurately model the geometric properties of these systems.
From there, the electronic and vibrational structures of the compounds
were investigated through projected density of states and phonon analysis
and compared to the experiment. Lastly, we present a DFT + thermodynamics
approach to calculate the formation enthalpies (ΔH
f) of these systems to directly relate to experimental
values. Through this methodology, we were able to accurately capture
trends observed in experimental results and saw good quantitative
agreement in predicted ΔH
f compared
to the value calculated through referencing each structure to its
standard state. Overall, results from this work will be used for future
combined experimental and computational studies on both uranyl and
neptunyl hybrid structures to delineate how varying intermolecular
interaction strengths relates to the overall values of ΔH
f.
Hydrogen bonding networks within hexavalent uranium materials
are
complex and may influence the overall physical and chemical properties
of the system. This is particularly true if hydrogen bonding takes
places between the donor and the oxo group associated with the uranyl
cation (UO
2
2+
). In the current study, we evaluate
the impact of charge-assisted hydrogen bonding on the vibrational
modes of the uranyl cation using uranyl tricarbonate [UO
2
(CO
3
)
3
]
4–
interactions with
[Co(NH
3
)
6
]
3+
as the model system.
Herein, we report the synthesis and structural characterization of
five novel compounds, [Co(NH
3
)
6
]Cl(CO
3
) (
Co_Cl_CO
3
), [Co(NH
3
)
6
]
4
[UO
2
(CO
3
)
3
]
3
(H
2
O)
11.67
(
Co4U3
), [Co(NH
3
)
6
]
3
[UO
2
(CO
3
)
3
]
2
Cl (H
2
O)
7.5
(
Co3U2_Cl
), [Co(NH
3
)
6
]
2
[UO
2
(CO
3
)
3
]Cl
2
(
Co2U_Cl
), and [Co(NH
3
)
6
]
2
[UO
2
(CO
3
)
3
]CO
3
(
Co2U_CO
3
), which
contain differences in the crystalline packing and extended hydrogen
bonding networks. We show that these slight changes in the supramolecular
assembly and hydrogen bonding networks result in the modification
of modes as observed by infrared and Raman spectroscopy. We use density
functional theory calculations to assign the vibrational modes and
provide an understanding about how uranyl bond perturbation and changes
in hydrogen bonding interactions can impact the resulting spectroscopic
signals.
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