Synthesis of germanium dioxide nanoparticles in benzyl alcohol - A comparison

Article abstract of DOI:10.1515/mgmc-2013-0038

The surfactant-free synthesis ofβphase germanium dioxide nanoparticles in ortho-methoxy benzyl alcohol and benzyl alcohol has been reported. Characterisation of the hexagonal β-GeO₂ crystals, which involves powder X-ray diffraction, nitrogen adsorption measurements (Brunauer-Emmett Teller method), dynamic light scattering measurements, IR spectroscopy, transmission electron microscopy and energy-dispersive X-ray analysis has been presented. Synthesis of β-GeO₂under ambient conditions in benzyl alcohol results in nanoparticles with diameters below 20 nm, whereas the synthesis under inert conditions in benzyl alcohol at reflux (205°C) gives larger nanoparticles. In ortho-methoxy benzyl alcohol, agglomerates with particle sizes above 100 nm are observed under inert atmosphere conditions at room temperature.

Full text of DOI:10.1515/mgmc-2013-0038

ꢁꢁꢁꢂ
ꢀMain Group Met. Chem. 2013; 36(5-6): 209–214
DOI 10.1515/mgmc-2013-0038ꢀ
PShyilipnptKhitsechskies, StoefffengSechrumlze,aMnicihuaeml HiedtscihooxldiadndeMinchaaenl Moephriangr*ticles in
benzyl alcohols – a comparison
Abstract: The surfactant-free synthesis of β-phase ger- variation in crystal structure, in morphology and in size
manium dioxide nanoparticles in ortho-methoxy benzyl from below 100 nm up to several hundreds of nanome-
alcohol and benzyl alcohol has been reported. Characteri- tres. For example, size control was previously achieved by
sation of the hexagonal β-GeO2 crystals, which involves hydrolysis of GeCl4 or Ge(OEt)4 in micelles and/or reverse
powder X-ray diffraction, nitrogen adsorption measure- micelle systems (Wu et al., 2006; Chiu and Huang, 2009;
ments (Brunauer-Emmett-Teller method), dynamic light Zou et al., 2011). A major drawback of these synthesis routes
scattering measurements, IR spectroscopy, transmission is the need for several different reactants often including
electron microscopy and energy-dispersive X-ray analysis special surfactants and precise adjustment of the synthe-
has been presented. Synthesis of β-GeO2 under ambient sis conditions. For instance, Chiu and Huang reported the
conditions in benzyl alcohol results in nanoparticles with synthesis of hexagonal GeO2 particles varying in size from
diameters below 20 nm, whereas the synthesis under inert around 100 to 300 nm depending on the reaction time by
conditions in benzyl alcohol at reflux (205°C) gives larger the use of a mixture of six reactants [precursor: Ge(OEt)4;
nanoparticles. In ortho-methoxy benzyl alcohol, agglom- oil phase: cyclohexane; surfactant: 4-octylphenol polyeth-
erates with particle sizes above 100 nm are observed oxylate; co-surfactant: n-hexanol; HCl; and water] (Chiu
under inert atmosphere conditions at room temperature.
and Huang, 2009). However, simple surfactant-free non-
aqueous synthesis routes for a great number of nanosized
Keywords: benzyl alcohol; germanium dioxide; nanopar- metal oxides were reported by Niederberger et al. using
ticles; surfactant-free synthesis.
one single metal containing precursor and simple organic
solvents such as benzyl alcohol, n-butyl ether or ethanol
(Niederberger et al., 2002; Pinna et al., 2004; Ba et al., 2005;
Pinna and Niederberger, 2008). Additionally, the synthesis
of metal oxide nanoparticles by surfactant-free non-hydro-
lytic sol-gel routes starting from the corresponding metal
chlorides were reported by Mutin and his coworkers (Abou-
laich et al., 2009, 2010, 2011). Nevertheless, reports on the
synthesis of GeO2 nanoparticles by a simple surfactant-free
synthesis route starting from GeCl4 are still lacking. We
are currently studying the process of twin polymerisation,
which has been reported recently for silicon-containing
compounds such as 2,2′-spirobi[4H-1,3,2-benzodioxasiline]
(see Scheme 1). This is a convenient method to form nano-
structured organic-inorganic hybrid materials by a one-
step synthesis (Grund et al., 2007; Spange et al., 2009;
Löschner et al., 2012). Additionally, this method also gives
*Corresponding author: Michael Mehring, Technische Universität
Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie,
Professur Koordinationschemie, D-09107 Chemnitz, Germany,
e-mail: michael.mehring@chemie.tu-chemnitz.de
Philipp Kitschke: Technische Universität Chemnitz, Fakultät
für Naturwissenschaften, Institut für Chemie, Professur
Koordinationschemie, D-09107 Chemnitz, Germany
Steffen Schulze and Michael Hietschold: Technische Universität
Chemnitz, Fakultät für Naturwissenschaften, Institut für Physik,
Professur Analytik an Festkörperoberflächen, D-09107 Chemnitz,
Germany
Introduction
In the last few years, a significant progress has been access to metal oxide nanoparticles (Mehner et al., 2008;
reported on the synthesis of GeO2 materials (Adachi et al., Böttger-Hiller et al., 2009).
2005; Zou et al., 2005; Armelao et al., 2012; Chen et al.,
However, our attempts to synthesise the correspond-
2012; Seng et al., 2013; Zhang et al., 2013). Especially, small ing germanium-containing compounds, which are struc-
particles show interesting features such as photolumines- turally related to 2,2′-spirobi[4H-1,3,2-benzodioxasiline],
cence under visible light irradiation, high refractive index starting from germanium alkoxides and GeCl4 failed so
as compared to that of silica glasses and optical transpar- far. Benzyl alcohol derivatives that were tested as reagents
ency in between 280 and 5000 nm (Kim et al., 2007; Chiu gave GeO2 and partial polymerisation of the benzyl alcohol
and Huang, 2009; Liu et al., 2010). It is of scientific as derivatives after addtion of the latter germanium contain-
well as commercial interest to prepare GeO2 particles with ing reagents. In addition, the formation of the respective
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210ꢀ
ꢀP. Kitschke et al.: Synthesis of GeO2 nanoparticles in benzyl alcohols
OH
O
O
O
O
i
S O2
n
i
S
n
2 n
Scheme 1ꢀTwin polymerisation of 2,2′-spirobi[4H-1,3,2-benzodioxasiline] resulting in nanostructured, interpenetrating SiO2/phenolic resin
networks (Spange et al., 2009).
dibenzyl ether derivative as a by-product was observed.
These observations prompted us to study the reactivity of
benzyl alcohols in the presence of GeCl4 in more detail.
We present here the preparation of β-GeO2 particles in
ortho-methoxy benzyl alcohol under inert conditions as
well as in benzyl alcohol under inert and ambient condi-
tions starting from GeCl4. Variation of the mean particle
size from tenths up to hundreds of nanometres depends
on both, the benzyl alcohol used and the synthesis
conditions.
Results and discussion
Figure 1ꢀX-ray powder diffraction pattern of the as-prepared β-GeO2
Germanium dioxide was synthesised starting from GeCl4
in benzyl alcohol by the following different synthetic
protocols: (i) GeCl4 was stirred in ortho-methoxy benzyl
alcohol under inert conditions at room temperature for
22 h (sample A); (ii) GeCl4 was dissolved and stirred in
particles. The red, blue and black curves depict the X-ray powder
diffraction patterns of the GeO2 particles of samples A, B and C. The
violet bars display the standard diffraction pattern of hexagonal
β-GeO2 (ICDD no. C00-036-1463).
benzyl alcohol under inert conditions at reflux for 24 h the particles are larger than 100 nm, which is significantly
(sample B); (iii) GeCl4 was added to benzyl alcohol and larger than the size of the primary particles as determined
stirred under ambient conditions at 40°C for 24 h (sample from the PXRD data and they vary in size. This is ascribed
C). All these methods gave β-GeO2, which was isolated to agglomeration of the crystalline nanoparticles and the
by centrifugation followed by washing with tetrahydro- presence of some amorphous material. A lower extent of
furan (THF) and ethanol, respectively. The GeO2 particles agglomeration and smaller particles are obtained by syn-
were characterised by powder X-ray diffraction (PXRD), thesising GeO2 in benzyl alcohol as demonstrated by the
nitrogen physisorption [Brunauer-Emmett-Teller (BET) TEM images of samples B and C. A noteworthy observa-
method], dynamic light scattering (DLS) measurements, tion is that GeO2 particles isolated after their synthesis
infrared (IR) spectroscopy, transmission electron micros- in benzyl alcohol under inert conditions exhibit sizes in
copy (TEM) and energy-dispersive X-ray (EDX) analysis. between 30 nm and several tens of nanometres (sample
The PXRD patterns of these particles are given in Figure 1. B), whereas the synthesis under ambient conditions
The PXRD data confirm the formation of crystalline gives GeO2 particles with diameters mainly below 20 nm
β-GeO2 particles for all samples. Determination of the par- (sample C). The deviations in primary particle sizes as
ticle sizes by applying the Scherrer equation based on the obtained from the PXRD data result from agglomeration
(101) reflection gave particle sizes of (43ꢀ ꢀ4) (sample A), as observed for sample A, but to a lower extent. The EDX
(27ꢀ ꢀ2) (sample B) and (9ꢀ ꢀ1) nm (sample C) for the primary spectra support the formation of GeO2 without any chlo-
particles. Nitrogen adsorption measurements gave BET rine impurities. Absence of the latter was also verified
surface areas of 9, 10 and 146 m2/g for samples A, B and C, by the lack of any precipitation after addition of a 0.2 m
respectively. The corresponding TEM images of the β-GeO2 AgNO3 solution to the filtrate of an aqueous suspension
particles (samples A–C) are shown in Figure 2.
of the particles that was heated at reflux for 1 h. However,
The TEM image of the β-GeO2, which was synthesised small amounts of carbon and hydrogen were detected by
in ortho-methoxy benzyl alcohol (sample A), shows that CH analysis for all samples in the range from 0.46% to
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Figure 2ꢀTEM images for samples A–C.
1.58% and from 0.13% to 0.33% for carbon and hydrogen,
respectively, which might be explained by a small amount
of residual organic material attached to the surface of the
particles. The hydrodynamic radii as determined by DLS
measurements are 535, 482 and 179 nm in THF and 360,
198 and 536 nm in toluene for samples A, B and C, respec-
tively. These hydrodynamic radii are in agreement with
the agglomeration of the particles as observed in the TEM
images of the samples A–C. However, the differences in the
hydrodynamic radii of each sample in different solvents
indicate specific agglomeration behaviour of the particles
with respect to the polarities of the employed solvents.
Samples A and B exhibit less agglomeration in toluene,
whereas sample C shows a larger hydrodynamic radius in
toluene as compared to its value determined in THF. The
IR spectroscopy reveals a significantly higher extent of OH
groups at the surface of the particles for sample C, which
is in accordance with the reverse behaviour of samples A
Figure 3ꢀIR spectra of the as-prepared GeO2 particles; samples A
(red), B (blue) and C (black).
and B as determined by the DLS measurements. It is note- conditions at room temperature. The NMR spectroscopic
worthy that the IR spectra of the samples A–C exhibit the analysis of the reaction mixture confirmed the presence
absorption band maxima (517, 552, 586, 728, 753, 882, 890, of different soluble ortho-methoxy benzyl alcohol deriva-
931 and 961 cm-1) which were recently reported for the hex- tives, which most likely are intermediate species in the
agonal β-modification of GeO2 (Figure 3). The characteris- formation process of an ortho-methoxy benzyl alcohol
tic three absorption band maxima at 517, 552 and 586 cm-1 resin. It is to be noted that the as-prepared β-GeO2 (sample
are indicative of the hexagonal structure. The absorption
band maximum at 1642 cm-1 indicates the presence of
Table 1ꢁAnalytical data for the as-synthesised GeO2 particles
(samples A–C).
water at the surface of the particles (Atuchin et al., 2009).
The IR spectra reveal the presence of minor amounts of
ꢂ
Sample A
ꢂ
Sample B
ꢂ
Sample C
adsorbed organic material, which is in accordance with
the low carbon content (Cꢀ< ꢀ1.6%) as determined by the CH
analysis.
Primary particle sizea
BET surfaceb
ꢃ
ꢃ
43ꢀ ꢀ4 nm
9 g/m2
ꢃ
ꢃ
27ꢀ ꢀ2 nm
10 g/m2
ꢃ
ꢃ
9ꢀ ꢀ1 nm
146 g/m2
Hydrodynamic radius:
ꢀIn THF
In Table 1, a summary of the primary particle sizes
as determined by PXRD and the results of the nitrogen
ꢃ
ꢃ
ꢃ
535 nm
360 nm
ꢃ
ꢃ
482 nm
198 nm
ꢃ
ꢃ
179 nm
536 nm
ꢀIn toluene
adsorption measurements (BET method), DLS measure- CH analysis (C/H%)
1.06/0.24% ꢃ 0.46/0.13% ꢃ 1.58/0.33%
ments and CH analysis of all samples are given.
aDetermined by the Scherrer equation (Kꢀ= ꢀ1) using the data of the
(101) reflection of the X-ray powder diffraction pattern; bSingle
The formation of GeO2 particles in ortho-methoxy
benzyl alcohol (sample A) was observed under inert point BET analysis p/p0ꢀ= ꢀ0.150.
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212ꢀ ꢀP. Kitschke et al.: Synthesis of GeO2 nanoparticles in benzyl alcohols
2
2
R13M-Cl R OH
R13M OH
-
+
+
-
R
Cl
A) exhibits a pale pink colour, which is typical for benzyl
alcohol resins obtained by cationically induced polymeri-
sation. Thus we propose that the formation of GeO2 parti-
cles in ortho-methoxy benzyl alcohol can be explained by
a Lewis acid, here GeCl4, initiated polymerisation (oligom-
erisation) of the ortho-methoxy benzyl alcohol, which in
situ generates water (Scheme 2). Consecutively, the water
reacts with GeCl4 to give GeO2 particles.
R1
R1
R1
R1
R2 H-Cl
2
R1
R
H
O
3M O
-
+
+
3M-Cl
+
1
R1
l
R
3M C
3M-OH
R1
H-Cl
-
-
-
+
3M O M
3
2
2
R1
R
R2
R2
R2
3M O
R
l
+
-
O
-
+
-
C
3M-Cl
+
1
R1
R
3M-Cl
3M O
3M-O-MR1
R
2
-
+
-
l
C
3
Scheme 3ꢀSummary of the proposed reactions of metal(IV) halides
in the non-hydrolytic sol-gel process as suggested by Debecker and
Mutin (2012); R1ꢀ= ꢀCl, OH and/or benzyl alcoholate; R2ꢀ= ꢀbenzyl group.
The formation of GeO2 particles in benzyl alcohol under
inert conditions (sample B) was observed by stirring the
mixture under reflux. The resulting mixture after removal chloride (4.6 mol% in the mixture), some dibenzyl ether (1.4
of the GeO2 particles consisted of 29.8 mol% benzyl alcohol, mol% in the mixture) and germanium alkoxide species. The
12.6 mol% benzyl chloride, 38.7 mol% dibenzyl ether and reaction of GeCl4 with dibenzyl ether to give benzyl chloride
18.9 mol% water, which was determined by NMR spec- (see Scheme 3) was also observed in a separate experiment.
troscopic analysis. It is noteworthy that the formation of Here, GeCl4 was added to pure dibenzyl ether in the same
benzyl chloride was quantitative with regard to the amount ratio as compared to the synthesis of sample B. Formation
of GeCl4 added. The quantitative formation of benzyl chlo- of benzyl chloride was proven by NMR spectroscopic analy-
ride indicates formation of GeO2 particles by an alkyl chlo- sis of the mixture after stirring at 206°C for 24 h, whereas
ride elimination reaction mechanism in accordance with this was not observed at room temperature. These observa-
the results reviewed by Debecker and Mutin (2012) for the tions support the hypothesis of an alkyl chloride reaction
synthesis of a variety of metal oxides (Scheme 3).
mechanism for GeO2 in benzyl alcohol. By contrast, the for-
However, the presence of dibenzyl ether (in a yield of mation of GeO2 in benzyl alcohol under ambient conditions
29% with regard to the amount of benzyl alcohol used for (sample C) was already observed by stirring the mixture at
the synthesis) and water in the resulting reaction mixture 40°C for 24 h (yield was 9%). Further stirring of the mixture
indicates condensation reactions to take place as well. at 40°C at ambient conditions gave an additional portion
These condensation reactions may be catalyzed by GeCl4, of β-GeO2 (yield was 37%). Therefore, we conclude that
other in situ generated germanium species or even by GeO2 the formation of GeO2 particles in benzyl alcohol under
particles as shown in Scheme 4.
ambient conditions results from hydrolysis and that benzyl
The eliminated water might additionally give hydroly- alcohol acts as a solvent and a surfactant in the formation
sis of germanium-containing species that finally results process of the nanoparticles.
in GeO2. It is to be noted that the formation of water and
consecutively the formation of GeO2 may also be explained
by condensation of germanoles generated by the alkyl
chloride elimination reaction (see Scheme 3). However,
Conclusions
the quantitative formation of benzyl chloride indicates that
Germanium(IV) oxide nanoparticles were synthesised
the alkyl chloride reaction mechanism is the predominant
in ortho-methoxy benzyl alcohol under inert conditions
reaction in benzyl alcohol under inert conditions. Although
and in benzyl alcohol under inert and under ambient
no formation of GeO2 was observed under inert conditions
conditions, respectively, starting from GeCl4 without
at lower temperature, the NMR spectroscopic analysis of
addition of any further reactant. The as-prepared β-GeO2
a reaction mixture consisting of benzyl alcohol and GeCl4
particles were characterised by PXRD, nitrogen adsorp-
in a molar ratio of 42:1 that was stirred under argon atmos-
tion measurements (BET method), DLS measurements,
phere at 40°C for 2 weeks revealed the formation of benzyl
IR spectroscopy, TEM and EDX analysis. The synthesis
in ortho-methoxy benzyl alcohol under inert conditions
OMe
OMe
GeR4
GeO2
/
OH
GeCl4
CH2OH
+ n H2O
n
O
+
2
H2O
n
Scheme 2ꢀReaction scheme to show the formation of water caused
by Lewis acid straight composition initiated polymerisation (oligomeri- ether under inert conditions; Rꢀ= ꢀCl, OH and/or benzyl alcoholate
sation) of ortho-methoxy benzyl alcohol under an inert atmosphere. intermediates.
Scheme 4ꢀReaction scheme showing the formation of dibenzyl
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ꢀ213
IQ2 (Quantachrome, Odelzhausen, Germany), which were evaluated
gave GeO2 particles with sizes ꢀ> ꢀ100 nm. It is proposed
that Lewis acid initiated partial polymerisation of ortho-
methoxy benzyl alcohol gave water, which results in the
formation of β-GeO2 upon hydrolysis. Nanoparticles below
by the BET method using p/p0 ratio of 0.150.
100 nm in size were obtained in benzyl alcohol under inert Syntheses
conditions. Their formation is assumed to be a result of
Reactions using ortho-methoxy benzyl alcohol were performed in an
an alkyl chloride elimination reaction mechanism. The
formation of β-GeO2 starting from benzyl alcohol under
ambient conditions is a result of slow diffusion of mois-
ture into the reaction mixture and gave the smallest GeO2
nanoparticles that exhibit sizes below 20 nm. The results
demonstrate that hydrolysis must be considered as an
important side reaction, even in a so-called non-hydro-
lytic processes, if water might be formed as a side product
or the presence of moisture is not fully excluded.
inert atmosphere (argon) glovebox. Reactions using benzyl alcohol
were performed in an inert atmosphere (argon) glovebox as well as
under ambient conditions to allow water diffusion into the reaction
mixture. Solvents were purified and dried by applying standard tech-
niques. Benzyl alcohol and ortho-methoxy benzyl alcohol were pur-
chased from Merck Schuchardt OHG (Hohenbrunn, Germany) and
Alfa Aesar (Ward Hill, MA, USA), respectively. Benzyl alcohol was used
without any purification for the synthesis under ambient conditions
(sample C). Ortho-methoxy benzyl alcohol and benzyl alcohol were
dried over molecular sieves for 3 weeks before using them for the syn-
theses under inert conditions. GeCl4 was purchased from ABCR GmbH
& Co. KG (Karlsruhe, Germany) and used without further purification.
Experimental
Synthesis of GeO2 in ortho-methoxy benzyl
alcohol – sample A
General
1H and 13C{1H}-NMR spectra were recorded on a Bruker (Bruker
Corporation, Billerica, MA, USA) ‘Avance III 500’ spectrometer at
ambient temperature. CH analysis was carried out with a ‘vario
MICRO’ from Elementar Analysensysteme GmbH (Hanau, Germany).
The PXRD patterns were collected using a STOE-STAD IP diffrac-
tometer from STOE (STOE and Cie GmbH, Darmstadt, Germany)
with Cu-Kα radiation (40 kV, 40 mA) and a Ge(111) monochroma-
tor. The crystallite size was estimated using the Scherrer equation:
K λ
GeCl4 (529.4 mg, 2.47 mmol) was added to ortho-methoxy benzyl
alcohol (12.79 mL, 103.7 mmol) and the mixture was stirred under an
inert atmosphere at room temperature for 22 h. The suspension was
centrifuged at 3000 rpm for 15 min for separating the pale pink GeO2
particles, which were then purified by centrifugation (at 3000 rpm for
15 min) of a suspension of the particles in THF (5 mL) and in ethanol
(5 mL) two times each, respectively, to quantitatively give pale pink
GeO2. The CH analysis [%] found for GeO2: C 1.06 and H 0.24. Both
PXRD and EDX analyses proved the formation of GeO2.
τ=
,
where τ is the volume weighted crystallite size, K is the
βcosθ
Scherrer constant here taken as 1.0, λ is the X-ray wavelength, θ is the
Bragg’s angle (in rad) and β is the full width of the diffraction line at
half of the maximum intensity (FWHM, background subtracted). The
FWHM is corrected for instrumental broadening using a LaB6 stand-
ard (SRM 660) purchased from NIST (National Institute of Standards
and Technology, Gaithersburg, MD, USA). The value of β was cor-
Synthesis of GeO2 in benzyl alcohol under inert
conditions – sample B
GeCl4 (942.0 mg, 4.39 mmol) was added to benzyl alcohol (20.00 mL,
192.3 mmol) and the mixture was stirred under an inert atmosphere at
reflux for 24 h. The pale yellow suspension was centrifuged at 3000 rpm
for 10 min to separate the GeO2 particles, which were then suspended
and purified by centrifugation (at 3000 rpm for 10 min) in THF (5 mL)
and in ethanol (5 mL) two times each, respectively, to quantitatively give
βi2nstrument
rected from ( βm2 easured and
are the FWHMs of measured and
standard profiles):
β2 =βm2 easured -βi2nstrument
.
The DLS measurements were performed on a Modell 802 from colourless GeO2. The CH analysis [%] found for GeO2: C 0.46 and H 0.13.
Viscotek™ (Malvern Instruments GmbH, Herrenberg, Germany) using Both PXRD and EDX analyses proved the formation of GeO2.
a laser light emitting diode at 830 nm. The THF and toluene suspen-
sions of the particles obtained by ultrasonic treatment were given in
a quartz glass cuvette for DLS measurements. Infrared spectra were
Synthesis of GeO2 in benzyl alcohol under ambient
recorded with a Nicolet IR 200 spectrometer from Thermo Scientific
conditions – sample C
(Thermo Fisher Scientific Inc., Waltham, MA, USA) in a KBr matrix.
Transmission electron micrographs and energy dispersive X-ray
spectroscopy experiments were obtained by a 200 kV-high resolution GeCl4 (713.8 mg, 3.33 mmol) was added to benzyl alcohol (14.54 mL,
transmission electron microscope [HRTEM, CM 20 FEG, Co. Philips 139.8 mmol) at 40°C. The mixture was stirred at 40°C under ambient con-
(FEI Europe, Europe NanoPort, Eindhoven, The Netherlands)] with ditions for 24 h. The colourless suspension was centrifuged at 3000 rpm
an imaging energy filter from Gatan (GIF). Specific surface analyses for 10 min to separate the GeO2 particles, which were then suspended
were performed with nitrogen adsorption-desorption isotherms at and purified by centrifugation (at 3000 rpm for 10 min) in THF (5 mL)
liquid nitrogen temperature (77 K) using a Quantachrome Autosorb and in ethanol (5 mL) two times each, respectively. Additional stirring of
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214ꢀ ꢀP. Kitschke et al.: Synthesis of GeO2 nanoparticles in benzyl alcohols
the transparent, colourless, overlaying liquid at 40°C at ambient condi-
tions for another 18 h gave further fractions of colourless GeO2. Yield:
56% (all fractions); the CH analysis [%] found for GeO2: C 1.58 and H
0.33. Both PXRD and EDX analyses proved the formation of GeO2.
inorganic nanocomposites through twin polymerisation’
and the Fonds der Chemischen Industrie for a fellowship
(P. Kitschke).
Acknowledgements: We gratefully acknowledge finan-
cial support by the DFG Forschergruppe 1497 ‘organic and Received July 12, 2013; accepted October 2, 2013
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