Crystal structure of Zn₂(HTeO₃)(AsO₄)

The crystal structure of Zn₂(HTeO₃)(AsO₄) consists of _∞ ²[ZnO_3/2(OH)_1/2O_1/1] layers extending parallel to (001) that are linked by [Te^IVO₃OH] and oxidoarsenate(V) groups.

Abstract

Single crystals of Zn₂(HTeO₃)(AsO₄), dizinc(II) hydroxidodioxidotellurate(IV) oxidoarsenate(V), were obtained as one of the by-products in a hydro­thermal reaction between Zn(NO₃)₂·6H₂O, TeO₂, H₃AsO₄ and NH₃ in molar ratios of 2:1:2:10 at 483 K for seven days. The asymmetric unit of Zn₂(HTeO₃)(AsO₄) contains one Te (site symmetry m), one As (m), one Zn (1), five O (three m, two 1) and one H (m) site. The Zn^II atom exhibits a coordination number of 5 and is coordinated by four oxygen atoms and a hydroxide group, forming a distorted trigonal bipyramid. The hydroxide ion is positioned at a significantly larger distance on one of the axial positions of the bipyramid. The [ZnO₄OH] polyhedra are connected to each other by corner-sharing to form _∞ ²[ZnO_3/2(OH)_1/2O_1/1] layers extending parallel to (001). The Te^IV atom is coordinated by three oxygen atoms and a hydroxide group in a one-sided manner in the shape of a bis­phenoid, revealing stereochemical activity of its 5s ² electron lone pair. The As^V atom is coordinated by four oxygen atoms to form the tetra­hedral oxidoarsenate(V) anion. By corner-sharing, [TeO₃OH] and [AsO₄] groups link adjacent _∞ ²[ZnO_3/2(OH)_1/2O_1/1] layers along [001] into a three-dimensional framework structure.

Chemical context  

Only a few elements have such a diverse crystal chemistry as tellurium, especially in its +IV oxidation state. This can be attributed to the stereochemically active non-bonding 5s ² electron pair of Te^IV (Galy et al., 1975 ▸) that has a similar space requirement as coordinating ligands and therefore often results in one-sided and low-symmetry coordination spheres around Te^IV atoms. An extensive review of the rich crystal chemistry of oxidotellurates(IV) was published recently by Christy et al. (2016 ▸).

The peculiar crystal chemistry of Te^IV makes it an inter­esting building block in the search for new compounds with crystal structures lacking inversion symmetry. As a prerequisite, a compound must be non-centrosymmetric in order to have ferro-, piezo- or pyroelectric properties or to possess non-linear optical properties (Ok et al., 2006 ▸). Another effect of the electron lone pair and its large space consumption is the frequent formation of open-framework structures in (transition) metal oxidotellurates(IV). Different structure units such as clusters, chains, layers or channels resulting from the presence of oxidotellurate(IV) anions are observed in various crystal structures (Stöger & Weil, 2013 ▸). Introducing secondary anions into transition-metal oxidotellurates(IV) can lead to even more structural diversification. Over the past few years, several anions have been incorporated into metal or transition-metal oxidotellurates, viz. sulfates [e.g. Cd₄(SO₄)(TeO₃)₃; Weil & Shirkhanlou, 2017a ▸], selenates [e.g. Zn₂(SeO₄)(TeO₃); Weil & Shirkhanlou, 2017b ▸], carbonates [e.g. Pb₅(SeO₄)₂(TeO₄)(CO₃); Weil & Shirkhanlou, 2017c ▸], nitrates [e.g. Ca₆Te₅O₁₅(NO₃)₂; Stöger & Weil, 2013 ▸], phosphates [e.g. Co₃Te₂O₂(PO₄)₂(OH)₄; Zimmermann et al., 2011 ▸] or, very recently, arsenates [Cu₅(TeO₃)₂(AsO₄)₂; Missen et al., 2020 ▸]. Crystals of Cu₅(TeO₃)₂(AsO₄)₂ have been grown by a chemical transport reaction (Binnewies et al., 2012 ▸), starting from CuO, TeO₂ and As₂O₅ at temperatures of 1023 K (source) and 953 K (sink). The title compound, Zn₂(HTeO₃)(AsO₄), however, was obtained at much milder temperatures (483 K) under hydro­thermal conditions.

Structural commentary  

The asymmetric unit of Zn₂(HTeO₃)(AsO₄) contains one Te, one As, one Zn, one H and five O atoms located either on a special position with site symmetry m (Wyckoff position 2 a; Te1, As1, O3, O4, O5, H1) or on general positions (Wyckoff position 4 b; Zn1, O1, O2). Selected bond lengths are collated in Table 1 ▸.

Table 1. Selected bond lengths (Å).

Te1—O2i	1.880 (2)	As1—O5	1.716 (3)
Te1—O2ii	1.880 (2)	Zn1—O2v	1.979 (3)
Te1—O3iii	2.070 (4)	Zn1—O1v	1.987 (3)
Te1—O5	2.131 (4)	Zn1—O2	1.993 (3)
As1—O1iv	1.673 (2)	Zn1—O4	2.0486 (16)
As1—O1	1.673 (2)	Zn1—O3vi	2.3259 (18)
As1—O4	1.709 (3)

Symmetry codes: (i) x+{\script{1\over 2}}, -y+{\script{1\over 2}}, z+1; (ii) x+{\script{1\over 2}}, y-{\script{1\over 2}}, z+1; (iii) x+1, y, z+1; (iv) x, -y, z; (v) x+{\script{1\over 2}}, -y+{\script{1\over 2}}, z; (vi) x+{\script{1\over 2}}, y+{\script{1\over 2}}, z.

The zinc cation (Zn1) is coordinated by five oxygen atoms with one (O3, as part of the hy­droxy group) being at a significantly longer distance [2.3259 (18) Å] than the other four [1.979 (3)–2.0486 (16) Å]. The resulting polyhedron has the shape of a distorted trigonal bipyramid, with the remote O3 site occupying one of the axial positions and the equatorial positions being slightly tilted towards it (Fig. 1 ▸). The geometry index τ₅ (Addison et al., 1984 ▸), which is 0 for an ideal square pyramid and 1 for an ideal trigonal bipyramid, amounts to 0.665 for the [ZnO₄OH] polyhedron. The [ZnO₄OH] polyhedra are connected to each other by sharing four corners with neighbouring polyhedra to form _∞ ²[ZnO_3/2(OH)_1/2O_1/1] layers extending parallel to (001). The bond-valence sum (BVS; Brown, 2002 ▸) of Zn1 was calculated to be 1.98 valence units (v.u.) using the values of Brese & O’Keeffe (1991 ▸).

Figure 1.

The distorted trigonal–bipyramidal [ZnO₄OH] polyhedron in the crystal structure of Zn₂(HTeO₃)(AsO₄). Displacement ellipsoids are drawn at the 90% probability level. Symmetry codes refer to Table 1 ▸.

The tellurium(IV) atom (Te1) is coordinated by four oxygen atoms with bond lengths in the range 1.880 (2)–2.131 (4) Å. The BVS of Te1 is 4.02 v.u. using the values of Brese & O’Keeffe (1991 ▸) for calculation. With the revised bond-valence values by Mills & Christy (2013 ▸), a lower BVS of 3.86 v.u. was calculated under consideration of the four nearest oxygen atoms. However, the BVS increases to 4.03 v.u. if all oxygen atoms within a distance of up to 3.5 Å are accounted for, as is suggested by Mills & Christy (2013 ▸). The resulting [TeO₃OH] coordination polyhedron is a bis­phenoid. Under consideration of the space requirement of the 5s ² electron lone pair, the corresponding [ΨTeO₃OH] polyhedron has the shape of a distorted trigonal bipyramid with the non-bonding electron pair occupying an equatorial position (Fig. 2 ▸). The geometry index τ ₅ of the [ΨTeO₃OH] polyhedron is 0.413. The LPLoc software (Hamani et al., 2020 ▸) revealed the position of the electron lone pair with resulting fractional coordinates of x = 0.7781, y = 0, z = 0.5519. The radius of the electron lone pair was calculated to be 1.32 Å with a distance of 1.680 Å from the Te1 position. The oxygen atom (O3) of the hy­droxy group is located on an axial position of the [ΨTeO₃OH] polyhedron. Its hydrogen atom is directed to the O5 site, forming a weak linear hydrogen bond towards the O5 site with a O3⋯O5 distance of 3.213 (5) Å (Table 2 ▸). It is remarkable that the hydrogen atom is located on the oxidotellurate(IV) unit instead of the oxidoarsenate(V) anion given that for 0.1–0.01 N solutions, the pK_b value of the [AsO₄]^3– anion is much smaller (2.40 at 291 K) than that of the [TeO₃]^2– anion (6.30 at 298 K) (Weast & Astle, 1982 ▸). Even though the conditions during the hydro­thermal experiment are far from the tabulated values, it is surprising that a difference in the equilibrium constants of almost four orders of magnitude was overridden in the resulting crystal. Nevertheless, as evidenced from a difference-Fourier map and BVS calculations (BVS without contribution of the H atom amounts to 1.15 v.u. for O3), the hydroxide group is located on the oxidotellurate(IV) unit.

Figure 2.

The bis­phenoidal [TeO₃OH] polyhedron in the crystal structure of Zn₂(HTeO₃)(AsO₄). Displacement ellipsoids are drawn at the 90% probability level. The 5s ² electron lone pair (Ψ, orange) is drawn with an arbitrary radius of 0.2 Å. Symmetry codes refer to Table 1 ▸.

Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H1⋯O5vii	0.94 (9)	2.28 (9)	3.213 (5)	179 (7)

Symmetry code: (vii) x, y, z-1.

The arsenic(V) atom (As1) is coordinated tetra­hedrally by four oxygen atoms with distances in the range 1.673 (2)–1.716 (3) Å. The mean As—O bond length of 1.693 (23) Å is slightly longer than those reported for AsO₄ ^3– groups [1.667 (18) Å; Schwendtner & Kolitsch, 2019 ▸] or for oxidoarsenate groups in general (also including As—OH bonds, with an overall mean of 1.687 (27) Å; Gagné & Hawthorne, 2018 ▸). The BVS is 4.91 v.u. using the values of Brese & O’Keeffe (1991 ▸) for calculation.

The crystal structure of Zn₂(HTeO₃)(AsO₄) is built up from _∞ ²[ZnO_3/2(OH)_1/2O_1/1] layers extending parallel to (001) (Fig. 3 ▸). The [TeO₃OH] units are situated below a _∞ ²[ZnO_3/2(OH)_1/2O_1/1] layer and are isolated from each other. An individual [TeO₃OH] unit shares three corners with two [ZnO₄OH] polyhedra each, and one corner with an [AsO₄] tetra­hedron. Likewise, the oxidoarsenate anions, situated above a _∞ ²[ZnO_3/2(OH)_1/2O_1/1] layer, are isolated from each other, but share corners with other building units: two corners with one [ZnO₄OH] polyhedron each, one corner with two [ZnO₄OH] polyhedra and one corner with a [TeO₃OH] unit. This way, a three-dimensional framework structure is established (Fig. 4 ▸).

Figure 3.

The crystal structure of Zn₂(HTeO₃)(AsO₄) in polyhedral representation, projected onto (001). [ZnO₄OH] polyhedra are blue, [TeO₃OH] polyhedra are green and [AsO₄] tetra­hedra are red; H atoms are represented as grey spheres of arbitrary radius. Displacement ellipsoids are drawn at the 90% probability level.

Figure 4.

Channels in the crystal structure of Zn₂(HTeO₃)(AsO₄) running parallel to [110]. Colour codes and displacement ellipsoids are as in Fig. 3 ▸. O—H⋯O hydrogen bonds are shown as orange lines.

In the crystal structure, the spatial requirements of the 5s ² electron lone pairs at the Te^IV atoms lead to the formation of channels parallel to [110] (Fig. 4 ▸). The weak O—H⋯O hydrogen bond is directed across these channels. There are also smaller channels oriented parallel to [100] that, however, remain empty (Fig. 5 ▸).

Figure 5.

Channels in the structure of Zn₂(HTeO₃)(AsO₄) running parallel to [100]. Colour codes and displacement ellipsoids are as in Fig. 3 ▸.

Synthesis and crystallization  

Crystals of Zn₂(HTeO₃)(AsO₄) were obtained by hydro­thermal synthesis. The reactants, 0.1949 g of Zn(NO₃)₂·6H₂O (0.670 mmol), 0.0512 g of TeO₂ (0.321 mmol), 0.1365 g 80%_wt of H₃AsO_{4 (aq)} (0.713 mmol) and 0.22 g of 25%_wt NH_{3 (aq)} (3.23 mmol) were weighed into a small Teflon vessel with an inner volume of ca 3 ml. The vessel was filled with deionized water to three-quarters of its volume and the reactants were mixed by manual stirring. The Teflon vessel was then put into a steel autoclave and heated to 483 K for 7 d at autogenous pressure. Afterwards, the autoclave was cooled to room temperature within about 4 h. The resulting product was a colourless multi-phase solid. In the X-ray powder pattern of the bulk, Zn₂(HTeO₃)(AsO₄) was found as a by-product, in addition to (NH₄)Zn(AsO₄) (Feng et al., 2001 ▸) and the educt TeO₂ (α-TeO₂; Stehlik & Balak, 1948 ▸). Under a polarizing microscope, small colourless block-shaped crystals of Zn₂(HTeO₃)(AsO₄) were visible that were manually separated for the single-crystal X-ray diffraction study.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. Atom labels and coordinates were standardized with Structure Tidy (Gelato & Parthé, 1987 ▸) implemented in PLATON (Spek, 2020 ▸). The H atom of the hy­droxy group was located in a difference-Fourier map and was refined freely. The crystal structure was refined under consideration of twinning by inversion, revealing a minor contribution of 3.2 (12)% for the inversion-related twin component.

Table 3. Experimental details.

Crystal data
Chemical formula	Zn2(HTeO3)(AsO4)
M r	446.27
Crystal system, space group	Monoclinic, C m
Temperature (K)	100
a, b, c (Å)	6.9040 (12), 7.7212 (13), 5.726 (1)
β (°)	101.196 (5)
V (Å3)	299.43 (9)
Z	2
Radiation type	Mo Kα
μ (mm−1)	18.25
Crystal size (mm)	0.06 × 0.04 × 0.03
Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 ▸)
T min, T max	0.538, 0.748
No. of measured, independent and observed [I > 2σ(I)] reflections	8261, 1986, 1918
R int	0.044
(sin θ/λ)max (Å−1)	0.915
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.019, 0.040, 0.92
No. of reflections	1986
No. of parameters	63
No. of restraints	2
H-atom treatment	All H-atom parameters refined
Δρmax, Δρmin (e Å−3)	1.79, −1.17
Absolute structure	Refined as an inversion twin
Absolute structure parameter	0.032 (12)

Computer programs: APEX3 and SAINT (Bruker, 2016 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL (Sheldrick, 2015b ▸), ATOMS for Windows (Dowty, 2006 ▸) and publCIF (Westrip, 2010 ▸).

Supplementary Material

CCDC reference: 2079463

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

Zn2(HTeO3)(AsO4)	F(000) = 404
Mr = 446.27	Dx = 4.950 Mg m−3
Monoclinic, Cm	Mo Kα radiation, λ = 0.71073 Å
a = 6.9040 (12) Å	Cell parameters from 5391 reflections
b = 7.7212 (13) Å	θ = 3.6–40.6°
c = 5.726 (1) Å	µ = 18.25 mm−1
β = 101.196 (5)°	T = 100 K
V = 299.43 (9) Å3	Block, colourless
Z = 2	0.06 × 0.04 × 0.03 mm

Data collection

Bruker APEXII CCD diffractometer	1918 reflections with I > 2σ(I)
ω– and φ–scans	Rint = 0.044
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θmax = 40.6°, θmin = 3.6°
Tmin = 0.538, Tmax = 0.748	h = −12→12
8261 measured reflections	k = −14→14
1986 independent reflections	l = −10→10

Refinement

Refinement on F2	All H-atom parameters refined
Least-squares matrix: full	w = 1/[σ2(Fo2)] where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.019	(Δ/σ)max < 0.001
wR(F2) = 0.040	Δρmax = 1.79 e Å−3
S = 0.92	Δρmin = −1.16 e Å−3
1986 reflections	Extinction correction: SHELXL (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
63 parameters	Extinction coefficient: 0.0043 (5)
2 restraints	Absolute structure: Refined as an inversion twin
Hydrogen site location: difference Fourier map	Absolute structure parameter: 0.032 (12)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refined as a two-component inversion twin.

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

	x	y	z	Uiso*/Ueq
Te1	0.70945 (3)	0.000000	0.81776 (3)	0.00418 (6)
As1	0.24451 (6)	0.000000	0.51174 (7)	0.00440 (9)
Zn1	0.46889 (7)	0.23359 (4)	0.17917 (8)	0.00521 (7)
O1	0.1089 (4)	0.1808 (3)	0.4941 (4)	0.0081 (4)
O2	0.1998 (4)	0.3177 (3)	0.0329 (4)	0.0062 (4)
O3	−0.0007 (6)	0.000000	0.0002 (6)	0.0087 (6)
O4	0.3941 (5)	0.000000	0.3064 (6)	0.0063 (5)
O5	0.3968 (5)	0.000000	0.7868 (6)	0.0065 (5)
H1	0.114 (13)	0.000000	−0.064 (14)	0.015 (19)*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Te1	0.00465 (12)	0.00392 (11)	0.00381 (11)	0.000	0.00040 (8)	0.000
As1	0.0040 (2)	0.0047 (2)	0.00427 (18)	0.000	0.00031 (16)	0.000
Zn1	0.00389 (15)	0.00549 (13)	0.00595 (15)	0.00021 (15)	0.00023 (11)	0.00043 (13)
O1	0.0090 (10)	0.0078 (10)	0.0068 (9)	0.0039 (8)	−0.0006 (8)	−0.0004 (7)
O2	0.0061 (9)	0.0058 (9)	0.0068 (9)	0.0000 (8)	0.0015 (7)	0.0021 (7)
O3	0.0055 (14)	0.0116 (14)	0.0085 (13)	0.000	0.0001 (11)	0.000
O4	0.0067 (14)	0.0064 (13)	0.0062 (12)	0.000	0.0025 (11)	0.000
O5	0.0049 (13)	0.0103 (14)	0.0041 (11)	0.000	0.0001 (10)	0.000

Geometric parameters (Å, º)

Te1—O2i	1.880 (2)	As1—O5	1.716 (3)
Te1—O2ii	1.880 (2)	Zn1—O2v	1.979 (3)
Te1—O3iii	2.070 (4)	Zn1—O1v	1.987 (3)
Te1—O5	2.131 (4)	Zn1—O2	1.993 (3)
As1—O1iv	1.673 (2)	Zn1—O4	2.0486 (16)
As1—O1	1.673 (2)	Zn1—O3vi	2.3259 (18)
As1—O4	1.709 (3)	O3—H1	0.94 (9)
O2i—Te1—O2ii	96.96 (14)	O2v—Zn1—O3vi	80.87 (12)
O2i—Te1—O3iii	79.82 (10)	O1v—Zn1—O3vi	92.08 (11)
O2ii—Te1—O3iii	79.82 (10)	O2—Zn1—O3vi	71.53 (12)
O2i—Te1—O5	83.70 (10)	O4—Zn1—O3vi	170.38 (14)
O2ii—Te1—O5	83.70 (10)	As1—O1—Zn1vii	120.01 (13)
O3iii—Te1—O5	155.01 (13)	Te1viii—O2—Zn1vii	124.12 (13)
O1iv—As1—O1	113.14 (19)	Te1viii—O2—Zn1	111.74 (13)
O1iv—As1—O4	111.36 (10)	Zn1vii—O2—Zn1	121.25 (11)
O1—As1—O4	111.36 (10)	Te1ix—O3—Zn1vii	93.51 (11)
O1iv—As1—O5	106.93 (11)	Te1ix—O3—Zn1x	93.51 (11)
O1—As1—O5	106.93 (11)	Zn1vii—O3—Zn1x	124.36 (16)
O4—As1—O5	106.69 (17)	Te1ix—O3—H1	128 (5)
O2v—Zn1—O1v	99.25 (11)	Zn1vii—O3—H1	109.1 (18)
O2v—Zn1—O2	130.47 (12)	Zn1x—O3—H1	109.1 (18)
O1v—Zn1—O2	121.53 (11)	As1—O4—Zn1	118.20 (8)
O2v—Zn1—O4	104.71 (11)	As1—O4—Zn1iv	118.20 (8)
O1v—Zn1—O4	94.69 (11)	Zn1—O4—Zn1iv	123.38 (16)
O2—Zn1—O4	99.06 (12)	As1—O5—Te1	120.43 (18)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H1···O5xi	0.94 (9)	2.28 (9)	3.213 (5)	179 (7)

Symmetry code: (xi) x, y, z−1.