Ca₂CuTe₄O₁₀Cl₂, a new synthetic tellurium(IV) oxochloride

Single crystals of dicalcium copper tetra­tellurium deca­oxide dichloride, Ca₂CuTe₄O₁₀Cl₂, were synthesized via a transport reaction in sealed evacuated quartz glass tubes. The building units of the structure are irregular CaO₇ polyhedra, centrosymmetric CuO₄Cl₂ octa­hedra and two crystallographically distinct TeO₄E distorted bipyramids (E being the 5s² lone pair of Te^IV). The TeO₄E and CuO₄Cl₂ polyhedra together form planes that are connected by the Ca atoms. The CuO₄Cl₂ octa­hedra are isolated from each other by the other building units.

S1. Comment

Oxohalogenides comprising transition metals and elements having an asymmetric coordination due to presence of stereochemically active lone pairs, such as Te^IV, Se^IV, As^III or Sb^III, have proved to be a very interesting family of compounds, in which there is a high probability of finding novel host–guest compounds, quantum spin systems and low-dimensional compounds (Johnsson et al., 2000, 2003, 2004). The lone-pair elements and the halogens constitute `structural scissors', hindering the development of three-dimensional networks. In these kinds of oxohalogenide compounds, the lone-pair elements are coordinated only by oxygen and the metal ions are coordinated by both oxygen and halogens. The synthesis strategy involves the use of the halogens Cl, Br and I but not F, as the latter is so electronegative that it will also bond to the lone-pair elements; in this case the F atom may then constitute a bridge directly to a transition metal ion and thus will not act as `scissors', forcing the transition metal ions to take low-dimensional arrangements in the crystal structures.

The present work is an outcome of an ongoing investigation of transition metal oxohalogenides containing alkaline earth elements and asymmetrically coordinated lone-pair elements. The crystal structures of a few compounds in this family have been described before [Ba₃Te₂O₆Cl₂ (Hottentot & Loopstra, 1983), Ba₂Co(SeO₃)₂Cl₂ (Johnston & Harrison, 2002), Ba₂Cu₄Te₄O₁₁Cl₄ and BaCu₂Te₂O₆Cl₂ (Feger & Kolis, 1998)]. To our best knowledge, the novel compound Ca₂CuTe₄O₁₀Cl₂ is the first oxohalogenide described with Ca^II in combination with Cu^II and Te^IV.

There are two crystallographically distinct Te atoms. Atom Te1 has a see-saw [TeO₄] coordination to oxygen. When the stereochemically active 5s² lone pair (designated E) is also taken into account, the coordination becomes a distorted trigonal bipyramid [TeO₄E], where E is located in the equatorial plane. The bonding distances are in the range 1.841 (3)–2.206 (2) Å. Atom Te2 has a threefold one-sided [TeO₃] coordination, having Te—O bond distances in the range 1.867 (2)–1.932 (2) Å. A fourth longer Te2—O4 bond [2.616 (3) Å] completes the see-saw coordination. Bond valence sum calculations (Brown & Altermatt, 1985) suggest that this long Te—O distance contributes to the bond valence and that it therefore should be regarded as coordinated. Taking the stereochemically active lone pair into account the coordination polyhedron becomes a [TeO_{3 + 1}E] trigonal bipyramid for Te2, with the lone pair in the equatorial plane. Geometrically placing the lone pairs assuming a Te—E distance (radius) of 1.25 Å (Galy et al., 1975) gives the fractional coordinates E1 (x = 0.3175, y = 0.4855, z = 0.2878) and E2 (x = −0.3943, y = 0.6409, z = 0.4123) for Te1 and Te2, respectively.

The Cu atom, located at a centre of symmetry, is coordinated by four O atoms in a square planar configuration, with Cu—O distances of 1.945 (2)–2.017 (3) Å, and two Cl atoms complete a [CuO₄Cl₂] octahedron, with Cu—Cl distances of 2.738 (2) Å. The Ca atom is coordinated by seven O atoms to form an irregular [CaO₇] polyhedron. The Ca—O distances are 2.330 (3)–2.583 (3) Å, except for the short Ca—O5 distance which is only 2.266 (3) Å. A long Ca—Cl distance of 3.379 (2) Å does not contribute significantly to the bond valence sum and the Cl atom is therefore not regarded as bonded.

An overview of the structure is shown in Fig. 1. The [Te1O₄E] and [Te2O_{3 + 1}E] polyhedra build infinite [TeO_2.5]_n chains along [011] by corner sharing and edge sharing. The [TeO_2.5]_n chains are linked by [CuO₄Cl₂] octahedra via the [Te₂O_{3 + 1}E] polyhedra to form layers in the (0–11) plane (see Fig. 2). Each [CuO₄Cl₂] octahedra share edges with two [CaO₇] polyhedra and with two [Te2O_{3 + 1}E] bipyramids and corners with two more such bipyramids (see Fig. 3). Each [CaO₇] polyhedron shares edges with two [Te1O₄E] and two [Te2O_{3 + 1}E] bipyramids and corners with two more of each kind of Te polyhedron. The [CaO₇] polyhedra also share edges with two more [CaO₇] polyhedra to build up [CaO₅]_n chains along [100]. The [CaO₅]_n chains link the Te–O–Cu–Cl layers to build up the three-dimensional structure and channels develop along [100] where the chlorine atoms and the lone pairs (E) are located (see Fig. 1).

S2. Experimental

Single crystals of Ca₂CuTe₄O₁₀Cl₂ were synthesized by chemical transport reactions in sealed evacuated quartz glass tubes. CaO (ABCR, 99.95%), CuCl₂ (Avocado Research Chemicals, +98%), CuO (Avocado Research Chemicals, +99%) and TeO₂ (ABCR, +99%) were mixed in the non stoichiometric molar ratio 1:1:1:2 in a mortar and put into a quartz glass tube (length ~5 cm), which was then evacuated. The tube was heated for 72 h at 900 K in a muffle furnace. The product appeared as bright green plate-like single crystals and powder of undetermined composition. The synthesis product was non-hygroscopic.

S3. Refinement

Two different diffraction data sets were recorded with the same crystal in different χ orientations. Scale factors for the individual data sets were computed with SHELXL97 and finally the individual data sets were scaled and averaged with the program REFLEX (Eriksson, 2004). The structure was refined by full matrix least squares on F². All heavy atoms were refined with anisotropic displacement parameters; the O atoms were refined with isotropic displacement parameters.

Computing details

Data collection: program (reference)?; cell refinement: program (reference)?; data reduction: program (reference)?; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Bergerhoff, 1996); software used to prepare material for publication: program (reference)?.

Figures

	Fig. 1. The structure of Ca2CuTe4O10Cl2 is composed of layers formed by [CuO4Cl2] octahedra (blue in the online version of the journal) and [Te1O4E] and [Te2O3 + 1E] trigonal bipyramids (pink online) that are connected by the Ca atoms (yellow spheres online). (Online, O atoms are red and Cl atoms are green.) The positions of the 5s^2 lone pairs (E) on the Te atoms are marked as black spheres. The lone pairs and the Cl atoms are located in channels in the structure.
	Fig. 2. The [Te1O4E] and the [Te2O3 + 1E] polyhedra build up infinite [TeO2.5]n chains along [011] by corner and edge sharing. The [TeO2.5]n chains are linked by [CuO4Cl2] octahedra to form layers in the (0–11) plane.
	Fig. 3. Each [CuO4Cl2] octahedron share edges with two [Te2O3 + 1E] bipyramids and corners with two more bipyramids of the same kind. Edges are also shared with two [CaO7] polyhedra (yellow).

dicalcium copper tetratellurium decaoxide dichloride

Crystal data

Ca2CuTe4O10Cl2	Z = 1
Mr = 885.00	F(000) = 391
Triclinic, P1	Dx = 4.656 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 5.421 (2) Å	Cell parameters from 1170 reflections
b = 7.266 (3) Å	θ = 1.9–28.1°
c = 8.717 (5) Å	µ = 12.07 mm^−1
α = 71.60 (6)°	T = 291 K
β = 79.26 (6)°	Plate, green
γ = 77.63 (5)°	0.16 × 0.14 × 0.12 mm
V = 315.6 (3) Å^3

Data collection

STOE IPDS diffractometer	1487 independent reflections
Radiation source: fine-focus sealed tube	1381 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.046
Detector resolution: 6.7 pixels mm^-1	θmax = 27.9°, θmin = 2.5°
ϕ–scan	h = −7→7
Absorption correction: numerical [X-RED (Stoe & Cie, 1996) and X-SHAPE (Stoe & Cie, 1997)]	k = −9→9
Tmin = 0.136, Tmax = 0.234	l = −11→11
4989 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.018	Secondary atom site location: difference Fourier map
wR(F^2) = 0.044	w = 1/[σ^2(Fo^2) + (0.0269P)^2 + 0.0814P] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max = 0.001
1487 reflections	Δρmax = 1.03 e Å^−3
88 parameters	Δρmin = −0.83 e Å^−3

Special details

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
Te1	0.38491 (4)	0.58760 (3)	0.14712 (2)	0.00890 (7)
Te2	−0.39092 (3)	0.81909 (3)	0.38968 (2)	0.00850 (7)
Cu1	0.0000	1.0000	0.5000	0.01125 (12)
Ca1	0.17134 (13)	1.10242 (9)	0.10488 (7)	0.01070 (12)
Cl1	−0.11270 (17)	0.39350 (13)	0.34489 (12)	0.02541 (19)
O1	0.3293 (4)	0.4007 (3)	0.0257 (3)	0.0121 (4)
O2	−0.1067 (4)	0.9451 (3)	0.3201 (2)	0.0134 (4)
O3	0.5523 (4)	0.8242 (3)	0.1759 (2)	0.0119 (4)
O4	−0.6544 (4)	1.0432 (3)	0.3753 (2)	0.0115 (4)
O5	0.1675 (4)	0.7991 (3)	0.0367 (3)	0.0136 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Te1	0.00890 (11)	0.00888 (11)	0.00852 (10)	−0.00125 (7)	−0.00136 (7)	−0.00197 (7)
Te2	0.00704 (11)	0.00997 (11)	0.00889 (10)	−0.00177 (8)	−0.00164 (7)	−0.00269 (7)
Cu1	0.0073 (2)	0.0201 (3)	0.0096 (2)	−0.0037 (2)	−0.00124 (18)	−0.00787 (19)
Ca1	0.0103 (3)	0.0109 (3)	0.0111 (3)	−0.0033 (2)	−0.0030 (2)	−0.0014 (2)
Cl1	0.0185 (4)	0.0192 (4)	0.0333 (4)	0.0003 (3)	−0.0058 (3)	−0.0011 (3)
O1	0.0107 (10)	0.0136 (10)	0.0136 (9)	−0.0043 (9)	0.0022 (8)	−0.0067 (8)
O2	0.0114 (11)	0.0225 (11)	0.0097 (9)	−0.0089 (9)	0.0000 (8)	−0.0061 (8)
O3	0.0133 (11)	0.0151 (10)	0.0106 (9)	−0.0017 (9)	−0.0049 (8)	−0.0068 (8)
O4	0.0075 (10)	0.0136 (10)	0.0133 (10)	0.0006 (8)	−0.0020 (8)	−0.0048 (8)
O5	0.0130 (11)	0.0115 (10)	0.0166 (10)	0.0020 (9)	−0.0079 (8)	−0.0035 (8)

Geometric parameters (Å, º)

Te1—O5	1.841 (3)	Cu1—Cl1^vii	2.738 (2)
Te1—O1^i	1.945 (3)	Cu1—Cl1^viii	2.738 (2)
Te1—O1	2.064 (2)	Cu1—Te2^vi	3.1456 (14)
Te1—O3	2.206 (2)	Cu1—Ca1	3.281 (2)
Te1—Te1^i	3.153 (2)	Cu1—Ca1^vi	3.281 (2)
Te1—Te2^ii	3.5854 (18)	Cu1—Te2^ii	3.363 (2)
Te1—Ca1	3.5920 (19)	Cu1—Te2^v	3.363 (2)
Te1—Ca1^iii	3.593 (3)	Ca1—O5^ix	2.266 (3)
Te2—O2	1.867 (2)	Ca1—O2	2.330 (3)
Te2—O4	1.910 (2)	Ca1—O1^vii	2.353 (3)
Te2—O3^iv	1.932 (2)	Ca1—O5	2.462 (3)
Te2—O4^v	2.616 (3)	Ca1—O3	2.575 (3)
Cu1—O2	1.945 (2)	Ca1—O4^ii	2.579 (3)
Cu1—O2^vi	1.945 (2)	Ca1—O3^iii	2.583 (3)
Cu1—O4^ii	2.017 (3)	Ca1—Cl1^vii	3.379 (2)
Cu1—O4^v	2.017 (3)	Ca1—Te2^ii	3.593 (3)
O5—Te1—O1^i	97.39 (11)	O5^ix—Ca1—O1^vii	99.20 (10)
O5—Te1—O1	94.28 (11)	O2—Ca1—O1^vii	136.04 (9)
O1^i—Te1—O1	76.28 (11)	O5^ix—Ca1—O5	79.76 (10)
O5—Te1—O3	81.82 (10)	O2—Ca1—O5	77.71 (9)
O1^i—Te1—O3	79.69 (10)	O1^vii—Ca1—O5	146.24 (8)
O1—Te1—O3	154.95 (8)	O5^ix—Ca1—O3	142.86 (9)
O2—Te2—O4	99.67 (11)	O2—Ca1—O3	93.49 (10)
O2—Te2—O3^iv	96.44 (11)	O1^vii—Ca1—O3	106.83 (9)
O4—Te2—O3^iv	87.52 (11)	O5—Ca1—O3	63.84 (8)
O2—Te2—O4^v	73.44 (9)	O5^ix—Ca1—O4^ii	148.15 (9)
O4—Te2—O4^v	75.35 (10)	O2—Ca1—O4^ii	70.95 (9)
O3^iv—Te2—O4^v	157.99 (8)	O1^vii—Ca1—O4^ii	84.62 (10)
O2—Cu1—O2^vi	180.000 (1)	O5—Ca1—O4^ii	114.06 (9)
O2—Cu1—O4^ii	92.22 (10)	O3—Ca1—O4^ii	62.08 (9)
O2^vi—Cu1—O4^ii	87.78 (10)	O5^ix—Ca1—O3^iii	86.05 (9)
O2—Cu1—O4^v	87.78 (10)	O2—Ca1—O3^iii	158.22 (8)
O2^vi—Cu1—O4^v	92.22 (10)	O1^vii—Ca1—O3^iii	65.22 (9)
O4^ii—Cu1—O4^v	180.000 (1)	O5—Ca1—O3^iii	81.09 (9)
O2—Cu1—Cl1^vii	88.81 (9)	O3—Ca1—O3^iii	81.48 (10)
O2^vi—Cu1—Cl1^vii	91.19 (9)	O4^ii—Ca1—O3^iii	123.31 (8)
O4^ii—Cu1—Cl1^vii	80.98 (9)	O5^ix—Ca1—Cl1^vii	90.17 (8)
O4^v—Cu1—Cl1^vii	99.02 (9)	O2—Ca1—Cl1^vii	68.43 (8)
O2—Cu1—Cl1^viii	91.19 (9)	O1^vii—Ca1—Cl1^vii	67.86 (7)
O2^vi—Cu1—Cl1^viii	88.81 (9)	O5—Ca1—Cl1^vii	145.35 (7)
O4^ii—Cu1—Cl1^viii	99.02 (9)	O3—Ca1—Cl1^vii	123.88 (7)
O4^v—Cu1—Cl1^viii	80.98 (9)	O4^ii—Ca1—Cl1^vii	61.80 (7)
Cl1^vii—Cu1—Cl1^viii	180.000 (1)	O3^iii—Ca1—Cl1^vii	131.59 (7)
O5^ix—Ca1—O2	85.36 (10)

Symmetry codes: (i) −x+1, −y+1, −z; (ii) x+1, y, z; (iii) −x+1, −y+2, −z; (iv) x−1, y, z; (v) −x−1, −y+2, −z+1; (vi) −x, −y+2, −z+1; (vii) x, y+1, z; (viii) −x, −y+1, −z+1; (ix) −x, −y+2, −z.