18 research outputs found
Insight into the uranyl oxyfluoride topologies through the synthesis, crystal structure and evidence of a new oxyfluoride layer in [(UO2)4F13][Sr3(H2O)8](NO3).H2O
International audienceA new strontium uranyl oxyfluoride, [(UO2)4F13][Sr3(H2O)8](NO3)·H2O, was synthesized under hydrothermal conditions. The single-crystal X-ray structure was determined. This compound crystallizes in the triclinic space group P1̅ (No. 2), with unit cell parameters a = 10.7925(16) Å, b = 10.9183(16) Å, c = 13.231(2) Å, α = 92.570(8)°, β = 109.147(8)°, γ = 92.778(8)°, V = 1468.1(4) Å3, and Z = 2. The structure is built from uranyl-containing chains of tetrameric units of corner-sharing UO2F5 pentagonal bipyramids. These chains are linked through trimeric strontium units to form strontium–uranyl oxyfluoride layers further assembled by nitrate groups. The interlayer space is occupied by free water molecules. This compound was characterized by spectroscopic methods, especially 19F NMR highlighting the many different fluoride sites. Structural relationships with other uranyl oxyfluorides were investigated through the different F/O ratios, the structural building unit, and the structural arrangement
Synthesis of a Uranyl Persulfide Complex and Quantum Chemical Studies of Formation and Topologies of Hypothetical Uranyl Persulfide Cage Clusters
The compound Na<sub>4</sub>[(UO<sub>2</sub>)Â(S<sub>2</sub>)<sub>3</sub>]Â(CH<sub>3</sub>OH)<sub>8</sub> was synthesized at room
temperature
in an oxygen-free environment. It contains a rare example of the [(UO<sub>2</sub>)Â(S<sub>2</sub>)<sub>3</sub>]<sup>4–</sup> complex
in which a uranyl ion is coordinated by three bidentate persulfide
groups. We examined the possible linkage of these units to form nanoscale
cage clusters analogous to those formed from uranyl peroxide polyhedra.
Quantum chemical calculations at the density functional and multiconfigurational
wave function levels show that the uranyl–persulfide–uranyl,
U–(S<sub>2</sub>)–U, dihedral angles of model clusters
are bent due to partial covalent interactions. We propose that this
bent interaction will favor assembly of uranyl ions through persulfide
bridges into curved structures, potentially similar to the family
of nanoscale cage clusters built from uranyl peroxide polyhedra. However,
the U–(S<sub>2</sub>)–U dihedral angles predicted for
several model structures may be too tight for them to self-assemble
into cage clusters with fullerene topologies in the absence of other
uranyl-ion bridges that adopt a flatter configuration. Assembly of
species such as [(UO<sub>2</sub>)Â(S<sub>2</sub>)Â(SH)<sub>4</sub>]<sup>4–</sup> or [(UO<sub>2</sub>)Â(S<sub>2</sub>)Â(C<sub>2</sub>O<sub>4</sub>)<sub>4</sub>]<sup>4–</sup> into fullerene topologies
with ∼60 vertices may be favored by use of large counterions
Synthesis of a Uranyl Persulfide Complex and Quantum Chemical Studies of Formation and Topologies of Hypothetical Uranyl Persulfide Cage Clusters
The compound Na<sub>4</sub>[(UO<sub>2</sub>)Â(S<sub>2</sub>)<sub>3</sub>]Â(CH<sub>3</sub>OH)<sub>8</sub> was synthesized at room
temperature
in an oxygen-free environment. It contains a rare example of the [(UO<sub>2</sub>)Â(S<sub>2</sub>)<sub>3</sub>]<sup>4–</sup> complex
in which a uranyl ion is coordinated by three bidentate persulfide
groups. We examined the possible linkage of these units to form nanoscale
cage clusters analogous to those formed from uranyl peroxide polyhedra.
Quantum chemical calculations at the density functional and multiconfigurational
wave function levels show that the uranyl–persulfide–uranyl,
U–(S<sub>2</sub>)–U, dihedral angles of model clusters
are bent due to partial covalent interactions. We propose that this
bent interaction will favor assembly of uranyl ions through persulfide
bridges into curved structures, potentially similar to the family
of nanoscale cage clusters built from uranyl peroxide polyhedra. However,
the U–(S<sub>2</sub>)–U dihedral angles predicted for
several model structures may be too tight for them to self-assemble
into cage clusters with fullerene topologies in the absence of other
uranyl-ion bridges that adopt a flatter configuration. Assembly of
species such as [(UO<sub>2</sub>)Â(S<sub>2</sub>)Â(SH)<sub>4</sub>]<sup>4–</sup> or [(UO<sub>2</sub>)Â(S<sub>2</sub>)Â(C<sub>2</sub>O<sub>4</sub>)<sub>4</sub>]<sup>4–</sup> into fullerene topologies
with ∼60 vertices may be favored by use of large counterions
Species Plantarum
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Series of Uranyl-4,4′-biphenyldicarboxylates and an Occurrence of a Cation–Cation Interaction: Hydrothermal Synthesis and in Situ Raman Studies
Three uraniumÂ(VI)-bearing materials
were synthesized hydrothermally using the organic ligand 4,4′-biphenyldicarboxylic
acid: (UO<sub>2</sub>)Â(C<sub>14</sub>O<sub>4</sub>H<sub>8</sub>) (<b>1</b>); [(UO<sub>2</sub>)<sub>2</sub>(C<sub>14</sub>O<sub>4</sub>H<sub>8</sub>)<sub>2</sub>(OH)]·(NH<sub>4</sub>)Â(H<sub>2</sub>O) (<b>2</b>); (UO<sub>2</sub>)<sub>2</sub>(C<sub>14</sub>O<sub>4</sub>H<sub>8</sub>)Â(OH)<sub>2</sub> (<b>3</b>). Compound <b>1</b> was formed after 1 day at 180 °C in an acidic environment
(pH<sub>i</sub> = 4.03), and compounds <b>2</b> and <b>3</b> coformed after 3 days under basic conditions (pH<sub>i</sub> = 7.95).
Coformation of all three compounds was observed at higher pH<sub>i</sub> (9.00). Ex situ Raman spectra of single crystals of <b>1</b>–<b>3</b> were collected and analyzed for signature
peaks. In situ hydrothermal Raman data were also obtained and compared
to the ex situ Raman spectra of the title compounds in an effort to
acquire formation mechanism details. At pH<sub>i</sub> = 4.00, the
formation of <b>1</b> was suggested by in situ Raman spectra.
At an increased pH<sub>i</sub> (7.90), the in situ data implied the
formation of compounds <b>1</b> and <b>3</b>. The most
basic conditions (pH<sub>i</sub> = 9.00) yielded a complex mixture
of phases consistent with that of increased uranyl hydrolysis
Raman Spectroscopic and ESI-MS Characterization of Uranyl Peroxide Cage Clusters
Strategies for interpreting mass
spectrometric and Raman spectroscopic data have been developed to
study the structure and reactivity of uranyl peroxide cage clusters
in aqueous solution. We demonstrate the efficacy of these methods
using the three best-characterized uranyl peroxide clusters, {U<sub>24</sub>}, {U<sub>28</sub>}, and {U<sub>60</sub>}. Specifically,
we show a correlation between uranyl–peroxo–uranyl dihedral
bond angles and the position of the Raman band of the symmetric stretching
mode of the peroxo ligand, develop methods for the assignment of the
ESI mass spectra of uranyl peroxide cage clusters, and show that these
methods are generally applicable for detecting these clusters in the
solid state and solution and for extracting information about their
bonding and composition without crystallization
Series of Uranyl-4,4′-biphenyldicarboxylates and an Occurrence of a Cation–Cation Interaction: Hydrothermal Synthesis and in Situ Raman Studies
Three uraniumÂ(VI)-bearing materials
were synthesized hydrothermally using the organic ligand 4,4′-biphenyldicarboxylic
acid: (UO<sub>2</sub>)Â(C<sub>14</sub>O<sub>4</sub>H<sub>8</sub>) (<b>1</b>); [(UO<sub>2</sub>)<sub>2</sub>(C<sub>14</sub>O<sub>4</sub>H<sub>8</sub>)<sub>2</sub>(OH)]·(NH<sub>4</sub>)Â(H<sub>2</sub>O) (<b>2</b>); (UO<sub>2</sub>)<sub>2</sub>(C<sub>14</sub>O<sub>4</sub>H<sub>8</sub>)Â(OH)<sub>2</sub> (<b>3</b>). Compound <b>1</b> was formed after 1 day at 180 °C in an acidic environment
(pH<sub>i</sub> = 4.03), and compounds <b>2</b> and <b>3</b> coformed after 3 days under basic conditions (pH<sub>i</sub> = 7.95).
Coformation of all three compounds was observed at higher pH<sub>i</sub> (9.00). Ex situ Raman spectra of single crystals of <b>1</b>–<b>3</b> were collected and analyzed for signature
peaks. In situ hydrothermal Raman data were also obtained and compared
to the ex situ Raman spectra of the title compounds in an effort to
acquire formation mechanism details. At pH<sub>i</sub> = 4.00, the
formation of <b>1</b> was suggested by in situ Raman spectra.
At an increased pH<sub>i</sub> (7.90), the in situ data implied the
formation of compounds <b>1</b> and <b>3</b>. The most
basic conditions (pH<sub>i</sub> = 9.00) yielded a complex mixture
of phases consistent with that of increased uranyl hydrolysis
Systematic Evolution from Uranyl(VI) Phosphites to Uranium(IV) Phosphates
Six new uranium phosphites, phosphates, and mixed phosphate–phosphite
compounds were hydrothermally synthesized, with an additional uranyl
phosphite synthesized at room temperature. These compounds can contain
U<sup>VI</sup> or U<sup>IV</sup>, and two are mixed-valent U<sup>VI</sup>/U<sup>IV</sup> compounds. There appears to be a strong correlation
between the starting pH and reaction duration and the products that
form. In general, phosphites are more likely to form at shorter reaction
times, while phosphates form at extended reaction times. Additionally,
reduction of uranium from U<sup>VI</sup> to U<sup>IV</sup> happens
much more readily at lower pH and can be slowed with an increase in
the initial pH of the reaction mixture. Here we explore the in situ
hydrothermal redox reactions of uranyl nitrate with phosphorous acid
and alkali-metal carbonates. The resulting products reveal the evolution
of compounds formed as these hydrothermal redox reactions proceed
forward with time