Incorporation of Sulfate or Selenate Groups into Oxotellurates(IV): I. Calcium, Cadmium, and Strontium Compounds

Article abstract of DOI:10.1002/zaac.201600406

Seven new mixed oxochalcogenate compounds in the systems M^II/X^VI/Te^IV/O/(H), (M^II= Ca, Cd, Sr; X^VI= S, Se) were obtained under hydrothermal conditions (210 °C, one week). Crystal structure determinati

Full text of DOI:10.1002/zaac.201600406

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201600406
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Incorporation of Sulfate or Selenate Groups into
Oxotellurates(IV): I. Calcium, Cadmium, and Strontium
Compounds
Matthias Weil*[a] and Mahdi Shirkhanlou[a]
Abstract. Seven new mixed oxochalcogenate compounds in the
systems MII/XVI/TeIV/O/(H), (MII = Ca, Cd, Sr; XVI = S, Se) were
Ca3(SeO4)(Te3O8), Cd3(SeO4)(Te3O8), Cd3(H2O)(SO4)(Te3O8), and
Sr3(H2O)2(SeO4)(TeO3)2 are metal-oxotellurate(IV) layers connected
obtained under hydrothermal conditions (210 °C, one week). Crystal by bridging XO4 tetrahedra and/or by hydrogen-bonding interactions
structure determinations based on single-crystal X-ray diffraction data involving hydroxyl or water groups, whereas Cd4(SO4)(TeO3)3 and
revealed the compositions Ca3(SeO4)(TeO3)2, Ca3(SeO4)(Te3O8), Cd5(SO4)2(TeO3)2(OH)2 crystallize as framework structures. Common
Cd3(SeO4)(Te3O8), Cd3(H2O)(SO4)(Te3O8),
Cd4(SO4)(TeO3)3, to all crystal structures is the stereoactivity of the TeIV electron lone
Cd5(SO4)2(TeO3)2(OH)2, and Sr3(H2O)2(SeO4)(TeO3)2 for these pair for each oxotellurate(IV) unit, pointing either into the inter-layer
phases. Peculiar features of the crystal structures of Ca3(SeO4)(TeO3)2,
space, or into channels and cavities in the crystal structures.
groups. This approach has already been proven successful for
mercury oxotellurates(IV) that were modified with tetrahedral
SeO4 anions, resulting in the two compounds Hg3(SeO4)-
(TeO3)2 and Hg3(SeO4)(Te4O10), both with non-centrosymmet-
ric structures.[17]
Introduction
The peculiar structural feature of oxotellurates(IV)[1] is the
5s2 lone electron lone pair situated at the TeIV atom, denoted
as E. In the majority of cases, E is stereochemically active[2]
due to its spatial requirement, consequently forming structures
with cavities, channels or layers in the neighbourhood of the
TeIV atom. In combination with the ability of the TeIV atom to
adopt varying coordination numbers from 3 to 5,[3–6] the re-
sulting [TeO3E], [TeO4E], or [TeO5E] building units are also
polar. These characteristics can be relevant for the formation
of non-centrosymmetric crystal structures or crystal structures
with polar directions, features that are indispensable for the
existence of interesting physical properties. Whereas pyroelec-
tric, piezoelectric, ferroelectric, or non-linear optical (NLO)
properties can principally occur only in crystals with non-cen-
trosymmetric structures, pyroelectric and ferroelectric proper-
ties additionally require the condition that the crystal structure
must be polar with a non-zero macroscopic dipole moment. As
a matter of fact, some of the alkaline earth oxotellurates(IV)
phases with composition MTeO3 (M = Ca, Sr) are ferroelec-
trics,[7–9] and several polymorphs have been structurally deter-
mined for each of the MTeO3 phases up to date.[10–16]
2–
2–
For the intended incorporation of SO4 or SeO4 anions
into the oxotellurate(IV) frameworks of calcium, cadmium,
and strontium (all with comparable ionic radii as the mercuric
ion), we chose hydrothermal methods[18] which bears some
advantages over typical solid state reactions using ceramic
methods. In comparison with the often harsh reaction condi-
tions required for the latter, e.g. in terms of high temperatures
for sufficient diffusion, hydrothermal synthesis usually takes
place at much milder conditions and also prevents an oxidation
of TeIV by air or an evaporation of compounds volatile at
higher temperatures. So far, only a few metal oxotellurate(IV)
phases with additional XO4 groups have been reported, mostly
prepared under hydrothermal conditions. This includes the
sulfates Al2(OH)2(SO4)(TeO3),[19] Fe2(TeO3)2(SO4)(H2O)3,[20]
Cu7(OH)6(TeO3)2(SO4)2,[21] Cu7TeO4(SO4)5KCl,[22] the series
RE2M(TeO3)2(SO4)2 (RE = rare earth metal; M = Cu, Co,
Zn),[23,24] Pu(TeO3)(SO4), Th(TeO3)(SO4), Ce2(Te2O5)(SO4)2,[25]
M2(TeO3)(SO4)H2O (M = Co, Mn),[26] and BiCu2(TeO3)(SO4)-
(OH)3,[27] and to a much lesser extend the selenates Sc2(TeO3)-
(SeO3)(SeO4) (also comprising an oxoselenate(IV) group),[28]
Bi2(TeO3)2(SeO4)[29] and the already noted mercury com-
pounds Hg3(SeO4)(TeO3)2 and Hg3(SeO4)(Te4O10).[17]
In the sense of crystal engineering, the idea behind the cur-
rent study is a modification of the crystal structures of MTeO3
(M = Ca, Sr, and Cd) compounds by introduction of tetrahedral
spacers, i.e. non-centrosymmetric building units into their
oxotellurate(IV) frameworks, which may originate in new
phases that likewise crystallize in non-centrosymmetric space
In this communication we report on hydrothermal syntheses
and crystal structure determinations of seven new phases in the
systems MII/XVI/TeIV/O/(H) (M = Ca, Cd, Sr, and X = S, Se).
* Prof. Dr. M. Weil
E-Mail: Matthias.Weil@tuwien.ac.at
[a] Institute for Chemical Technologies and Analytics
Division Structural Chemistry
TU Wien
Experimental Section
Synthesis: For hydrothermal synthesis of all phases, salts of the corre-
sponding metals were mixed in stoichiometric amounts with TeO2 and
Getreidemarkt 9/164-SC
1060 Vienna, Austria
Z. Anorg. Allg. Chem. 0000, ᭿,0–0
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Table 1. Details of representative experiments for phase formation studies in the systems MII/XVI/TeIV/O/(H) (M = Ca, Cd, Sr; X = Se, S)
performed under hydrothermal conditions.
Starting materials; stoichiometric ratios Phases determined by X-ray powder diffraction
of the bulka)
Additional phase(s) determined by single-crystal
X-ray diffraction
[31]
[32]
CaCl2·2H2O/H2SeO4/TeO2/KOH;
0.215 g / 0.25 mL / 0.152 g / 0.170 g;
3:2:1.5:2
Ca(OH)2/H2SeO4/TeO2;
0.117 g / 0.25 mL / 0.165 g;
3:2:1.5
CdCl2/H2SeO4/TeO2/KOH;
0.217 g / 0.23 mL / 0.113 g / 0.121 g;
3:2:1.7:2
CdSO4·8/3H2O/H6TeO6/KOH;
0.30 g, 0.20 g, 0.10 g;
1:1.3:1.5
CdCl2/H2SO4/TeO2/NaOH;
0.230 g / 0.25 mL / 0.060 g / 0.100 g;
2:2:1:2
CdO/H2SO4/TeO2/NaOH;
0.147 g / 0.20 mL / 0.120 g / 0.092 g;
3:2:1.5:2
Sr(OH)2·8H2O/H2SeO4/TeO2/NaOH;
0.315 g / 0.26 mL / 0.124 g / 0.100 g;
1.5:2:1:2
TeO2,[29] α-CaTeO3,[15] CaTeO4
Ca3(SeO4)(TeO3)2;b) CaTe3O8
Ca3(SeO4)(Te3O8);b) CaTe2O5;[34] Ca4Te5O14
[33]
[35]
TeO2, α-CaTeO3, CaTeO4, CaTe2O5
CdTe2O5,[33] CdTeO3
Cd3(SeO4)(Te3O8)b)
[36]
Cd(OH)2,[37] CdO[38]
Cd3(H2O)(SO4)(Te3O8)b)
[39]
b)
TeO2, CdTeO3, CdTe2O5, Cd3TeO6
CdTe2O5, TeO2, CdTeO3, CdO
Cd4(SO4)(TeO3)3
b)
Cd5(SO4)2(TeO3)2(OH)2
SrTeO3,[10] TeO2, SrTe2O5
Sr3(H2O)2(SeO4)(TeO3)2,b) Sr5Te4O14(OH)2
[33]
[40]
a) Main phases appear first, minor phases last in terms of semi-quantitative phase analysis. For all batches additional weak reflections were
present that could not be assigned to known phases or the new phases determined by single-crystal X-ray diffraction given in the right column.
b) This work.
selenic acid (ca. 80 wt%, prepared by oxidizing SeO2 in aqueous solu- Inspection of the diffraction pattern of Cd3(H2O)(SeO4)(Te3O8) with
tion with an H2O2/HNO3 mixture) or sulfuric acid; for some experi-
ments KOH or NaOH were also added to ensure slightly basic condi-
tions. The respective mixture was placed in Teflon containers with ca.
10 mL capacity and filled up with water to about two-thirds of the
the program RLATT[41] revealed two distinct domains with one twin
domain rotated by 180° about the reciprocal c* axis relative to the
other twin domain. Reflections belonging to the two domains were
separated and further processed in a HKLF5-type reflection file, for
¯
container volume. After sealing the container with a Teflon lid and which the reflections were merged according to point group 1. This
placement in a steel autoclave, the mixture was heated at 210 °C for
one week. The autoclave was then cooled to room temperature over-
night. The solid products were filtered off, washed subsequently with
resulted in the following intensity statistics: Mean I/σ = 2.7 for domain
1 only; mean I/σ = 3.5 for domain 2 only; mean I/σ = 5.2 for reflec-
tions belonging to both domains. The refined ratio of the two twin
mother liquor, water, and ethanol. All reaction batches consisted of domains was 0.6:0.4. Two O atoms of the sulfate group (O12, O13)
phase-mixtures when inspected optically under a polarising micro- and one O atom of the cadmium oxotellurate(IV) layer (O11) in this
scope. These findings were confirmed by subsequent powder X-ray structure were modelled as equally disordered over two sets of sites,
diffraction studies of the bulk products. Representative results of the denoted as A and B. Since some of the O atoms showed a physically
hydrothermal experiments, together with determined reaction products, meaningless behaviour when refined anisotropically, all O atoms were
are gathered in Table 1.
refined with a common isotropic displacement parameter; hydrogen
atoms of the water molecule present in this structure could not be
located from difference maps and thus were excluded from the model
but were considered in the formula.
Powder X-ray Diffraction: Samples of the bulk material were ground,
fixed with small amounts of petroleum jelly on silicon wafers and
measured with Cu-Kα1,2 radiation in Bragg-Brentano geometry on a
PanAlytical X’PertPro system.
Cd3(SeO4)(Te3O8), crystallizing in space group Cmc21, was refined as
an inversion twin with a ratio of 0.52:0.48 for the two twin compo-
nents. For the crystal structure model of Sr3(H2O)2(SeO4)-
(TeO3)2 hydrogen atoms of the water molecules could likewise not be
determined reliably and consequently were excluded, but are part of
the formula. The position of the OH hydrogen atom in the structure
of Cd5(SO4)2(TeO3)2(OH)2 was clearly discernible from a difference
Fourier synthesis and was refined freely.
Single Crystal Diffraction: For each batch, crystals of good optical
quality showing sharp extinctions when imaged between crossed polar-
izers were pre-selected and were embedded in perfluorinated polyether
and fixed on thin silica glass fibres or MiTeGen MicroLoopsTM. Dif-
fraction data were recorded at room temperature or at 100 K using
Mo-Kα radiation either with a Siemens SMART CCD (ω-scans) or a
Bruker APEX-II diffractometer (ω- and φ-scans),[41] resulting in data
sets of the complete reciprocal spheres. After integration of the data
with the program SAINT,[41] an absorption correction based on The remaining electron density peaks for all structure models were
the semi-empirical “multi-scan” approach was performed with unobstrusive. Numerical data of the data collections and structure re-
SADABS[41] for all measurements; for the data set of Cd3(H2O)
(SeO4)-(Te3O8) TWINABS[41] was used (see below). All crystal struc-
finements are detailed in Table 2 and Table 3. Selected bond lengths
and angles are collated in Table 4 and Table 5, together with results
tures were solved by direct methods and were refined using the of bond valence sums (BVS) calculations[43] for which bond valence
SHELXTL program package.[42]
parameters of Brese and O’Keeffe[44] or Brown[43] were used.
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Table 2. Details of data collections and structure refinements.
Ca3(SeO4)(TeO3)2
Ca3(SeO4)(Te3O8)
Cd3(SeO4)(Te3O8)
Formula sum
MR
Ca3O10SeTe2
614.40
Ca3O12SeTe3
774.00
Cd3O12SeTe3
990.96
Crystal size /mm3
Temperature /°C
Radiation; λ /Å
Diffractometer
Crystal colour; form
Space group (no.)
Formula units Z
a /Å
0.02ϫ0.02ϫ0.36
0.04ϫ0.04ϫ0.12
23
Mo-Kα; 0.71073
Siemens SMART
colourless, lath
P21/n
0.01ϫ0.02ϫ0.24
Siemens SMART
colourless, needle
P21 (4)
Siemens SMART
colourless, needle
Cmc21
2
4
8
8.3616(10)
5.6075(7)
11.1853(13)
108.611(2)
497.03(10)
11.116
6.9498(12)
9.5789(17)
17.483(3)
94.469(3)
1160.3(4)
12.014
18.3402(8)
6.6723(3)
18.4360(8)
b /Å
c /Å
β /°
V /Å3
2256.04(17)
16.496
5.835
2.21–30.49
–26 Յ h Յ 26
–9 Յ k Յ 9
–26 Յ l Յ 26
16572
μ /mm–1
X-ray density /g·cm–3
Range θmin – θmax
Range
4.105
4.431
3.51–32.51
–12 Յ h Յ 12
–8 Յ k Յ 8
–16 Յ l Յ 16
8181
3313
3125
0.0299
2.34–29.00
–9 Յ h Յ 9
–13 Յ k Յ 13
–23 Յ l Յ 23
14953
3083
2254
0.0876
Measured reflections
Independent reflections
Obs. reflections [I Ͼ 2σ(I)]
Ri
3539
3311
0.0428
Absorption correction
Trans. coeff. Tmin; Tmax
Number of parameters
Ext. coeff. (SHELXL97)
Flack parameter
SADABS
0.673; 0.851
146
SADABS
0.327; 0.645
172
–
–
4.91 [0.87, Ca3];
–2.04 [1.10, O7]
0.0483
SADABS
0.110; 0.827
183
–
–
0.08(3)
0.477(13)
1.41 [0.79, Te3];
–1.20 [1.17, O13]
0.0251
Diff. elec. dens. max;min /e–·Å–3
(dist. /Å, atom)
2.16 [0.77, Te1];
–1.24 [0.64, Ca3]
0.0432
R[F2 Ͼ 2σ(F2)]
wR2(F2 all)
0.0944
0.1079
0.0557
GooF
1.097
1.055
1.047
Drawings of structural details were produced using the program
ATOMS.[45]
usually requires a long-lasting optimization of dependable re-
action parameters, in particular for multi-phase systems with
different solubility products or redox potentials of individual
salts and components, respectively, which were used as starting
materials or can form during the reaction. Such difficulties
were also observed for hydrothermal reactions in the MII/XVI/
TeIV/O/(H) (M = Ca, Cd, Sr and X = S, Se) systems. None of
the batches resulted in the formation of a single-phase product
(Table 1). Also if some of the hydrothermal reactions were
subsequently repeated, then taking into account the exact stoi-
chiometric ratio with respect to the composition of the new
phases determined by single crystal diffraction, multi-phase
formation prevailed. In all cases the overall amount of incorpo-
rated sulfate or selenate in the solid reaction products was
much less than nominal present in the reaction mixture.
Further details of the crystal structures investigations may be obtained
from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-
Leopoldshafen, Germany (Fax: +49-7247-808-666; E-Mail:
crysdata@fiz-karlsruhe.de, https://www.fiz-karlsruhe.de/en/leistungen/
kristallographie/kristallstrukturdepot/order-form-request-for-deposited-
data.html) on quoting the depository numbers CSD-432124
[Ca3(SeO4)(TeO3)2], CSD-432125 [Ca3(SeO4)(Te3O8)], CSD-432126
[Cd3(SeO4)(Te3O8)], CSD-432127 [Cd3(H2O)(SO4)(Te3O8)], CSD-
432128 [Cd4(SO4)(TeO3)3], CSD-432129 [Cd5(SO4)2(TeO3)2(OH)2],
and CSD-432130 [Sr3(H2O)2(SeO4)(TeO3)2].
Results and Discussion
In this regard, compounds containing tellurium and sulfur/
selenium were minority products, whereas compounds contain-
ing tellurium as the only chalcogen were majority products. As
a general trend, formation of Te- and S/Se-containing phases
becomes more successful at increasing pH values, i.e. at
slightly basic conditions. However, under these conditions a
reduction of tellurium(VI), employed in the form of telluric
acid, to tellurium(IV) can also take place as was the case for
the crystallization of Cd3(H2O)(SeO4)(Te3O8). On the other
Formation
A notable disadvantage of hydrothermal methods in com-
parison with ceramic methods is the high(er) number of adjust-
able parameters, i.e. pressure, concentration, temperature, time,
filling degree, used solvent, container material etc. This might
be the reason why a prediction of hydrothermally obtained re-
action products is usually very difficult (or nearly impossible).
In addition, the formation of single-phase products resulting
from a hydrothermal reaction is a rather rare phenomenon and hand, an oxidation of the employed tellurium(IV) to tel-
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Table 3. Details of data collections and structure refinements.
Cd3(H2O)(SO4)(Te3O8)
Cd4(SO4)(TeO3)3
Cd5(SO4)2(TeO3)2(OH)2
Sr3(H2O)2(SeO4)(TeO3)2
Formula sum
MR
Cd3H2O13STe3
962.08
Cd4O13STe3
1072.46
Cd5H2O16S2Te2
1139.34
H4O12SeSr3Te2
793.05
Crystal size /mm3
Temperature /°C
Radiation; λ /Å
Diffractometer
Crystal colour; form
Space group (no.)
Formula units Z
a /Å
b /Å
c /Å
α /°
β /°
0.01ϫ0.06ϫ0.10
–173
0.02ϫ0.02ϫ0.20
–173
0.04ϫ0.06ϫ0.08
23
0.06ϫ0.13ϫ0.09
23
Mo-Kα; 0.71073
Bruker APEX-II
colourless, plate
Bruker APEX-II
colourless, needle
Bruker APEX-II
colourless, block
Bruker APEX-II
colourless, fragment
¯
¯
¯
¯
P1 (2)
P1 (2)
P1 (2)
P1 (2)
2
2
1
4
6.7533(8)
9.3520(11)
9.4696(11)
88.719(4)
70.134(4)
89.634(4)
562.34(11)
13.506
5.4219(2)
9.9545(3)
11.6232(3)
89.1579(16)
87.9578(17)
74.7552(16)
604.86(3)
14.269
5.4227(1)
8.4179(2)
8.5154(2)
69.2258(8)
82.8241(8)
79.1830(9)
356.258(14)
11.735
9.7831(16)
11.781(2)
11.874(2)
90.23(8)
106.578(9)
103.783(8)
1270.1(4)
19.974
γ /°
V /Å3
μ /mm–1
X-ray density /g·cm–3
Range θmin – θmax
Range
5.682
5.888
5.311
4.147
2.18–29.00
–8 Յ h Յ 9
–12 Յ k Յ 12
0 Յ l Յ 12
2991
2991
2405
–
2.74–40.05
–9 Յ h Յ 9
–18 Յ k Յ 18
–21 Յ l Յ 21
57924
7634
6423
0.0583
2.56–39.19
–9 Յ h Յ 9
–14 Յ k Յ 14
–15 Յ l Յ 15
36923
4172
3773
0.0336
1.79–36.70
–16 Յ h Յ 16
–19 Յ k Յ 19
–19 Յ l Յ 19
75826
12384
8496
0.0966
Measured reflections
Independent reflections
Obs. reflections [I Ͼ 2σ(I)]
Ri
Absorption correction
Trans. coeff. Tmin; Tmax
Number of parameters
Ext. coeff. (SHELXL97)
TWINABS
0.299; 0.435
114
SADABS
0.495; 0.748
194
SADABS
0.559; 0.748
120
0.00568(12)
1.04 [1.39, Te1];
–0.83 [0.81, Te1]
0.0148
SADABS
0.410; 0.747
325
–
–
–
Diff. elec. dens. max;min /e–·Å–3 4.18 [0.16, O12B];
2.30 [0.71, Cd4];
–2.95 [0.40, Te2]
0.0274
0.0437
1.044
4.92 [0.46, Se1];
–2.17 [0.56, Te4]
0.0508
0.1075
1.049
(dist. /Å, atom)
R [F2 Ͼ 2σ(F2)]
wR2 (F2 all)
GooF
–4.78 [0.09, O10]
0.0504
0.1214
0.0281
1.041
1.073
lurium(VI) can also occur, in this case associated with the for- channels. The two TeO3 units are isolated from each other and
mation of the oxotellurates(VI) CdTeO4, CaTeO4, or mixed- are not linked to the SeO4 tetrahedron. The crystal structure of
valent CaTe3O8.
Ca3(SeO4)(TeO3)2 is displayed in Figure 1. It exemplifies a
rare case of isotypism with a mercury(II) analogue with its
peculiar crystal chemistry,[46] another example being the pair
Crystal Structures
[47]
CaAs2O6
and HgAs2O6.[48] Although Hg3(SeO4)(TeO3)2
Ca3(SeO4)(TeO3)2
has been determined with the enantiomorph being present in
the crystal structure,[17] a comparison of the two standardized
structures with the compstru program at the Bilbao Crystallo-
graphic server[49] revealed a measure of similarity[50] of Δ =
0.11, that clearly points to the close relation of the two struc-
tures. The degree of lattice distortion (S) for the two structures
is 0.0102, and the maximal displacement between the atomic
positions of a related pair of atoms is in this case 0.64 Å for
the pair O10; the arithmetic mean of the distances between
two related pairs is 0.307 Å for the two isotypic structures.
The crystal structure of Ca3(SeO4)(TeO3)2 is polar (space
group P21). It contains three Ca2+ cations, two of which (Ca1,
Ca2) are in a distorted octahedral coordination environment by
oxygen atoms and one (Ca3) in a distorted bicapped octahedral
coordination mode. Cations Ca2 and Ca3 are located at x ≈ 0;
together with the surrounding oxygen atoms, a metal-oxygen
layer is formed parallel to (100) through edge- and corner-
sharing of the coordination polyhedra. The third Ca2+ cation
(Ca1) sits in an alternating fashion above and below the layer,
thereby bridging one Ca2O6 and three Ca3O8 polyhedra by
sharing common edges. Adjacent layers are linked by SeO4
tetrahedra along [100] into a three-dimensional framework
structure encapsulating channels propagating along [010]. The
Ca3(SeO4)(Te3O8) and Cd3(SeO4)(Te3O8)
The two compounds have the same formula type and show
two independent TeIV atoms are located at the outer array of similar structural features but are not isotypic or related in the
these channels, each capping three oxygen atoms in the shape sense of a group-subgroup relationship. Both crystal structures
of a trigonal pyramid, and with the electron lone pair pointing (Figure 2 and Figure 3) are composed of three metal-
away from the calcium-oxygen layer into the free space of the oxygen polyhedra CdO6 (Cd1), CdO7 (Cd2, Cd3) and CaO7
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Table 4. Selected interatomic distances /Å, angles /°, and bond valence sums /v.u.a)
Ca3(SeO4)(TeO3)2 Ca3(SeO4)(Te3O8) Cd3(SeO4)(Te3O8)
Cd3(H2O)(SO4)(Te3O8)b)
Ca1
Ca1
Ca1
Ca1
Ca1
Ca1
Ca2
Ca2
Ca2
Ca2
Ca2
Ca2
Ca3
Ca3
Ca3
Ca3
Ca3
Ca3
Ca3
Ca3
Se1
Se1
Se1
Se1
Te1
Te1
Te1
Te2
Te2
Te2
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
O2
O4
O9
O8
O1
O3
O5
O6
O3
O5
O10
O4
O1
O7
O6
O1
O3
O2
O4
O2
O6
O3
O7
O8
O5
O3
O4
O6
O2
O1
2.225(7)
2.232(7)
2.345(8)
2.443(7)
2.499(7)
2.532(7)
2.256(6)
2.264(7)
2.351(7)
2.377(7)
2.456(8)
2.528(7)
2.393(6)
2.434(7)
2.439(7)
2.442(7)
2.573(7)
2.604(8)
2.633(8)
2.715(7)
1.625(7)
1.628(7)
1.640(7)
1.641(7)
1.840(6)
1.855(6)
1.858(7)
1.846(6)
1.861(7)
1.875(6)
Ca1
Ca1
Ca1
Ca1
Ca1
Ca1
Ca1
Ca2
Ca2
Ca2
Ca2
Ca2
Ca2
Ca2
Ca3
Ca3
Ca3
Ca3
Ca3
Ca3
Ca3
Ca3
Se1
Se1
Se1
Se1
Te1
Te1
Te1
Te1
Te2
Te2
Te2
Te3
Te3
Te3
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
O5
O6
O7
O2
O2
O4
O1
O1
O2
O3
O4
O10
O4
O9
O9
O8
O3
O3
O1
O11
O5
O5
O11
O12
O10
O6
O2
O1
O8
O7
O9
O4
O7
O5
O3
O8
2.314(7) Cd1
2.347(8) Cd1
2.422(7) Cd1
2.435(7) Cd1
2.452(7) Cd1
2.463(7) Cd1
2.535(8) Cd2
2.304(7) Cd2
2.313(7) Cd2
2.364(7) Cd2
2.369(7) Cd2
2.424(9) Cd2
2.505(8) Cd2
2.655(9) Cd3
2.290(8) Cd3
2.388(8) Cd3
2.456(8) Cd3
2.516(8) Cd3
2.534(7) Cd3
2.541(9) Se1
2.651(8) Se1
2.860(8) Se1
1.623(8) Se1
1.624(9) Se2
1.628(8) Se2
1.639(8) Te1
1.861(7) Te1
1.866(6) Te1
2.109(7) Te1
2.158(7) Te2
1.826(8) Te2
1.855(7) Te2
1.901(7) Te2
1.847(7) Te3
1.856(7) Te3
1.883(8) Te3
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
O6
O2
O7
O7
O4
2.213(5)
2.305(4)
2.306(4)
2.320(4)
2.334(5)
Cd1
Cd1
Cd1
Cd1
Cd1
Cd1
Cd1
Cd2
Cd2
Cd2
Cd2
Cd2
Cd2
Cd2
Cd3
Cd3
Cd3
Cd3
Cd3
Cd3
Cd3
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
O8
O6
O2
O5
O5
O9
O3
O3
O5
O2
O4
O11A
O2
2.183(13)
2.329(12)
2.333(13)
2.382(12)
2.403(12)
2.482(13)
2.534(13)
2.215(13)
2.234(13)
2.322(13)
2.322(13)
2.35(3)
O10 2.478(5)
O4
O8
O5
O7
O8
O1
O4
O3
O6
O9
O8
O5
O5
2.221(4)
2.222(4)
2.282(4)
2.399(5)
2.407(5)
2.442(5)
2.530(5)
2.265(5)
2.331(5)
2.333(5)
2.382(5)
2.435(5)
2.460(4)
2.471(13)
2.533(13)
2.15(2)
O7
O11B
O11A
O1
O4
O3
O4
O8
O10
O9
O13B
O12B
O12A 1.483(10)
O13A 1.486(9)
O7
O4
O8
O1
O3
O5
O6
2.26(2)
2.327(12)
2.377(13)
2.406(13)
2.428(12)
2.429(13)
2.502(13)
1.465(14)
1.472(10)
1.476(9)
O11 1.610(7)
O13 1.646(6)
O10 1.650(4) 2x Cd3
O14 1.610(8)
O12 1.631(7)
O1
O5
O6
O9
O3
O4
O8
O9
O2
O3
O2
O7
S1
S1
1.635(5) 2x S1
1.860(5)
1.871(4)
1.968(4)
2.480(5)
1.864(4)
1.864(4)
2.058(5)
2.335(5)
1.869(5)
1.884(4)
1.926(4)
S1
S1
S1
1.487(13)
1.861(13)
1.868(13)
1.910(13)
1.859(13)
1.868(13)
2.107(13)
2.125(12)
1.83(2)
Te1
Te1
Te1
Te2
Te2
Te2
Te2
Te3
Te3
Te3
Te3
Ca1 2.08; Ca2 2.07; Ca3
1.83; Se1 6.07; Te1 4.22;
Te2 4.11; O1 (Te, 3Ca)
2.15; O2 (Te, 2Ca) 2.24;
O3 (Se, Ca) 1.81; O4 (Te,
3 Ca) 2.16; O5 (Te, 2 Ca)
2.15; O6 (Se, Ca) 1.84;
O7 (Se, Ca) 1.77; O8 (Se,
Ca) 1.85; O9 (Te, 3Ca)
2.18; O10 (Te, 3Ca) 2.25
O1
O11B
O2
O6
O11A
1.876(13)
1.911(13)
1.93(3)
Ca1 2.07; Ca2 2.15; Ca3
1.91; Se1 6.16; Te1 4.04;
Te2 4.12; Te3 4.10; O1 (Te,
3Ca) 2.18; O2 (Te, 3Ca)
2.31; O3 (Te, 3Ca) 2.24; O4
(Te, 3Ca) 2.22; O5 (Te,
3Ca) 2.06; O6 (Se, Ca)
1.86; O7 (2Te, Ca) 2.13; O8
(2Te, Ca) 2.31; O9 (Te, 2
Ca) 2.08; O10 (Se, Ca)
1.83; O11 (Se, Ca) 1.77;
O12 (Se) 1.56
Cd1 1.96; Cd2 2.15; Cd3
1.75; Se1 5.99; Se2 6.16;
Te1 3.99; Te2 3.90; Te3
3.77; O1 (Se, Cd) 1.74;
O2 (2Te, Cd) 2.00; O3
(2Te, Cd) 1.97; O4
(Te, 3Cd) 2.28; O5 (Te,
3Cd) 2.19; O6 (Te, 2Cd)
2.08; O7 (Te, 3Cd) 2.07;
O8 (Te, 3Cd) 2.31; O9
(2Te, Cd) 2.14; O10 (Se,
Cd) 1.67; O11 (Se) 1.62;
O12 (Se) 1.63; O13 (Se)
1.47; O14 (Se) 1.61
O10
O10
O10
O10
···
···
···
···
O12A 2.62(3)
O13B 2.62(3)
O12A 2.62(2)
O10 2.76(3)
Cd1 2.03; Cd2 2.04; Cd3 1.98;
S1 5.22; Te1 3.91; Te2 4.09;
Te3 3.82; O1 (2Te, Cd) 2.19;
O2 (Te, 3Cd) 2.17; O3 (Te,
3Cd) 2.19; O4 (Te, 3Cd) 2.21;
O5 (Te, 3Cd) 2.29; O6 (2Te,
Cd) 2.21; O7 (S, Cd) 1.63; O8
(Te, 2Cd) 2.06; O9 (S, Cd) 1.75;
O10* (Cd) 0.20; O11A (Te, Cd)
1.53; O12B (Te, Cd) 1.99;
O12A (S) 1.47; O12B (S) 1.49;
O13A (S) 1.45; O13B(S) 1.51
a) Coordination of a specific O atoms to the type and number of chalcogen or metal atoms is indicated in parentheses. b) * Hydrogen atoms
not considered for calculation of bond valence sums.
(Ca1–Ca3), respectively, sharing corners and edges. In this The three independent TeIV atoms flank the metal-
way a layered arrangement parallel (001) at z ≈ 0 and ½ for oxygen layers above and below the layer planes and
the centrosymmetric Ca structure and parallel (100) at y ≈ ¼ are connected to the outer oxygen atoms in form of TeO3
and ¾ for the non-centrosymmetric Cd structure is established. trigonal pyramids (Ca structure Te2, Te3; Cd structure Te1)
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
5
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Table 5. Selected interatomic distances /Å, angles /°, and bond valence sums /v.u.a)
Cd4(SO4)(TeO3)3 Cd5(SO4)2(TeO3)2(OH)2 Sr3(H2O)2(SeO4)(TeO3)2
O8
b)
Cd1
Cd1
Cd1
Cd2
Cd2
Cd2
Cd3
Cd3
Cd3
Cd3
Cd3
Cd3
Cd4
Cd4
Cd4
Cd4
Cd4
Cd4
Cd5
Cd5
Cd5
Cd5
Cd5
Cd5
Cd5
S1
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2.208(2) 2x Cd1 –
O13 2.296(2) 2x Cd1 –
O8 2.2293(11)
O4 2.2544(11)
O5 2.2941(13)
O3 2.3376(11)
O7 2.3557(12)
O2 2.3648(12)
Sr1
Sr1
Sr1
Sr1
Sr1
Sr1
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
O11
O9
2.443(5)
2.511(5)
2.524(5)
2.539(5)
2.571(5)
Se1
Se1
Se1
Se1
Se2
Se2
Se2
Se2
Te1
Te1
Te1
Te2
Te2
Te2
Te3
Te3
Te3
Te4
Te4
Te4
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
O13
O14
O15
O16
O18
O17
O19
O20
O1
O3
O2
O4
O5
O6
O7
O8
O9
O10
O11
O12
1.577(8)
1.708(6)
1.708(6)
1.726(5)
1.635(5)
1.637(6)
1.643(5)
1.648(5)
1.849(6)
1.866(5)
1.867(5)
1.848(5)
1.862(4)
1.875(5)
1.833(7)
1.851(5)
1.865(5)
1.833(5)
1.839(5)
1.857(5)
O7
O9
O5
O6
O2
2.330(2) 2x Cd1 –
2.272(2) 2x Cd1 –
2.273(2) 2x Cd1 –
2.375(2) 2x Cd1 –
O5
O2
O20
O2W 2.660(6)
O1W 2.687(6)
O3
O6
O12
O8
2.196(2)
Cd2 –
Cd2 –
Cd2 –
Cd3 –
Cd3 –
Cd3 –
Cd3 –
Cd3 –
Cd3 –
O4 2.2447(11) 2x Sr1
O1 2.2813(12) 2x Sr2
O6 2.4035(12) 2x Sr2
O12 2.232(2)
O8 2.293(2)
O11 2.319(2)
O3 2.393(2)
O10 2.470(2)
2.480(5)
2.484(5)
2.539(5)
2.545(6)
2.581(5)
O4 2.2071(11)
O1 2.3057(11)
O3 2.3152(11)
O8 2.3622(11)
O8 2.4111(12)
O3 2.4414(12)
O5 1.4665(13)
O2 1.4678(13)
O7 1.4774(11)
O6 1.4887(12)
O1 1.8658(11)
O3 1.8723(11)
O8 1.8900(11)
Sr2
Sr2
Sr2
Sr2
Sr2
Sr2
Sr3
Sr3
Sr3
Sr3
Sr3
Sr3
Sr3
Sr3
Sr4
Sr4
Sr4
Sr4
Sr4
Sr4
Sr4
Sr5
Sr5
Sr5
Sr5
Sr5
Sr5
Sr5
Sr5
Sr5
Sr6
Sr6
Sr6
Sr6
Sr6
O16
O7
O6
O9
O3
O2
O5
O1
O4
O3
O1
O4
O2
O6
2.241(2)
2.257(2)
2.290(2)
2.365(2)
2.407(2)
2.431(2)
2.292(2)
2.292(2)
2.327(2)
2.368(2)
2.399(2)
2.450(2)
2.482(2)
O3W 2.660(6)
O4W 2.791(7)
O1
O2
O5
O6
O9
O5
O8
O14
O1
O10
O1
3.201(6)
2.565(5)
2.587(5)
2.653(5)
2.653(5)
2.670(5)
2.688(6)
2.722(6)
3.269(6)
2.447(5)
2.478(5)
2.556(6)
2.578(5)
2.600(6)
2.659(6)
2.743(6)
2.440(6)
2.467(5)
2.509(6)
2.633(6)
2.637(5)
2.725(7)
2.773(6)
2.825(8)
3.057(7)
2.556(5)
2.608(5)
2.638(6)
2.678(5)
2.721(6)
S1
S1
S1
S1
Te1
Te1
Te1
–
–
–
–
–
–
–
O1W ···
O1W ···
O1W ···
O1W ···
O2W ···
O2W ···
O2W ···
O2W ···
O3W ···
O3W ···
O3W ···
O3W ···
O4W ···
O4W ···
O17
O16
O9
O20
O18
O16
O20
O2
O20
O15
O16
O3
O13
O20
O8
2.864(9)
2.873(8)
3.164(8)
3.230(8)
2.864(9)
2.877(8)
3.158(8)
3.169(8)
2.915(8)
2.931(11)
3.133(9)
3.242(11)
2.759(12)
3.036(9)
3.090(9)
3.258(9)
D–H···A
D···A (D–H···A)
O10 1.474(2)
O11 1.474(2)
O12 1.479(2)
O13 1.487(2)
O4–H1···O5 2.918 145
O8
S1
S1
S1
O12
O19
O15
O19
O7
Cd1 2.04; Cd2 2.04; Cd3
1.99; S1 5.98; Te1 3.94;
Te1
Te1
Te1
Te2
Te2
Te2
Te3
Te3
Te3
O1
O2
O3
O4
O5
O6
O7
O8
O9
1.868(2)
1.875(2)
1.904(2)
1.855(2)
1.887(2)
1.913(2)
1.857(2)
1.875(2)
1.883(2)
O1 (Te, 2Cd) 2.05; O2 (S,
Cd) 1.82; O3 (Te, 3 Cd) 2.20;
O4* (3 Cd) 1.23; O5 (S, Cd)
1.88; O6 (S, Cd) 1.70; O7 (S,
Cd) 1.78; O8 (Te, 3 Cd) 2.22
O4
O10
O14
O9
O7
O4W ···
O4W ···
O17
O13
O11
O4
O3
O18
O2
O16
Sr1 2.16; Sr2 2.06; Sr3 1.69; Sr4
2.07; Sr5 1.84; 2.16; Sr6 1.84;
Se1 5.45; Se2 5.96; Te1 4.11;
Te2 4.10; Te3 4.23; Te4 4.37;
O1 (Te, 2Sr) 1.96; O2 (Te, 3Sr)
2.18; O3 (Te, 3Sr) 2.18; O4
(Te,2Sr)
Cd1 2.20; Cd2 2.04; Cd3
2.02; Cd4 1.93; Cd5 2.00; S1
5.93; Te1 3.88; Te2 3.86;
Te3 3.97; O1 (Te, 2Cd) 1.98;
O2 (Te, 3Cd) 2.26; O3 (Te, 3
O12
Cd) 2.09; 2Cd) 1.87; O6 (Te,
Sr6
–
O3
2.733(5)
2.11; O5 (Te, 3Sr) 2.21; O6 (Te,
3Sr)
3Cd) O4 (Te, 2Cd) 2.01; O5
(Te, 2.06; O7 (Te, 2Cd) 2.10;
Sr6
Sr6
–
–
O1
O11
2.768(6)
2.862(6)
2.04; O7 (Te, 2Sr) 2.09; O8
(Te, 3 Sr) 2.24; O9 (Te, 3Sr)
2.18;
O8 (Te, 2Cd) 2.11; O9 (Te,
2Cd) 2.01; O10 (S, Cd) 1.72;
O11 (S, Cd); 1.83; O12 (S,
Sr6
–
O6
2.925(6)
O10 (Te, 2Sr) 2.23; O11(Te, 2Sr)
2.00; O12 (Te, 3Sr) 1.93; O13
(Se, Sr) 1.92; O14 (Se, 2Sr)
1.69;
Cd) 1.89; O13 (S, Cd) 1.80
O15 (Se, Sr) 1.47; O16 (Se, Sr)
1.47;
O17 (Se, Sr) 1.67; O18 (Se, Sr)
1.76;
O19 (Se, 2Sr) 1.94; O20 (Se, Sr)
1.75; O1W* (Sr) 0.22; O2W*
(Sr)
0.23; O3W* (Sr) 0.23; O4W*
(Sr) 0.16
a) Coordination of a specific O atoms to the type and number of chalcogen or metal atoms is indicated in parentheses. b) * Hydrogen atoms
not considered for calculation of bond valence sums.
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
6
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Figure 1. The crystal structure of Ca3(SeO4)(TeO3)2 in a projection
Figure 2. The crystal structure of Ca3(SeO4)(Te3O8) in a projection
along [010]. Te atoms and corresponding polyhedra are given in red,
Se atoms and corresponding polyhedra in yellow, Ca atoms in blue, O
atoms are colourless. Displacement ellipsoids are drawn at the 74%
probability level.
along [100]. Te atoms with coordination number three and correspond-
ing polyhedra are given in red, Te atoms with coordination number
four and corresponding polyhedra are given in orange. Se atoms and
corresponding polyhedra, Ca atoms, O atoms as well as displacement
ellipsoids are as in Figure 1.
and TeO4 disphenoids (Ca structure Te1; Cd structure Te1,
Te2). In both structures the electron lone pairs of the
TeIV atoms are pointing away from the metal-oxygen layer.
The connectivity of the TeO3 and TeO4 polyhedra is
markedly different in the two structures. Whereas finite
Te3O8 groups [Te2O2/1O1/2Te1O2/2O2/1Te3O1/2O2/1
]
or
in
[(TeO2/1O1/2)2TeO2/2O2/1
Ca3(SeO4)(Te3O8), infinite
[Te1O2/1O2/2Te1O1/1O2/2Te3O2/1O2/2 ϱ
]
are
realized
chains
are
zigzag
Te3O8
present in
1
]
Cd3(SeO4)(Te3O8). The connection of adjacent layers in both
structures is accomplished by isolated SeO4 tetrahedra that are
relatively loosely bonded to the metal cations. In fact, some of
the selenate oxygen atoms do not show any bonding with the
metal cations at all, which explains their rather low bond val-
ence sums (Table 4) and their high displacement parameters
(Figure 2 and Figure 3). On the other hand, these single-
bonded O atoms show, as expected, the shortest Se–O dis-
tances.
Figure 3. The crystal structure of Cd3(SeO4)(Te3O8) in a projection
along [010]. Cd atoms are blue, all other atoms, polyhedra and ellip-
soids are drawn as in Figure 2.
Cd3(H2O)(SO4)(Te3O8)
The principal structural set-up of this hydrous phase (Fig-
ure 4) is very similar to that of the two M3(SeO4)(Te3O8) trigonal pyramids (Te1, Te3) and a TeO4 bisphenoid (Te2) with
phases, i.e. a layered arrangement of metal–oxygen (M = Cd) the electron lone pair pointing away from the layer. The anion
and tellurium–oxygen polyhedra sandwiched by XO4 tetrahe- has the same finite Te3O8 configuration than that in Ca3(SeO4)-
dra (X = Se, S). The three cadmium cations exhibit coordina- (Te3O8) ([(TeO2/1O1/2)2TeO2/2O2/1]). In comparison with the
tion numbers of seven (Cd1, Cd3) and of six or seven (Cd2), latter structure, an additional water molecule (O10) is bonded
taking into account the half-occupancy of an oxygen atom to one of the Cd atoms (Cd3) and is positioned between two
(O11A) that is part of the coordination sphere of the latter layers. Although the hydrogen atoms of the water molecule
cation. The corresponding CdOx (x = 6, 7) polyhedra are dis- could not be located in the present study, bond valence sums
torted and condensed into a layered arrangement through and typical O···O donor···acceptor distances (Table 4) clearly
corner- and edge-sharing. The layers spread parallel to (001) support the presence of O10 as part of a water molecule that
at z ≈ 0. Again, the TeIV atoms flank the layers above and is involved in hydrogen bonding of medium strengths
below the outer oxygen atoms of the layers, forming two TeO3 (O10···O(acceptor) distances 2.62–2.76 Å).
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electron lone pairs towards the empty space of the channels.
As noted above, Cd4(SO4)(TeO3)3 does not contain condensed
oxotellurate anions but isolated trigonal-pyramidal TeO3
groups only. The S atoms of the slightly distorted sulfate tetra-
hedra are arranged in layers parallel to (002). A remarkable
difference to the Ca3(SeO4)(Te3O8), Cd3(SeO4)(Te3O8), and
Cd3(H2O)(SeO4)(Te3O8) structures is the coordination of all
sulfate O atoms to a Cd2+ cation.
Figure 4. The crystal structure of Cd3(H2O)(SO4)(Te3O8) in a projec-
tion along [100]. O atoms belonging to the OH group are green, all
other atoms, polyhedra and ellipsoids are drawn as in Figure 3. Pos-
sible hydrogen-bonding interactions are depicted as dashed lines. Only
one of the orientations of the disordered O atoms is shown.
The sulfate tetrahedra are disordered over two sets of
sites and are situated at z ≈ ½ between the cadmium oxo-
tellurate(IV) layers. The SO4 anions alternate pairwise with the
water molecule along [010]. A notable difference between the
M3(SeO4)-(Te3O8) and the Cd3(H2O)(SO4)(Te3O8) structure
pertains to the distance between two layers. The interlayer gap,
measured as the shortest distance between the most outer oxy-
gen atoms of adjacent layers, is 3.44 Å in Ca3(SeO4)(Te3O8),
3.95 Å in Cd3(SeO4)(Te3O8), and 4.26 Å in Cd3(H2O)(SO4)
(Te3O8). Although the SO4 tetrahedron is smaller than the
SeO4 tetrahedron, the interlayer gap is the longest for the sulf-
ate compound and hence might explain the disorder of the SO4
anion with its O atoms bound either loosely to the cadmium
atoms of the layer or hydrogen-bonded to the water molecule.
Figure 5. The crystal structure of Cd4(SO4)(TeO3)3 in a projection
along [100]. S atoms and SO4 polyhedra are yellow, all other atoms,
polyhedra and ellipsoids are drawn as in Figure 3.
Cd5(SO4)2(TeO3)2(OH)2
Although the crystal structure of Cd5(SO4)2(TeO3)2(OH)2
(Figure 6) is likewise built up from metal oxotellurate(IV) lay-
ers, it shows resemblance to the framework structure of
Cd4(SO4)(TeO3)3 rather than to the three layered structures
Cd4(SO4)(TeO3)3
In contrast to the distinct layered arrangements of the
Ca3(SeO4)(Te3O8), Cd3(SeO4)(Te3O8), and Cd3(H2O)(SeO4)-
(Te3O8) structures, each of which is also characterized by the
presence of condensed oxotellurate anions [Te3O8]4–, the struc-
ture of Cd4(SO4)(TeO3)3 represents a three-dimensional frame-
work of individual building blocks, whereby the tellurate
anions are not condensed with each other (Figure 5). Five
unique Cd2+ cations are present in the asymmetric unit, two
(Cd1, Cd2) located on a centre of inversion. Except Cd5 with
a distorted monocapped octahedral coordination by O atoms,
all other Cd cations exhibit distorted octahedral coordination
spheres, most prominently pronounced for Cd4. The various
CdOx polyhedra share O atoms through vertices and edges,
thereby constructing a three-dimensional framework. The latter
is crossed by channels parallel to [100] where the three inde-
pendent Te atoms are located. Again, the stereochemical ac-
Figure 6. The crystal structure of Cd5(SO4)2(TeO3)2(OH)2 in a projec-
tion along [100]. Hydrogen atoms are represented as grey spheres with
an arbitrary radius; colour codes for other atoms and polyhedra, as
tivity of the TeIV atoms is evident from the direction of the well as the probability function of the ellipsoids are as in Figure 5.
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discussed above. All three independent Cd2+ cations in independent SeO4 tetrahedron are also involved as acceptor
¯
Cd5(SO4)2(TeO3)2(OH)2 (Cd2 with site symmetry 1) are sur- atoms for hydrogen-bonding with the water molecules, here
rounded by six O atoms in the form of distorted octahedra. with significant shorter OW···O distances compared to the in-
Cd2 and Cd3 are situated at z ≈ 0 and are condensed through ter-sheet interactions, ranging from 2.75–3.1 Å. The role as
common O atom vertices and edges into layers parallel to hydrogen-bonding acceptor atoms also compensates for the
(001). The Cd1 cations flank these layers in an alternating up considerable underbonding of these atoms (Table 5), which,
and down mode at z ≈ 1/3 and z ≈ –1/3. Adjacent layers are next to their features as selenate oxygen atoms, are bonded
held together by sulfate tetrahedra, here again with all sulfate only at large distances to the Sr2+ ions of the sheets. Like in
O atoms additionally bonded to a Cd2+ cation. This arrange- all other structures presented in this communication, the ar-
ment delimits channels propagating parallel to [100] into rangement of the metal–oxygen sheets and the tetrahedral
which the electron lone pairs of the TeIV atoms of the isolated oxochalcogenate(VI) units leads to the formation of free space,
Te1O3 trigonal pyramids protrude. Additional stabilization of in this case associated with channels running parallel to [001].
this arrangement is achieved through a weak hydrogen bonding Here the four unique Te atoms are located at the outer array
interaction between the OH group (O4) and one of the sulfate of the sheets, alternating with the Se atoms along [010] on
O atoms (O4···O5 2.918 Å; Table 5, Figure 6).
each side of the sheet. The motif of trigonal-pyramidal TeO3
units pointing with their electron lone pairs into the empty
space of the channels is also found in the structure of
Sr3(H2O)2(SeO4)(TeO3)2.
Sr3(H2O)2(SeO4)(TeO3)2
Six Sr cations, four with a coordination number of seven
(Sr1–Sr4) and two with coordination number eight (Sr5–6) are
present in the asymmetric unit. The crystal structure of this
phase is depicted in Figure 7. Cations Sr3–Sr6 are situated at
x ≈ 0 and build up strontium-oxygen sheets parallel (100) with
the remaining two Sr1 and Sr2 cations located on both sides
of the sheets. Next to the O atoms that are part of the stron-
tium-oxygen sheet, these two cations each are additionally
bonded to two water molecules directed towards the neigh-
bouring sheet. Besides rather weak possible inter-sheet
hydrogen bonds between the water molecules and O atoms of
adjacent sheets (OW···O distance between 3.1 and 3.2 Å), the
connection between the sheets is mainly accomplished through
bridging SeO4 tetrahedra along [100]. Atom Se1 shows a dis-
parate Se–O bond lengths distribution with one short and three
longer bonds, whereas Se2 is more uniformly structured with
more or less the same bond lengths. Three O atoms of each
General Features
In all seven crystal structures, the oxochalcogenate(VI)
anions are isolated from the oxotellurate(IV) anions and show
bond lengths distributions characteristic for tetrahedral XO4
(X = S, Se) groups.[51,52] The same applies for the respective
metal–oxygen polyhedra[53–55] with coordination numbers
ranging between six and eight for Ca2+, six and seven for Cd2+
and seven and eight for Sr2+ compounds, in accordance with
the increasing ionic radii from Cd to Sr.[56]
Conclusions
The idea to modify metal oxotellurate(IV) frameworks
(metal = Ca, Cd, Sr) through incorporation of tetrahedral XO4
anions (X = S, Se) as spacers with formation of compounds
with non-centrosymmetric structures has proven to be success-
ful for two out of seven new compounds. Corresponding reac-
tion batches were conducted under hydrothermal conditions
and led to multi-phase mixtures with low yields for the
mixed oxochalcogenate(IV,VI) phases in each case. Ca3(-
SeO4)-(TeO3)2 and Cd3(SeO4)(Te3O8) crystallize in space
grouptypesP21andCmc21,respectively,whereasCa3(SeO4)(Te3O8)
(P21/n),
Cd3(H2O)(SO4)(Te3O8),
Cd4(SO4)(TeO3)3,
¯
Cd5(SO4)2(TeO3)2(OH)2, and Sr3(H2O)2(SeO4)(TeO3)2 (all P1)
crystallize in centrosymmetric space group types. Common to
all crystal structures are the stereoactivity of the Te 5s2 elec-
2–
tron lone pair E and the separation of the tetrahedral XO4
anions and oxotellurate anions, the latter being present either
as single TeO32– anions or as condensed [Te3O8]4– anions. Low
yields and multi-phase formation prevented further examina-
tion of physical properties of the title compounds.
Acknowledgements
Figure 7. The crystal structure of Sr3(H2O)2(SeO4)(TeO3)2 in a projec-
tion along [001]. Sr atoms are blue, O atoms belonging to water mol-
ecules are green. Colour codes for other atoms and polyhedra, as well
as the probability function of the ellipsoids are as in Figure 1.
The X-ray Centre of TU Wien is acknowledged for providing access
to the single-crystal and powder diffractometers.
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M. Weil,* M. Shirkhanlou ............................................... 1–11
Incorporation of Sulfate or Selenate Groups into
Oxotellurates(IV): I. Calcium, Cadmium, and Strontium Com-
pounds
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