supplementary materials


Acta Cryst. (2013). E69, i13    [ doi:10.1107/S1600536813001608 ]

Dihydronium tetrachromate(VI), (H3O)2Cr4O13

V. Kulikov and G. Meyer

Abstract top

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.

Comment top

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) Å3 at room temperature. It exceeds the cell volume of the potassium analogue measured at 173 K by roughly 44 Å3. 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 top

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).

Experimental top

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.

Refinement top

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 top

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 top
[Figure 1] 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.
[Figure 2] Fig. 2. Hydrogen bonding framework within the unit cell of the compound. See Fig. 1 for legend.
Dihydronium tetrachromate(VI) top
Crystal data top
(H3O)2Cr4O13F(000) = 444
Mr = 454.05Dx = 2.353 Mg m3
Monoclinic, PcMo Kα radiation, λ = 0.71073 Å
Hall symbol: P -2ycCell parameters from 1754 reflections
a = 8.9765 (13) Åθ = 1.9–28.2°
b = 7.6431 (8) ŵ = 3.37 mm1
c = 9.3451 (14) ÅT = 293 K
β = 91.888 (18)°Block, orange-red
V = 640.80 (15) Å31.0 × 0.4 × 0.2 mm
Z = 2
Data collection top
Stoe IPDS I
diffractometer
2696 independent reflections
Radiation source: fine-focus sealed tube2497 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.040
φ scansθmax = 28.1°, θmin = 2.3°
Absorption correction: numerical
[X-RED (Stoe & Cie, 2001) and X-SHAPE (Stoe & Cie, 1999)]
h = 1111
Tmin = 0.121, Tmax = 0.314k = 99
5900 measured reflectionsl = 1212
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: full w = 1/[σ2(Fo2) + (0.0842P)2]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.040(Δ/σ)max < 0.001
wR(F2) = 0.110Δρmax = 0.69 e Å3
S = 1.06Δρmin = 0.58 e Å3
2696 reflectionsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
174 parametersExtinction coefficient: 0.083 (5)
2 restraintsAbsolute structure: Flack (1983), 1212 Friedel pairs
Primary atom site location: structure-invariant direct methodsFlack parameter: 0.53 (4)
Crystal data top
(H3O)2Cr4O13V = 640.80 (15) Å3
Mr = 454.05Z = 2
Monoclinic, PcMo Kα radiation
a = 8.9765 (13) ŵ = 3.37 mm1
b = 7.6431 (8) ÅT = 293 K
c = 9.3451 (14) Å1.0 × 0.4 × 0.2 mm
β = 91.888 (18)°
Data collection top
Stoe IPDS I
diffractometer
2696 independent reflections
Absorption correction: numerical
[X-RED (Stoe & Cie, 2001) and X-SHAPE (Stoe & Cie, 1999)]
2497 reflections with I > 2σ(I)
Tmin = 0.121, Tmax = 0.314Rint = 0.040
5900 measured reflectionsθmax = 28.1°
Refinement top
R[F2 > 2σ(F2)] = 0.040?
wR(F2) = 0.110Δρmax = 0.69 e Å3
S = 1.06Δρmin = 0.58 e Å3
2696 reflectionsAbsolute structure: Flack (1983), 1212 Friedel pairs
174 parametersFlack parameter: 0.53 (4)
2 restraints
Special details top

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 (Å2) top
xyzUiso*/Ueq
Cr20.44108 (9)1.10692 (11)1.05710 (8)0.0219 (2)
Cr10.12169 (8)0.92974 (12)1.17627 (8)0.0242 (2)
Cr30.44219 (9)1.44260 (12)0.83187 (8)0.0263 (2)
Cr40.78483 (9)1.42919 (12)0.79827 (9)0.0283 (2)
O210.4560 (6)0.9751 (8)0.9295 (4)0.0437 (12)
O310.4312 (7)1.3165 (9)0.7003 (5)0.0542 (13)
O140.2882 (5)1.0642 (5)1.1542 (4)0.0324 (9)
O330.6117 (5)1.5476 (5)0.8324 (4)0.0296 (8)
O120.1024 (6)0.7916 (8)1.0473 (6)0.0497 (12)
O220.5891 (5)1.0957 (7)1.1545 (4)0.0401 (11)
O230.4224 (5)1.3239 (6)0.9907 (4)0.0334 (9)
O430.9211 (5)1.5638 (6)0.8196 (5)0.0360 (10)
O110.0193 (5)1.0612 (6)1.1705 (5)0.0395 (11)
O130.1342 (5)0.8307 (8)1.3278 (6)0.0522 (14)
O420.7792 (7)1.3587 (12)0.6374 (7)0.074 (2)
O320.3119 (5)1.5822 (7)0.8197 (6)0.0477 (13)
O410.8015 (6)1.2744 (8)0.9121 (7)0.0595 (16)
O1W0.0967 (6)0.4158 (8)1.0652 (6)0.0469 (12)
O2W0.7959 (6)0.9005 (7)0.9169 (5)0.0456 (12)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cr20.0205 (3)0.0256 (4)0.0197 (3)0.0006 (3)0.0010 (2)0.0020 (3)
Cr10.0221 (4)0.0208 (5)0.0296 (4)0.0019 (3)0.0017 (3)0.0052 (3)
Cr30.0235 (4)0.0274 (5)0.0278 (4)0.0021 (3)0.0004 (3)0.0068 (3)
Cr40.0255 (4)0.0222 (5)0.0374 (4)0.0005 (3)0.0057 (3)0.0052 (3)
O210.047 (3)0.060 (4)0.0242 (18)0.010 (2)0.0025 (17)0.0114 (18)
O310.063 (3)0.062 (4)0.038 (2)0.024 (3)0.0033 (19)0.008 (2)
O140.034 (2)0.029 (3)0.0349 (19)0.0062 (15)0.0083 (16)0.0006 (13)
O330.0289 (19)0.024 (2)0.036 (2)0.0003 (16)0.0045 (15)0.0024 (14)
O120.048 (3)0.035 (3)0.065 (3)0.003 (2)0.004 (2)0.017 (2)
O220.027 (2)0.058 (3)0.035 (2)0.0030 (18)0.0041 (16)0.0082 (17)
O230.038 (2)0.028 (2)0.0344 (19)0.0032 (18)0.0057 (15)0.0107 (14)
O430.026 (2)0.036 (3)0.046 (2)0.0044 (15)0.0092 (17)0.0016 (16)
O110.030 (2)0.040 (3)0.049 (2)0.0044 (16)0.0039 (18)0.0018 (17)
O130.038 (2)0.061 (4)0.057 (3)0.010 (2)0.002 (2)0.034 (3)
O420.059 (4)0.092 (5)0.071 (4)0.006 (3)0.007 (3)0.047 (4)
O320.029 (3)0.057 (4)0.057 (3)0.006 (2)0.0039 (19)0.022 (2)
O410.048 (3)0.034 (3)0.097 (4)0.002 (2)0.010 (3)0.026 (3)
O1W0.044 (3)0.051 (3)0.046 (2)0.007 (2)0.0014 (19)0.0030 (19)
O2W0.043 (3)0.049 (4)0.044 (2)0.009 (2)0.0039 (19)0.0003 (19)
Geometric parameters (Å, º) top
Cr2—O211.570 (4)Cr3—O311.563 (6)
Cr2—O221.588 (4)Cr3—O321.584 (5)
Cr2—O141.701 (4)Cr3—O331.720 (5)
Cr2—O231.776 (4)Cr3—O231.754 (4)
Cr1—O131.606 (4)Cr4—O411.595 (5)
Cr1—O121.607 (5)Cr4—O421.596 (6)
Cr1—O111.615 (5)Cr4—O431.606 (5)
Cr1—O141.831 (4)Cr4—O331.836 (5)
O21—Cr2—O22108.1 (3)O32—Cr3—O33109.7 (3)
O21—Cr2—O14111.9 (2)O31—Cr3—O23110.0 (3)
O22—Cr2—O14111.0 (2)O32—Cr3—O23108.3 (2)
O21—Cr2—O23110.1 (3)O33—Cr3—O23110.7 (2)
O22—Cr2—O23108.5 (2)O41—Cr4—O42112.2 (4)
O14—Cr2—O23107.3 (2)O41—Cr4—O43109.7 (3)
O13—Cr1—O12110.7 (3)O42—Cr4—O43109.5 (4)
O13—Cr1—O11110.8 (3)O41—Cr4—O33108.1 (2)
O12—Cr1—O11108.6 (3)O42—Cr4—O33109.3 (3)
O13—Cr1—O14109.3 (2)O43—Cr4—O33108.0 (2)
O12—Cr1—O14110.6 (2)Cr2—O14—Cr1147.5 (3)
O11—Cr1—O14106.8 (2)Cr3—O33—Cr4121.6 (2)
O31—Cr3—O32109.3 (3)Cr3—O23—Cr2140.1 (3)
O31—Cr3—O33108.9 (3)
Acknowledgements top

VK is grateful to the Studienstiftung des Deutschen Volkes for a PhD scholarship.

references
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