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Dicaesium tetrachromium(VI) tridecaoxide, Cs2Cr4O13, contains finite [Cr4O13]2− anions composed of four corner-linked CrO4 tetrahedra. These anions are linked by Cs+ cations whose Cs—O bond lengths range between 3.015 (2) and ∼3.7 Å. Although Cs2Cr4O13 is not isotypic with its NH4, K or Rb analogs, the [Cr4O13]2− anions in all these compounds exhibit a similar zigzag-like geometry.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103029068/iz1038sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270103029068/iz1038Isup2.hkl
Contains datablock I

Comment top

Three alkali chromates containing polymerized CrO4 tetrahedra were recently obtained during attempts to prepare kröhnkite [Na2CuII(SVIO4)2·2H2O]-type chromate oxysalts (Fleck et al., 2002; Fleck & Kolitsch, 2003). The crystal structures of two of these compounds, α-Cs2Cr3O10 and Rb2Cr2O7 (a new, fourth modification) were characterized by Kolitsch (2003a,b). The present article reports the structure of the third polychromate, Cs2Cr4O13, which has a structure type previously unknown among alkali chromates.

The title compound contains two nonequivalent Cs atoms, four Cr atoms and 13 O atoms, all of which are in general positions. The main building unit in the crystal structure is a discrete [Cr4O13]2− anion, in which four CrO4 tetrahedra are joined via common corners into a finite zigzag-like chain (Figs. 1 and 2). This anion, to be discussed further below, is counterbalanced by the two Cs+ cations, which are both irregularly coordinated to ten O atoms within 3.53 Å. For each of the Cs+ cations there exist two additional, fairly remote, O-atom neighbors (at distances of between 3.67 and 3.80 Å; Table 1), which are not considered as ligands. The Cs+ cations are characterized by slightly different mean Cs—O bond lengths [mean Cs1—O = 3.202 Å and mean Cs2—O = 3.304 Å]. Bond-valence sums for all atoms were calculated using the metal–O parameters of Brese & O'Keeffe (1991). For the metal atoms, the bond-valence sums are 5.93 (Cr1), 5.99 (Cr2), 6.00 (Cr3), 6.08 (Cr4), 1.27 (Cs1) and 0.97 (Cs2) valence units (v.u.), if an arbitrary 'cut-off limit' at a Cs—O distance of 3.53 Å is chosen. Bond-valence sums of the O atoms are 2.11 (O1), 1.93 (O2), 1.99 (O3), 2.23 (O4), 1.88 (O5), 1.90 (O6), 2.18 (O7), 1.90 (O8), 2.01 (O9), 2.19 (O10), 2.07 (O11), 2.03 (O12) and 1.84 (O13) v.u.. The `unusually' high value obtained for atom Cs1 reflects the insufficiently flexible bond-valence parameters for very large cations, whereas the `unusually' high values calculated for the Obridge atoms O4, O7 and O10 (cf. Fig. 2) are caused by the inflexibility of these parameters in the case of strongly distorted polyhedra (compare also the difficulties reported during the calculation of bond-valence sums for the atoms in α-Cs2Cr3O10; Kolitsch, 2003a).

Cs2Cr4O13 represents a new structure type among alkali tetrachromates. However, the three structurally characterized chemical analogues Rb2Cr4O13 (Löfgren, 1971, 1973), K2Cr4O13 (Löfgren, unpublished, cited in Blum & Tran Qui Duc, 1979), and (NH4)2Cr4O13 (Blum & Tran Qui Duc, 1979), which are all isotypic (monoclinic, space group P21/c, with a ~17.8 Å, b ~7.7 Å, c ~9.4 Å, β ~92°), contain similar zigzag-like [Cr4O13]2− anions. Only the mutual arrangement between these anions and the alkali cations is different (Fig. 3). The zigzag-like character of the tetrachromate anion may be explained by the need to achieve a configuration with minimum electrostatic repulsion between adjacent CrO4 tetrahedra. The crystal structure of CrO3 (Byström & Wilhelmi, 1950) consists of infinite zigzag-like chains of corner-linked CrO4 tetrahedra, which, as shown in Fig. 4, are topologically fairly similar to the finite chains in Cs2Cr4O13 (the similarity is less pronounced in the case of Rb2Cr4O13). [It must be noted here that the structure model reported for K2Cr4O13 by Golovachev et al. (1970) and Kuz'min et al. (1972) appears topologically identical to that of the Rb analogue, although these authors give a different, possibly erroneous space group (Pc) and possibly erroneous unit-cell parameters (a is halved with respect to the otherwise similar cell data given for the Rb analogue).]

The four CrO4 tetrahedra in the [Cr4O13]2− anion exhibit similar mean Cr—O bond lengths [mean Cr1—O = 1.660 Å, Cr2—O = 1.653 Å, Cr3—O = 1.654 Å and Cr4—O = 1.654 Å]. The longest Cr—O bonds [Cr1—O4 = 1.832 (2) Å and Cr4—O10 = 1.846 (2) Å] are those between the bridging O atoms (O4 and O7) and the terminal Cr1 and Cr4 atoms (Table 1 and Fig. 2), a situation similar to that encountered in alkali trichromates M2Cr3O10 (M = alkali metal; e.g., Kolitsch, 2003a, and references therein). The observation of Löfgren (1973) that the deformation of CrO4 tetrahedra in a given (poly)chromate increases with the number of tetrahedra forming the anionic chain is confirmed by the structure of the title compound.

The O—Cr—O angles in all four CrO4 tetrahedra do not deviate significantly from ideal tetrahedral angles (Table 1). The Cr—Obridge—Cr bond angles lie within a narrow range of between about 132 and 136° (Table 1). The angular range is much larger in Rb2Cr4O13 (120.5– 147.2°; Löfgren, 1973). The angular values are slightly smaller than those in the orthorhombic caesium trichromate polymorph (α- Cs2Cr3O10; Kolitsch, 2003a) but larger than those in the trigonal polymorph (β-Cs2Cr3O10; Mattes & Meschede, 1973). Thus these Cr—Obridge—Cr bond angles seem to be strongly dependent on the mutual arrangement between the chromate anions and the alkali cations in a given polychromate structure.

Experimental top

The title compound crystallized from an acidic solution (pH 2–3) containing dissolved CrO3, Cs2CO3 and CdCO3. On slow evaporation at room temperature, blocky dark-orange crystals of β-Cs2Cr3O10 (Mattes & Meschede, 1973) precipitated from this solution. During the course of several weeks, these crystals reacted with the mother liquid, forming lath-like-to-acicular crystals of Cs2Cr4O13, of up to several millimeters in length, which protruded from the surface of the β-Cs2Cr3O10 crystals.

Computing details top

Data collection: COLLECT (Nonius, 2003); cell refinement: HKL SCALEPACK (Otwinowski & Minor 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Shape Software, 1999) and ORTEP-3 for Windows (Farrugia, 1997) _computing_publication_material 'SHELXL97'.

Figures top
[Figure 1] Fig. 1. A view of Cs2Cr4O13 along [100]. Isolated zigzag [Cr4O13]2− anions are linked via two Cs+ cations. The unit cell is outlined.
[Figure 2] Fig. 2. A view of the atoms in the asymmetric unit of Cs2Cr4O13, shown with ellipsoids at the 50% probability level.
[Figure 3] Fig. 3. A comparison of the packing in the structures of (a) Cs2Cr4O13 (this work) and (b) Rb2Cr4O13 (Löfgren, 1973). Note the different mutual arrangement between the [Cr4O13]2− anions and the alkali cations.
[Figure 4] Fig. 4. A comparison of the configuration of the [Cr4O13]2− anion in (a) Cs2Cr4O13 and (b) Rb2Cr4O13 (Löfgren, 1973) with (c) a fragment of the infinite tetrahedral chains in CrO3 (Byström & Wilhelmi, 1950).
dicesium tetrachromium(VI) oxide top
Crystal data top
Cs2Cr4O13F(000) = 1240
Mr = 681.82Dx = 3.310 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 5065 reflections
a = 8.021 (2) Åθ = 2.0–32.6°
b = 20.457 (4) ŵ = 8.39 mm1
c = 8.739 (2) ÅT = 293 K
β = 107.41 (3)°Brick-shaped, orange-red
V = 1368.3 (6) Å30.08 × 0.04 × 0.04 mm
Z = 4
Data collection top
Nonius KappaCCD
diffractometer
4934 independent reflections
Radiation source: fine-focus sealed tube4108 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.014
ψ and ω scansθmax = 32.5°, θmin = 2.8°
Absorption correction: multi-scan
HKL SCALEPACK (Otwinowski & Minor, 1997)
h = 1212
Tmin = 0.553, Tmax = 0.730k = 3030
9739 measured reflectionsl = 1313
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.024 w = 1/[σ2(Fo2) + (0.024P)2 + 1.5P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.059(Δ/σ)max = 0.001
S = 1.04Δρmax = 0.87 e Å3
4934 reflectionsΔρmin = 0.90 e Å3
173 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.00175 (11)
Crystal data top
Cs2Cr4O13V = 1368.3 (6) Å3
Mr = 681.82Z = 4
Monoclinic, P21/nMo Kα radiation
a = 8.021 (2) ŵ = 8.39 mm1
b = 20.457 (4) ÅT = 293 K
c = 8.739 (2) Å0.08 × 0.04 × 0.04 mm
β = 107.41 (3)°
Data collection top
Nonius KappaCCD
diffractometer
4934 independent reflections
Absorption correction: multi-scan
HKL SCALEPACK (Otwinowski & Minor, 1997)
4108 reflections with I > 2σ(I)
Tmin = 0.553, Tmax = 0.730Rint = 0.014
9739 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.024173 parameters
wR(F2) = 0.0590 restraints
S = 1.04Δρmax = 0.87 e Å3
4934 reflectionsΔρmin = 0.90 e Å3
Special details top

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
Cs10.81125 (2)0.094754 (9)0.40127 (2)0.03585 (5)
Cs20.90312 (2)0.234983 (10)0.00807 (2)0.04166 (6)
Cr10.92688 (5)0.27421 (2)0.54169 (5)0.02748 (8)
Cr20.74627 (6)0.39431 (2)0.30841 (5)0.02998 (9)
Cr31.13598 (6)0.44792 (2)0.35930 (5)0.03189 (9)
Cr41.25147 (6)0.57747 (2)0.19510 (5)0.03021 (9)
O11.0949 (3)0.29568 (13)0.6832 (3)0.0568 (7)
O20.9846 (3)0.24603 (12)0.3939 (3)0.0440 (5)
O30.8135 (3)0.22139 (11)0.6045 (3)0.0460 (5)
O40.7851 (3)0.34524 (11)0.4730 (3)0.0431 (5)
O50.5641 (3)0.42953 (13)0.2766 (3)0.0561 (6)
O60.7431 (4)0.35113 (12)0.1579 (3)0.0539 (6)
O70.9089 (3)0.45408 (11)0.3351 (3)0.0453 (5)
O81.1639 (4)0.40267 (13)0.2237 (4)0.0627 (7)
O91.2271 (4)0.41478 (15)0.5262 (3)0.0670 (8)
O101.2172 (3)0.52385 (11)0.3529 (3)0.0444 (5)
O111.0761 (4)0.61608 (18)0.1168 (4)0.0822 (10)
O121.3091 (4)0.53420 (11)0.0678 (3)0.0528 (6)
O131.4036 (4)0.62830 (14)0.2744 (4)0.0687 (9)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cs10.03703 (9)0.03414 (9)0.03837 (9)0.00480 (7)0.01433 (7)0.00699 (7)
Cs20.03526 (10)0.04826 (12)0.04238 (10)0.00348 (7)0.01302 (7)0.00663 (8)
Cr10.02869 (19)0.02532 (19)0.02787 (18)0.00160 (15)0.00762 (15)0.00020 (15)
Cr20.0309 (2)0.0288 (2)0.0288 (2)0.00053 (16)0.00684 (16)0.00341 (15)
Cr30.0385 (2)0.0279 (2)0.0326 (2)0.00178 (17)0.01571 (18)0.00258 (16)
Cr40.0304 (2)0.02686 (19)0.0376 (2)0.00192 (16)0.01655 (17)0.00140 (16)
O10.0509 (14)0.0499 (14)0.0545 (14)0.0056 (11)0.0072 (11)0.0136 (11)
O20.0435 (12)0.0513 (13)0.0402 (11)0.0064 (10)0.0170 (10)0.0060 (10)
O30.0539 (14)0.0370 (11)0.0525 (13)0.0066 (10)0.0240 (11)0.0073 (10)
O40.0603 (14)0.0385 (11)0.0366 (10)0.0184 (10)0.0241 (10)0.0107 (9)
O50.0346 (12)0.0583 (15)0.0680 (17)0.0120 (11)0.0042 (11)0.0103 (13)
O60.0864 (19)0.0415 (12)0.0338 (11)0.0094 (12)0.0182 (12)0.0046 (9)
O70.0412 (11)0.0407 (12)0.0584 (14)0.0069 (9)0.0216 (11)0.0065 (10)
O80.0710 (18)0.0576 (16)0.0730 (18)0.0066 (13)0.0420 (15)0.0249 (13)
O90.0753 (19)0.0669 (18)0.0536 (15)0.0059 (15)0.0112 (14)0.0279 (13)
O100.0605 (14)0.0368 (11)0.0442 (12)0.0112 (10)0.0281 (11)0.0012 (9)
O110.0545 (16)0.104 (2)0.096 (2)0.0344 (17)0.0343 (16)0.046 (2)
O120.0829 (18)0.0347 (11)0.0509 (13)0.0011 (12)0.0355 (13)0.0047 (10)
O130.086 (2)0.0671 (17)0.0704 (18)0.0472 (16)0.0501 (16)0.0294 (14)
Geometric parameters (Å, º) top
Cs1—O12i3.015 (2)Cs2—O1iii3.431 (3)
Cs1—O11ii3.095 (3)Cs2—O4viii3.523 (3)
Cs1—O1iii3.112 (2)Cs2—O1vii3.698 (3)
Cs1—O33.138 (2)Cs2—O8iii3.797 (3)
Cs1—O9iii3.148 (3)Cr1—O11.594 (2)
Cs1—O13iv3.188 (3)Cr1—O21.604 (2)
Cs1—O12iv3.223 (3)Cr1—O31.611 (2)
Cs1—O5v3.337 (3)Cr1—O41.832 (2)
Cs1—O8i3.366 (3)Cr2—O51.577 (2)
Cs1—O23.401 (3)Cr2—O61.578 (2)
Cs1—O7ii3.672 (3)Cr2—O41.704 (2)
Cs1—O6v3.688 (3)Cr2—O71.752 (2)
Cs2—O13iv3.073 (3)Cr3—O81.572 (2)
Cs2—O11vi3.211 (3)Cr3—O91.576 (3)
Cs2—O2iii3.230 (2)Cr3—O101.692 (2)
Cs2—O63.242 (3)Cr3—O71.774 (2)
Cs2—O3vii3.256 (3)Cr4—O111.579 (3)
Cs2—O3viii3.265 (3)Cr4—O121.595 (2)
Cs2—O23.383 (2)Cr4—O131.595 (3)
Cs2—O9iii3.424 (3)Cr4—O101.846 (2)
O1—Cr1—O2110.04 (14)O9—Cr3—O10110.43 (15)
O1—Cr1—O3110.68 (14)O8—Cr3—O7108.96 (14)
O2—Cr1—O3111.20 (13)O9—Cr3—O7108.42 (15)
O1—Cr1—O4109.50 (12)O10—Cr3—O7108.82 (11)
O2—Cr1—O4108.77 (11)O11—Cr4—O12112.45 (18)
O3—Cr1—O4106.58 (12)O11—Cr4—O13109.2 (2)
O5—Cr2—O6108.98 (15)O12—Cr4—O13108.73 (14)
O5—Cr2—O4110.09 (13)O11—Cr4—O10107.98 (14)
O6—Cr2—O4109.09 (12)O12—Cr4—O10109.29 (11)
O5—Cr2—O7108.56 (13)O13—Cr4—O10109.16 (13)
O6—Cr2—O7109.11 (12)Cr2—O4—Cr1133.03 (12)
O4—Cr2—O7110.98 (13)Cr2—O7—Cr3131.55 (14)
O8—Cr3—O9108.27 (17)Cr3—O10—Cr4135.66 (14)
O8—Cr3—O10111.87 (13)
Symmetry codes: (i) x1/2, y+1/2, z+1/2; (ii) x+3/2, y1/2, z+1/2; (iii) x1/2, y+1/2, z1/2; (iv) x+5/2, y1/2, z+1/2; (v) x+1/2, y+1/2, z+1/2; (vi) x+2, y+1, z; (vii) x, y, z1; (viii) x+1/2, y+1/2, z1/2.

Experimental details

Crystal data
Chemical formulaCs2Cr4O13
Mr681.82
Crystal system, space groupMonoclinic, P21/n
Temperature (K)293
a, b, c (Å)8.021 (2), 20.457 (4), 8.739 (2)
β (°) 107.41 (3)
V3)1368.3 (6)
Z4
Radiation typeMo Kα
µ (mm1)8.39
Crystal size (mm)0.08 × 0.04 × 0.04
Data collection
DiffractometerNonius KappaCCD
diffractometer
Absorption correctionMulti-scan
HKL SCALEPACK (Otwinowski & Minor, 1997)
Tmin, Tmax0.553, 0.730
No. of measured, independent and
observed [I > 2σ(I)] reflections
9739, 4934, 4108
Rint0.014
(sin θ/λ)max1)0.756
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.024, 0.059, 1.04
No. of reflections4934
No. of parameters173
Δρmax, Δρmin (e Å3)0.87, 0.90

Computer programs: COLLECT (Nonius, 2003), HKL SCALEPACK (Otwinowski & Minor 1997), HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ATOMS (Shape Software, 1999) and ORTEP-3 for Windows (Farrugia, 1997) _computing_publication_material 'SHELXL97'.

Selected geometric parameters (Å, º) top
Cr1—O11.594 (2)Cr3—O81.572 (2)
Cr1—O21.604 (2)Cr3—O91.576 (3)
Cr1—O31.611 (2)Cr3—O101.692 (2)
Cr1—O41.832 (2)Cr3—O71.774 (2)
Cr2—O51.577 (2)Cr4—O111.579 (3)
Cr2—O61.578 (2)Cr4—O121.595 (2)
Cr2—O41.704 (2)Cr4—O131.595 (3)
Cr2—O71.752 (2)Cr4—O101.846 (2)
O1—Cr1—O2110.04 (14)O9—Cr3—O10110.43 (15)
O1—Cr1—O3110.68 (14)O8—Cr3—O7108.96 (14)
O2—Cr1—O3111.20 (13)O9—Cr3—O7108.42 (15)
O1—Cr1—O4109.50 (12)O10—Cr3—O7108.82 (11)
O2—Cr1—O4108.77 (11)O11—Cr4—O12112.45 (18)
O3—Cr1—O4106.58 (12)O11—Cr4—O13109.2 (2)
O5—Cr2—O6108.98 (15)O12—Cr4—O13108.73 (14)
O5—Cr2—O4110.09 (13)O11—Cr4—O10107.98 (14)
O6—Cr2—O4109.09 (12)O12—Cr4—O10109.29 (11)
O5—Cr2—O7108.56 (13)O13—Cr4—O10109.16 (13)
O6—Cr2—O7109.11 (12)Cr2—O4—Cr1133.03 (12)
O4—Cr2—O7110.98 (13)Cr2—O7—Cr3131.55 (14)
O8—Cr3—O9108.27 (17)Cr3—O10—Cr4135.66 (14)
O8—Cr3—O10111.87 (13)
 

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