Dihydro­nium tetra­chromate(VI), (H₃O)₂Cr₄O₁₃

The crystal structure of (H₃O)₂Cr₄O₁₃ is isotypic with K₂Cr₄O₁₃. The finite tetra­chromate anion in the title structure consists of four vertex-sharing CrO₄ tetra­hedra and exhibits a typical zigzag arrangement. The crystal packing is stabilized by hydrogen bonds between these anions and hydro­nium cations. The two different hydro­nium cations are surrounded by nine O atoms of tetra­chromate anions, with O...O distances ranging between 2.866 (8) and 3.282 (7) Å.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](Cr-O) = 0.005 Å
• H-atom completeness 1%
• R factor = 0.040
• wR factor = 0.110
• Data-to-parameter ratio = 15.5

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT029_ALERT_3_B _diffrn_measured_fraction_theta_full Low .......      0.946
PLAT306_ALERT_2_B Isolated Oxygen Atom (H-atoms Missing ?) .......        O1W
PLAT306_ALERT_2_B Isolated Oxygen Atom (H-atoms Missing ?) .......        O2W
PLAT934_ALERT_3_B Number of (Iobs-Icalc)/SigmaW .gt. 10 Outliers .          1

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                    2
           From the CIF: _chemical_formula_weight           454.05
           TEST: Calculate formula weight from _atom_site_*
           atom     mass    num     sum
           O        16.00   15.00  239.99
           H         1.01    0.00    0.00
           Cr       52.00    4.00  207.98
           Calculated formula weight              447.97
STRVA01_ALERT_4_C           Flack test results are ambiguous.
           From the CIF: _refine_ls_abs_structure_Flack    0.530
           From the CIF: _refine_ls_abs_structure_Flack_su    0.040
PLAT041_ALERT_1_C Calc. and Reported SumFormula    Strings  Differ          ?
PLAT043_ALERT_1_C Check Reported Molecular Weight ................     454.05
PLAT044_ALERT_1_C Calculated and Reported Dx Differ ..............          ?
PLAT068_ALERT_1_C Reported F000 Differs from Calcd (or Missing)...          ?
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        Cr1
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        Cr4
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          1
              Cr4 O13
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600         39
PLAT915_ALERT_3_C Low Friedel Pair Coverage ......................         78 Perc.
PLAT975_ALERT_2_C Positive Residual Density at 0.97A from O1W    .       0.42 eA-3
PLAT976_ALERT_2_C Negative Residual Density at 0.99A from O13    .      -0.49 eA-3
PLAT976_ALERT_2_C Negative Residual Density at 0.90A from O13    .      -0.48 eA-3
PLAT976_ALERT_2_C Negative Residual Density at 0.93A from O32    .      -0.42 eA-3

Alert level G
FORMU01_ALERT_1_G  There is a discrepancy between the atom counts in the
            _chemical_formula_sum and _chemical_formula_moiety. This is
            usually due to the moiety formula being in the wrong format.
            Atom count from _chemical_formula_sum:   H6 Cr4 O15
            Atom count from _chemical_formula_moiety:H9 Cr4 O16
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:H6 Cr4 O15
            Atom count from the _atom_site data:  Cr4 O15
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    2
           From the CIF: _chemical_formula_sum  Cr4 H6 O15
           TEST: Compare cell contents of formula and atom_site data

           atom    Z*formula  cif sites diff
           Cr         8.00      8.00    0.00
           H         12.00      0.00   12.00
           O         30.00     30.00    0.00
PLAT005_ALERT_5_G No _iucr_refine_instructions_details  in the CIF          ?
PLAT042_ALERT_1_G Calc. and Reported MoietyFormula Strings  Differ          ?
PLAT063_ALERT_4_G Crystal Size Likely too Large for Beam Size ....       1.00 mm
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600         40

   0 ALERT level A = Most likely a serious problem - resolve or explain
   4 ALERT level B = A potentially serious problem, consider carefully
  15 ALERT level C = Check. Ensure it is not caused by an omission or oversight
  11 ALERT level G = General information/check it is not something unexpected

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

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S1. Comment

One of the characteristic properties of the elements of group 6 of the periodic table is their ability to build anionic polyoxo compounds with the corresponding elements in high oxidation states - the so called polyoxometalates. This property is profoundly exhibited by the oxoanions of the heavier elements Mo(VI) and W(VI), whereas the respective compounds of Cr(VI), i.e. polyoxochromates, are not built readily. Despite of this fact, polyoxochromates are of chemical and industrial importance due to their high oxidation potential. Accordingly, they are used as oxidants of organic compounds (Cainelli & Cardillo, 1984) and in hexavalent chromium plating (Çengeloǧlu et al., 2003).

The title compound, (H₃O)₂Cr₄O₁₃, is only the fourth tetrachromate(VI) described and characterized by single-crystal X-ray diffraction so far. The first three are salts of alkali metals, viz. the potassium (Casari & Langer, 2005), the rubidium (Löfgren, 1973), and the caesium salt (Kolitsch, 2004). (H₃O)₂Cr₄O₁₃ was isolated from a reaction mixture containing Na₂Cr₂O₇, nitric acid and a large excess of CrO₃ along with several possibly unrelated species.

The crystal structure of (H₃O)₂Cr₄O₁₃ is isotypic with that of K₂Cr₄O₁₃ (Casari & Langer, 2005) and accordingly exhibits the space group Pc. The cell volume of (H₃O)₂(Cr₄O₁₃) is 640.80 (15) ų at room temperature. It exceeds the cell volume of the potassium analogue measured at 173 K by roughly 44 ų. The finite tetrachromate anion is composed of four condensed CrO₄ tetrahedra and exhibits the typical zigzag arrangement (Figs. 1,2) described by Casari & Langer (2005). The two hydronium ions have two crystallographically different positions. They interact with nine oxygen atoms of the tetrachromate anions through hydrogen bonds. Although the H atoms of the hydronium cations could not be located, the distances between the hydronium O atoms and the surrounding tetrachromate O atoms between 2.866 (8) and 3.282 (7) Å point to moderate to weak O—H···O hydrogen bonds. These distances are quite similar to the distances between O atoms of water molecules and dichromate ions in Na₂Cr₂O₇^.H₂O (Casari et al., 2007) which indicates hydrogen bonds of typical strength for this class of compounds.

Related literature

The title chromate is isotypic with its potassium analogue (Casari & Langer, 2005). Löfgren (1973) and Kolitsch (2004) determined the structures of the corresponding Rb and Cs salts, respectively. For industrial applications of tetrachromates, see: Cainelli & Cardillo (1984); Çengeloǧlu et al. (2003). For related bond-length data, see: Casari et al. (2007). For cell parameters of further isolated compounds stated in the experimental procedure, see: Durif & Averbuch-Pouchot (1978) and Rahman et al. (2003).

S2. Experimental

Na₂Cr₂O₇ (26 mg, 0.1 mmol) and CrO₃ (1.600 g, 16 mmol) were dissolved in 0.5 ml H₂O. This solution was added to a solution of AgClO₄ (22.5 mg, 0.1 mmol) and theobromine (18 mg, 0.1 mmol) in 16.5 ml of nitric acid. After 2.5 months crystals of (H₃O)(ClO₄) (Rahman et al., 2003) and Ag₂(Cr₂O₇) (Durif & Averbuch-Pouchot, 1978) were isolated and characterized by X-ray difractometric unit-cell determinations. Orange-red crystals of the title compound were obtained from the mother liquor after another half year.

S3. Refinement

The investigated crystal was racemically twinned, similarly to the potassium compound (Casari & Langer, 2005). The refined Flack paramter indicates a twin component ratio of 53 (4):47 (4). It was not possible to unambiguously locate the H atoms of the hydronium cations. They were therefore omitted from the refinement.

Computing details

Data collection: IPDS (Stoe & Cie, 1997); cell refinement: IPDS (Stoe & Cie, 1997); data reduction: IPDS (Stoe & Cie, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Crystal Impact, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. Hydrogen bonds between the hydronium ion (O1W) and the surrounding tetrachromate anions. The oxygen atom of the hydronium ion is shown with anisotropic displacement parameters at the 50% probability level. Chromate anions are shown as green-blue tetrahedra. Dashed lines denote O···O contacts between the cation and the anions.
	Fig. 2. Hydrogen bonding framework within the unit cell of the compound. See Fig. 1 for legend.

Dihydronium tetrachromate(VI)

Crystal data

(H3O)2Cr4O13	F(000) = 444
Mr = 454.05	Dx = 2.353 Mg m^−3
Monoclinic, Pc	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P -2yc	Cell parameters from 1754 reflections
a = 8.9765 (13) Å	θ = 1.9–28.2°
b = 7.6431 (8) Å	µ = 3.37 mm^−1
c = 9.3451 (14) Å	T = 293 K
β = 91.888 (18)°	Block, orange-red
V = 640.80 (15) Å^3	1.0 × 0.4 × 0.2 mm
Z = 2

Data collection

Stoe IPDS I diffractometer	2696 independent reflections
Radiation source: fine-focus sealed tube	2497 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.040
ϕ scans	θmax = 28.1°, θmin = 2.3°
Absorption correction: numerical [X-RED (Stoe & Cie, 2001) and X-SHAPE (Stoe & Cie, 1999)]	h = −11→11
Tmin = 0.121, Tmax = 0.314	k = −9→9
5900 measured reflections	l = −12→12

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0842P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.040	(Δ/σ)max < 0.001
wR(F^2) = 0.110	Δρmax = 0.69 e Å^−3
S = 1.06	Δρmin = −0.58 e Å^−3
2696 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
174 parameters	Extinction coefficient: 0.083 (5)
2 restraints	Absolute structure: Flack (1983), 1212 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.53 (4)

Special details

Experimental. A suitable single-crystal was carefully selected under a microscope and mounted in a glass capillary. The scattering intensities were collected on an imaging plate diffractometer (IPDS I, Stoe & Cie) equipped with a fine focus sealed tube X-ray source (Mo Kα, λ = 0.71073 Å) operating at 50 kV and 40 mA. Intensity data for the title compound were collected at room temperature by ϕ-scans in 100 frames (0 < ϕ < 200°, Δϕ = 2°, exposure time of 7 min) in the 2 Θ range 3.8 to 56.3°. Structure solution and refinement were carried out using the programs SIR92 (Altomare et al., 1993) and SHELXL97 (Sheldrick, 1997) embedded into WinGX program package (Farrugia, 1999). A numerical absorption correction (X-RED (Stoe & Cie, 2001) was applied after optimization of the crystal shape (X-SHAPE (Stoe & Cie, 1999)). The last cycles of refinement included atomic positions and anisotropic parameters for all non-hydrogen atoms. Positions of hydrogen atoms were not determined. The final difference maps were free of any chemically significant features. The refinement was based on F² for ALL reflections.

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
Cr2	0.44108 (9)	1.10692 (11)	1.05710 (8)	0.0219 (2)
Cr1	0.12169 (8)	0.92974 (12)	1.17627 (8)	0.0242 (2)
Cr3	0.44219 (9)	1.44260 (12)	0.83187 (8)	0.0263 (2)
Cr4	0.78483 (9)	1.42919 (12)	0.79827 (9)	0.0283 (2)
O21	0.4560 (6)	0.9751 (8)	0.9295 (4)	0.0437 (12)
O31	0.4312 (7)	1.3165 (9)	0.7003 (5)	0.0542 (13)
O14	0.2882 (5)	1.0642 (5)	1.1542 (4)	0.0324 (9)
O33	0.6117 (5)	1.5476 (5)	0.8324 (4)	0.0296 (8)
O12	0.1024 (6)	0.7916 (8)	1.0473 (6)	0.0497 (12)
O22	0.5891 (5)	1.0957 (7)	1.1545 (4)	0.0401 (11)
O23	0.4224 (5)	1.3239 (6)	0.9907 (4)	0.0334 (9)
O43	0.9211 (5)	1.5638 (6)	0.8196 (5)	0.0360 (10)
O11	−0.0193 (5)	1.0612 (6)	1.1705 (5)	0.0395 (11)
O13	0.1342 (5)	0.8307 (8)	1.3278 (6)	0.0522 (14)
O42	0.7792 (7)	1.3587 (12)	0.6374 (7)	0.074 (2)
O32	0.3119 (5)	1.5822 (7)	0.8197 (6)	0.0477 (13)
O41	0.8015 (6)	1.2744 (8)	0.9121 (7)	0.0595 (16)
O1W	0.0967 (6)	0.4158 (8)	1.0652 (6)	0.0469 (12)
O2W	0.7959 (6)	0.9005 (7)	0.9169 (5)	0.0456 (12)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cr2	0.0205 (3)	0.0256 (4)	0.0197 (3)	−0.0006 (3)	0.0010 (2)	0.0020 (3)
Cr1	0.0221 (4)	0.0208 (5)	0.0296 (4)	−0.0019 (3)	0.0017 (3)	0.0052 (3)
Cr3	0.0235 (4)	0.0274 (5)	0.0278 (4)	−0.0021 (3)	0.0004 (3)	0.0068 (3)
Cr4	0.0255 (4)	0.0222 (5)	0.0374 (4)	−0.0005 (3)	0.0057 (3)	−0.0052 (3)
O21	0.047 (3)	0.060 (4)	0.0242 (18)	0.010 (2)	0.0025 (17)	−0.0114 (18)
O31	0.063 (3)	0.062 (4)	0.038 (2)	−0.024 (3)	0.0033 (19)	−0.008 (2)
O14	0.034 (2)	0.029 (3)	0.0349 (19)	−0.0062 (15)	0.0083 (16)	0.0006 (13)
O33	0.0289 (19)	0.024 (2)	0.036 (2)	−0.0003 (16)	0.0045 (15)	0.0024 (14)
O12	0.048 (3)	0.035 (3)	0.065 (3)	−0.003 (2)	−0.004 (2)	−0.017 (2)
O22	0.027 (2)	0.058 (3)	0.035 (2)	−0.0030 (18)	−0.0041 (16)	0.0082 (17)
O23	0.038 (2)	0.028 (2)	0.0344 (19)	−0.0032 (18)	0.0057 (15)	0.0107 (14)
O43	0.026 (2)	0.036 (3)	0.046 (2)	−0.0044 (15)	0.0092 (17)	0.0016 (16)
O11	0.030 (2)	0.040 (3)	0.049 (2)	0.0044 (16)	0.0039 (18)	0.0018 (17)
O13	0.038 (2)	0.061 (4)	0.057 (3)	−0.010 (2)	0.002 (2)	0.034 (3)
O42	0.059 (4)	0.092 (5)	0.071 (4)	0.006 (3)	0.007 (3)	−0.047 (4)
O32	0.029 (3)	0.057 (4)	0.057 (3)	0.006 (2)	−0.0039 (19)	0.022 (2)
O41	0.048 (3)	0.034 (3)	0.097 (4)	0.002 (2)	0.010 (3)	0.026 (3)
O1W	0.044 (3)	0.051 (3)	0.046 (2)	0.007 (2)	0.0014 (19)	−0.0030 (19)
O2W	0.043 (3)	0.049 (4)	0.044 (2)	0.009 (2)	−0.0039 (19)	0.0003 (19)

Geometric parameters (Å, º)

Cr2—O21	1.570 (4)	Cr3—O31	1.563 (6)
Cr2—O22	1.588 (4)	Cr3—O32	1.584 (5)
Cr2—O14	1.701 (4)	Cr3—O33	1.720 (5)
Cr2—O23	1.776 (4)	Cr3—O23	1.754 (4)
Cr1—O13	1.606 (4)	Cr4—O41	1.595 (5)
Cr1—O12	1.607 (5)	Cr4—O42	1.596 (6)
Cr1—O11	1.615 (5)	Cr4—O43	1.606 (5)
Cr1—O14	1.831 (4)	Cr4—O33	1.836 (5)
O21—Cr2—O22	108.1 (3)	O32—Cr3—O33	109.7 (3)
O21—Cr2—O14	111.9 (2)	O31—Cr3—O23	110.0 (3)
O22—Cr2—O14	111.0 (2)	O32—Cr3—O23	108.3 (2)
O21—Cr2—O23	110.1 (3)	O33—Cr3—O23	110.7 (2)
O22—Cr2—O23	108.5 (2)	O41—Cr4—O42	112.2 (4)
O14—Cr2—O23	107.3 (2)	O41—Cr4—O43	109.7 (3)
O13—Cr1—O12	110.7 (3)	O42—Cr4—O43	109.5 (4)
O13—Cr1—O11	110.8 (3)	O41—Cr4—O33	108.1 (2)
O12—Cr1—O11	108.6 (3)	O42—Cr4—O33	109.3 (3)
O13—Cr1—O14	109.3 (2)	O43—Cr4—O33	108.0 (2)
O12—Cr1—O14	110.6 (2)	Cr2—O14—Cr1	147.5 (3)
O11—Cr1—O14	106.8 (2)	Cr3—O33—Cr4	121.6 (2)
O31—Cr3—O32	109.3 (3)	Cr3—O23—Cr2	140.1 (3)
O31—Cr3—O33	108.9 (3)