Redetermination of di-μ-hydroxido-bis­[diaqua­chlorido­dioxido­uranium(VI)] from single-crystal synchrotron data

The title compound, [(UO₂)₂Cl₂(OH)₂(H₂O)₄], was obtained unintentionally as the product of an attempted reaction between uranium(VI) oxide dihydrate, UO₃·2H₂O, and hydrogen bis­(trifluoro­methyl­sulfon­yl)imide (HTf₂N), in an experiment to obtain crystals of uranyl bis­(trifluoro­methyl­sulfon­yl)imide, UO₂(Tf₂N)₂·xH₂O. The structure consists of neutral dimers of uranyl (UO₂²⁺) units, double bridged by OH⁻ anions. Each uranyl unit is surrounded by one Cl and four O atoms, which form an irregular penta­gon, in a plane perpendicular to the linear uranyl groups. The coordination geometry around each U atom can be considered to be distorted penta­gonal-bipyramidal. In the crystal structure the uranyl dimers are connected to each other by hydrogen-bonding inter­actions [O...Cl = 3.23 (1) Å].

Key indicators

• Single-crystal synchrotron study
• T = 100 K
• Mean [sigma](U-O) = 0.009 Å
• H-atom completeness 1%
• R factor = 0.045
• wR factor = 0.131
• Data-to-parameter ratio = 14.5

checkCIF/PLATON results

No syntax errors found



Alert level A
DIFF019_ALERT_1_A  _diffrn_standards_number is missing
            Number of standards used in measurement.

Author Response: not applicable

DIFF020_ALERT_1_A  _diffrn_standards_interval_count and
            _diffrn_standards_interval_time are missing. Number of measurements
            between standards or time (min) between standards.

Author Response: not applicable

DIFF022_ALERT_1_A  _diffrn_standards_decay_% is missing
            Percentage decrease in standards intensity.

Author Response: not applicable

REFI014_ALERT_1_G  _refine_ls_hydrogen_treatment is missing
            Code for H-atom treatment.
            The following tests will not be performed
            HYDTR_01
PLAT971_ALERT_2_A Large Calcd. Non-Metal Positive Residual Density       4.26 eA-3
PLAT924_ALERT_1_A The Reported and Calculated Rho(min) Differ by .      35.64 eA-3
PLAT926_ALERT_1_A Reported and Calculated   R1 * 100.0 Differ by .     -11.34
PLAT927_ALERT_1_A Reported and Calculated  wR2 * 100.0 Differ by .     -26.31

Alert level B
CHEMS01_ALERT_1_B  The sum formula contains elements in the wrong order.
            H  precedes Cl
            Sequence must be alphabetical for inorganic structures.
PLAT971_ALERT_2_B Large Calcd. Non-Metal Positive Residual Density       3.28 eA-3
PLAT971_ALERT_2_B Large Calcd. Non-Metal Positive Residual Density       2.86 eA-3
PLAT971_ALERT_2_B Large Calcd. Non-Metal Positive Residual Density       2.61 eA-3
PLAT928_ALERT_1_B Reported and Calculated    S value   Differ by .      -1.73

Alert level C
CHEMW03_ALERT_2_C The ratio of given/expected molecular weight as
            calculated from the _atom_site* data lies outside
            the range 0.99 <> 1.01
           From the CIF: _cell_formula_units_Z                    4
           From the CIF: _chemical_formula_weight           717.04
           TEST: Calculate formula weight from _atom_site_*
           atom     mass    num     sum
           O        16.00   10.00  159.99
           Cl       35.45    2.00   70.91
           U       238.03    2.00  476.06
           Calculated formula weight              706.95
THETM01_ALERT_3_C  The value of sine(theta_max)/wavelength is less than 0.590
            Calculated sin(theta_max)/wavelength =    0.5783
PLAT431_ALERT_2_C Short Inter HL..A Contact  Cl1    ..  O8      ..       3.08 Ang.
PLAT431_ALERT_2_C Short Inter HL..A Contact  Cl2    ..  O3      ..       3.11 Ang.
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.578         22
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          7
PLAT971_ALERT_2_C Large Calcd. Non-Metal Positive Residual Density       2.41 eA-3
PLAT971_ALERT_2_C Large Calcd. Non-Metal Positive Residual Density       2.36 eA-3
PLAT971_ALERT_2_C Large Calcd. Non-Metal Positive Residual Density       2.35 eA-3
PLAT971_ALERT_2_C Large Calcd. Non-Metal Positive Residual Density       2.35 eA-3
PLAT971_ALERT_2_C Large Calcd. Non-Metal Positive Residual Density       2.32 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -2.36 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -2.29 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -2.29 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -2.27 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -2.11 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -2.07 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -2.01 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -2.00 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.98 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.98 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.96 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.92 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.92 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.82 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.81 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.80 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.79 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.78 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.77 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.76 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.75 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.75 eA-3
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.74 eA-3
PLAT041_ALERT_1_C Calc. and Reported SumFormula    Strings  Differ          ?
PLAT042_ALERT_1_C Calc. and Reported MoietyFormula Strings  Differ          ?
PLAT043_ALERT_1_C Check Reported Molecular Weight ................     717.04
PLAT044_ALERT_1_C Calculated and Reported Dx Differ ..............          ?
PLAT774_ALERT_1_C Suspect X-Y Bond in CIF:   U1     --  U2      ..       3.95 Ang.
PLAT925_ALERT_1_C The Reported and Calculated Rho(max) Differ by .       1.65 eA-3

Alert level G
FORMU01_ALERT_2_G  There is a discrepancy between the atom counts in the
            _chemical_formula_sum and the formula from the _atom_site* data.
            Atom count from _chemical_formula_sum:H10 Cl2 O10 U2
            Atom count from the _atom_site data:  Cl2 O10 U2
  ABSMU_01  Radiation type not identified. Calculation of
            _exptl_absorpt_correction_mu not performed.
CELLZ01_ALERT_1_G Difference between formula and atom_site contents detected.
CELLZ01_ALERT_1_G WARNING: H atoms missing from atom site list. Is this intentional?
           From the CIF: _cell_formula_units_Z    4
           From the CIF: _chemical_formula_sum  H10 Cl2 O10 U2
           TEST: Compare cell contents of formula and atom_site data

           atom    Z*formula  cif sites diff
           H         40.00      0.00   40.00
           Cl         8.00      8.00    0.00
           O         40.00     40.00    0.00
           U          8.00      8.00    0.00
PLAT092_ALERT_4_G Check: Wavelength given is not Cu,Mo or Ag Ka ..       0.77 Ang.
PLAT128_ALERT_4_G Non-standard setting of Space-group P21/c   ....      P21/n

   7 ALERT level A = In general: serious problem
   5 ALERT level B = Potentially serious problem
  40 ALERT level C = Check and explain
   6 ALERT level G = General alerts; check

  17 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
  36 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

S1. Comment

Uranyl bis(trifluoromethylsulfonyl)imide is a useful starting material for the study of the spectroscopic properties of uranyl complexes in ionic liquids (Nockemann et al., 2007; Binnemans, 2007). The presence of chloride ions in the final product was surprising, because no chloride had been added to the reaction mixture. The chloride contamination of the reaction mixture can probably be attributed to chloride impurities in the aqueous hydrogen bis(trifluoromethylsulfonyl)imide solution. It should be noted that the presence of chloride traces in the HTf₂N solution is not surprising, since the bis(trifluoromethylsulfonyl)imide anion can be synthesized by reaction between trifluorometylsulfonylamide and trifluoromethylsulfonyl chloride. Moreover, the uranyl ion has a strong tendency to form chloro complexes when both chloride ions and bis(trifluoromethylsulfonyl)imide ions are present (Nockemann et al., 2007). The acidity of coordinated water molecules, especially those in bridging positions, easily leads to the formation of hydroxo dimers or oligomers in neutral aqueous medium (Åberg, 1970; Tsushima et al., 2007).

The structure of the title compound [(UO₂)₂(OH)₂Cl₂(H₂O)₄] (Figure 1) is analogous to the structure as previously determined by the Weissenberg photographical technique (Åberg, 1969), with ICSD entry 31006 (ICSD Version 1.4.6) (Bergerhoff et al., 1983; ICSD, 2009).

However, in the latter structure, no meaningful anisotropic refinement could be carried out for the positions of the oxygen atoms (Åberg, 1969).

The asymmetric unit consists of uranyl dimers, double bridged by OH^--anions. Each uranyl cation is surrounded by one chlorine and four oxygen atoms, which form an irregular pentagon, in a plane perpendicular to the linear uranyls. The coordination geometry around each uranium atom can be considered as a distorted pentagonal bipyramid (Figure 2). As in the structure of Åberg, no hydrogen atoms could be unambiguously located on the water molecules, nor on the hydroxyl anions.

The U1—U2 distance in a uranyl dimer is 3.949 (1) Å. U—Cl distances are 2.751 (3) Å and 2.772 (4) Å, for U1—Cl1 and U2—Cl2, respectively.

The uranyl U=O distances vary between 1.746 (9) Å and 1.790 (9) Å, while the two uranyl groups themselves are quasi-linear, with O=U=O angles of 177.7 (4)° and 177.8 (4)°, respectively.

The U—O distances vary between 2.37 (1) Å and 2.49 (1) Å. The U—O distances within the bridge formed by O9 and O10 range from 2.37 (1) to 2.382 (9) Å. The most lateral positioned oxygen atoms O4 and O7 show both a larger U—O distance of 2.49 (1) Å.

Notably, the a- and c-axis of the structure of Åberg are interchanged, compared to the reported structure, hence caution should be paid when comparing the crystal packing environments.

As in the previously reported structure (Åberg, 1969), hydrogen bonding is observed between the dimers, mainly extending in the (001)-plane in the [100] direction (Figure 3). These hydrogen bonds are directed from uranium-coordinating oxygen atoms to chloride atoms on a neighboring dimer: Cl1···O8 (3.08 (1) Å), Cl2···O3 (3.11 (1) Å) and between bridging hydroxyl oxygen atoms and uranyl oxygen atoms: O10···O2 (2.80 (1) Å), O9···O5 (2.87 (1) Å). The same bridging hydroxyl oxygen atoms O9 and O10 are further connected through hydrogen bonds in the [010] direction (b-direction) to the uranium coordinated oxygen atoms O8 (2.66 (1) Å) and O3 (2.65 (1) Å), respectively.

Only one hydrogen bond is observed between one of the lateral coordinating oxygen atoms O4 and the Cl2-atom of a subsequent dimer (3.23 (1) Å), which additionally links the dimers together in the [001] direction (c-direction).

Related literature

For general background to the use of uranyl bis(trifluoromethylsulfonyl)imide as a starting material for the study of the spectroscopic properties of uranyl complexes in ionic liquids, see: Nockemann et al. (2007); Binnemans (2007). For related structures, see: Åberg (1969); Åberg (1970); Tsushima et al. (2007). For databases of inorganic structures, see: Bergerhoff et al. (1983); ICSD (2009).

S2. Experimental

Uranium(VI)oxide dihydrate UO₃.2H₂O (966 mg, 3 mmol), suspended in 10 ml of deionized water. To this suspension, 2 equivalents (2.4 g) of a 80% solution of hydrogen bis(trifluoromethylsulfonyl)imide (from IoLiTec) was added and the mixture was refluxed while stirred for 1 h. After leaving the solution to cool to room temperature, the excess of UO₃ was filtered off and the clear liquid was evaporated to dryness using a rotary evaporator. The remaining thick slurry was further dried at 60 °C using a Schlenk apparatus for 36 h, yielding 885 mg of a glassy residue. A small solid sample was removed from the batch and the remaining solid was redissolved in a minimal amount of water, while slightly heating using a heat gun. The liquid was transferred to a small crystallization dish and cooled to 5 °C in a refrigerator. A very small amount of the dry solid product was then carefully added to the solution and the crystallization dish was put in a desiccator at room temperature. After 10 weeks, small hygroscopic crystals were obtained.

S3. Refinement

No hydrogen atoms could be unambiguously located on the water molecules, nor on the hydroxyl anions.

Computing details

Data collection: MAR345 Program Manual (Mar, 2000); cell refinement: CrysAlis PRO (Oxford Diffraction, 2006); data reduction: CrysAlis PRO (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLUTON (Spek, 2009); software used to prepare material for publication: PLATON (Spek, 2009).

Figures

	Fig. 1. Coordination geometry of the title compound, showing the atom-labelling scheme of the asymmetric unit and 50% probability displacement ellipsoids.
	Fig. 2. Packing diagram of the title compound, showing the hydrogen bonding between symmetry equivalent molecules.

Di-µ-hydroxido-bis[diaquachloridodioxidouranium(VI)]

Crystal data

[U2Cl2O4(OH)2(H2O)4]	F(000) = 1232
Mr = 717.04	Dx = 4.131 Mg m^−3
Monoclinic, P21/n	Synchrotron radiation, λ = 0.77000 Å
Hall symbol: -P 2yn	Cell parameters from 4751 reflections
a = 10.712 (2) Å	θ = 2.3–26.2°
b = 6.1212 (12) Å	µ = 63.63 mm^−1
c = 17.662 (4) Å	T = 100 K
β = 95.47 (3)°	Block, yellow
V = 1152.8 (4) Å^3	0.15 × 0.1 × 0.1 mm
Z = 4

Data collection

ESRF, SNBL, BM01A diffractometer	1846 independent reflections
Radiation source: bending magnet	1620 reflections with I > 2σ(I)
Double crystal monochromator	Rint = 0.067
φ scans	θmax = 26.4°, θmin = 2.3°
Absorption correction: multi-scan (SCALE3 in ABSPACK; Oxford Diffraction, 2006)	h = −12→12
Tmin = 0.008, Tmax = 0.056	k = 0→7
13020 measured reflections	l = 0→20

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.045	Secondary atom site location: difference Fourier map
wR(F^2) = 0.131	w = 1/[σ^2(Fo^2) + (0.0885P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.11	(Δ/σ)max < 0.001
1846 reflections	Δρmax = 3.37 e Å^−3
127 parameters	Δρmin = −1.67 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
U1	0.45262 (4)	0.79563 (9)	0.83956 (3)	0.0174 (2)
U2	0.54899 (4)	1.08385 (9)	0.65373 (3)	0.0172 (2)
Cl1	0.3096 (3)	1.0768 (5)	0.91681 (19)	0.0219 (8)
Cl2	0.6957 (3)	0.8008 (6)	0.5776 (2)	0.0228 (8)
O1	0.5897 (9)	0.8918 (15)	0.8900 (5)	0.023 (2)
O2	0.3157 (9)	0.6944 (16)	0.7847 (5)	0.020 (2)
O3	0.5411 (9)	0.4358 (15)	0.8468 (5)	0.020 (2)
O4	0.3839 (10)	0.5906 (16)	0.9501 (6)	0.029 (2)
O5	0.6817 (9)	1.1917 (16)	0.7088 (5)	0.021 (2)
O6	0.4135 (9)	0.9824 (15)	0.6013 (5)	0.020 (2)
O7	0.6135 (10)	1.2896 (16)	0.5424 (6)	0.028 (2)
O8	0.4552 (9)	1.4395 (16)	0.6490 (5)	0.021 (2)
O9	0.5643 (8)	0.7649 (17)	0.7297 (5)	0.019 (2)
O10	0.4367 (9)	1.1133 (14)	0.7628 (5)	0.018 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
U1	0.0166 (4)	0.0182 (4)	0.0173 (3)	0.00014 (19)	0.0014 (2)	0.00002 (17)
U2	0.0173 (4)	0.0174 (4)	0.0169 (3)	−0.00055 (19)	0.0016 (2)	−0.00013 (17)
Cl1	0.0245 (19)	0.0218 (18)	0.0200 (17)	0.0052 (14)	0.0052 (14)	−0.0007 (13)
Cl2	0.0264 (19)	0.0220 (18)	0.0205 (16)	0.0029 (14)	0.0048 (14)	−0.0024 (13)
O1	0.027 (6)	0.019 (5)	0.023 (5)	0.004 (4)	0.003 (4)	−0.001 (4)
O2	0.025 (5)	0.021 (6)	0.014 (4)	−0.007 (4)	0.000 (4)	−0.003 (4)
O3	0.021 (5)	0.016 (5)	0.022 (5)	0.009 (4)	−0.002 (4)	0.002 (4)
O4	0.028 (6)	0.026 (6)	0.034 (6)	0.006 (5)	0.012 (5)	0.003 (4)
O5	0.015 (5)	0.026 (6)	0.021 (5)	−0.011 (4)	0.000 (4)	0.000 (4)
O6	0.020 (5)	0.017 (5)	0.023 (5)	−0.002 (4)	−0.006 (4)	0.002 (4)
O7	0.031 (6)	0.022 (6)	0.032 (6)	−0.011 (5)	0.004 (5)	0.004 (4)
O8	0.019 (5)	0.022 (5)	0.021 (5)	0.003 (4)	−0.004 (4)	0.004 (4)
O9	0.013 (5)	0.023 (5)	0.019 (5)	−0.008 (4)	−0.007 (4)	0.003 (4)
O10	0.023 (5)	0.011 (5)	0.018 (5)	−0.004 (4)	−0.002 (4)	−0.002 (4)

Geometric parameters (Å, º)

U1—O1	1.746 (10)	U2—O6	1.759 (9)
U1—O2	1.789 (10)	U2—O5	1.772 (9)
U1—O10	2.367 (9)	U2—O9	2.366 (10)
U1—O9	2.382 (9)	U2—O10	2.373 (9)
U1—O3	2.397 (9)	U2—O8	2.396 (10)
U1—O4	2.490 (10)	U2—O7	2.488 (10)
U1—Cl1	2.751 (3)	U2—Cl2	2.772 (3)
U1—U2	3.9492 (10)
O1—U1—O2	177.7 (4)	O6—U2—O9	90.9 (4)
O1—U1—O10	91.5 (4)	O5—U2—O9	89.3 (4)
O2—U1—O10	87.9 (4)	O6—U2—O10	89.8 (4)
O1—U1—O9	88.8 (4)	O5—U2—O10	88.2 (4)
O2—U1—O9	88.9 (4)	O9—U2—O10	67.4 (3)
O10—U1—O9	67.2 (3)	O6—U2—O8	88.9 (4)
O1—U1—O3	88.5 (4)	O5—U2—O8	89.6 (4)
O2—U1—O3	90.6 (4)	O9—U2—O8	140.9 (3)
O10—U1—O3	142.3 (3)	O10—U2—O8	73.5 (3)
O9—U1—O3	75.2 (3)	O6—U2—O7	92.3 (4)
O1—U1—O4	93.8 (4)	O5—U2—O7	88.7 (4)
O2—U1—O4	87.8 (4)	O9—U2—O7	148.9 (3)
O10—U1—O4	148.5 (3)	O10—U2—O7	143.5 (3)
O9—U1—O4	143.9 (3)	O8—U2—O7	70.1 (3)
O3—U1—O4	68.9 (3)	O6—U2—Cl2	90.1 (3)
O1—U1—Cl1	91.0 (3)	O5—U2—Cl2	92.1 (3)
O2—U1—Cl1	91.1 (3)	O9—U2—Cl2	75.4 (2)
O10—U1—Cl1	76.0 (2)	O10—U2—Cl2	142.7 (2)
O9—U1—Cl1	143.1 (3)	O8—U2—Cl2	143.8 (2)
O3—U1—Cl1	141.7 (2)	O7—U2—Cl2	73.7 (3)
O4—U1—Cl1	72.9 (2)	O6—U2—U1	90.7 (3)
O1—U1—U2	90.0 (3)	O5—U2—U1	88.3 (3)
O2—U1—U2	88.3 (3)	O9—U2—U1	33.8 (2)
O10—U1—U2	33.6 (2)	O10—U2—U1	33.5 (2)
O9—U1—U2	33.6 (2)	O8—U2—U1	107.0 (2)
O3—U1—U2	108.7 (2)	O7—U2—U1	175.8 (2)
O4—U1—U2	175.4 (3)	Cl2—U2—U1	109.21 (8)
Cl1—U1—U2	109.56 (7)	U2—O9—U1	112.6 (4)
O6—U2—O5	177.8 (4)	U1—O10—U2	112.9 (4)