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Dizinc selenium dichloride trioxide, β-Zn2(SeO3)Cl2, a monoclinic polymorph of the ortho­rhom­bic mineral sophiite, has a structure built of distorted ZnO4Cl2 octa­hedra, ZnO2Cl2 tetra­hedra and SeO3E tetra­hedra (E being the 4s2 lone pair of the SeIV ion), joined through shared edges and corners to form charge-neutral layers. The Cl atoms and the Se lone pairs protrude from each layer towards adjacent layers. The main structural difference between the mineral and synthetic polymorphs lies in the packing of the layers.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270107012541/bc3038sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270107012541/bc3038Isup2.hkl
Contains datablock I

Comment top

The synthesis and crystal structure determination of the new compound β-Zn2(SeO3)Cl2, (I), a synthetic polymorph of the mineral sophiite (Semenova et al., 1992), is a result of an ongoing investigation of the structural chemistry of selenium and tellurium oxohalides. Transition metal oxohalides containing p-element cations, such as SeIV or TeIV with stereochemically active lone pairs, frequently show a low-dimensional arrangement of the metal ions. In these compounds, the transition metals tend to bond to both oxygen and halogens, while the main group elements preferably form bonds only with oxygen. A simple explanation is that the hard Lewis acid Se4+ prefers the hard Lewis base O2-, while the softer Lewis acid Zn2+ accepts both O2- and Cl- in an oxohalide environment. A consequence of the different bonding preferences is that only the O atoms bond to both types of cations and that the SeIV lone pairs and the halogen atoms act as `chemical scissors' by reducing the dimensionality of the crystal structure (Johnsson et al., 2000, 2003; Johnsson & Törnroos, 2003a,b). The aim of this study was to test this concept of synthesis on the system ZnO2–ZnCl2–SeO2.

The crystal structure of (I) consists of charge neutral layers connected only via van der Waals interactions (Fig. 1). The Se atom has a typical one-sided threefold coordination owing to the presence of its stereochemically active 4s2 lone pair (designated E), and its coordination polyhedron is therefore a slightly distorted [SeO3E] tetrahedron. Atom Zn1 is coordinated by two O atoms and two Cl atoms, forming a distorted [ZnO2Cl2] tetrahedron, and atom Zn2 is coordinated by four O atoms and two Cl atoms, completing a distorted [ZnO4Cl2] octahedron (Table 1). The Zn2—Cl2 distance is 2.4306 (4) Å while the Zn2—Cl1 distance is 2.7645 (5) Å. The latter is quite long, but bond valence sum calculations (Brown & Altermatt, 1985) suggest that atom Cl2 should be treated as coordinated by the Zn atom.

The three different building units, viz. the [Zn1O2Cl2], [Zn2O4Cl2] and [SeO3E] groups, are connected to form infinite (010) layers. Each [ZnO4Cl2] polyhedron is linked to two others by corner sharing, forming infinite [001] chains within the layers. The chains are separated by [ZnO2Cl2] and [SeO3E] groups and each [ZnO4Cl2] polyhedron shares two corners and one edge with three [ZnO2Cl2] groups, as well as two corners and one edge with three [SeO3E] groups (Fig. 2).

The stereochemically active Se lone pairs are located between the layers, pointing in between the protruding Cl atoms of the opposite layer. The shortest cation–anion distances between adjacent layers [Se···Cl1 = 3.5145 (5) Å, Zn1···Cl1 = 3.6827 (5) Å, Zn1···Cl2 = 4.7786 (5) Å and Zn2···Cl2 = 5.4849 (7) Å] are similar to, or larger than, the cation–cation separations within the layers [Se···Zn2 = 2.9404 (3) Å, Zn1···Zn2 = 3.2319 (3) Å, Se···Zn1 = 3.3241 (4) Å, Zn2···Zn2 = 3.8734 (4) Å and Zn1···Zn1 = 4.1349 (5) Å; symmetry codes as in Table 1]. The long interlayer distances imply that the layers are held together only by dispersion forces. Assuming an Se—E radius of 1.22 Å (Galy et al., 1975), the fractional coordinates for the lone pair E (x = 0.69, y = 0.47, z = 0.10) yield E···Cl1 and E···Cl2 contact distances of ~2.72 and ~ 2.71 Å, respectively.

The orthorhombic (Pccn) mineral sophiite shows the same connectivity of the building units within the layers as the synthetic form (I). The main structural difference between the two polymorphs is that every second layer in the mineral structure is rotated 180° around the a axis; the layer rotation results in a doubling of the a axis.

Three other compounds are quite similar to the mineral sophiite, viz. CuZn(TeO3)Cl2 (Johnsson & Törnroos, 2003a), Zn2(TeO3)Cl2 (Johnsson & Törnroos, 2003b) and Co2(TeO3)Br2 (Becker et al., 2006). They all crystallize in the orthorhombic space group Pccn. The main structural difference is that the octahedron around the atom corresponding to Zn2 is so distorted that it should rather be regarded as a square pyramid according to the idea that, for a ligand to be regarded as bonded, it should contribute more than 4% of the cation valence (Brown, 2002). A fourth related compound, Co2(TeO3)Cl2 (Becker et al., 2006), crystallizes in the monoclinic space group P21/m. However, instead of tetrahedral and octahedral coordination of the metal cations, it contains two types of distorted octahedra, resulting in a completely different connectivity within the layers.

Related literature top

For related literature, see: Becker et al. (2006); Brown (2002); Brown & Altermatt (1985); Galy et al. (1975); Johnsson & Törnroos (2003a, 2003b); Johnsson et al. (2000, 2003); Semenova et al. (1992).

Experimental top

Compound (I) was synthesized by chemical transport reactions in sealed evacuated soda-glass tubes. ZnCl2 (Avocado Research Chemicals Ltd, 98+%), ZnO (ABCR, 99+%), and SeO2 (ABCR, 99+%) were used as starting materials. Equimolar amounts of ZnCl2 (0.135 g), ZnO (0.081 g) and SeO2 (0.110 g) were mixed in a mortar and placed in a glass tube (length ~5 cm), which was evacuated and heated at 700 K for 72 h in a muffle furnace. The product appeared as colourless transparent plate-like single crystals, with a maximum size of 0.5 mm, 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. Analysis found: Zn 38.0 (17), Se 20.8 (7), Cl 41.2 (23)%. No Si originating from the glass tube was detected.

Computing details top

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, 2001a); molecular graphics: SHELXTL/PC (Sheldrick, 2001b); software used to prepare material for publication: DIAMOND (Brandenburg, 2006) and PLATON (Spek, 2001).

Figures top
[Figure 1] Fig. 1. The layer structure of (I) seen along [001]. Atomic displacement parameters are given at the 50% probability level. O and Cl atoms are dark grey and white, respectively, and lone pairs (E) are black spheres of arbitrary radius.
[Figure 2] Fig. 2. Connectivity of the Zn2O4Cl2 octahedra (striped light grey), Zn1O2Cl2 tetrahedra (light gray) and SeO3E tetrahedra (dark gray) in (I). [Symmetry codes: (i) -x + 1, y - 1/2, -z + 3/2; (ii) x - 1, y, z + 1; (iii) x - 1, y, z + 1; (iv) -x + 1, -y + 1, -z + 1; (v) x - 1, -y + 1/2, z + 1/2; (vi) -x + 1, y - 1/2, -z + 1/2; (vii) x - 1, y, z; (viii) x - 1, y, z; (ix) -x + 1, -y + 1, -z.]
Dizinc selenium dichloride trioxide top
Crystal data top
Zn2(SeO3)Cl2F(000) = 608
Mr = 328.60Dx = 3.678 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 4391 reflections
a = 7.6699 (8) Åθ = 2.7–32.6°
b = 10.2612 (11) ŵ = 15.02 mm1
c = 7.6571 (8) ÅT = 123 K
β = 100.004 (2)°Thin plate, colourless
V = 593.47 (11) Å30.26 × 0.24 × 0.02 mm
Z = 4
Data collection top
Bruker SMART 2K CCD
diffractometer
2147 independent reflections
Radiation source: normal-focus sealed tube2015 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.023
ω scansθmax = 32.6°, θmin = 2.7°
Absorption correction: numerical
(SHELXTL/PC; Sheldrick, 2001b)
h = 1111
Tmin = 0.026, Tmax = 0.722k = 1515
10582 measured reflectionsl = 1111
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)] = 0.013 w = 1/[σ2(Fo2) + (0.0152P)2 + 0.0506P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.032(Δ/σ)max = 0.002
S = 1.08Δρmax = 0.46 e Å3
2147 reflectionsΔρmin = 0.39 e Å3
74 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0022 (2)
Crystal data top
Zn2(SeO3)Cl2V = 593.47 (11) Å3
Mr = 328.60Z = 4
Monoclinic, P21/cMo Kα radiation
a = 7.6699 (8) ŵ = 15.02 mm1
b = 10.2612 (11) ÅT = 123 K
c = 7.6571 (8) Å0.26 × 0.24 × 0.02 mm
β = 100.004 (2)°
Data collection top
Bruker SMART 2K CCD
diffractometer
2147 independent reflections
Absorption correction: numerical
(SHELXTL/PC; Sheldrick, 2001b)
2015 reflections with I > 2σ(I)
Tmin = 0.026, Tmax = 0.722Rint = 0.023
10582 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.01374 parameters
wR(F2) = 0.0320 restraints
S = 1.08Δρmax = 0.46 e Å3
2147 reflectionsΔρmin = 0.39 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. The maximum reidual peak (0.46 e A%-3) at 0.70 Å from Cl1 and the largest hole (-0.39 A%-3) at 0.62 Å from Zn1.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Se0.814070 (17)0.532687 (12)0.185624 (16)0.00879 (4)
Zn11.23059 (2)0.512495 (15)0.39561 (2)0.01097 (4)
Zn20.91497 (2)0.778634 (15)0.37326 (2)0.01199 (4)
Cl11.40404 (5)0.40258 (4)0.24339 (4)0.01666 (7)
Cl21.22516 (5)0.72269 (3)0.46610 (4)0.01458 (7)
O10.80793 (13)0.58925 (9)0.39417 (12)0.01222 (18)
O21.01471 (13)0.45454 (9)0.22034 (13)0.01211 (18)
O30.87607 (13)0.68185 (9)0.12038 (12)0.01166 (18)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Se0.01005 (7)0.00769 (6)0.00854 (6)0.00035 (4)0.00135 (4)0.00062 (4)
Zn10.01247 (8)0.01043 (8)0.01031 (7)0.00046 (5)0.00284 (5)0.00028 (5)
Zn20.01889 (9)0.00836 (8)0.00924 (7)0.00206 (5)0.00391 (6)0.00084 (5)
Cl10.01446 (15)0.02138 (16)0.01493 (15)0.00337 (12)0.00473 (12)0.00135 (11)
Cl20.01543 (15)0.01019 (14)0.01694 (15)0.00068 (11)0.00045 (12)0.00019 (11)
O10.0176 (5)0.0100 (4)0.0100 (4)0.0012 (3)0.0049 (4)0.0011 (3)
O20.0119 (4)0.0100 (4)0.0139 (4)0.0014 (3)0.0007 (4)0.0021 (3)
O30.0173 (5)0.0082 (4)0.0095 (4)0.0010 (3)0.0022 (4)0.0005 (3)
Geometric parameters (Å, º) top
Se—O31.7032 (9)Zn1—Cl1iv3.6827 (5)
Se—O11.7074 (9)Zn1—Zn1ii4.1349 (5)
Se—O21.7146 (10)Zn1—Cl2iv4.7786 (5)
Se—Zn22.9404 (3)Zn2—O3v2.0075 (9)
Se—Zn13.3241 (4)Zn2—O2vi2.0487 (10)
Se—Cl1i3.5145 (5)Zn2—O12.1265 (10)
Zn1—O1ii1.9833 (9)Zn2—O32.1503 (9)
Zn1—O22.0308 (10)Zn2—Cl22.4306 (4)
Zn1—Cl12.2225 (4)Zn2—Cl1vi2.7645 (5)
Zn1—Cl22.2255 (4)Zn2—Zn2v3.8734 (4)
Zn1—Zn2iii3.2319 (3)Zn2—Cl2i5.4894 (7)
O3—Se—O191.34 (4)O3v—Zn2—Cl294.03 (3)
O3—Se—O2100.19 (5)O3v—Zn2—Cl1vi86.76 (3)
O1—Se—O2100.59 (5)O2vi—Zn2—O1163.76 (4)
O1ii—Zn1—O299.38 (4)O2vi—Zn2—O395.49 (4)
O1ii—Zn1—Cl1110.22 (3)O2vi—Zn2—Cl290.38 (3)
O2—Zn1—Cl189.91 (3)O2vi—Zn2—Cl1vi75.74 (3)
O1ii—Zn1—Cl2107.56 (3)O1—Zn2—O369.56 (4)
O2—Zn1—Cl2113.37 (3)O1—Zn2—Cl297.66 (3)
Cl1—Zn1—Cl2131.082 (15)O1—Zn2—Cl1vi96.50 (3)
O3v—Zn2—O2vi104.07 (4)O3—Zn2—Cl297.46 (3)
O3v—Zn2—O189.49 (4)O3—Zn2—Cl1vi86.85 (3)
O3v—Zn2—O3157.22 (4)Cl2—Zn2—Cl1vi165.831 (12)
Symmetry codes: (i) x1, y, z; (ii) x+2, y+1, z+1; (iii) x+2, y1/2, z+1/2; (iv) x+3, y+1, z+1; (v) x, y+3/2, z+1/2; (vi) x+2, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaZn2(SeO3)Cl2
Mr328.60
Crystal system, space groupMonoclinic, P21/c
Temperature (K)123
a, b, c (Å)7.6699 (8), 10.2612 (11), 7.6571 (8)
β (°) 100.004 (2)
V3)593.47 (11)
Z4
Radiation typeMo Kα
µ (mm1)15.02
Crystal size (mm)0.26 × 0.24 × 0.02
Data collection
DiffractometerBruker SMART 2K CCD
diffractometer
Absorption correctionNumerical
(SHELXTL/PC; Sheldrick, 2001b)
Tmin, Tmax0.026, 0.722
No. of measured, independent and
observed [I > 2σ(I)] reflections
10582, 2147, 2015
Rint0.023
(sin θ/λ)max1)0.758
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.013, 0.032, 1.08
No. of reflections2147
No. of parameters74
Δρmax, Δρmin (e Å3)0.46, 0.39

Computer programs: SMART (Bruker, 1999), SAINT (Bruker, 2001), SAINT, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 2001a), SHELXTL/PC (Sheldrick, 2001b), DIAMOND (Brandenburg, 2006) and PLATON (Spek, 2001).

Selected bond lengths (Å) top
Se—O31.7032 (9)Zn2—O3ii2.0075 (9)
Se—O11.7074 (9)Zn2—O2iii2.0487 (10)
Se—O21.7146 (10)Zn2—O12.1265 (10)
Zn1—O1i1.9833 (9)Zn2—O32.1503 (9)
Zn1—O22.0308 (10)Zn2—Cl22.4306 (4)
Zn1—Cl12.2225 (4)Zn2—Cl1iii2.7645 (5)
Zn1—Cl22.2255 (4)
Symmetry codes: (i) x+2, y+1, z+1; (ii) x, y+3/2, z+1/2; (iii) x+2, y+1/2, z+1/2.
 

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