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Single crystals of tricobalt(II) tellurium(VI) hexa­oxide, Co3TeO6, were synthesized via transport reactions using HCl as transporting agent. The compound crystallizes in the monoclinic system (space group C2/c). The Te atoms are positioned in 4b (\overline{1}) and 8f positions, while the Co atoms are in 4e (2) and 8f positions. The structure consists of (100) oxygen layers packed in a hhchhc sequence, with TeVI in octa­hedral coordination and CoII in both octa­hedral and tetra­hedral coordination. The structure contains face-sharing CoO6 octa­hedra, as well as edge-sharing CoO4 tetra­hedra. Co3TeO6 is the first oxide that is isostructural with the β-Li3MF6 family of compounds (M = Al, Cr, Ga, Ti and V).

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010602347X/bc3008sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010602347X/bc3008Isup2.hkl
Contains datablock I

Comment top

The crystal chemistry of the metal tellurates, M3TeO6, has proved to be rich, and a number of compounds with various crystal structures have previously been described, for example Ni3TeO6 (Bayer, 1967; Newnham & Meagher, 1967), Cu3TeO6 (Falck et al., 1978) and Mg3TeO6 (Schulz & Bayer, 1971). Ni3TeO6 and Mg3TeO6 crystallize in the rhombohedral space group R3 with a corundum-related structure of octahedrally coordinated Ni, Mg and Te substituting for Al. Cu3TeO6 crystallizes in the cubic space group Ia3 with a bixbyite-type structure of cubic close packed O atoms and octahedrally coordinated Cu and Te. The crystal structure of Co3TeO6 was thus impossible to predict, since CoII can occur in both tetrahedral and octahedral coordinations, as seen for instance in Co6(TeO3)2(TeO6)Cl2 (Becker & Johnsson, 2004). Indeed, Co3TeO6 was found to crystallize with a different structure type corresponding to that of the lithium cryolite family, β-Li3MF6. Several β-Li3MF6 compounds have been described previously for M = Al, Cr, Ga, Ti and V (Massa & Rüdorff, 1971; Tyagi & Köhler, 1992, 1997, 1999, 2000; Tyagi et al. 1996). To the best of our knowledge, Co3TeO6 is the first oxide with this structure type.

Co3TeO6 crystallizes in the monoclinic space group C2/c. The two crystallographically distinct TeVI cations occupy octahedral sites such that TeO6 octahedra are not directly connected to each other. Four of the five crystallograpically distinct CoII cations (Co1, Co2, Co3 and Co4) occupy octahedral sites, although Co3 is only five coordinated in a square-pyramidal fashion because the Co3—O2 bond is elongated [2.925 (3) Å]. Atom Co5 occupies a tetrahedral site. The Te and Co atoms can be regarded as being arranged in layers (Fig. 1). The Co atoms form a pseudo hexagonal arrangement in the [201] direction and the Te atoms are located in the channels. The O atoms are approximately close packed in a mixed hexagonal–cubic hhchhc six-layer sequence along [100]. The `c' layer contains atoms O4, O8 and O9, while the two `h' layers contain atoms O1, O2, O3, O5, O6 and O7 (Fig. 1).

Bond valence sum (BVS) calculations for the Te atoms give values of 5.90 and 5.79 v.u. (valence units) for Te1 and Te2, respectively, with an R0 value of 1.917 (Brown & Altermatt, 1985). BVS calculations for the Co atoms yield values of 1.93, 1.87 and 1.85 v.u. for Co1, Co2 and Co4, respectively with an R0 value of 1.685 (Wood & Palenik, 1998). BVS calculations for Co3 (Fig. 2) give the value of 1.86 v.u. when including the five primary Co—O bonds. The sixth O atom (O2) contributes 0.035 v.u. only, which is significantly below the lower limit of 0.08 v.u. (4% of the cation valence) to be regarded as bonded (Brown, 2002). A likely reason for the distortion of the Co3 coordination is discussed below. A similar but smaller distortion is also seen for atom Co2, which retains a formal octahedral coordination. The distortions seen for the Co2O6 and Co3O6 octahedra are also observed in the LiO6 octahedra of the isostructural β-Li3MF6 phases. Finally, Co5 has a tetrahedral coordination with a bond valence sum of 1.86 vu.

The Co polyhedra are connected via corner, edge and face sharing through the Co—O bonds. Two of the more remarkable situations within the structure are (i) the edge sharing between two adjacent Co5O4 tetrahedra, an unusual situation that can only occur in a cubic close packing (Fig. 3), and (ii) the face sharing between Co3O5 + 1 and Co4O6, which could account for the elongation of the Co3—O2 bond (Fig. 2).

Experimental top

Single crystals of Co3TeO6 were synthesized via chemical vapour transport redox reactions in sealed evacuated silica tubes. The starting materials were Co3O4 (Alfa Aesar 99.7%), TeO2 (Acros 99%) and CoCl2 (Alfa Aesar 99.9%) mixed in the off-stoichiometric molar ratio 4:3:1. The starting mixture was loaded at one end of a silica tube, which was subsequently evacuated to 10 −5 Torr. HCl gas (electronic grade purity) was introduced as a transporting agent and the tube was sealed off. The ampoule was subsequently placed in a two-zone furnace with charge- and growth-zone temperatures of 973 and 873 K, respectively. After 15 d, dark-violet single crystals of Co3TeO6 with a size of about 3 × 2 × 1 mm had grown in the centre of the ampoule. The crystal used for the data collection was a fragment of a larger crystal. A number of small crystals of an unknown compound also formed at the cold end of the silica tube.

Refinement top

The maximum residual electron density is located 0.76 Å away from atom Te2 at (0.1119, 0.0058, 0.7768) and the minimum is located 1.03 Å away from atom Te1 at (0.4388, −0.0029, 0.0399).

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2005); cell refinement: CrysAlis RED (Oxford Diffraction, 2005); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2001); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Oxygen packing and cation coordination in Co3TeO6.
[Figure 2] Fig. 2. Face sharing between Co3O5 + 1 and Co4O6 octahedra with an elongated Co3—O2 bond. [Symmetry codes: (i) −x + 1, −y − 1, −z; (ii) −x + 1, −y, −z; (iii) −x + 1, y, −z + 1/2; iv) x, −y − 1, z − 1/2; (v) −x + 3/2, y + 1/2, −z + 1/2.]
[Figure 3] Fig. 3. Edge sharing between two Co5O4 tetrahedra. [Symmetry codes: (i) − x + 3/2, −y + 1/2, −z + 1.]
tricobalt(II) tellurium(VI) hexaoxide top
Crystal data top
Co3TeO6F(000) = 2172
Mr = 400.39Dx = 5.892 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C2ycCell parameters from 8340 reflections
a = 14.8167 (18) Åθ = 4.6–33.2°
b = 8.8509 (11) ŵ = 17.18 mm1
c = 10.3631 (14) ÅT = 292 K
β = 94.90 (1)°Block, purple
V = 1354.1 (3) Å30.14 × 0.08 × 0.03 mm
Z = 12
Data collection top
Oxford Xcalibur
diffractometer
1333 independent reflections
Radiation source: fine-focus sealed tube, Oxford diffraction Xcalibur31256 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.076
ω scan at different ϕθmax = 26.4°, θmin = 4.6°
Absorption correction: numerical
[X-RED (Stoe & Cie, 2001) and X-SHAPE (Stoe & Cie, 1999)]'
h = 1818
Tmin = 0.186, Tmax = 0.542k = 1111
8340 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)] = 0.031 w = 1/[σ2(Fo2) + (0.0581P)2 + 1.2572P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.088(Δ/σ)max < 0.001
S = 1.17Δρmax = 2.24 e Å3
1333 reflectionsΔρmin = 1.64 e Å3
139 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0051 (2)
Crystal data top
Co3TeO6V = 1354.1 (3) Å3
Mr = 400.39Z = 12
Monoclinic, C2/cMo Kα radiation
a = 14.8167 (18) ŵ = 17.18 mm1
b = 8.8509 (11) ÅT = 292 K
c = 10.3631 (14) Å0.14 × 0.08 × 0.03 mm
β = 94.90 (1)°
Data collection top
Oxford Xcalibur
diffractometer
1333 independent reflections
Absorption correction: numerical
[X-RED (Stoe & Cie, 2001) and X-SHAPE (Stoe & Cie, 1999)]'
1256 reflections with I > 2σ(I)
Tmin = 0.186, Tmax = 0.542Rint = 0.076
8340 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.031139 parameters
wR(F2) = 0.0880 restraints
S = 1.17Δρmax = 2.24 e Å3
1333 reflectionsΔρmin = 1.64 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
Te11.00000.50000.50000.0085 (2)
Te20.66140 (2)0.49847 (2)0.30043 (3)0.00848 (19)
Co10.50000.18779 (10)0.25000.0103 (2)
Co20.85832 (5)0.35403 (7)0.23358 (6)0.0117 (2)
Co30.52309 (5)0.65457 (6)0.04004 (7)0.0112 (2)
Co40.66469 (4)0.29348 (7)0.05500 (6)0.0125 (2)
Co50.79676 (5)0.36336 (7)0.57242 (7)0.0118 (2)
O10.9274 (2)0.3351 (3)0.5611 (3)0.0122 (7)
O20.5935 (2)0.3450 (3)0.2024 (3)0.0119 (7)
O30.6030 (2)0.6554 (3)0.1980 (3)0.0122 (7)
O40.7484 (2)0.5267 (4)0.6687 (3)0.0127 (7)
O50.9293 (2)0.5144 (3)0.3377 (4)0.0111 (7)
O60.5818 (3)0.5117 (3)0.4377 (4)0.0122 (8)
O70.9269 (2)0.6591 (3)0.5662 (3)0.0126 (7)
O80.7377 (2)0.3503 (3)0.3932 (3)0.0124 (7)
O90.7272 (2)0.6611 (3)0.3887 (3)0.0114 (7)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Te10.0120 (4)0.0062 (3)0.0074 (3)0.00007 (13)0.0019 (2)0.00020 (13)
Te20.0117 (3)0.0066 (2)0.0073 (3)0.00021 (10)0.00180 (17)0.00009 (9)
Co10.0134 (6)0.0089 (4)0.0087 (5)0.0000.0021 (4)0.000
Co20.0161 (5)0.0086 (3)0.0103 (4)0.0008 (2)0.0005 (3)0.0004 (2)
Co30.0140 (4)0.0094 (3)0.0102 (4)0.0005 (2)0.0015 (3)0.0006 (2)
Co40.0132 (4)0.0152 (4)0.0093 (4)0.0014 (2)0.0025 (3)0.0009 (2)
Co50.0140 (4)0.0100 (3)0.0115 (4)0.0007 (2)0.0019 (3)0.0027 (2)
O10.0178 (19)0.0088 (16)0.0101 (16)0.0021 (12)0.0012 (13)0.0001 (13)
O20.0142 (19)0.0112 (15)0.0106 (16)0.0023 (12)0.0030 (13)0.0035 (13)
O30.016 (2)0.0100 (15)0.0100 (16)0.0005 (12)0.0011 (14)0.0002 (13)
O40.019 (2)0.0096 (13)0.0106 (16)0.0011 (13)0.0037 (14)0.0020 (13)
O50.014 (2)0.0106 (15)0.0080 (16)0.0041 (11)0.0016 (14)0.0010 (11)
O60.018 (2)0.0111 (15)0.0086 (17)0.0001 (12)0.0048 (15)0.0003 (11)
O70.0165 (19)0.0099 (16)0.0115 (16)0.0043 (12)0.0017 (14)0.0002 (13)
O80.0157 (19)0.0090 (15)0.0123 (16)0.0025 (12)0.0006 (14)0.0016 (13)
O90.0151 (19)0.0094 (15)0.0100 (15)0.0046 (12)0.0027 (13)0.0035 (13)
Geometric parameters (Å, º) top
Te1—O51.908 (3)Co2—O52.023 (3)
Te1—O5i1.908 (3)Co2—O7ii2.087 (4)
Te1—O71.938 (3)Co2—O9iv2.419 (3)
Te1—O7i1.938 (3)Co2—O82.538 (4)
Te1—O11.951 (3)Co3—O31.936 (3)
Te1—O1i1.951 (3)Co3—O6iii2.032 (4)
Te2—O31.910 (3)Co3—O6ii2.050 (3)
Te2—O91.925 (3)Co3—O1viii2.078 (3)
Te2—O61.927 (4)Co3—O7ix2.212 (3)
Te2—O21.927 (3)Co3—O2x2.925 (3)
Te2—O81.933 (3)Co4—O21.982 (3)
Te2—O4ii1.969 (3)Co4—O9iv2.030 (3)
Co1—O22.054 (3)Co4—O9ii2.065 (3)
Co1—O2iii2.054 (3)Co4—O7iv2.131 (3)
Co1—O5iv2.107 (3)Co4—O4ii2.282 (3)
Co1—O5v2.107 (3)Co4—O6ii2.389 (3)
Co1—O1vi2.161 (3)Co5—O41.929 (3)
Co1—O1vii2.161 (3)Co5—O11.966 (4)
Co2—O3iv1.963 (3)Co5—O81.988 (4)
Co2—O4ii2.008 (3)Co5—O8vi1.998 (3)
O5—Te1—O5i180.0 (2)O3iv—Co2—O7ii95.90 (13)
O5—Te1—O7i91.04 (14)O4ii—Co2—O7ii100.91 (14)
O5i—Te1—O7i88.96 (14)O5—Co2—O7ii102.41 (14)
O5—Te1—O788.96 (14)O3iv—Co2—O9iv71.38 (12)
O5i—Te1—O791.04 (14)O4ii—Co2—O9iv79.74 (12)
O7i—Te1—O7180.00 (17)O5—Co2—O9iv179.34 (14)
O5—Te1—O193.43 (14)O7ii—Co2—O9iv78.20 (12)
O5i—Te1—O186.57 (14)O3iv—Co2—O887.30 (12)
O7i—Te1—O184.92 (15)O4ii—Co2—O868.21 (13)
O7—Te1—O195.08 (15)O5—Co2—O891.41 (13)
O5—Te1—O1i86.57 (14)O7ii—Co2—O8163.97 (12)
O5i—Te1—O1i93.43 (14)O9iv—Co2—O888.02 (11)
O7i—Te1—O1i95.08 (15)O3—Co3—O6iii108.93 (14)
O7—Te1—O1i84.92 (15)O3—Co3—O6ii100.62 (14)
O1—Te1—O1i180.0O6iii—Co3—O6ii88.54 (15)
O3—Te2—O984.70 (14)O3—Co3—O1viii101.94 (13)
O3—Te2—O695.13 (14)O6iii—Co3—O1viii147.34 (14)
O9—Te2—O685.48 (14)O6ii—Co3—O1viii96.14 (13)
O3—Te2—O291.61 (15)O3—Co3—O7ix104.35 (13)
O9—Te2—O2176.09 (13)O6iii—Co3—O7ix86.73 (13)
O6—Te2—O296.14 (14)O6ii—Co3—O7ix154.78 (14)
O3—Te2—O8171.05 (14)O1viii—Co3—O7ix75.38 (14)
O9—Te2—O891.16 (15)O3—Co3—O2x178.50 (12)
O6—Te2—O892.45 (14)O6iii—Co3—O2x72.37 (12)
O2—Te2—O892.32 (14)O6ii—Co3—O2x78.58 (12)
O3—Te2—O4ii89.37 (14)O1viii—Co3—O2x76.92 (11)
O9—Te2—O4ii94.55 (14)O7ix—Co3—O2x76.38 (11)
O6—Te2—O4ii175.48 (13)O2—Co4—O9iv111.72 (14)
O2—Te2—O4ii84.12 (14)O2—Co4—O9ii154.77 (13)
O8—Te2—O4ii83.04 (14)O9iv—Co4—O9ii87.31 (13)
O2iii—Co1—O294.69 (18)O2—Co4—O7iv103.23 (14)
O2iii—Co1—O5iv165.37 (13)O9iv—Co4—O7iv107.11 (13)
O2—Co1—O5iv91.11 (13)O9ii—Co4—O7iv85.70 (13)
O2iii—Co1—O5v91.11 (13)O2—Co4—O4ii75.12 (13)
O2—Co1—O5v165.37 (13)O9iv—Co4—O4ii82.74 (12)
O5iv—Co1—O5v86.52 (19)O9ii—Co4—O4ii91.85 (13)
O2iii—Co1—O1vi98.02 (13)O7iv—Co4—O4ii169.70 (12)
O2—Co1—O1vi89.27 (13)O2—Co4—O6ii86.67 (13)
O5iv—Co1—O1vi95.47 (13)O9iv—Co4—O6ii157.22 (13)
O5v—Co1—O1vi76.61 (13)O9ii—Co4—O6ii71.47 (12)
O2iii—Co1—O1vii89.27 (13)O7iv—Co4—O6ii80.17 (12)
O2—Co1—O1vii98.02 (13)O4ii—Co4—O6ii89.56 (12)
O5iv—Co1—O1vii76.61 (13)O4—Co5—O1122.53 (14)
O5v—Co1—O1vii95.47 (13)O4—Co5—O8111.92 (14)
O1vi—Co1—O1vii169.26 (16)O1—Co5—O8107.12 (15)
O3iv—Co2—O4ii142.68 (13)O4—Co5—O8vi120.35 (14)
O3iv—Co2—O5108.26 (13)O1—Co5—O8vi99.07 (13)
O4ii—Co2—O5100.36 (14)O8—Co5—O8vi90.72 (13)
Symmetry codes: (i) x+2, y1, z+1; (ii) x, y1, z1/2; (iii) x+1, y, z+1/2; (iv) x+3/2, y+1/2, z+1/2; (v) x1/2, y+1/2, z; (vi) x+3/2, y1/2, z+1; (vii) x1/2, y1/2, z1/2; (viii) x+3/2, y1/2, z+1/2; (ix) x1/2, y3/2, z1/2; (x) x+1, y1, z.

Experimental details

Crystal data
Chemical formulaCo3TeO6
Mr400.39
Crystal system, space groupMonoclinic, C2/c
Temperature (K)292
a, b, c (Å)14.8167 (18), 8.8509 (11), 10.3631 (14)
β (°) 94.90 (1)
V3)1354.1 (3)
Z12
Radiation typeMo Kα
µ (mm1)17.18
Crystal size (mm)0.14 × 0.08 × 0.03
Data collection
DiffractometerOxford Xcalibur
diffractometer
Absorption correctionNumerical
[X-RED (Stoe & Cie, 2001) and X-SHAPE (Stoe & Cie, 1999)]'
Tmin, Tmax0.186, 0.542
No. of measured, independent and
observed [I > 2σ(I)] reflections
8340, 1333, 1256
Rint0.076
(sin θ/λ)max1)0.626
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.031, 0.088, 1.17
No. of reflections1333
No. of parameters139
Δρmax, Δρmin (e Å3)2.24, 1.64

Computer programs: CrysAlis CCD (Oxford Diffraction, 2005), CrysAlis RED (Oxford Diffraction, 2005), CrysAlis RED, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), DIAMOND (Brandenburg, 2001), SHELXL97.

Selected bond lengths (Å) top
Te1—O51.908 (3)Co2—O82.538 (4)
Te1—O71.938 (3)Co3—O31.936 (3)
Te1—O11.951 (3)Co3—O6v2.032 (4)
Te2—O31.910 (3)Co3—O6i2.050 (3)
Te2—O91.925 (3)Co3—O1vi2.078 (3)
Te2—O61.927 (4)Co3—O7vii2.212 (3)
Te2—O21.927 (3)Co3—O2viii2.925 (3)
Te2—O81.933 (3)Co4—O21.982 (3)
Te2—O4i1.969 (3)Co4—O9iv2.030 (3)
Co1—O22.054 (3)Co4—O9i2.065 (3)
Co1—O5ii2.107 (3)Co4—O7iv2.131 (3)
Co1—O1iii2.161 (3)Co4—O4i2.282 (3)
Co2—O3iv1.963 (3)Co4—O6i2.389 (3)
Co2—O4i2.008 (3)Co5—O41.929 (3)
Co2—O52.023 (3)Co5—O11.966 (4)
Co2—O7i2.087 (4)Co5—O81.988 (4)
Co2—O9iv2.419 (3)Co5—O8iii1.998 (3)
Symmetry codes: (i) x, y1, z1/2; (ii) x1/2, y+1/2, z; (iii) x+3/2, y1/2, z+1; (iv) x+3/2, y+1/2, z+1/2; (v) x+1, y, z+1/2; (vi) x+3/2, y1/2, z+1/2; (vii) x1/2, y3/2, z1/2; (viii) x+1, y1, z.
 

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