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Single crystals of distrontium(II) dicopper(II) tellurium(VI) hexa­oxide dibromide, Sr2Cu2TeO6Br2, were synthesized via solid state/gas phase reactions in sealed evacuated silica tubes. The building units are irregular SrO4Br3 polyhedra (a new type of coordination polyhedron around SrII), CuO5 square pyramids and TeO6 octa­hedra. The CuO5 square pyramids and the TeO6 octa­hedra together form layers in the bc plane bridged by Sr atoms. The Cu atoms are arranged to form puckered honeycomb layers. The Te atom lies on an inversion centre.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270106013047/fa3009sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106013047/fa3009Isup2.hkl
Contains datablock I

Comment top

The title compound is the first tellurate halide compound in the system AE–CuII–TeVI–O–X (AE = alkaline earth and X = halide). In the family AE–CuII–TeVI–O, very few compounds have been described before, viz. triclinic and tetragonal Ba2CuTeO6 (Koehl & Reinen, 1974; Iwanaga et al., 1999) and tetragonal Sr2CuTeO6 (Reinen & Weitzel, 1976).

An overview of the structure of the title compound is shown in Fig. 1; selected interatomic distances are given in Table 1. Atom Te1 has an octahedral TeO6 coordination with Te—O bond distances in the range 1.915 (9)–1.943 (9) Å. Atom Cu1 is coordinated by five O atoms to form a CuO5 square pyramid with Cu—O bond distances in the range 1.933 (9)–2.022 (10) Å in the square plane and 2.355 (10) Å to the pyramid apex. A more distant Br atom, sitting in the opposite apical position, completes an elongated CuO5Br octahedron with a Cu—Br distance of 2.974 (2) Å. However, bond valence sum (BVS) calculations (Brown & Altermatt, 1985; Brese & O'Keeffe, 1991) suggest that the primary coordination sphere around Cu is less than 2.93 Å, so this distant Br atom is just at the border and is not considered as bonded.

The Cu—Te—O layers extend in the bc plane and are arranged such that each TeO6 octahedron has common edges with four and common corners with two CuO5 polyhedra. Furthermore, each CuO5 square pyramid has a common edge with one and common corners with two more such pyramids (Fig. 2a). The Cu atoms form a distorted pseudo-hexagonal puckered honeycomb network, with Cu—Cu distances of 3.067 (3) and 3.615 (2) Å (Fig. 2b).

The Sr1 atom is coordinated by four O and three Br atoms to form an irregular SrO4Br3 polyhedron that, according to the best of our knowledge and a search of the ICSD (2005), actually constitutes a new coordination polyhedron for SrII (Fig. 3). The Sr—O distances are in the range 2.471 (9)–2.793 (10) Å and the Sr – Br distances are in the range 3.064 (2)–3.175 (2) Å. A fourth Br atom perches at a distance of 3.655 (2) Å, but does not contribute significantly to the BVS and is therefore not considered as bonded. It is common that BVSs give very low values for halide ions in oxohalides (0.3–0.4), thus indicating that such ions frequently have an unsaturated bond valence and take on the role of counter-ion rather than being integrated into the covalent/ionic network; an example is Te6O11Cl2 (Giester, 1994). However, for the title compound, BVS calculations indicate that the Br ions are well integrated into the covalent/ionic network, as they have a value of ~0.9, which is near the expected value of 1 (see Table 2).

Each SrO4Br3 polyhedron is linked to four others by corner sharing (two via Br and two via O) and to two others via Br—Br edge sharing to form double layers that connect the Cu—Te—O layers (Fig. 1).

Experimental top

Single crystals of Sr2Cu2TeO6Br2 were synthesized by chemical transport reactions in sealed evacuated silica tubes. SrO (ABCR, 99.95%), CuBr2 (Avocado Research Chemicals, +98%), CuO (Avocado Research Chemicals, +99%) and TeO2 (ABCR, +99%) were used as starting materials and mixed in the molar ratio 1:1:3:1 in a mortar; the mixture was put into a silica tube (length ~5 cm), which was subsequently evacuated. The tube was heated for 72 h at 900 K in a muffle furnace. The product appeared as green single crystals, and black and light-yellow powders. Chemical analysis of the elements heavier than oxygen by use of a scanning electron microscope (JEOL820) equipped with an energy dispersive spectrometer (LINK AN10000) indicate that the black powder is unreacted CuO and the light-yellow powder has a composition of 0.8 at% Sr, 75.3 at% Cu, 22.1 at% Te and 1.9 at% Br. The light-yellow colour indicates that this unknown phase contains CuI and not CuII. There must be a redox reaction taking place during the reactions so that TeIV is transformed to TeVI to form the title compound and CuII is transformed to CuI to form the light-yellow powder. The synthesis products were non-hygroscopic.

Refinement top

The maximum residual electron density is at the fractional coordinates (0.7971, 0.0106, 0.7975) and the minimum is at (0.3424, 0.0672, 0.3253). The peak and hole are 0.88 and 1.68 Å, respectively, from atom Sr1.

Computing details top

Data collection: EXPOSE in IPDS (Stoe & Cie, 1997); cell refinement: CELL in IPDS; data reduction: INTEGRATE in IPDS; 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. An overview of the structure of Sr2Cu2TeO6Br2. CuO5 square pyramids are grey; TeO6 octahedra are white.
[Figure 2] Fig. 2. (a) The local coordination around a TeO6 octahedron in a Cu—Te—O layer. CuO5 square pyramids are grey, The Cu, Te and O atoms are dark grey, light grey and white, respectively. (b) The pseudo-hexagonal Cu honeycomb network in the Cu—Te—O layers. Two different Cu—Cu distances are present, viz. 3.615 (2) Å (thick lines) and 3.067 (3) Å (thiner lines). The symmetry codes are as in Table 1.
[Figure 3] Fig. 3. The irregular SrO4Br3 polyhedron. There is also a long Sr—Br distance marked with a dashed line. The symmetry codes are as in Table 1.
distrontium dicopper(II) tellurium(VI) hexaoxide dibromide top
Crystal data top
Sr2Cu2TeO6Br2F(000) = 608
Mr = 685.74Dx = 4.990 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 1006 reflections
a = 9.422 (3) Åθ = 1.9–28.2°
b = 5.1788 (17) ŵ = 28.10 mm1
c = 9.388 (3) ÅT = 291 K
β = 94.92 (3)°Plate, green
V = 456.4 (3) Å30.07 × 0.06 × 0.02 mm
Z = 2
Data collection top
Stoe IPDS
diffractometer
1099 independent reflections
Radiation source: fine-focus sealed tube629 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.113
Detector resolution: 6.7 pixels mm-1θmax = 28.0°, θmin = 4.3°
ϕ scansh = 1212
Absorption correction: numerical
[X-RED (Stoe & Cie, 2001) and X-SHAPE (Stoe & Cie, 1999)]
k = 66
Tmin = 0.045, Tmax = 0.135l = 1212
4112 measured reflections
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.050Secondary atom site location: difference Fourier map
wR(F2) = 0.126 w = 1/[σ2(Fo2) + (0.0659P)2]
where P = (Fo2 + 2Fc2)/3
S = 0.88(Δ/σ)max < 0.001
1099 reflectionsΔρmax = 3.79 e Å3
61 parametersΔρmin = 1.45 e Å3
Crystal data top
Sr2Cu2TeO6Br2V = 456.4 (3) Å3
Mr = 685.74Z = 2
Monoclinic, P21/cMo Kα radiation
a = 9.422 (3) ŵ = 28.10 mm1
b = 5.1788 (17) ÅT = 291 K
c = 9.388 (3) Å0.07 × 0.06 × 0.02 mm
β = 94.92 (3)°
Data collection top
Stoe IPDS
diffractometer
1099 independent reflections
Absorption correction: numerical
[X-RED (Stoe & Cie, 2001) and X-SHAPE (Stoe & Cie, 1999)]
629 reflections with I > 2σ(I)
Tmin = 0.045, Tmax = 0.135Rint = 0.113
4112 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.05061 parameters
wR(F2) = 0.1260 restraints
S = 0.88Δρmax = 3.79 e Å3
1099 reflectionsΔρmin = 1.45 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
Te10.00000.00000.50000.0145 (3)
Sr10.27752 (15)0.3978 (3)0.31832 (16)0.0224 (3)
Br10.38759 (17)0.8884 (3)0.16320 (18)0.0271 (4)
Cu10.08010 (18)0.4855 (4)0.36478 (15)0.0163 (4)
O10.0354 (11)0.6641 (17)0.1857 (10)0.0148 (19)
O20.1142 (10)0.2992 (19)0.5465 (9)0.016 (2)
O30.1624 (11)0.1847 (18)0.4423 (10)0.017 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Te10.0202 (6)0.0120 (6)0.0112 (5)0.0012 (5)0.0009 (4)0.0001 (5)
Sr10.0230 (7)0.0189 (7)0.0243 (7)0.0014 (6)0.0030 (5)0.0015 (6)
Br10.0248 (8)0.0237 (8)0.0331 (8)0.0006 (7)0.0033 (6)0.0024 (7)
Cu10.0241 (9)0.0129 (8)0.0117 (7)0.0002 (8)0.0005 (6)0.0003 (7)
O10.025 (5)0.010 (5)0.010 (4)0.003 (4)0.006 (4)0.002 (3)
O20.025 (5)0.013 (4)0.009 (4)0.004 (4)0.005 (4)0.005 (3)
O30.024 (5)0.009 (5)0.019 (5)0.005 (4)0.006 (4)0.003 (4)
Geometric parameters (Å, º) top
Te1—O21.915 (9)Sr1—Cu1i3.395 (2)
Te1—O31.922 (9)Sr1—Cu1ii3.425 (2)
Te1—O1i1.943 (9)Sr1—Br1vii3.655 (2)
Te1—Cu12.9439 (19)Cu1—O11.933 (9)
Te1—Cu1ii3.0734 (19)Cu1—O21.962 (9)
Te1—Sr13.6367 (17)Cu1—O3viii1.988 (10)
Sr1—O2ii2.471 (9)Cu1—O1i2.022 (10)
Sr1—O1i2.586 (10)Cu1—O2ii2.355 (10)
Sr1—O3iii2.651 (10)Cu1—Br1i2.974 (2)
Sr1—O3iv2.793 (10)Cu1—Cu1ii3.067 (3)
Sr1—Br13.064 (2)Cu1—Te1viii3.0734 (19)
Sr1—Br1v3.146 (2)Cu1—Sr1iv3.395 (2)
Sr1—Br1vi3.175 (2)Cu1—Sr1ii3.425 (2)
Sr1—Cu13.391 (2)Cu1—Cu1iv3.615 (2)
O2iii—Te1—O388.8 (4)O3iv—Sr1—Br1vi120.5 (2)
O2—Te1—O391.2 (4)Br1—Sr1—Br1vi75.01 (6)
O2—Te1—O1ix95.7 (4)Br1v—Sr1—Br1vi73.90 (6)
O3—Te1—O1ix87.5 (4)O2ii—Sr1—Br1vii64.2 (2)
O2iii—Te1—O1i95.7 (4)O1i—Sr1—Br1vii118.2 (2)
O2—Te1—O1i84.3 (4)O3iii—Sr1—Br1vii60.1 (2)
O3—Te1—O1i92.5 (4)O3iv—Sr1—Br1vii169.5 (2)
O2ii—Sr1—O1i78.1 (3)Br1—Sr1—Br1vii93.42 (5)
O2ii—Sr1—O3iii68.7 (3)Br1v—Sr1—Br1vii123.83 (7)
O1i—Sr1—O3iii61.3 (3)Br1vi—Sr1—Br1vii66.27 (6)
O2ii—Sr1—O3iv106.0 (3)O1—Cu1—O2176.8 (4)
O1i—Sr1—O3iv60.4 (3)O1—Cu1—O3viii87.5 (4)
O3iii—Sr1—O3iv121.2 (3)O2—Cu1—O3viii94.3 (4)
O2ii—Sr1—Br183.6 (2)O1—Cu1—O1i96.7 (2)
O1i—Sr1—Br1130.1 (2)O2—Cu1—O1i81.0 (4)
O3iii—Sr1—Br1147.7 (2)O3viii—Cu1—O1i168.0 (4)
O3iv—Sr1—Br181.5 (2)O1—Cu1—O2ii87.9 (4)
O2ii—Sr1—Br1v159.4 (2)O2—Cu1—O2ii90.0 (4)
O1i—Sr1—Br1v81.8 (2)O3viii—Cu1—O2ii75.8 (4)
O3iii—Sr1—Br1v97.9 (2)O1i—Cu1—O2ii93.1 (4)
O3iv—Sr1—Br1v66.6 (2)Cu1—O1—Cu1iv132.1 (5)
Br1—Sr1—Br1v112.99 (7)Cu1—O2—Cu1ii90.0 (4)
O2ii—Sr1—Br1vi124.0 (2)Cu1ii—Cu1—Cu1i108.59 (9)
O1i—Sr1—Br1vi151.1 (2)Cu1ii—Cu1—Cu1iv104.39 (9)
O3iii—Sr1—Br1vi106.5 (2)Cu1i—Cu1—Cu1iv91.49 (7)
Symmetry codes: (i) x, y1/2, z+1/2; (ii) x, y+1, z+1; (iii) x, y, z+1; (iv) x, y+1/2, z+1/2; (v) x, y1, z; (vi) x1, y1/2, z+1/2; (vii) x, y+3/2, z+1/2; (viii) x, y+1, z; (ix) x, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaSr2Cu2TeO6Br2
Mr685.74
Crystal system, space groupMonoclinic, P21/c
Temperature (K)291
a, b, c (Å)9.422 (3), 5.1788 (17), 9.388 (3)
β (°) 94.92 (3)
V3)456.4 (3)
Z2
Radiation typeMo Kα
µ (mm1)28.10
Crystal size (mm)0.07 × 0.06 × 0.02
Data collection
DiffractometerStoe IPDS
diffractometer
Absorption correctionNumerical
[X-RED (Stoe & Cie, 2001) and X-SHAPE (Stoe & Cie, 1999)]
Tmin, Tmax0.045, 0.135
No. of measured, independent and
observed [I > 2σ(I)] reflections
4112, 1099, 629
Rint0.113
(sin θ/λ)max1)0.659
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.050, 0.126, 0.88
No. of reflections1099
No. of parameters61
Δρmax, Δρmin (e Å3)3.79, 1.45

Computer programs: EXPOSE in IPDS (Stoe & Cie, 1997), CELL in IPDS, INTEGRATE in IPDS, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), DIAMOND (Brandenburg, 2001), SHELXL97.

Selected geometric parameters (Å, º) top
Te1—O21.915 (9)Sr1—Br1vi3.175 (2)
Te1—O31.922 (9)Sr1—Br1vii3.655 (2)
Te1—O1i1.943 (9)Cu1—O11.933 (9)
Sr1—O2ii2.471 (9)Cu1—O21.962 (9)
Sr1—O1i2.586 (10)Cu1—O3viii1.988 (10)
Sr1—O3iii2.651 (10)Cu1—O1i2.022 (10)
Sr1—O3iv2.793 (10)Cu1—O2ii2.355 (10)
Sr1—Br13.064 (2)Cu1—Cu1ii3.067 (3)
Sr1—Br1v3.146 (2)Cu1—Cu1iv3.615 (2)
Cu1—O1—Cu1iv132.1 (5)Cu1—O2—Cu1ii90.0 (4)
Symmetry codes: (i) x, y1/2, z+1/2; (ii) x, y+1, z+1; (iii) x, y, z+1; (iv) x, y+1/2, z+1/2; (v) x, y1, z; (vi) x1, y1/2, z+1/2; (vii) x, y+3/2, z+1/2; (viii) x, y+1, z.
Bond valence sum values (BVS) for the different atoms in (I). top
AtomBVSAtomBVS
Te15.85O12.11
Sr11.97O22.02
Br10.90O31.82
Cu11.96
 

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