In2Ge6O15(en)2: A In-Ge compound composed of germanate layers linked by pillars of In2O 6N4 double octahedra

Article abstract of DOI:10.1002/anie.200351115

Two metals in one net: GeO₄ tetrahedra and InO₆N ₂ octahedra are primary building units in a new indium germanate. The germanium layers (yellow) are linked by the InO₆N₂ units (red) to form a 3D network. The compound is prepared by a hydrothermal synthesis using GeO₂ and In(OH)₃ in an aqueous solution of ethylenediamine.

Full text of DOI:10.1002/anie.200351115

Angewandte
Chemie
Mixed In/Ge Oxide
In2Ge6O15(en)2: A In–Ge Compound Composed
of Germanate Layers Linked by Pillars of In2O6N4
Double Octahedra**
Dragan Pitzschke and Wolfgang Bensch*
During the last few years not only porous compounds based
on SiO4/AlO4 tetrahedra as the main building units have been
explored but also germanates have received considerable
attention.[1–10] In contrast to silicon, which is usually in a
tetrahedral environment of oxygen atoms, germanium is
coordinated by four, five, or even six oxygen atoms.[1–10]
Interestingly, until now no efforts have been made to enhance
the structural diversity of porous compounds by combining
the flexible coordination behavior of germanium with that of
indium. For instance, InO4 tetrahedra are found in InNa5O4 or
in InOF;[11] in Ba2In2O5 InO4 tetrahedra and InO6 octahedra
coexist,[12] and in Ba3In2O6 distorted InO5 trigonal bipyramids
are observed.[13] Finally, very unusual InOx polyhedra are
found in In3Mo11O17 .[14] The syntheses of microporous solids
are typically carried out under solvothermal conditions in the
presence of an organic molecule that should exert a structure-
directing effect, the aim usually being to prepare an open-
framework inorganic material. Herein we report the synthesis
and characterization of a new and unusual indium–germa-
nium compound in which germanate layers are linked by
In2O6N4 moieties to form a three-dimensional network with
composition In2Ge6O15(en)2 (1; en = ethylenediamine). The
solvothermal reaction of ethylenediamine, germanium diox-
ide, and indium hydroxide yields transparent needle-shaped
crystals of 1 in high yield. The X-ray structure determination
demonstrates the 3D character of 1.[15]
The asymmetric unit contains six crystallographically
independent germanium atoms, fifteen oxygen atoms and
two independent indium atoms as well as two en molecules
acting as bidentate ligands. The Ge atoms are all coordinated
by four O atoms to form moderately distorted tetrahedra with
ꢀ
Ge O bond lengths ranging from 1.691(5) to 1.770(4) Š and
O-Ge-O angles between 99.2(2) and 117.1(2)8. The Ge-O-Ge
angles vary between 123.1(2) and 134.3(2)8 and are in the
ꢀ
expected range. The Ge O separations are in the same range
as those reported for GeO2 in the quartz modification
(1.741 Š) and in other germanates.[1–3,9,16] The In1 and In2
atoms are coordinated by four oxygen atoms and two nitrogen
atoms of the en ligand yielding a strongly distorted octahedral
ꢀ
environment. The In O separations range from 2.076(5) to
ꢀ
2.257(4) Š and the In N bond lengths lie between 2.261(7)
[*] Prof. Dr. W. Bensch, D. Pitzschke
Institut für Anorganische Chemie
Universität Kiel
Olshausenstrasse 40, 24098 Kiel (Germany)
Fax: (+49)431-880-1520
E-mail: wbensch@ac.uni-kiel.de
[**] This work was supported by the State of Schleswig-Holstein and the
Fonds der Chemischen Industrie. en=ethylenediamine.
Angew. Chem. Int. Ed. 2003, 42, 4389 –4391
DOI: 10.1002/anie.200351115
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4389

Communications
and 2.285(5) Š. The oxygen atoms connect with either two or
ꢀ
three metal (one Ge and two In) atoms. The In O bond
lengths of the three-coordinate atoms are longer
O
(2.180(4)–2.257(4) Š) than for two-coordinate O atoms
(2.0762(5)–2.0843(4) Š).
The six GeO4 tetrahedra are corner linked to form two
different single chains (denoted I and II in Figure 1). Chain I
is composed of the tetrahedra around Ge1–3 and chain II by
¯
the tetrahedra about Ge4–6. Owing to the 1 symmetry
Figure 2. Two InO4(en) octahedra sharing a common edge (atoms
with primes are generated by symmetry operations, the H and C
atoms of the amine are omitted for clarity).
Figure 1. The six GeO4 tetrahedra are corner linked, forming two differ-
ent single chains denoted in the (011) plane. Chain I (light gray) and
chain II (dark gray).
operation pairs of like chains are joined to form double chains
(Figure 1). Finally, these double chains are linked by oxygen
atoms to form anionic germanate layers in the (011) plane.
The connection pattern yields an unbranched dreier[*] single
layer which according to the Liebau notation can be described
as {uB, 3, 121}.[17] The layer contains four-, six-, and eight-
membered rings with approximate dimensions of 4.8 ” 3.0,
6.2 ” 5.0, and 8 ” 4.5 Š, respectively. The germanate layers are
stacked perpendicular to [010]. Unbranched dreier single
layers are reported for several silicate minerals, such as
Dalyite and Nekoite,[17] but to our knowledge have never
been observed in germanates. Recently, the interconnection
of dreier single chains into a single layer was reported for the
synthetic gallate Sr3Ga4O9,[18] but in contrast to 1 an open-
branched dreier single layer is formed.
Two symmetry-related InO4N2 octahedra share a common
edge to form In2O6N4 entities (Figure 2). The average
distance between the indium atoms within these units is
about 3.5 Š. The six oxygen atoms of each In2O6N4 moiety are
joined to GeO4 tetrahedra of the germanate layers above and
below, through O1, O2, and O3 (Figure 2). Hence, the
structure may be described as anionic germanate layers
which are pillared by In2O6N4 units yielding a 3D network.
The framework density of 1 is 15.6 polyhedra per 1000 Š3.
Three distinct channels with different apertures run along
¯
[011], [100], and [010] (Figure 3). The first is composed of
eight GeO4 polyhedra and two InO4N2 octahedra and has an
Figure 3. The different channels in 1 (InO4(en) octahedra are light-gray
and GeO4-tetrahedra are dark-gray; the H and C atoms of the amine
are omitted for clarity). A) View along [011], B) view down the a axis,
C) view down the b axis.
[*] The term “dreier” was coined by Liebau[17] and is derived from the
German word drei, which means three.
¯
4390
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Angewandte
Chemie
202258 (1) contains the supplementary crystallographic data for this
opening of about 7.5 ” 7.3 Š (Figure 3A). The second channel
with approximate dimensions of 8.4 ” 3 Š is formed by six
GeO4 tetrahedra and two InO4N2 octahedra (Figure 3B). The
last channel is formed by the eight-membered rings of
successive stacked germanate layers and the aperture is 8 ”
4.5 Š (Figure 3c). The en units point partially into the
channels thus reducing the free space.
paper. These data can be obtained free of charge via www.ccdc.
cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax:
(+ 44)1223-336-033; or deposit@ccdc.cam.ac.uk).
DTA–TG–MS measurements were performed with an STA-
409CD thermobalance with Skimmer coupling (Netzsch), equipped
with a quadrupole mass spectrometer QMA 400 (Balzers). The
measurements were made simultaneously in Al2O3 crucibles under a
The thermal stability of 1 was investigated using simulta-
neous differential thermoanalysis (DTA) and thermogravim-
etry (TG) as well as simultaneous DTA–TG–MS measure-
ments. The compound decomposes in three steps with a total
weight loss of 25.4%. The first two steps cover a wide
temperature range from about 450 to 7208C and is accom-
panied by a weight loss of 11.7%. The third step with a weight
loss of 13.7% starts at 7208C and is finished at 8508C. The
decomposition reactions are accompanied by two endother-
mic events at TP = 5108C and 7778C. In the gray residue left
after the DTA–TG experiment, elemental Ge and In2Ge2O7
could be identified in the X-ray powder pattern. The
elemental analysis yields less than 0.2% C, H, N content.
The experimental weight loss of 25.4% is in good agreement
with that calculated for the removal of the two en molecules
(DMcalcd = 11.8%) and eight oxygen atoms (DMcalcd = 12.5%).
The mass spectra show that during the first two thermal-
decomposition steps NH3 (m/z 17), H2O (m/z 18), and CO2
(m/z 44) are emitted. During the last step the remaining
nitrogen and carbon are emitted as N2 (m/z 28, small amounts
of CO are also present) and CO2 (m/z 44).
dynamic helium or nitrogen atmosphere (flow-rate: 75 mLminꢀ1
,
purity: 5.0) using different heating rates. X-Ray powder diffraction
experiments were performed using a STOE STADIP transmission
powder diffractometer with a position sensitive detector and CuKa
radiation (l = 1.540598 Š).
Received: February 5, 2003 [Z51115]
Keywords: crystal structure · germanium ·
.
hydrothermal synthesis · indium · thermochemistry
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In further experiments the heating process was stopped at
5608C and 7208C. According to the X-ray powder pattern of
the sample obtained at 5608C the intermediate is amorphous,
that is, the framework is destroyed. In the brown residue after
the 7208C step appreciable amounts of organic components
were found (C 3.395, H 0.074, N 3.348%; ꢀCHN = 6.817%).
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Experimental Section
Compound 1 was synthesized under hydrothermal conditions using
GeO2 (314 mg, 3 mmol) and In(OH)3 (332 mg, 2 mmol) in a 33%
aqueous solution of ethylenediamine (44 mmol) at pH > 13. The
mixture was heated to 1708C for 7 days in a teflon-lined steel
autoclave (ca. 30 mL) then cooled within 3 h to room temperature.
The homogeneous product consisting of colorless needle-shaped
crystals was collected by filtration, washed with distilled water, and
dried in air. Typical dimensions of the crystals are 0.3 ” 0.03 ”
0.03 mm3.
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¯
Crystallographic data for 1: triclinic, space group P1, a =
7.9568(16), b = 8.3835(17), c = 17.651(4) Š, a = 81.30(3)8, b =
77.08(3)8, g = 63.79(3)8, V= 1027.7(4) Š3; Z = 2; 1calcd = 3.314 gcmꢀ3
,
[18] V. Kahlenberg, J. B. Parise, Z. Kristallogr. 2001, 216, 210.
F(000) = 956, l(MoKa) = 0.71073 Š. Single-crystal X-ray work was
performed using a Image Plate Diffraction System (IPDS). 10008
reflections collected, 4593 independent (Rint = 0.036). Face-indexed
absorption correction; structure solution with SHELXS-97;[15] struc-
ture refinement against F2 using SHELXL-97.[15] 281 parameters, R
for 4031 reflections (Fo > 4s(Fo)) = 0.0425, wR2 for all data = 0.1168,
ꢀ3
GoF = 1.054. Residual electron density: 1.7/ꢀ2.2 eŠ
. CCDC-
Angew. Chem. Int. Ed. 2003, 42, 4389 –4391
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