A synthetic zinc tellurium oxochloride, Zn₂(TeO₃)Cl₂

Single crystals of dizinc tellurium dichloride trioxide, Zn₂(TeO₃)Cl₂, were synthesized via a transport reaction in sealed evacuated glass tubes. The compound has a layered structure in which the building units are [ZnO₄Cl] square pyramids, distorted [ZnO₂Cl₂] tetrahedra and [TeO₃E] tetrahedra (E is the 5s² lone pair of the Te^IV atom), joined through shared edges and corners to form charge-neutral layers. Cl atoms and Te-atom lone pairs protrude from the surfaces of each layer towards adjacent layers, and the layers are held together by dispersion forces only. The compound is isostructural with the synthetic compound CuZn(TeO₃)Cl₂ and the mineral sophiite, Zn₂(SeO₃)Cl₂.

S1. Comment

The synthesis and crystal structure determination of the new compound Zn₂(TeO₃)Cl₂, (I), is a further result of an ongoing study investigating the chemistry of tellurium oxohalogenides. The Te atom in (I) has a typical one-sided threefold coordination because of the presence of its 5 s² lone pair (designated E) and its coordination polyhedron is therefore a [TeO₃E] tetrahedron.

Atom Zn1 is coordinated by two O atoms and two Cl atoms, thus forming a distorted [ZnO₂Cl₂] tetrahedron. Atom Zn2 is coordinated by four O atoms and one Cl atom, which complete a distorted square [ZnO₄Cl] pyramid. A distorted [ZnO₄Cl₂] octahedron is also formed if atom Cl1 is taken into account. However, the Zn2—Cl1 distance is long [3.2904 (5) Å], and atom Zn2 is located on the Cl2-atom side of the O-atom plane. Furthermore, bond valence sum calculations (Brown & Altermatt, 1985) give a negligible contribution from atom Cl1, suggesting that it should not be considered to be bonded to atom Zn2.

The three different building units, viz. [Zn1O₂Cl₂], [Zn2O₄Cl] and [TeO₃E], are connected so that infinite layers extending in the ac plane are formed (Fig 1). Each [ZnO₄Cl] polyhedron is linked to two others by corner sharing so that infinite chains of [ZnO₄Cl] polyhedra develop along the [001] direction within the layers. The chains are separated by [ZnO₂Cl₂] and [TeO₃E] groups. Each [ZnO₄Cl] polyhedron shares two corners with two [ZnO₂Cl₂] groups, as well as one corner and one edge with [TeO₃E] groups (Fig 2).

The stereochemically active Te lone pairs are located in the space between the layers of the structure, pointing towards the space between the similarly protruding Cl atoms of the opposite layer. The shortest cation–anion distances between adjacent layers (Te···Cl1, Zn1···Cl1, Zn2···Cl1 and Zn1···Cl2) are similar to, or larger than, the cation–cation separation within the layers (Te···Zn2, Zn1···Zn2, Te···Zn1, Zn2···Zn2, Zn1···Zn1 and Te···Te; Table 2).

The long interlayer distances imply that the layers are only held together by attractive dispersion forces. Each layer can thus be considered as an infinite two-dimensional molecule. Assuming a Te—E radius of 1.25 Å (Galy et al., 1975), the fractional coordinates for the lone pair E (x = −0.02015, y = 0.33335 and z = 0.15126) yield E···Cl1 and E···Cl2 contact distances of \sim2.61 and \sim3.00 Å, respectively.

Compound (I) is isostructural with CuZn(TeO₃)Cl₂ (Johnsson & Törnroos, 2003). The mineral sophiite, Zn₂(SeO₃)Cl₂ (Semenova et al., 1992), can also be considered as isostructural with (I), although, in contrast to (I), the coordination around atom Zn2 in the mineral creates a distorted [ZnO₄Cl₂] octahedron (Zn2—Cl1 = 2.68 Å and Zn2—Cl2 = 2.75 Å) with Zn2 located in the equatorial O-atom square plane. In sophiite, the coordination of both atom Cl1 and atom Cl2 to atom Zn2 is supported by bond-valence sum calculations.

S2. Experimental

Compound (I) was synthesized by chemical transport reactions in sealed evacuated soda-glass tubes. ZnO (ABCR, +99%), ZnCl₂ (Avocado Research Chemicals Ltd., +98%) and TeO₂ (ABCR, +99%) were used as starting materials. Equimolar amounts of ZnCl₂, ZnO and TeO₂ were mixed in a mortar and put in a glass tube (length ~6 cm), which was then evacuated and heated for 140 h at 770 K in a muffle furnace. The product appeared as colourless transparent plate-like single crystals and powder. The crystals are hygroscopic. The synthesis product was characterized in a scanning electron microscope (SEM, Jeol 820) with an energy-dispersive spectrometer (EDS, LINK AN10000) on ten different single crystals, giving a composition of 41.2 ± 1.3 at % Zn, 20.4 ± 0.6 at % Te, and 38.3 ± 1.2 at % Cl. No Si originating from the glass tubes was detected.

S3. Refinement

The maximum residual peak (0.78) is located 0.76 Å from the Te atom and the largest hole (−0.85) 0.73 Å from the Te atom.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 2001b); molecular graphics: DIAMOND (Brandenburg, 2000); software used to prepare material for publication: SHELXTL/PC (Sheldrick, 2001a) and PLATON (Spek, 2003).

Figures

	Fig. 1. The layer features in (I) along [001]. [TeO3E] polyhedra are pink, [ZnO4Cl] polyhedra are green and [ZnO2Cl2] polyhedra are blue. O atoms are red, Cl atoms are light blue and Te lone pairs (E) are yellow.
	Fig. 2. The arrangement of coordination polyhedra around a central [ZnO4Cl] square pyramid. Colors are as described in Fig. 1.

dizinc tellurium dichloride trioxide

Crystal data

Zn2(TeO3)Cl2	F(000) = 1360
Mr = 377.24	Dx = 4.048 Mg m^−3
Orthorhombic, Pccn	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ab 2ac	Cell parameters from 5733 reflections
a = 10.4467 (9) Å	θ = 2.4–32.5°
b = 15.4969 (13) Å	µ = 13.14 mm^−1
c = 7.6471 (6) Å	T = 123 K
V = 1238.00 (18) Å^3	Plate, colourless
Z = 8	0.33 × 0.31 × 0.03 mm

Data collection

Bruker SMART 2K CCD diffractometer	2248 independent reflections
Radiation source: normal-focus sealed tube	2119 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.036
ω scans	θmax = 32.6°, θmin = 2.4°
Absorption correction: numerical (SHELXTL/PC (Sheldrick, 2001a) and PLATON (Spek, 2003)	h = −15→15
Tmin = 0.035, Tmax = 0.709	k = −23→23
20130 measured reflections	l = −11→11

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)] = 0.016	Secondary atom site location: difference Fourier map
wR(F^2) = 0.039	w = 1/[σ^2(Fo^2) + (0.0156P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.26	(Δ/σ)max = 0.002
2248 reflections	Δρmax = 0.78 e Å^−3
73 parameters	Δρmin = −0.85 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. The maximum reidual peak (0.78 e A% ⁻³) at 0.76 Å from Te and the largest hole (−0.85 e A% ⁻³) at 0.73 Å from Te.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Te	0.027310 (10)	0.402129 (7)	0.206734 (14)	0.00851 (4)
Zn1	−0.00533 (2)	0.611195 (14)	0.34136 (3)	0.01034 (5)
Zn2	0.262829 (19)	0.472915 (13)	0.39691 (3)	0.01050 (5)
Cl1	−0.08591 (5)	0.71091 (3)	0.16362 (6)	0.01791 (9)
Cl2	0.20529 (4)	0.62193 (3)	0.42240 (5)	0.01485 (8)
O1	0.08543 (12)	0.41703 (8)	0.43657 (15)	0.0109 (2)
O2	0.18948 (11)	0.44213 (8)	0.14190 (15)	0.0109 (2)
O3	−0.05712 (12)	0.51026 (8)	0.19405 (15)	0.0110 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Te	0.00795 (6)	0.01028 (6)	0.00730 (6)	0.00006 (3)	−0.00070 (3)	−0.00087 (3)
Zn1	0.01156 (9)	0.01211 (10)	0.00736 (9)	−0.00078 (7)	0.00012 (7)	0.00044 (7)
Zn2	0.00824 (9)	0.01573 (10)	0.00752 (9)	−0.00144 (7)	−0.00034 (6)	0.00048 (6)
Cl1	0.0275 (2)	0.01342 (19)	0.01281 (18)	0.00274 (16)	−0.00504 (16)	0.00109 (14)
Cl2	0.01096 (18)	0.01445 (18)	0.01915 (19)	−0.00067 (14)	−0.00075 (14)	−0.00190 (14)
O1	0.0107 (5)	0.0144 (5)	0.0076 (5)	−0.0024 (4)	−0.0005 (4)	0.0002 (4)
O2	0.0087 (5)	0.0165 (6)	0.0076 (5)	−0.0004 (4)	0.0000 (4)	−0.0002 (4)
O3	0.0088 (5)	0.0126 (6)	0.0117 (5)	0.0010 (5)	−0.0019 (4)	−0.0005 (4)

Geometric parameters (Å, º)

Te—O1	1.8738 (11)	Zn1—Cl2	2.2919 (5)
Te—O2	1.8708 (12)	Zn2—O1	2.0680 (13)
Te—O3	1.8962 (13)	Zn2—O2	2.1488 (12)
Zn1—O1^i	1.9430 (12)	Zn2—O2^ii	1.9965 (12)
Zn1—O3	2.0021 (12)	Zn2—O3^iii	2.0223 (12)
Zn1—Cl1	2.2235 (5)	Zn2—Cl2	2.3941 (5)
O2—Te—O1	85.08 (5)	O2^ii—Zn2—O1	89.19 (5)
O2—Te—O3	96.59 (5)	O3^iii—Zn2—O1	159.71 (5)
O1—Te—O3	95.15 (5)	O2^ii—Zn2—O2	152.57 (7)
O1^i—Zn1—O3	101.51 (5)	O3^iii—Zn2—O2	92.76 (5)
O1^i—Zn1—Cl1	121.85 (4)	O1—Zn2—O2	73.77 (5)
O3—Zn1—Cl1	95.55 (4)	O1—Zn2—Cl2	99.61 (4)
O1^i—Zn1—Cl2	101.15 (4)	O2^ii—Zn2—Cl2	102.52 (4)
O3—Zn1—Cl2	117.92 (4)	O2—Zn2—Cl2	101.45 (4)
Cl1—Zn1—Cl2	118.575 (19)	O3^iii—Zn2—Cl2	97.88 (4)
O2^ii—Zn2—O3^iii	96.98 (5)

Symmetry codes: (i) −x, −y+1, −z+1; (ii) −x+1/2, y, z+1/2; (iii) x+1/2, −y+1, −z+1/2.