Aqueous telluridoindate chemistry: Water-soluble salts of monomeric, dimeric, and trimeric In/Te anions [InTe4]5-, [In 2Te6]6-, and [In3Te 10]11-

Article abstract of DOI:10.1021/ic101881j

Water-soluble salts of monomeric, dimeric, and/or trimeric telluridoindate anions, [K₅(H₂O)_2.16][InTe₄] (1), [K₅(H₂O)₅][InTe₄] (2), [K ₆(H₂O)₆][In₂Te₆] (3), [K₁₆(H₂O)_9.62][InTe₄] ₂[In₂Te₆] (4), [K₁₃₃(H ₂O)₂₄][In₃Te₁₀]₁₂Te _0.5 (5), and [Rb₆(H₂O)₆][In ₂Te₆] (6), were prepared by a fusion/extraction method starting from the elements and characterized by single-crystal X-ray diffraction as well as spectroscopic methods. The compounds are the first hydrates of telluridoindate salts and thus point toward an aqueous coordination chemistry with binary In/Te ligands. Both crystallization from the extracts as mixtures of salts as well as preliminary spectroscopic investigation of the solutions indicate the presence of an equilibrium of different anionic species. Here, the indates differ from related stannates, which also show pH-dependent aggregation, but to a much lesser extent and in a better distinguishable manner. We present syntheses and crystal structures and discuss observation of the coexistence of different anions both in the solid state and in solution.

Full text of DOI:10.1021/ic101881j

11216 Inorg. Chem. 2010, 49, 11216–11222
DOI: 10.1021/ic101881j
Aqueous Telluridoindate Chemistry: Water-Soluble Salts of Monomeric, Dimeric,
and Trimeric In/Te Anions [InTe4]5-, [In2Te6]6-, and [In3Te10]11-
Johanna Heine and Stefanie Dehnen*
Fachbereich Chemie and Wissenschaftliches Zentrum fu€r Materialwissenschaften (WZMW),
€
Philipps-Universitat Marburg, Hans Meerwein Strasse, D-35043 Marburg, Germany
Received September 14, 2010
Water-soluble salts of monomeric, dimeric, and/or trimeric telluridoindate anions, [K5(H2O)2.16][InTe4] (1),
[K5(H2O)5][InTe4] (2), [K6(H2O)6][In2Te6] (3), [K16(H2O)9.62][InTe4]2[In2Te6] (4), [K133(H2O)24][In3Te10]12Te0.5
(5), and [Rb6(H2O)6][In2Te6] (6), were prepared by a fusion/extraction method starting from the elements and
characterized by single-crystal X-ray diffraction as well as spectroscopic methods. The compounds are the first
hydrates of telluridoindate salts and thus point toward an aqueous coordination chemistry with binary In/Te ligands.
Both crystallization from the extracts as mixtures of salts as well as preliminary spectroscopic investigation of the
solutions indicate the presence of an equilibrium of different anionic species. Here, the indates differ from related
stannates, which also show pH-dependent aggregation, but to a much lesser extent and in a better distinguishable
manner. We present syntheses and crystal structures and discuss observation of the coexistence of different anions
both in the solid state and in solution.
Introduction
is known about the heavier congeners, the least about indium
tellurides.
Indium chalcogenides possess many interesting properties,
such as photocatalytic activity,1 photoluminescence2 and ion
conductivity,3 and have found technical application in the
field of thin film solar cells, where doped variants of the
chalcopyrite CuInS2 hold the record of more than 19% in
conversion efficiency.4 They have been the subject of research
since the turn of the last century,5 and much effort has gone
into the preparation of a diverse range of materials, from
molecular salts6 to extended, porous frameworks composed
of large supertetrahedral clusters.7 While indium sulfides
have been the focus of attention in the last years, much less
This is exemplified by the fact that, while anionic structures
of composition transition metal (TM)/In/S have shown many
interesting properties, no example of a similar structure
containing TM/In/Te has been known up to now. So,
building on the foundation of our experiences with the
chemistry of chalcogenidotetrelates8 and their reactions to-
ward diverse ternary anionic structures, forming ternary
clusters and networks of the general type [TMxTyChz]q-
(T=tetrel=group 14 atom; Ch=chalcogen),9 we attempted
to establish a similar route employing telluridoindates. In
order to achieve this, water- or alcohol-soluble precur-
sors [InxTey]q- were needed. Although one example of a
*To whom correspondence should be addressed. E-mail: dehnen@
chemie.uni-marburg.de.
(1) Zheng, N.; Bu, X.; Vu, H.; Feng, P. Angew. Chem., Int. Ed. 2005, 44,
5299–5303.
(8) (a) Dehnen, S.; Melullis, M. Coord. Chem. Rev. 2007, 251, 1259–1280.
(b) Ruzin, E.; Jakobi, S.; Dehnen, S. Z. Anorg. Allg. Chem. 2008, 634, 995–
1001. (c) Ruzin, E.; Kracke, A.; Dehnen, S. Z. Anorg. Allg. Chem. 2006, 632,
1018–1026.
(2) Zheng, N.; Bu, X.; Wang, B.; Feng, P. Science 2002, 298, 2366–2369.
(3) Zheng, N.; Bu, X.; Feng, P. Nature 2003, 426, 428–432.
(4) Green, M. A.; Emery, K.; Hishikawa, Y.; Warta, W. Prog. Photo-
voltaics 2009, 17, 320–326.
(9) (a) Haddadpour, S.; Melullis, M.; Staesche, H.; Mariappan, C. R.;
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Roling, B.; Clerac, R.; Dehnen, S. Inorg. Chem. 2009, 48, 1689–1698. (b) Lips,
(5) Schneider, R. J. Prakt. Chem. 1874, 9, 209–216.
F.; Dehnen, S. Inorg. Chem. 2008, 47, 5561–5563. (c) Ruzin, E.; Zimmermann,
C.; Hillebrecht, P.; Dehnen, S. Z. Anorg. Allg. Chem. 2007, 633, 820–829.
(d) Ruzin, E.; Fuchs, A.; Dehnen, S. Chem. Commun. 2006, 4796–4798.
(e) Ruzin, E.; Dehnen, S. Z. Anorg. Allg. Chem. 2006, 632, 749–755.
(6) For examples, see: (a) Eisenmann, B.; Hofmann, A. Z. Kristallogr.
1991, 197, 169–170. (b) Eisenmann, B.; Hofmann, A.; Zagler, R. Z. Naturforsch.
1990, 45b, 8–14. (c) Sportouch, S.; Belin, C.; Tillard-Charbonnel, M. Acta
Crystallogr. 1994, C50, 1861–1862. (d) Eisenmann, B.; Hofmann, A. Z.
Kristallogr. 1991, 197, 151–152. (e) Deiseroth, H. J. Z. Naturforsch. 1980,
35b, 953–958. (f) Wang, C.; Haushalter, R. C. Inorg. Chem. 1997, 36, 3806–
3807. (g) Park, C.-W.; Salm, R. J.; Ibers, J. A. Angew. Chem. 1995, 107, 2044–
2045. (h) Heine, J.; Dehnen, S. Z. Anorg. Allg. Chem. 2008, 634, 2303–2308.
(7) For a comprehensive review of this class of materials, see: Feng, P.; Bu,
X.; Zheng, N. Acc. Chem. Res. 2005, 38, 293–303.
ꢀ
(f) Zimmermann, C.; Anson, C. E.; Weigend, F.; Clerac, R.; Dehnen, S. Inorg.
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Chem. 2005, 44, 5686–5695. (g) Melullis, M.; Clerac, R.; Dehnen, S. Chem.
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Commun. 2005, 6008–6010. (h) Brandmayer, M. K.; Clerac, R.; Weigend, F.;
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r
pubs.acs.org/IC
Published on Web 11/04/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 23, 2010 11217
Table 1. Data of the Single-Crystal X-ray Diffraction Analyses of Compounds 1-6a
1
2
3
4
5
6
empirical formula
fw (g mol-1
cryst color/shape
cryst size (mm3)
H4.32InK5O2.16Te4
859.72
H10InK5O5Te4
910.80
H12In2K6O6Te6
1337.94
yellow block
0.08 ꢀ 0.08
ꢀ 0.02
H19.25In4K16O9.62Te14
3044.68
brown cube
0.05 ꢀ 0.05
ꢀ 0.05
H4In3K11.08O2Te10.4
2095.17
black cube
0.12 ꢀ 0.1 2
ꢀ 0.06
H12In2O6Rb6Te6
1616.16
yellow block
0.15 ꢀ 0.12
ꢀ 0.11
)
yellow block
0.06 ꢀ 0.05
ꢀ 0.04
yellow block
0.18 ꢀ 0.05
ꢀ 0.03
cryst syst
space group
monoclinic
P21/c
orthorhombic
P212121
8.788(3)
11.111(4)
20.156(5)
90
monoclinic
P21/c
tetragonal
P42/mnm
16.325(4)
16.325(4)
22.777(5)
90
cubic
monoclinic
P21/c
I m3
˚
a (A)
13.350(3)
14.136(4)
18.209(4)
90
94.18(3)
90
3427.2(14)
8
3.332
8.993(3)
14.372(4)
11.602(4)
90
118.62(3)
90
1316.3(7)
2
3.345
22.960(2)
22.960(2)
22.960(2)
90
90
90
12104(2)
12
3.449
8.881(3)
9.693(3)
18.728(4)
90
117.71(3)
90
1427.3(7)
2
3.747
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
90
90
90
90
6070(2)
4
3.332
9.218
ψ scan
0.411/0.842
50.00
39416
3
˚
V (A )
Z
F
1968.1(11)
4
3.074
calcd (g cm-3
)
μ(Mo KR) (mm-1
abs corrn type
min/max transmn
max 2θ (deg)
reflns measd
R(int)
)
9.242
8.066
9.225
9.963
17.799
Gaussian
0.4350/0.6186
51.82
23499
0.1090
Gaussian
0.368/0.794
53.36
5314
0.0674
Gaussian
0.465/0.804
51.44
10042
0.0365
Gaussian
0.23174/0.43131
51.92
6637
0.1287
Gaussian
0.052/0.203
53.50
13637
0.1234
0.1961
2675
2432
indep reflns
indep reflns
6636
4140
3014
2825
2799
2501
2120
867
3007
2757
[I > 2σ(I)]
no, of param
R1 [I > 2σ(I)]
wR2 (all data)
S (all data)
221
126
91
111
74
91
0.0443
0.0700
0.914
0.0418
0.1736
1.046
0.0236
0.0545
1.023
0.0549
0.1381
0.919
0.0709
0.1702
0.818
0.0457
0.1178
1.030
res diff peak/hole
)
1.35/-1.45
2.80/-3.74
1.02/-1.16
3.44/-2.07
10.05/-4.85
2.36/-3.15
-3
˚
(e A
3
a The structures were solved and refined using SHELXTL software.12
sulfidoindate and its homologous selenidoindate hydrate has
been reported,10 the existence of telluridoindates in aqueous
phase has been suggested by the works of O’Connor et al.11
but has only been confirmed by elemental analysis so far.
Using an extraction/evaporation route, similar to the one
that we established for the generation of analogous selenido-
indate6h or telluridostannate salts,8b,c we succeeded in the
synthesis and characterization of the first telluridoindate
hydrates, which are presented in this work.
Synthesis of A5InTe4 (A = Na, Rb, Cs). The corresponding
sodium, rubidium, and cesium materials were prepared in a
fashion similar to that of K5InTe4.
Synthesis of [K5(H2O)2.16][InTe4] (1), [K5(H2O)5][InTe4] (2),
[K6(H2O)6][In2Te6] (3), [K16(H2O)9.62][InTe4]2[In2Te6] (4), and
[K133(H2O)24][In3Te10]12Te0.5 (5). K5InTe4 was dissolved in
water and filtered to yield a bright-yellow solution. The solvent
was removed slowly to yield pale-yellow crystals of 1-3. Upon
standing, brown cubes of 4 and black, metallic cubes of 5
appeared within the mass of yellow crystals.
Synthesis of [Rb6(H2O)6][In2Te6] (6). Rb5InTe4 was dissolved
in water and filtered to yield a bright-yellow solution. Slow
removal of the solvent yielded small yellow crystals of 6.
Single-Crystal X-ray Diffraction. Data were collected on a
diffractometer equipped with a STOE imaging-plate detector
system IPDS2, using graphite-monochromized Mo KR radia-
Experimental Section
General Procedures. All synthesis steps were performed under
an argon atmosphere. Water was degassed by applying a
dynamic vacuum (1 ꢀ 10-3 mbar) for several hours. A5InTe4
(A = Na, K, Rb, Cs) was prepared according to a modified
literature procedure.11 Na5InTe4 was also prepared according to
a different literature procedure.6b
˚
tion (λ=0.710 73 A) at 100 K. Structure solution and refinement
were performed by direct methods and full-matrix least squares
on F2, respectively, using SHELXTL software.12 Table 1 sum-
marizes the crystallographic data for 1-6. Details of the refine-
ments: 1: refinement of K, In, and Te atomic positions
employing anisotropic displacement parameters; refinement of
O atomic positions employing isotropic displacement para-
meters; a disordered model was used to describe one O atom
and another one was described by a partially occupied position;
H atoms were not calculated. 2: refinement of K, In, and Te
atomic positions employing anisotropic displacement para-
meters; refinement of O atomic positions employing isotropic
displacement parameters; a disordered model was used to
describe one O atom; H atoms were not calculated. 3: refinement
of K, In, Te and O atomic positions employing anisotropic dis-
placement parameters; H atoms were not calculated. 4: refine-
ment of K, In, and Te atomic positions employing anisotropic
Synthesis of [K5InTe4]. A total of 714 mg (18.3 mmol, 5 equiv)
of potassium in small pieces and 3354 mg (29.2 mmol, 5 equiv) of
indium powder were mixed and transferred to a quartz ampule.
The mixture was fused by heating with a Bunsen burner, yielding
the brittle, metallic material K5In8. K5In8 was ground into a fine
black powder in a mortar, and 1864 mg (14.6 mmol, 4 equiv) of
tellurium powder was added. Both powders were carefully
mixed because the mixture is highly reactive and an exothermic
reaction will set in even under strictly inert conditions if there is
too much agitation. The mixture was transferred to a quartz
ampule and fused to yield the bright-red material K5InTe4 and
metallic indium fragments.
(10) Krebs, B.; Voelker, D.; Stiller, K. O. Inorg. Chim. Acta 1982, 65,
L101–L102.
(11) Zhang, J. H.; van Duyneveldt, A. J.; Mydosh, J. A.; O’Connor, C. J.
Chem. Mater. 1989, 1, 404–406.
(12) Sheldrick, G. M. SHELXTL 5.1; Bruker AXS Inc.: Madison, WI, 1997.

11218 Inorganic Chemistry, Vol. 49, No. 23, 2010
Heine and Dehnen
displacement parameters; refinement of O atomic positions
employing isotropic displacement parameters; H atoms were
not calculated. 5: refinement of K, In, and Te atomic positions
employing anisotropic displacement parameters; refinement of
O atomic positions employing isotropic displacement param-
eters; a mixed-site refinement was used to describe occupation of
the (0, 0, 0) lattice position by 0.5 equiv of K2Te per formula
unit; H atoms were not calculated. The residual electron
densities of þ10.05 and -4.84 e A-3 are located about 1.61 and
˚
3
˚
0.62 A from In2, respectively. This indicates that they are mainly
artifacts of the cubic symmetry. Upon careful examination of
the diffraction data, a larger cell may be found, which possibly
represents the superstructure, taking into account the exact
occupancy of the (0, 0, 0) site. Unfortunately, we have been
unable to gain a structure solution from integration of this cell
because of insufficient resolution. 6: refinement of K, In, Te and
O atomic positions employing anisotropic displacement param-
eters; H atoms were not calculated.
Figure 1. Black cubes of 5 and yellow crystals of compounds 1-3.
Spectroscopy. UV-vis spectra were recorded on a Perkin-Elmer
Cary 5000 UV-vis-near-infrared spectrometer in the range of
800-200 nm employing a double-beam technique. The samples
were prepared as suspensions in Nujol oil between two quartz
plates.
Scheme 1. General Synthetic Fusion/Extraction Procedure for the
Efficient Generation of Water-Soluble Telluridoindate Salts, Given
for Potassium Compounds as an Example
Results and Discussion
Syntheses. A material of nominal composition K5InTe4
was prepared according to a modified literature proce-
dure.11 In the first step, potassium and indium were fused
with a bunsen burner employing a ratio of 5:8. This yields
the intermetallic phase K5In8, which is the only known
one in the K/In system to melt congruously,13 thus enabl-
ing us to get a homogeneous precursor. The resulting brit-
tle, metallic material was finely ground and then mixed
with 4 equiv of tellurium powder. This mixture was fused
to yield K5InTe4 as a reddish powder and the superfluous
indium as metallic fragments. K5InTe4 was then subjected
to aqueous extraction and filtration to yield a bright-
yellow solution. Upon slow removal of most of the
solvent, pale-yellow crystals of a mixture of compounds
1-3 were obtained. Within several days, brown crystals
of 4 appeared within the crystalline mass of 1-3. Further
standing resulted in the formation of 5 as intergrown,
black cubes with a metallic sheen, as shown in Figure 1.
A similar procedure using rubidium instead of potas-
sium resulted in a material of poor crystallinity, from
which 6 was isolated in the form of very small, pale-yellow
crystals. Employing cesium as the alkali-metal compo-
nent yielded only material of insufficient crystallinity. In
both cases, the formation of significant amounts of
RbInTe2 or CsInTe2 could be observed. The only crystal-
line product that could be isolated from the analogous
reaction sequence with sodium was a hydrate of sodium
telluride. This could also be observed when employing
Na5InTe4, which had been prepared by a different litera-
ture procedure.6b
of the ternary phases of composition AInTe2, which has
also been observed for the material K5InTe4 upon sub-
jection to extended periods of tempering. Yet, in every
case, the resulting solid phase could be extracted to yield a
yellow solution, an indication that telluridoindate species
have formed at least to some extent in solution.
Crystal Structures. All compounds were structurally
characterized by means of single-crystal X-ray diffraction
(see the Experimental Section). Selected bond lengths,
angles, and coordination environments are summarized
in Table S5 in the Supporting Information.
The structural aspects of compounds 1-3 are in accor-
dance with known solvates such as K5InTe4 KCl6c and
3
K6In2Te6 4en,6f yet their formation serves to illuminate
3
several aspects of the aqueous chemistry of these anions,
which has before only briefly been touched on and not
been accompanied by the evidence of crystallographic
data. They represent the first known hydrates of tellu-
ridoindates, prove the existence of molecular telluridoin-
dates in aqueous solution, and give the indication that a
more complicated equilibrium of telluridoindate species is
present in solution than the mere dissolution of K5InTe4
into Kþ and [InTe4]5-
.
The ortho-telluridoindate 1 crystallizes in the monoclinic
space group P21/c (No. 14). The main structural features
are [InTe4]5- tetrahedra, whose charge is compensated
for by partially hydrated potassium ions (Figure 2a). The
bond lengths and angles of compound 1 are very similar
6b
to those of the related solid phase Na5InTe4 [In-Te
The general procedure for the reaction employing
potassium is shown in Scheme 1. The outlined studies of
the influence of the cation on telluridoindate formation
indicate that potassium is the ideal counterion for this
system. A smaller ion like Naþ appears to favor forma-
tion of the binary alkali-metal telluride, while bigger
cations like Rbþ and Csþ seem to induce rapid formation
˚
bond lengths of 2.7660(13)-2.8566(12) A in 1 and 2.758-
˚
2.811 A in Na5InTe4; Te-In-Te angles of 103.27(4)-
113.02(4)° in 1 and 104.9-114.5° in Na5InTe4]. The
barycenters of the [InTe4]5- tetrahedra form layers of
distorted hexagons perpendicular to the crystallographic
b axis, with an AB stacking order of the layers as enforced
by the crystallographic symmetry (Figure 2b).
The closely related ortho-telluridoindate 2 (Figure 3a) crys-
tallizes in the orthorhombic space group P212121 (No. 19).
(13) Thuemmel, R.; Klemm, W. Z. Anorg. Allg. Chem. 1970, 376, 44–63.

Article
Inorganic Chemistry, Vol. 49, No. 23, 2010 11219
Figure 2. Fragment of the crystal structure in 1 (a) and representation of the arrangement topology of the [InTe4]5- anions in 1, illustrated by the position
and connection of their barycenters (b).
Figure 3. Fragment of the crystal structure in 2 (a) and representation of the arrangement topology of the [InTe4]5- anions in 2, illustrated by the position
and connection of their barycenters (b).
Again, the bond lengths and angles are similar to those
found in 1 and in Na5InTe4. As can be deduced from the
sum formula, the degree of solvation of the potassium
ions is greater than that in 1. Curiously, as we have also
found in our studies of the selenidoindates,6h more solvent
molecules do not necessarily induce a reduction of the
crystallographic symmetry but may instead afford a
higher symmetry in the salt containing more solvent. In
this compound, the barycenters of the anions form waved
layers along the crystallographic c axis (Figure 3b). It
seems remarkable that the anions in both 1 and 2 form
layerlike structures within a similar range of distances
4 represents the first known mixed chalcogenidoindate
anion salt in the chemistry of chalcogenidoindates. It crys-
tallizes in the tetragonal space group P42/mnm (No. 136).
4 features ortho-telluridoindate anions as well as dimeric
units, being in essence a less hydrated double salt of
compounds 1 and 3 (Figure 5a). The barycenters of the
dimeric units are located on the (1/2, 0, 0) lattice position,
forming a primitive tetragonal lattice that is interwoven
by waved layers of the barycenters of the o-telluridoindate
anions, occupying the lattice position (0.77322, 0.22678,
0.21819), similar to those in 2, perpendicular to the
crystallographic c axis (Figure 5b).
Compound 5 contains the previously unknown deca-
telluridotriindate anion [In3Te10]11-, consisting of three
corner-sharing [InTe4] tetrahedra (Figure 6). The forma-
tion of this species underlines yet again the diversity of the
chemistry of the telluridoindates and their complex solu-
tion behavior. Yet, it is also remarkable for its low degree
of condensation. In all multinuclear molecular chalco-
genidoindate anions, the single [InTe4] tetrahedra are
connected through edge or even face sharing. To find a
related structure, one has to look as far up the periodic
table as the oxoindates. Here, a tetrameric chain fragment
of composition K14[In4O13] has been reported, which is
made up of four corner-sharing InO4 units.14 Trimeric
chains of conformation similar to that of [In3Te10]11- can
˚
between barycenters [6.9307(3)-7.9027(4) A in 1 and
˚
7.4045(9)-7.7899(10) A in 2]. This should result in a
pronounced optical anisotropy and, because of the non-
centrosymmetric symmetry adopted by 2, possibly even
nonlinear optical properties.
The dimeric telluridoindate 3 (Figure 4a) crystallizes
in the monoclinic space group P21/c (No. 14). The
dimeric [In2Te6]6- anions have been reported in solid-
phase structures as well as in the solvate K6In2Te6 4en.
3
Unsurprisingly, the bond lengths and angles of the
anion are similar in all three compounds. The potas-
sium cations are only partly hydrated, affording a heli-
cal chain of potassium and water molecules along the
a axis. The barycenters of the dimeric anions form
a network of distorted, completely edge-sharing octa-
hedra (Figure 4b).
(14) Lulei, M.; Hoppe, R. Z. Anorg. Allg. Chem. 1993, 619, 1818–1826.

11220 Inorganic Chemistry, Vol. 49, No. 23, 2010
Heine and Dehnen
Figure 4. Fragment of the crystal structure in 3 (a) and representation of the arrangement topology of the [In2Te6]6- anions in 3, illustrated by the position
and connection of their barycenters (b).
Figure 5. Fragment of the crystal structure in 4 (a) and representation of the arrangement topology of the [InTe4]5- and [In2Te6]6- anions in 4, illustrated
by the position and connection (gray, [InTe4]5-; blue, [In2Te6]6-) of their barycenters (b).
tetrahedra, although an additional condensation into
double chains via Te-Te bonds is present here.6b
Compound 5 crystallizes in the cubic space group Im3
(No. 204). Within the crystal lattice, the barycenters of the
trimeric [In3Te10]11- units are arranged in an octahedral
way around mixed sites containing one K and 0.5 Te
atoms (Figure 7b). The mixed sites are a sign of a super-
structure that we have not been able to account for in the
structure solution because of the large cell size and the fact
that potassium and a half-occupied tellurium position are
indistinguishable as a result of equal electron numbers.
Yet, we are sure that, while some uncertainty remains
regarding the mixed sites, we were able to obtain an
accurate picture of the main structural features of this
compound.
Compound 6 (Figure 8a), which represents the first
Rbþ salt of the dimeric telluridoindate anion, crystallizes
in the monoclinic space group P21/c (No. 14). While
compounds 6 and 3 show homologous compositions,
and both contain dimeric telluridoindate units, the two
are not isostructural. This is clearly illustrated by the
arrangement of the barycenters of the dimeric units: As
in 3, a network of distorted, edge-sharing octahedra is
formed, yet the distortion is much more pronounced in
this case (Figure 8b), being better described as an arrange-
ment of edge-sharing tetrahedra. Thus, the supramolecular
Figure 6. Molecular structure of the [In3Te10]
11- anion in 5.
be found in the chemistry of the silicates, namely, the
mineral ardennite15a and the rare-earth silicate Ho4[Si3O10]-
[SiO4];15b further silicates containing the [Si3O10]11- unit,
such as those of the fluorothalenite-type M3F[Si3O10],16
prefer a horseshoe-type conformation of the trimer in-
stead of a linear chain.
Yet, if the search for related structural motifs is broad-
ened to extended anionic structures, an example from the
chemistry of solid-state telluridoindates can be found.
Here, the one-dimensional structure of Na5[InTe3]2 gives
an example of a polymeric chain of corner-sharing [InTe4]
(15) (a) Donnay, G.; Allmann, R. Acta Crystallogr. 1968, B24, 845–855.
(b) Felsche, J. Naturwissenschaften 1972, 59, 35–36.
€
(16) Muller-Bunz, H.; Schleid, T. Z. Anorg. Allg. Chem. 1998, 624, 1082–
1084.

Article
Inorganic Chemistry, Vol. 49, No. 23, 2010 11221
11-
Figure 7. Fragment of the crystal structure in 5 (a) and representation of the arrangement topology of the [In3Te10] anions in 5, illustrated by the
position and connection of their barycenters (black), which form octahedra around the K atoms (blue) on (0, 0, 0) and symmetry-equivalent positions (b).
11-
Figure 8. Fragment of the crystal structure in 5 (a) and representation of the arrangement topology of the [In3Te10
position and connection of their barycenters (b).
]
anions in 5, illustrated by the
Scheme 2. Possible Condensation Pathways for Telluridoindate
Anions in Solution
arrangement of the anions self-resembles their molecular
structure, a feature that was previously observed, for
instance, at the crystal structure of the selenidogermanate
salt [K4(H2O)3][Ge2Se6].17
The surprising number of different anions and corre-
sponding telluridoindate salts that may be isolated from a
single reaction mixture is in good accordance with similar
observations in different areas of chalcogenidoindate
chemistry18 and gives further evidence to a trend that
has already been noted in the chemistry of the borates in
comparison with silicates:19 the chalcogenidotrielates
have a much broader phase width than their tetrelate ana-
logues. Yet, while this has enabled us to isolate all of the
above compounds using a single method, it also gives
evidence to a complex equilibrium of anions in solution,
as depicted in Scheme 2. This has thus far hindered the
isolation of the products of further reactions of the tellu-
ridoindate anions with TM cations toward multinary
clusters by leading to complex reaction mixtures with
little tendency to crystallize. We intended to explore the
behavior in solution by 125Te NMR spectroscopy; how-
ever, probably because of the high quadrupole moment of
indium,20 only very tentative results were obtained, which
are summarized in the Supporting Information.
(17) Melullis, M.; Dehnen, S. Z. Anorg. Allg. Chem. 2007, 633, 2159–2167.
(18) Deiseroth, H. J. Z. Naturforsch. B 1980, 35, 953–958.
(20) 115In, 95.7%, I=9/2, Ξ=21.914 MHz, Q=1.16ꢀ10-28 m2, Dc=1890:
Mason, J. Multinuclear NMR; Plenum: New York, 1987.
€
(19) Emme, H.; Valldor, M.; Pottgen, R.; Huppertz, H. Chem. Mater.
2005, 17, 2707–2715.

11222 Inorganic Chemistry, Vol. 49, No. 23, 2010
Heine and Dehnen
of color going from the selenidoindate hydrates, which
are colorless even as tetrameric aggregates,6h to the tellu-
ridoindate hydrates, whose color ranges from yellow for
the monomeric and dimeric anions to black for the tri-
meric one.
Conclusions and Outlook
In summary, we have succeeded in preparing the first tellu-
ridoindate hydrates from the solid-state material K5InTe4
via a simple extraction and evaporation route. The obtained
structural motifs range from single [InTe4]5- tetrahedra
through the classic dimeric [In2Te6]6- unit to the previously
unknown trimeric [In3Te10]11- anion. Our findings point to-
ward a complex equilibrium in aqueous solution, which is
also reflected by a strong tendency for the cocrystallization of
different Kx[InyTez] salts in one single-crystalline compound.
Although “neighbors” in the periodic system, this is in con-
trast to all observations concerning stannate chemistry but is
inagreement with the phase widthofborates. The coexistence
of different anions in solution has thus far hindered the
selective utilization of the [InTe4]5- anion as a starting mate-
rial for the preparation of multinary cluster compounds, such
as was previously reported for chalcogenidostannte anions.
Therefore, we are now aiming to use these building blocks by
employing different reaction conditions, like other solvents or
solvothermal reaction techniques, to obtain multinary
materials.
Figure 9. Solid-state UV-vis spectra of as-prepared K5InTe5 (solid
line) and of a mixture of as-prepared compounds 1-4 (dashed line),
recorded from suspensions of the solid material in Nujol oil.
Optical Absorption Behavior. We have investigated the
optical absorption behavior of the title compounds by
measuring solid-state absorption spectra of the starting
material K5InTe4 and of compound 1 (Figure 9). As
outlined above, the salts have a high tendency for co-
crystallization. Thus, the sample of 1 also contains non-
negligible amounts of 2-4, which is reflected in the
UV-vis spectrum. Both lines show an onset of absorp-
tion between 1.92 eV (K5InTe4) or 1.96 eV (1-4) and 2.01
eV (K5InTe4) or 2.09 eV (1-4) before reaching a small
plateau. This corresponds well with the visible dark-red
and brownish color of K5InTe5 and compound 4, respec-
tively. The mixture of the latter with yellow compounds
1-3 is, however, reflected in the stronger increase of
absorption in the UV region when compared to the start-
ing material. The excitations are presumably based on
Te(5p) f In(5p) charge transfer. The color of compounds
1-3 corresponds well with the prior findings of O’Connor
et al.,11 indicating that K5InTe4 dissolves to give “an
orange solution”. The reddish color of K5InTe4 is in
accordance with the color of Na5InTe4 described by
Eisenmann et al.6b In agreement with the decreasing band
gap going from In2Se3 (1.3-1.8 eV, depending on its
modification)21 to In2Te3 (1.2 eV),22 there is a deepening
Acknowledgment. The authors thank the Deutsche
Forschungsgemeinschaft for financial support of this
work.
Supporting Information Available: CIFs for 1-6, structural
details of 1-6 (Table S5), and 125Te NMR and Raman spec-
troscopy along with corresponding quantum chemical investi-
gations. This material is available free of charge via the Internet
at http://pubs.acs.org.
(21) Julien, C.; Chevy, A.; Siapkas, D. Phys. Status Solidi A 1990, 118,
553–559.
(22) Golding, T. D.; Boyd, P. R.; Martinka, M.; Amirtharaj, P. M.;
Dinan, J. H.; Qadri, S. B.; Zahn, D. R. T.; Whitehouse, C. R. J. Appl. Phys.
1989, 65, 1936–1941.