Porous Ge@C materials via twin polymerization of germanium(II) salicyl alcoholates for Li-ion batteries

Article abstract of DOI:10.1039/c5ta09891b

The germylenes, germanium(ii) 2-(oxidomethyl)phenolate (1), germanium(ii) 4-methyl-2-(oxidomethyl)phenolate (2) and germanium(ii) 4-bromo-2-(oxidomethyl)phenolate (3) were synthesized and their thermally induced twin polymerization to give organic-inorganic hybrid materials was studied. The compounds 1-3 form oligomers including dimers, trimers and tetramers as a result of intermolecular coordination of the benzylic oxygen atom to germanium. The structural motifs were studied by single crystal X-ray diffraction analysis and DFT-D calculations. Thermally induced twin polymerization of these germylenes gave hybrid materials based on germanium-containing phenolic resins. Carbonization of these resins under reductive conditions resulted in porous materials that are composed of germanium and carbon (Ge@C materials), while oxidation with air provided non-porous germanium dioxide. The porous Ge@C materials were tested as potential anode materials for rechargeable Li-ion batteries. Reversible capacities of 540 mA h g^-1 were obtained at a current density of 346 mA g^-1 without apparent fading for 100 cycles, which demonstrates that germanium is well accessible in the hybrid material.

Full text of DOI:10.1039/c5ta09891b

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Mehring, J. Mater. Chem. A, 2016, DOI: 10.1039/C5TA09891B.
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Page 1 of 14
Jo uP rl ne aa sl eo fd oM na ot et r ai ad l jsu sCt hme am r gi si nt rs y A
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DOI: 10.1039/C5TA09891B
Journal Name
ARTICLE
Porous Ge@C materials via Twin polymerization of germanium(II)
salicyl alcoholates for Li-ion batteries
a
b
c
d
e
e
d
c
P. Kitschke, M. Walter, T. Rüffer, A. Seifert, F. Speck, T. Seyller, S. Spange, H. Lang, A. A.
Received 00th January 20xx,
Accepted 00th January 20xx
f
b
*a
Auer, M. V. Kovalenko and M. Mehring
DOI: 10.1039/x0xx00000x
The germylenes, germanium(II)-2-(oxidomethyl)phenolate (1), germanium(II)-4-methyl-2-(oxidomethyl)phenolate (2) and
germanium(II)-4-bromo-2-(oxidomethyl)phenolate (3) were synthesized and their thermally induced twin polymerization to
give organic-inorganic hybrid materials was studied. The compounds 1 – 3 form oligomers including dimers, trimers and
tetramers as a result of intermolecular coordination of the benzylic oxygen atom to germanium. The structural motifs were
studied by single crystal X-ray diffraction analysis and DFT-D calculations. Thermally induced twin polymerization of these
germylenes gave hybrid materials based on germanium-containing phenolic resins. Carbonization of these resins under
reductive conditions resulted in porous materials that are composed of germanium and carbon (Ge@C materials), while
oxidation with air provided non-porous germanium dioxide. The porous Ge@C materials were tested as potential anode
materials for rechargeable Li-ion batteries. Reversible capacities of 540 mAhg–1 were obtained at a current density of 346
www.rsc.org/
-
1
mAg without apparent fading for 100 cycles, which demonstrates that germanium is well accessible in the hybrid material.
-
1
-1
mAhg / 7367 AhL for Li15Ge
4
), high electrical conductivity and
33-41
lithium-ion diffusivity.
Nevertheless, bulk germanium shows
Introduction
The chemistry of low valent germanium compounds has been
studied intensely within the last four decades, starting with the
pioneering work of Curtis, Lappert and Satgé and their
coworkers at the 1970s. The early studies mainly focused on
the use as ligands in transition metal complexes,
only poor cycling stability due to the large volume changes of
up to 246% upon lithiation and delithiation. Nanostructuring of
germanium has been reported as effective method to improve
42-51
both cycling stability and rate capability,
and following this
1-5
30
or diphenyl germylene,31, 32 anode
concept starting from GeI
2
2, 6-10
the
and
materials exhibiting promising capacity retentions were
synthesized. Intrigued by this approach, we decided to adopt
the novel concept of twin polymerization (TP) to germylenes. TP
is defined as a concerted formation of two polymers in one
synthetic step starting from a single monomer (twin monomer)
and provides a simple method to obtain nanostructured hybrid
5,
11-13
reactivity in organogermanium chemistry
fundamental characterization.1
4-16
While research on
germylenes e.g., as model compounds in addition reactions
such as of germanium into N-H and P-Cl bonds, progressed
17-27
28
rapidly,
studies focusing on applications e.g., in catalysis
29
or as precursors for atomic layer deposition, have rarely been
reported until now. Quite recently molecular germanium(II)
compounds were used to prepare germanium-based anode
materials for Li-ion batteries,
germanium is a highly promising anode material considering its
high gravimetric and volumetric theoretical capacities (1384
5
2-
materials that can be converted into highly porous materials.
60
Diverse metal salicyl alcoholates (M = Si, Ge and Sn) have
been demonstrated to provide nanostructured organic-
3
0-32
motivated by the fact that
inorganic hybrid materials by this novel concept.5
2, 61-64
Conversion of such hybrid materials gave e.g., mesoporous
6
1, 62
62
metal oxides,
microporous carbon and mesoporous /
6
3
microporous nanocomposites such as Sn@C/SiO
2
.
We
anticipated that porous materials composed of germanium
incorporated in a carbon matrix (Ge@C material) are accessible
by applying the concept of twin polymerization to the germa-
a.Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für
Chemie, Professur Koordinationschemie, 09107 Chemnitz (Germany).
Email: michael.mehring@chemie.tu-chemnitz.de
Eidgenössische Technische Hochschule Zürich, Department of Chemistry and
nium(II) salicyl alcoholates 1 - 3 (Scheme 1). Ge@C materials are
b.
expected to meet requirements such as exhibiting a high
capacity and a good cycling stability for anode materials of
Applied Biosciences, Laboratory of Inorganic Chemistry, Vladimir-Prelog-Weg 1,
8
093 Zürich (Switzerland) and Empa-Swiss Federal Laboratories for Materials
Science and Technology, Laboratory for thin films and photovoltaics,
34
advanced Li-ion batteries. Recently, we reported on the
Überlandstraße 129, 8600 Dübendorf, (Switzerland).
c.
d.
e.
synthesis of germanium(II)-2-(tert-butyl)-4-methyl-6-(oxido-
Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für
Chemie, Professur Anorganische Chemie, 09107 Chemnitz (Germany)
Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für
Chemie, Professur Polymerchemie, 09107 Chemnitz (Germany)
methyl)phenolate (
is, however, not suitable for TP. The tert-butyl and methyl
4), a germanium(II) salicyl alcoholate, which
65
substituents at the aromatic moiety of
of the phenolic resin resulting in
4 hamper the formation
Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für
Physik, Professur Experimentalphysik mit dem Schwerpunkt Technische Physik,
0
9107 Chemnitz (Germany)
f.
Max-Planck-Institut für Chemische Energiekonversion, Stiftsstraße 34-36, 45470
Mülheim an der Ruhr (Germany).
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ARTICLE
Journal Name
obtained in the solid state, whereas the
View Article Online
DOI: 10.1039/C5TA09891B
compounds
Noteworthy,
2
a
and
3
form dimers.
trimer was previously
upon
crystallization from a saturated diethyl
ether solution, whereas in CDCl solution an
equilibrium between the trimer and the
determined for germylene
4
3
65
dimer/tetramer was observed. Thus, the
presence of different oligomers of the
Scheme 1 Illustration of the basic structural motif of the germylenes 1 - 4 (n = 2 - 4) and the concept for the synthesis
of e.g. a porous Ge@C material for rechargeable Li-ion batteries starting from 1 - 3 according to the concept of twin
polymerization followed by reduction of the hybrid material.
compounds
1 - 3 in solution is presumed.
DFT-D calculations support this assumption,
which is in accordance with the relative formation energies of
their oligomers (Scheme 2). The formation of the tetramers was
calculated to be energetically slightly favored in comparison
with the corresponding trimer formation, whereas the dimers
are energetically less favored. However, the small energy
differences between the oligomers, especially between their
trimers and tetramers, support the assumption that they are in
oligomeric structures rather than polymers upon thermal
treatment. However, the new germylenes, germanium(II)-2-
(
oxidomethyl)phenolate (
methyl)phenolate ( ) and germanium(II)-4-bromo-2-(oxido-
methyl)phenolate ( ) are well suited for TP due to the lack of a
1), germanium(II)-4-methyl-2-(oxido-
2
3
substituent in the ortho position of their phenolate moieties.
Moreover, the substituent in the para positions of their
phenolate moieties possess distinguishable steric and
electronic features, which is expected to influence their a chemical equilibrium in solution.
reactivity towards TP as reported for spirocyclic salicyl
62
alcoholates recently. Characterization including single crystal
X-ray diffraction analysis and DFT-D calculations, and studies on
their reactivity in TP using differential scanning calorimetry
(
DSC) are presented. The as-obtained germanium-containing
phenolic resin hybrid materials (HM-1 HM-3) and the
consecutively synthesized GeO and Ge@C materials were
characterized by analytical techniques such as solid state NMR
spectroscopy (HM-1 HM-3), X-ray photoelectron spectroscopy
XPS), infrared (IR), Raman and energy-dispersive X-ray (EDX)
-
2
-
(
spectroscopy, powder X-ray diffraction (PXRD), nitrogen-
sorption measurements and CHN analysis. Ge@C materials as Scheme 2 Illustration of the equilibrium between oligomers of 1 - 4 in solution (top) and
obtained starting from germylene
1
were tested as anode relative energies of the respective oligomers (bottom) calculated on the B3LYP-D3/def2-
materials for rechargeable Li-ion batteries and their TZVPP level of theory with regard to the respective monomers.
performance is discussed.
Compound
1
crystallizes in the monoclinic space group P2
1
/n
and forms trimers (1)
3
in the solid state. The molecular structure
Results
is given in Figure 1 and selected bond lengths and bond angles
are presented in the caption of this figure. Details of the
structure determination are summarized in Table 3.
Synthesis and Characterization of germylenes
The germylenes
1
-
3
were prepared according to the synthesis
starting from Ge[N(SiMe and the respective
salicyl alcohol with yields in the range from 64 % to 73 %. Poor
solubility in non-polar solvents was observed for germylene
The trimer (
reported for (
membered -[Ge-O-]
3
1) possesses a similar molecular structure as
6
5
protocol of
4
3
)
2
]
2
65
4
)
3
.
A distorted boat conformation of a six-
ring with three-coordinated germanium
3
3
,
atoms, one terminal phenolic oxygen atom and two bridging
benzylic oxygen atoms, is observed. The germanium oxygen
whereas the compounds
organic solvents. H NMR and H- C{ H} HSQC NMR
spectroscopic analysis of freshly prepared solutions of the
germylenes
resonance signals (five signals for
signals for ) indicating a dynamic coordination behavior
1 and 2 are soluble in all common
1
1
13
1
bond lengths [OAryl-Ge bonds: 1.8408(19) Å - 1.848(2) Å, OAlkyl
-
Ge bonds: 1.939(2) Å - 1.988(2) Å] are in the typical ranges
reported for Ge-O bonds in compounds with a threefold
1
-
3
in d
8
-THF at ambient temperature gave broad
1
and in each case, and four
2
66-68
pyramidal coordination of low valent germanium.
The
3
values reported for the germanium oxygen bonds for (4) [OAryl-
3
including oligomeric species, presumably dominated by their
monomers. Single crystals suitable for X-ray diffraction analysis
were obtained from saturated diethyl ether solutions of the
Ge bonds: 1.829(2) Å - 1.890(2) Å, OAlkyl-Ge bonds: 1.945(2) Å -
.044(2) Å] resemble those in ( but are slightly longer (with
the exception of Ge3-O5: 1.8447(19) Å for ( and 1.829(3) Å
for ( ) due to sterically more demanding substituents at the
aromatic moieties in (
2
1)
3
1)
3
germylenes
and from the cloudy reaction mixture (7:4 mixture of n-pentane
and diethyl ether) containing compound after filtration and
slow evaporation of the volatile solvents, respectively. In case
of germylene , a trimer (crystallization from diethyl ether) and
a tetramer (crystallization from the reaction mixture) were
1 and 2, from a saturated 1,4-dioxane solution of 3
4)
3
65
3
4) .
1
1
2
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The tetramer [2·(
space group I-4 exhibiting two crystallographically independent
1
)
4
· n-pentane] crystallizes in the tetragonal
View Article Online
DOI: 10.1039/C5TA09891B
tetramers, α-(
motifs (Figure S1) and thus only α-(
molecular structure of α-( is given in Figure 2 and selected
1
)
4
and β-(
1
4
) , which show similar structural
1)
4
is discussed. The
1)
4
bond lengths and bond angles are presented in the caption of
this figure. Details of the structure determination are
summarized in Table 3. Tetramer α-(
equivalent monomeric building blocks of
superimposed as a result of a S axis (Figure 2b). The core units
of the tetramer shows an eight-membered -[Ge-O-] ring in
which the germanium atoms span a distorted tetrahedron
Figure 2b). The germanium atoms are three-coordinate by one
1
)
4
consists of four
1
that can be
4
4
(
terminal phenolic oxygen atom and two bridging benzylic
oxygen atoms. The Ge1-O1 [1.987(3) Å] bond length is shorter
Figure 1 Molecular structure of (1)
3
in the solid state. Thermal ellipsoids are drawn with
50% probability. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and
bond angles [°]: Ge1-O1 1.8408(19), Ge1-O2 1.986(2), Ge1-O4 1.975(2), Ge2-O3 than the Ge1-O1' [2.025(3) Å] bond indicating secondary
1
.848(2), Ge2-O4 1.939(2), Ge2-O6 1.988(2), Ge3-O2 1.988(2), Ge3-O5 1.8447(19), Ge3-
bonding of O
atoms. The small deviations in the bond lengths and bond
angles between α-( and β-( may result from crystal packing
due to the presence of one molecule n-pentane in the unit cell.
Please note, when 2·( · n-pentane is slowly heated, a
The shorter Ge1-O2 [1.986(2) Å], Ge3-O6 [1.951(2) Å] and Ge2- reconstruction of the framework to give (
)3 and release of the
Ge that stabilizes the low valent germanium
O6 1.951(2); Ge1-O4-Ge2 128.28(11), Ge2-O6-Ge3 115.94(10), Ge1-O2-Ge3 132.48(10),
O1-Ge1-O2 92.45(9), O1-Ge1-O4 92.50(9), O2-Ge1-O4 86.80(9), O3-Ge2-O4 91.35(9),
O3-Ge2-O6 97.57(9), O4-Ge2-O6 88.82(8), O2-Ge3-O5 97.60(8), O2-Ge3-O6 86.64(8),
O5-Ge3-O6 92.77(9).
1
)
4
1)
4
1)
4
1
O4 [1.939(2) Å] bonds in comparison to the Ge1-O4 [1.975(2) Å], n-pentane were observed by temperature-dependent PXRD
Ge3-O2 [1.988(2) Å] and Ge2-O6 [1.988(2) Å] bond lengths, and thermogravimetric analysis (TGA), respectively (Figure S2
1
respectively, indicate secondary bonding of O4
Ge1, O6

Ge2 and S3). In addition, H NMR spectroscopic analysis in CDCl3
and O2 Ge3 stabilizing the low valent species.

at -60 °C gave two sets of signals that are assigned to the trimer
(
(
1
1
)3 and the tetramer
. The observation of
)
4
only one set of signals
for the tetramer of
indicates that α-( and
β-( relax in their
geometries to result in a
single tetrameric
structure in solution
Figure S4).
The dimer (
lizes in the triclinic space
1
1)
4
1)
4
(
2
2) crystal-
̅
group P
1
. The molecular
is
structure of
(2)
2
depicted in Figure 3 and
selected bond lengths
and bond angles are
presented in the caption
4
Figure 2 Molecular structure α-(1) a) in the solid state and b) with salicyl alcoholate moieties depicted in wireframe style and the tetrahedron
spanned by the germanium atoms highlighted in grey. The scheme in b) illustrates the coordination pattern of the bridging benzylic oxygen
atoms as indicated by the direction of the arrows. Thermal ellipsoids are drawn with 50% probability. Hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and bond angles [°]: Ge1-O1 1.987(3), Ge1-O2 1.884(3) and Ge1-O1' 2.025(3); Ge1-O1-Ge1' 126.37(16), O1-Ge1-O2 of this figure. Details of
9
1.36(13), O1-Ge1-O1' 85.29(14) and O2-Ge1-O1' 94.14(12). Symmetry transformations used to generate equivalent atoms:
the structure determi-
nation are summarized
in Table 3. A similar
'
= x-0.5, -y+1.5, -z+0.5; '' = -x+2, -y+1, z; ''' = -x+1.5, y+0.5, -z+0.5.
Additionally, the small O-Ge-O bond angles of the salicylic
moieties [O1-Ge1-O2 92.45(9)°, O3-Ge2-O4 91.35(9)° and O5-
Ge3-O6 92.77(9)°] and the angles
structure to (
therefore, only the molecular structure of (
discussed. The dimer ( exhibits C symmetry with a center of
2
)
2
was determined for (
3
)
2
(Figure S5), and
2)
2
is briefly
O4-O1Ge1O2 89.337(3)°,
O2-O5Ge3O6 92.840(2)° and O6-O3Ge2O4 94.408(3)° are in
2
)
2
i


inversion located in the plane spanned by the Ge1, O2, Ge1' and
O2' atoms. The equivalent benzylic oxygen atoms O2 and O2'
bridge the germanium atoms, which exhibit a threefold
pyramidal coordination. The germanium oxygen bond lengths
and bond angles are in agreement with the values determined
agreement with low valent germanium atoms possessing a
stereochemically active lone pair of electrons and donation of
electron density from the bridging benzylic oxygen atoms
(O4Ge1, O6Ge2 and O2Ge3) into the vacant p-orbitals.
for (1
)
3
, (1
)
4
and (
4
)
3
and thus are not further discussed.65
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2
Figure 3 Molecular structure of (2) in the solid state. Thermal ellipsoids are drawn with
5
0% probability. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and
bond angles [°]: Ge1-O1 1.862(7), Ge1-O2 1.986(6), Ge1-O2' 1.966(7); Ge1-O2-Ge1'
04.6(3), O1-Ge1-O2 91.6(3), O1-Ge1-O2' 94.9(3), O2-Ge1-O2' 75.4(3). Symmetry
1
transformations used to generate equivalent atoms: ' = -x, -y+1, -z+1.
Twin polymerization
Thermally induced twin polymerization of the germylenes
1 - 3
Figure 4 Differential scanning calorimetry of the amorphous materials of the germylenes
resulted in the formation of germanium-containing phenolic
resin hybrid materials. According to the concept of TP the
idealized structural motif of the hybrid material is illustrated by
Equation (1).
-
1
1
N
2
(black curve), 2 (red curve) and 3 (blue curve); heating rate 10 K min , N atmosphere,
volume flow 50 mL min-1.
2
formation of the phenolic resin and/or condensation to give the
final germanium-containing resin. The observation of
two minima in all DSC experiments indicate that the
polymerization follows similar reaction processes for
1
-
3
, but the compounds show a different reactivity.
However, the order of the onset temperatures does
not follow the electronic and steric features of the
substituents as was expected based on previous
reports for spirocyclic silicon salicyl alcoholates.62
Thus, we conclude that the nature of the substituents
1 - 3 plays a minor role for the initiation process here. This
The molecular structures of the compounds
2 and 3, exhibiting
in
a substituent in para position to the phenolic oxygen atom,
favor the ortho/orthoʹ connectivity of the bridging methylene
groups interconnecting the benzene rings in the phenolic resin
assumption is further supported by comparison of the onset
temperatures of the polymerization process for amorphous
102 °C) and the crystalline materials ( (142 °C) and 2·( · n-
pentane (119 °C) (Figure 5).
1
(
1
)
3
1)
4
as obtained after polymerization. By contrast, precursor
1
allows additional ortho/paraʹ connectivity. It is noteworthy that
our attempts to obtain polymeric hybrid materials by proton
induced twin polymerization as reported for other metal salicyl
6
1, 62, 64
alcoholates (M = Si, Ge and Sn)
failed. However, thermally
induced twin polymerization is feasible as it is outlined in the
following section.
Studies on the reactivity
Studies on the reactivity of the compounds
1 - 3 regarding the
process of thermally induced TP were performed by differential
scanning calorimetry (DSC) measurements up to 300 °C. The
thermograms starting from amorphous materials are depicted
in Figure 4. The compounds
show exothermic processes, which are assigned to thermally
induced TP. The onset temperatures are 102 °C ( ), 163 °C (
and 151 °C ( ). Two distinguishable minima at 110 °C and 145 °C
for , 183 °C and 194 °C for , and 161 °C and 200 °C for
1 - 3 do not melt and the DSC curves
1
2)
3
Figure 5 Differential scanning calorimetry of amorphous 1 (black curve), crystals of (1)
3
2
1
2
3
-1
(
red curve) and crystals of 2·(1)
4
· n-pentane (blue curve); heating rate 10 K min , N
-
1
2
atmosphere, N volume flow 50 mL min . The inlet magnifies the range between 95 °C
indicate that different formation processes take place at
specific temperatures during the polymerization processes e.g.,
and 155 °C. The determined 푑푄/푑푚 values and the as-calculated molar reaction
enthalpies (ΔH) that are referred to one monomeric unit of 1 of the exothermic processes
are depicted in black for amorphous 1, red for crystals of (1)
·(1) · n-pentane.
3
and blue for crystals of
2
4
4
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The different onset temperatures indicate that the initiation of analysis, XPS (exemplarily carried out for HM-V1ie)w Aartnicdle OEnDlinXe
the polymerization process depends on structural parameters spectroscopy. A summary of the polymerDizOaIt:i1o0n.10te39m/Cp5eTrAa0t9u8r9e1sB,
of the germylenes e.g., structure of the oligomer and/or crystal the product identities and the yields of the as-obtained hybrid
13
1
packing effects. The crystalline forms of germylene
higher onset temperatures and narrower temperature ranges NMR spectra of these materials.
Δ 15 °C) for the exothermic processes than observed for the
1 gave materials is given in Table 1. Figure 6 depicts the C{ H} CP-MAS
(
amorphous material. The exothermic processes gave a 푑푄/푑푚
J
J
value of -345 /
g
for amorphous
1
, -377 /
g 3
for crystalline (1)
J
and -340 /
g
for crystalline 2·(
1
)
4
· n-pentane. Thus, the as-
calculated molar reaction enthalpies (ΔH) that are referred to
g
kJ
one monomeric unit of
1
(M = 194.73 /mol) are -67 /mol for
kJ
kJ
amorphous
1
, -73
/
mol for crystalline (
1
)
3
and -66
/
mol for
crystalline 2·(
1
)
4
· n-pentane. As the 푑푄/푑푚 values and as a
consequence the molar reaction enthalpies (ΔH) are
comparable for the amorphous and the crystalline materials of
1
, the reaction energies do not rely on the structures of the
precursors. It is noteworthy that the DSC curve of 2·( · n-
pentane exhibits a second minimum at 146 °C as it is also
observed for amorphous (145 °C). These minima are close to
the single minimum detected for the twin polymerization of (1)
3
1)
4
1
Figure 6 13C{ H} CP-MAS NMR spectra of the germanium-containing phenolic resin hybrid
1
materials as obtained by thermally induced twin polymerization of 1 - 3. The spectra of
(143 °C) indicating that at least some formation processes in HM-1, HM-2 and HM-3 are depicted as black, red and blue lines, respectively. The
order to form the hybrid material e.g., formation of the asterisks * mark spinning side bands. Assignment of the resonance signals is given for
the assigned connectivity patterns of the bridging methylene groups (ortho/paraʹ only
for HM-1).
germanium oxide, take place at higher temperatures. We
conclude that amorphous materials possess smaller reaction
barriers for the initiation process of thermally induced twin
polymerization. The initiation of TP for the crystalline materials
All expected signals for the phenolic resin of the hybrid
materials HM-1
- HM-3 were observed with typical chemical
is aggravated presumably due to crystal packing. However, as
the polymerization process is initiated, the thermally induced
TP of the germylenes is facilitated by a pre-organized
arrangement of the precursors considering the narrow
temperature ranges of the polymerization process for the
shifts as reported for hybrid materials obtained by thermally
52, 62
induced TP.
The broad resonance signals with chemical
shifts of δ = 20 - 30 ppm and the resonance signals between
δ = 110 - 120 ppm (unsubstituted ortho carbons: δ = 113 -
69
1
17 ppm ) indicate the presence of nonequivalent bridging
crystalline forms of 1.
methylene groups in the phenolic resin for all hybrid
69-71
materials.
Nevertheless, the resonance signals assigned to
Characterization of the hybrid materials obtained by
thermally induced twin polymerization
the bridging methylene groups (δ = 20 - 30 ppm) exhibit the
most intense resonance signals centered at δ = 23 ppm
Thermally induced twin polymerization of
1 - 3 was carried out indicating that an ortho/orthoʹ connectivity of the bridging
by bulk phase experiments under inert atmosphere. methylene groups is prevalent in the phenolic resin even for
Polymerization temperatures of 200 - 230 °C were chosen HM-1. These values match with reference data reported for
according to the results of the DSC measurements of the ortho/orthoʹ bridging methylene carbons of phenol-
7
0
germylenes
1
-
3
.
formaldehyde resins (δ = 20 - 27 ppm). In addition, a trend for
the content of unsymmetrical connectivity patterns of
Table 1 Polymerization temperatures, product identities and yields of the
germanium-containing phenolic resin hybrid materials as obtained by
thermally induced TP of 1 - 3.
the bridging methylene groups with respect to
electronic and steric features of the substituents is not
observed, which is in contrast to our studies of the
phenolic resin-silica hybrid materials obtained by
thermally induced TP of spirocyclic silicon salicyl
Germylene
R
Polymerization
Product
Yielda)
[%]
temperature [°C]
1
2
3
H
200
HM-1, pale
yellow monolith
HM-2, yellow
monolith
HM-3, colorless
clumps
92
97
98
62
alcoholates. The latter and the prevalent ortho/orthoʹ
connectivity of the bridging methylene groups indicate
that the connectivity motif of the phenolic resin in the
hybrid materials is only marginally influenced by the
nature of the substituents at the aromatic moieties of
the germylenes. It is noteworthy that the resonance
signals, which are assigned to the bridging methylene
Me 220
Br 230
a) based on the mass of the germylene.
groups, exhibit shoulders with chemical shifts centered at
The as-obtained germanium-containing phenolic resin hybrid
materials were characterized by C{ H} cross polarization magic
angle spinning (CP-MAS) NMR and IR spectroscopy, PXRD, CHN
13
1
1
3
1
δ = 16 ppm in all C{ H} CP-MAS NMR spectra. This observation
is assigned to the presence of small amounts of Ge-CH
2
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Journal Name
connectivity within the Table 2 Summary of the product identities of the as-obtained Ge@C and GeO materials, theVirieswinArgtilcelepOonilninte
2
hybrid materials (Figure BET surface areas and in case of the Ge@C materials the pore volumes determined DbOyIn: 1it0r.o10g3e9n/Ca5dTsAo0rp98ti9o1nB
S6). The latter is a result of measurements in addition with their germanium content.
an oxidative insertion
reaction of the germylenes
as reported previously for Starting
2
GeO materials obtained under
Ge@C materials obtained under reductive conditions[a]
Pore volume[d] Germanium
Product BET
[
b]
oxidative conditions
Starting Product BET
surface
compound
converts into 2,4,6,8-tetra-
3-tert-butyl-5-methyl-2-
oxidophenyl)methanide-
,3,5,7,2,4,6,8-tetraoxido-
germocane ( ) in solution
4
, which slowly material
surface [cm /g]
3
content[e] [%] material
area[c]
area[c]
(micropore
content [%])
(
[m
2
/g]
[m
2
/g]
HM-1
HM-1
HM-2
HM-3
C-1a
C-1b
C-2
268
238
244
418
0.217 (25.1)
0.165 (34.5)
0.236 (14.9)
0.273 (46.7)
46.5±2.8
39.8±2.4
36.6±2.0
26.5±1.6
HM-1
HM-2
HM-3
Ox-1
Ox-2
Ox-3
12
9
20
1
5
6
5
(
Figure S6). Compound
5
C-3
serves as
a
model
[
a] at 800 °C (600 °C for C-1b) for 3 h under Ar/H
2
flux (95/5, 20 l/h), heating rate 10 K/min. [b] at 800 °C
= 0.150±0.002. [d] determined by the QSDFT
model for slit and cylindrical pores using the adsorption branch of the isotherms. [e] determined by EDX
spectroscopy.
compound for XPS analysis
that was exemplarily
carried out for HM-1 due
for 3 h under air flux (200 l/h), heating rate 10 K/min. [c] p/p
0
to its Ge-CH
XPS data indicate that the germanium atoms in HM-1 exhibit a
similar chemical environment as it was determined for (Figure
S7). However, the XPS data are also consistent with data
2
groups. The
conversion reactions of the germanium-containing phenolic
resin hybrid materials (HM-1
- HM-3) under reductive and
oxidative conditions in order to obtain porous materials
consisting of germanium incorporated in a carbon matrix
5
72-82
reported for germanium oxides.
allow to differentiate between the presence of Ge-CH
connectivity and germanium oxides within HM-1. However, in
Thus the XPS data do not
(Ge@C) and porous GeO
2
, respectively (Scheme 1). The product
materials, their
2
identities of the as-obtained Ge@C and GeO
2
BET surface areas and in case of the Ge@C composites the pore
volumes determined by nitrogen adsorption measurements in
addition with their germanium content are summarized in Table
13
1
accordance with the C{ H} CP-MAS NMR data, we suggest that
thermally induced TP of the germylenes provides hybrid
materials consisting of germanium oxide incorporated in a
2
.
phenolic resins, which contains small portions of Ge-CH
connectivity.
2
The as-prepared Ge@C materials exhibit large BET surface areas
with C-3 (418 m /g) offering the largest value. The adsorption
isotherms of the Ge@C composites are assigned to type I
isotherms showing hysteresis loops (Figure S9), which may
result from bottleneck pores. Analysis of the adsorption
isotherms using QSDFT gave 14.9 % (C-2), 25.1 % (C-1a), 34.5 %
2
-1
Typical IR absorption bands for ν(O-H) (3600 - 3200 cm ), ν(C=C)
-1
-1
(
1600 - 1400 cm ), ν(C-O) (1250 - 1200 cm ), aromatic
-
1
backbone vibrational modes (850 - 700 cm ) and Ge-O
vibrational modes (430 - 650 cm ) were observed in the FT-IR
spectra of all hybrid materials (Figure S8). An additional
absorption band maximum at 1096 cm was observed in the IR
spectrum of HM-3, which is assigned to the C-Br stretching
vibrational mode. CHN analyses revealed carbon contents of the
hybrid materials that are slightly lower than the values
-
1
(
C-1b) and 46.7 % (C-3) micropore contents. CHN analyses gave
carbon contents of 32.66 % (C-1a), 34.41 % (C-1b), 31.58 % (C-
) and 60.89 % (C-3). In addition, EDX spectroscopy revealed
germanium contents of (46.5±2.8) % (C-1a), (39.8±2.4) % (C-1b),
36.6±2.0) % (C-2) and (26.5±1.6) % (C-3). Bromine was not
detected by EDX analysis of C-3. The materials C-1a C-1b and C-
exhibit low carbon but high germanium contents, whereas a
low germanium and a high carbon content were determined for
C-3. The mass losses during the synthesis of C-1a C-1b and C-2
-1
2
(
(ΔC < 1.1 %) calculated for complete conversions of the
,
germylenes. The latter is in agreement with the determined
minor weight losses (Figure S3) during the polymerization
processes. However, the rather small deviations in the
determined carbon and hydrogen contents in comparison with
their calculated values indicate a high amount of conversion of
the germylenes into the hybrid materials. This is further
supported by EDX analysis and the high yields as obtained for
the hybrid materials after the work up procedures.
2
,
were about 50 %, whereas 68 % was observed for C-3. The
latter, in addition with the high carbon value, low germanium
and lacking bromine content as determined for C-3, indicate
that larger amounts of germanium and almost all bromine were
removed during the synthesis of C-3 resulting in a material
exhibiting a much higher carbon content (C: 60.89 %) as initially
present in the starting material HM-3 (C: 30.10 %) or germylene
Synthesis and characterization of porous materials
Conversion of phenolic resin-silica hybrid materials obtained by
3 (C: 30.40 %). Hence, the higher specific surface-to-mass ratio
TP of spirocyclic silicon salicyl alcoholates into microporous of C-3 results from larger proportions of carbonized material in
carbon and into mesoporous silica was reported by us addition with the higher micropore content that may result
62
recently. Variations of the molecular structure of the from decomposition processes (Figures S3 and S10) causing the
precursors e.g., different substituents at the aromatic moieties removal of all bromine and some germanium. Crystalline
were shown to affect the properties of the porous materials.62 germanium particles with average primary particle sizes of
Expecting qualitatively similar results, we carried out the (51±6) nm (C-1a), (13±1) nm (C-1b), (39±3) nm (C-2) and
6
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Jo uP rl ne aa sl eo fd oM na ot et r ai ad l jsu sCt hme am r gi si nt rs y A
Journal Name
38±3) nm (C-3) were determined by PXRD
analyses (Figure S11). Smaller crystalline
particle sizes were obtained at 600 °C
ARTICLE
(
View Article Online
DOI: 10.1039/C5TA09891B
[
[
(13±1) nm for C-1b] as compared to 800 °C
(51±6) nm for C-1a], while the BET surface
area does not differ significantly. Raman
spectroscopy using a confocal micro Raman
system revealed for Ge@C areas that exhibit
either high germanium but low carbon or
high carbon but low germanium contents
(Figure S12). The latter is indicative that
phase separation between germanium and
carbon on the μm-scale occurred during the
synthesis of the Ge@C composites under
reductive conditions, which was confirmed
by scanning electron microscopy in
combination with EDX mapping (SEM/EDX)
(Figure S13).
The as-prepared GeO
2
exhibit low BET
surface areas, which is indicative for a non-
porous material. This is further supported by
the adsorption isotherms that were assigned
to type II isotherms, which is typical for non- Figure 7 Electrochemical performance of Ge@C materials C1-a and C1-b as anode material for Li-ion batteries.
The approximate size of germanium domains is (51±6) nm for C1-a and (13±1) nm for C1-b. a) Cycling stability at a
porous and/or macroporous materials
-
1
-1
current of 346 mAg . b) Cycling stability at a current of 1384 mAg . c) and d) Galvanostatic charge and discharge
(Figure S9). The isotherms show pronounced
-
1
curves of composites C1-a and C1-b at a current of 346 mAg . All cells were cycled in the potential range 0.005 –
hysteresis down to p/p < 0.05, which may
0
1.0 V. Capacities and currents are related to the mass of the Ge@C composite corresponding to 80 % of the whole
result from hampering adsorption and/or electrodes.
hindered desorption of nitrogen due to
interactions between the adsorbate and the adsorbent. PXRD carboxymethyl cellulose (CMC) with the mass ratio of 8:1:1
analysis and Raman spectroscopy revealed the formation of using a planetary ball-mill. Electrochemical tests were carried
hexagonal GeO
2
for all oxidized materials. However, minor out in Li-ion half cells using 1 M LiPF
6
in a mixture (1:1 by weight)
were also detected for Ox-1 and of ethylene carbonate (EC) and dimethyl carbonate (DMC) as
electrolyte. Fluoroethylene carbonate (FEC) was used as
portions of tetragonal GeO
2
Ox-2 (Figure S11 and S12).
43
In conclusion, porous Ge@C composites and non-porous GeO
were obtained following the synthesis concept of TP (Scheme the electrochemical measurements for C1-a and C1-b are
). The properties of the as-obtained Ge@C and GeO
materials shown in Figure 7. Cells were cycled in the potential range of
is only marginally influenced by the molecular structure of the 0.005 – 1.0 V using a current of 346 mAg or 1384 mAg
2
electrolyte additive to improve cycling stability. The results of
1
2
-
1
-1
precursors with the exception that bromine within the hybrid respectively. For the first discharge cycle high irreversible
material (HM-3) results in larger loss of germanium by removal capacities are obtained due to the formation of the solid
of all bromine during the synthesis of the Ge@C material (C-3). electrolyte interface and the reduction of surface oxides
+
-
This results in higher carbon contents and larger BET surface according to GeO
area for Ge@C composites (C-3 vs C-1
C-2). The finally obtained subsequent cycling in all cases the coulombic efficiency, the
non-porous GeO
materials indicate that the proposed ratio between charge and discharge capacity, increased to
germanium oxide networks within the hybrid materials ~99 %. For cycling at 346 mAg composite C1-b delivers stable
2 2
+ 4Li + 4e → Ge + 2Li O. However, during
/
2
-
1
-
1
(
Equation 1) is not stable with respect to further conversion capacities of 540 mAhg with no fading for at least 100 cycles.
processes. However, the formation of the as-obtained In contrast, composite C1-a only provides capacities of
-
1
-1
microporous Ge@C composites containing germanium approximately 400 mAhg . Even at a current of 1384 mAg both
nanocrystals indicates that the hybrid materials consisting of samples of porous Ge@C material afforded stable capacities for
phenolic-resin and germanium oxide as dominant germanium 500 cycles with C1-b showing clearly better rate capability
-1
-1
species exhibit indeed phase nanodomains.
delivering a capacity of ~390 mAhg compared to ~220 mAhg
for C1-a. It is important to note that in all cases currents and
capacities were related to the total mass of the Ge@C
composite. Considering that EDX-analysis yields a Ge-content of
Electrochemical measurements
In order to provide a proof of principle, the Ge@C materials C-
4
6.5±2.8 % for C-1a and 39.8±2.4 % for C-1b the corresponding
1
a and C-1b were tested as potential anode material for
Ge-content in the electrodes can be estimated at 37 % and 32 %
respectively. Relating currents and capacities only to this
fraction of Ge in Ge@C, composite C1-b therefore reaches
rechargeable Li-ion batteries. Electrodes were prepared by
mixing the respective Ge@C sample with carbon black (CB) and
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Page 8 of 14
ARTICLE
Journal Name
-
1
stable capacities of 1360 mAhg for 100 cycles at a rate of polymerization. Its initiation is hampered by a densely packed
View Article Online
DOI: 10.1039/C5TA09891B
-1
-1
-
8
70 mAg and 980 mAhg for 500 cycles at a rate of 3480 mAg structure in the first place but as the polymerization process is
Despite the fact that direct comparison of electrochemical initiated, a pre-organized arrangement of the precursors
1
.
results has to be done carefully due to typically differences in facilitates the polymerization.
electrode composition (e.g. Ge-content) or electrochemical Porous Ge@C composites and non-porous GeO were obtained
2
cycling (e.g. current, potential range), we note that the by either conversion of the as-obtained hybrid materials under
performance of the herein presented Ge@C composite C1-b is reductive or oxidative conditions. Testing the obtained Ge@C
indeed comparable with recent reports on Ge/C materials composites as anode materials for rechargeable Lithium-ion
37, 48, 50, 83, 84
(Table S1 for detailed comparsion).
These good batteries in order to provide a proof of principle on our concept
electrochemical properties can be attributed to several factors. revealed that excellent cyclability, rate capability and high
Due to nanoscale dimension of crystalline germanium in the coulombic efficiency were obtained, especially for the Ge@C
Ge@C composites, and appropriate porosity, the massive composite possessing smaller crystalline germanium primary
volume changes occurring during lithiation/delithiation can be particle sizes [(13±1) nm]. Despite the fact that the present cost
effectively accommodated, leading to excellent cycling stability. for germanium compounds is possibly too high for
Further, due to the small size of germanium domains, intimate implementing germanium-based anodes in commercial
contact with carbon and porous structure of Ge@C, the ionic Lithium-ion batteries, the herein presented concept of twin
and electronic conductivity are enhanced allowing fast polymerization provides a general strategy to prepare high-
charging/discharging. In this regard, the significantly superior performance electrode materials by embedding the active
rate capability obtained for composite C1-b compared to C1-a material efficiently into a conductive carbon matrix and holds
can be attributed to the smaller size of crystalline primary considerable potential to be expanded to further systems in the
germanium particles [(13±1) nm vs. (51±6) nm, see Table 2] and future.
therefore shorter diffusion distances. The fact that the capacity
does not reach the theoretical maximum at ambient
temperature of 1384 mAhg (assuming formation of Li15Ge ),
4
-1
Experimental Section
might be attributed to the relatively high currents used and
possibly fractions of germanium oxides as indicated by EDX
measurements (Table S2), which leads to lower capacities. For
comparison, whereas germanium has a theoretical capacity of
All reactions were performed under argon using Schlenk
techniques or in a glovebox. Solvents were purified and dried by
applying standard techniques. The reactions were carried out
1
13
1
1
13
1
with freshly distilled, dried solvents. H, C{ H} and H C{ H}
HSQC NMR spectra were recorded with a Bruker Avance III 500
spectrometer. Solid-state NMR spectra were measured at 9.4 T
with a Bruker Avance 400 spectrometer equipped with double-
-
1
1
9
384 mAhg the reversible theoretical capacity of GeO
61 mAhg . Figures 7c and 7d show the galvanostatic
2
is
-1
charge/discharge curves of composite C1-a and C1-b. In both
cases the average delithiation potential is relatively low (~0.5 V)
indicating high suitability of such Ge@C materials for future full
cell applications as a high performance alternative to
commercial graphite anodes.
13
1
tuned probes capable of magic angle spinning (MAS). C{ H}
CP-MAS NMR spectra were measured at 100.6 MHz in 3.2 mm
standard zirconium oxide rotors (BRUKER) spinning at 15 kHz.
Cross polarization (CP) with a contact time of 3 ms was used to
enhance sensitivity. The recycle delay was 5 s. The spectrum
was referenced externally to tetramethylsilane (TMS) as well as
Conclusions
13
to adamantane as secondary standard (38.48 ppm for C). All
1
The germanium(II) salicyl alcoholates, germanium(II)-2-(oxido- spectra were collected with H decoupling using a two-pulse
methyl)phenolate (
yl)phenolate ( ) and germanium(II)-4-bromo-2-(oxidomethyl)- with a BioRad FTS-165 spectrometer. FT-IR were recorded with
phenolate ( ), have been synthesized by the reaction of a Nicolet IR 200 spectrometer from Thermo Scientific (Thermo
Ge[N(SiMe and the respective salicyl alcohols. Dimeric, Fisher Scientific Inc., Waltham, MA, USA) in a KBr Matrix. Raman
1), germanium(II)-4-methyl-2-(oxidometh- phase modulation sequence. ATR-FT-IR spectra were recorded
2
3
3 2 2
) ]
trimeric and tetrameric structures of the germylenes were spectra were collected on a LabRam HR800 confocal mirco
determined in the solid state and equilibriums between Raman system equipped with a Helium-Neon-laser (λ =
oligomers of these compounds were observed in solution. Twin 632.8 nm, P = 3.08 mW) without usage of any filter (D0) at
polymerization of the compounds
1 - 3 that was thermally fiftyfold magnification. Energy-dispersive X-ray spectroscopy
induced by heating up to 230 °C gave germanium-containing (EDX) and scanning electron microscopy (SEM) were performed
phenolic resin hybrid materials. In contrast to spirocyclic silicon using a NovaNano SEM from FEI with the following parameters:
-5
salicyl alcoholates, no influence following the steric and pressure (~ 10 mbar), work distance (5 to 7 mm) and
electronic features of their substituents [R = H ( ), Me ( ) and acceleration voltage (18 kV) using a Si Drift Detector XFlash
Br ( )] was observed on the process of thermally induced twin 3001 from Bruker AXS. Melting points were determined with a
polymerization. Moreover, analyses of the as-obtained hybrid Melting Point B-540 apparatus from Büchi. CHN analyses were
materials and bulk syntheses of Ge@C composites and GeO determined using a FlashEA 1112 NC Analyzer from Thermo
1
2
3
2
support this observation. However, a significant dependency on Fisher Scientific. DSC experiments were determined with a
the solid form of the germylenes e.g., amorphous vs. crystalline, Mettler Toledo DSC 30 using 40 μL aluminum crucibles. The
was observed for the process of thermally induced twin measurements were performed up to 400 °C with a heating rate
8
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Jo uP rl ne aa sl eo fd oM na ot et r ai ad l jsu sCt hme am r gi si nt rs y A
Journal Name
ARTICLE
of 10 K/min in N
TGA/DSC experiments were determined with a Mettler Toledo mixture of diethyl ether (4 mL) and n-pentDaOnIe: 1(04.1m03L9)/Cw5aTsA0a9d8d9e1dB
TGA/DSC1 1600 system with a MX1 balance. The measurement dropwise to a solution of Ge[N(SiMe (1.096 g, 2.78 mmol)
was performed from 40 to 800 °C with a heating rate of in n-pentane (10 mL) at ambient temperature. A colorless
0 K/min in Ar atmosphere and a volume flow of 60 mL/min. precipitate occurred within 5 min upon stirring. The mixture
Nitrogen physisorption isotherms were obtained at -196 °C was filtered off and washed with n-pentane (3 * 3 mL) to give
using an Autosorb IQ2 apparatus from Quantachrome. All amorphous compound (0.227 g) after evaporating volatile
samples were activated in vacuum at 150 °C for 3 h prior to the residues under reduced pressure (10 mbar). Slow evaporation
measurements. Specific surface areas were calculated applying of the volatile solvent gave crystalline ( from the filtrate over
the BET equation (p/p = 0.150 ±0.002). The micropore content a period of 2 hours. The colorless crystals were filtered off and
was estimated according to a QSDFT model (QSDFT: Quenched all volatile residues were removed by evaporation under
2
atmosphere and a volume flow of 50 mL/min. A solution of 2-hydroxybenzyl alcohol (0.346 g, 2.7V8iewmAmrticolel)Oinnlinae
3 2 2
) ]
1
1
-2
1)
4
0
-1
4
Solid Density Functional Theory, model for slit and cylindrical reduced pressure (10 mbar) to give crystalline 1 [(1) , 0.174 g].
pores using the adsorption branch) for carbon samples using Yield (both fractions): 0.401 g, 73 %; mp - (decomposition above
the Autosorb 1.56 software from Quantachrome.85-92 The ~ 101 °C); H NMR (500 MHz, d
1
-THF, 25 °C, TMS): δ = 4.59 [s
], 6.66 [m (broad), H, C ], 6.74 [m (broad), H,
], 6.76 [m (broad), H, C ], 7.12 ppm [m (broad), H, C ];
-THF, 25 °C, TMS): δ = 62.1 (CH ),
), 130.4
8
specific micropore and total pore volume were also calculated (broad), 2 H, CH
2
6 4
H
by the above mentioned DFT models. For X-ray photoelectron
spectroscopy (XPS) measurements, the powder samples were
C
6
3
H
4
1
6
H
4
6 4
H
1
C{ H} NMR (125 MHz, d
), 119.6 (C
), 158.4 ppm (C
8
2
pressed on indium foil (99.99 %, from MaTeck GmbH) that was 119.4 (C
cleaned with standard solvents in an ultrasonic bath. (C
6
H
4
6
H
4
4
), 120.3 (C
6
H
4
), 128.3 (C
6
H
4
); 1H 13C{ H} HSQC NMR (125 MHz, d
1
6
H
4
6
H
8
-
Measurements were performed in ultra-high vacuum (UHV) THF, 25 °C, TMS): δ = 4.60/59.1 (CH
employing a hemispherical electron analyzer (PHOIBOS 150 6.73/117.2 (C ), 6.77/125.1 (C ), 7.10/127.0 ppm (C
from SPECS GmbH) and an Al-K
SPECS GmbH) equipped with a monochromator (FOCUS from (ν CH
SPECS GmbH). The pass energy was set to 10 eV for acquisition 1453 (δ CH
of the core-level and Auger electron spectra. The estimated (γ C ), 633 (ν Ge-O), 604 (ν Ge-O), 556 and 525 and 486 and
error in binding energies is ±0.2 eV. No charge compensation 444 cm (O-Ge-O/Ge-O-Ge); CHN analysis calcd (%) for
was applied. Powder X-ray diffraction (PXRD) patterns were GeO : C, 43.17; H, 3.11; found: C, 43.26; H, 3.55. Single
collected using a STOE-STADI P diffractometer from STOE with crystals suitable for X-ray diffraction analysis were obtained i)
Cu-K radiation (40 kV, 40 mA) and a Ge(111) monochromator. directly from the filtrate of the reaction mixture after filtration
The crystallite size was estimated using the Scherrer equation: of the precipitate to give ( , ii) by evaporation of the solvent
휏 = 퐾휆/훽푐표푠휃, where τ is the volume weighted crystallite size, at ambient temperature of a saturated solution of
K is the Scherrer constant here taken as 1.0, λ is the X-ray ether and iii) by cooling a saturated solution of (
2
), 6.64/116.6 (C
6
H
4
),
6
H
4
6
H
4
6
H
4
);
α
X-ray source (XR50M from ATR-FT-IR: 3066 (ν Caryl-H), 3037 (ν Caryl-H), 3015 (ν Caryl-H), 2921
), 2857 (ν CH ), 1599 (ν C=C), 1578 (ν C=C), 1478 (δ CH ),
), 1254 (ν C-O), 1198 (ν C-O), 756 (γ C ), 731
2
2
2
2
6 4
H
6 4
H
-
1
C H
7 6
2
α
1)
4
1
in diethyl
4
1) in diethyl
3
wavelength, θ is the Bragg angle in ° and β is the full width of ether to -18 °C to give (1) , respectively.
the diffraction line at half of the maximum intensity (FWHM,
Synthesis of germanium(II)-4-methyl-2-(oxidomethyl)phenolate (2)
background subtracted). The FWHM is corrected for
instrumental broadening using a LaB standard (SRM 660)
A solution of 2-hydroxy-5-methylbenzyl alcohol (0.454 g,
6
3
.29 mmol) in a mixture of diethyl ether (6 mL) and n-pentane
purchased from NIST (National Institute of Standards and
2
(2 mL) was added dropwise to a solution of Ge[N(SiMe3)2]2
(1.294 g, 3.29 mmol) in n-pentane (10 mL) at ambient
temperature. A colorless precipitate occurred within 5 min
upon stirring. The mixture was filtered off and washed with n-
Technology). The value of β was corrected from (β measured and
2
β
instrument are the FWHMs of measured and standard profiles):
2
2
2
훽 = 훽
− 훽푖푛ꢁ푡푟푢ꢀ푒푛푡.
ꢀ
푒푎ꢁ푢푟푒ꢂ
Germanium(IV) chloride and 1,1,1,3,3,3-hexamethyldisilazane
were purchased from ABCR GmbH & Co KG. 2.5 M n-
Butyllithium and 5-bromo-2-hydroxybenzaldehyde were
purchased from Merck Schuchardt OHG (Hohenbrunn). 2-
Hydroxybenzyl alcohol and 4-methylphenol were purchased
pentane (3 * 2 mL) to give amorphous compound
2
(0.168 g)
-
after evaporating volatile residues under reduced pressure (10
2
mbar). Slow evaporation of the volatile solvent gave crystalline
2
from the filtrate over a period of 2 hours. Filtration and
-
evaporation of all volatile residues under reduced pressure (10
from Alfa Aesar GmbH & Co KG (Karlsruhe). GeCl
2
*1,4
1
mbar) gave
2 (0.288 g) as colorless crystals. Yield (both
15
15
3
dioxane, LiN(SiMe
methylbenzaldehyde were synthesized according to the
literature procedures. 2-Hydroxy-5-methylbenzyl alcohol, 5-
3
9
)
2
3
,
3 2 2
Ge[N(SiMe ) ]
and 2-hydroxy-5-
fractions): 0.456 g, 66 %; mp - (decomposition above ~ 164 °C);
1
8
H NMR (500 MHz, d -THF, 25 °C, TMS): δ = 2.20 [s (broad), 3 H,
Me], 4.61 [s (broad), 2 H, CH
2
], 6.57 [m (broad), H, C
6
H
3
], 6.82
94
bromo-2-hydroxybenzyl alcohol were synthesized according
to modified literature procedures. 2-Hydroxybenzyl alcohol was
purified by column chromatography (on silica gel using an ethyl
acetate/n-hexane mixture (20/80) as eluent) before usage. All
details including syntheses and characterizations of the
molecular precursors are given in the Supporting Information.
13
1
[
(
(
m (broad), H, C
125 MHz, d
), 128.4 (C
54.5 ppm (C
5 °C, TMS): δ = 2.20/23.1 (Me), 4.61/64.9 (CH
), 6.82/131.3 (C ), 6.97/131.2 ppm (C
3014 (ν Caryl-H), 2909 (ν CH /CH ), 2861 (ν CH
6
H
3
], 6.97 ppm [m (broad), H, C
6
H
3
]; C{ H} NMR
8
-THF, 25 °C, TMS): δ = 20.8 (Me), 62.5 (CH
), 128.6 (C ), 128.7 (C ), 129.0 (C
); H C{ H} HSQC NMR (125 MHz, d -THF,
), 6.57/118.3
); ATR-FT-IR:
/CH ), 1613 (ν
2
), 115.9
C
6
H
3
6
H
3
H
6 3
6
H
3
6 3
H
),
1
13
1
1
2
6
H
3
8
2
(C
6
H
3
6
H
3
6 3
H
Synthesis of germanium(II)-2-(oxidomethyl)phenolate (1)
3
2
3
2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
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Page 10 of 14
ARTICLE
Journal Name
C=C), 1578 (ν C=C), 1484 (δ CH
3
/CH
2 3 2
View Article Online
), 1451 (δ CH /CH ), 1252 (ν HM-1 (0.136 g) was carbonized under reductive conditions in a
DOI: 10.1039/C5TA09891B
C-O), 1214 (ν C-O), 872 (γ C
6
H
3
), 818 (γ C H ), 644 (ν Ge-O), 556 stove (deposited in a quartz glass tube) for 3 h with a final
6 3
-
1
and 490 and 459 cm (O-Ge-O/Ge-O-Ge); CHN analysis calcd (%) temperature of 800 °C (heating ramp of 10 K/min) under Ar/H
for C GeO : C, 46.02; H, 3.86; found: C, 45.79; H, 4.00. Single flux (95/5, 20 l/h) to give C-1a [0.065 g, single point BET-surface
crystals suitable for X-ray diffraction analysis were obtained by area determined at p/p
slow evaporation of the solvent at ambient temperature of a (%) found: C, 32.66; H, 0.29; EDX analysis (%) found: C, 44.3±4.1;
2
H
8 8
2
2
0
= 0.150±0.002: 268 m /g; CHN analysis
saturated solution of
2
in diethyl ether to give (
2
)
2
.
O, 9.2±1.4; Ge, 46.5±2.8; crystalline Ge particle size determined
by applying the Scherer equation based on the (220) reflection
of Ge ICDD no. C03-065-0333: 51±6 nm] as metallic shiny black
solid; Carbonization of: HM-1 (0.229 g) at 600 °C gave C-1b
Synthesis of germanium(II)-4-bromo-2-(oxidomethyl)phenolate (3)
A solution of 5-bromo-2-hydroxybenzyl alcohol (0.525 g,
2
(
(
.58 mmol) in a mixture of diethyl ether (10 mL) and n-hexane
5 mL) was added dropwise to a solution of Ge[N(SiMe
1.018 g, 2.59 mmol) in a mixture of diethyl ether (2 mL) and n-
2
[
(
0.110 g, single point BET-surface area: 238 m /g; CHN analysis
%) found: C, 34.41; H, 0.86; EDX analysis (%) found: C, 58.5±7.5;
3 2 2
) ]
O, 1.7±0.3; Ge, 39.8±2.4; crystalline Ge particle size: 13±1 nm];
hexane (10 mL) at ambient temperature. A colorless precipitate
occurred within 5 min upon stirring. The mixture was filtered off
and washed with n-hexane (3 * 3 mL) to give amorphous
HM-2 (0.123 g) at 800 °C gave C-2 [0.057 g, single point BET-
surface area: 244 m /g; CHN analysis (%) found: C, 31.58; H,
2
0
3
.18; EDX analysis (%) found: C, 55.2±6.7; O, 8.2±1.2; Ge,
6.6±2.0; crystalline Ge particle size: 39±3 nm]; HM-3 (0.371 g)
compound 3 (0.387 g) after evaporating volatile residues under
-
2
reduced pressure (10 mbar). Yield: 0.457 g, 64 %; mp -
at 800 °C gave C-3 [0.119 g, single point BET-surface area:
1
(
°
6
3
decomposition above ~ 151 °C); H NMR (500 MHz, d
8
-THF, 25
2
4
18 m /g; CHN analysis (%) found: C, 60.89; H, 0.38; EDX analysis
3
C, TMS): δ = 4.59 (s, 2 H, CH
2
), 6.65 (d, H, C
6
H
3
, Jortho = 8.5 Hz),
(%) found: C, 70.4±8.7; O, 3.1±0.5; Ge, 26.5±1.6; Br, -; crystalline
4
.97 (d, H, C
6
H
3
, Jmeta = 1.9 Hz), 7.23 ppm (dd, H, C
ortho = 8.5 Hz, Jmeta = 1.9 Hz); 13C{ H} NMR (125 MHz, d
6
3
H ,
Ge particle size: 13±1 nm].
4
1
J
8
-THF,
), 130.8
General procedure for the synthesis of germanium oxide -
exemplified for hybrid material HM-1
2
5 °C, TMS): δ = 62.0 (CH
), 131.4 (C ), 132.8 (C
HSQC NMR (125 MHz, d
.65/119.0 (C ), 6.98/127.7 (C
ATR-FT-IR: 3066 (ν Caryl-H), 2973 (ν Caryl-H), 2913 (ν CH
CH ), 1590 (ν C=C), 1561 (ν C=C), 1472 (δ CH ), 1406 (δ CH
254 (ν C-O), 1225 (ν C-O), 1073 (ν C-Br), 874 (γ C
2
), 111.2 (C
6
H
3
), 122.1 (C
6
H
3
1
13
1
(C
6
H
3
H
6 3
6
H
3
), 157.5 ppm (C
H
6 3
); H C{ H}
8
-THF, 25 °C, TMS): δ = 4.59/58.9 (CH
), 7.24/129.9 ppm (C
), 2867 (ν ramp of 10 K/min) under air flux (200 l/h) to give Ox-1 [0.115 g,
2
), HM-1 (0.218 g) was oxidized in a stove (deposited in a quartz
6
6
H
3
6
H
3
6 3
H ); glass tube) for 3 h with a final temperature of 800 °C (heating
2
2
2
2
), single point BET-surface area determined at p/p
0
= 0.150±0.002:
2
1
(
6
H
4
), 822 12 m /g; CHN analysis (%) found: C, 0.51; EDX analysis (%)
-
1
γ C
CHN analysis calcd (%) for C
C, 30.40; H, 1.69. Single crystals suitable for X-ray diffraction (α-quartz-like structure ICDD no. C00-036-1463) and tetragonal
analysis were obtained by slow evaporation of the solvent at (rutile-like structure ICDD no. C00-035-0729) GeO ] as gray
6
H
4
), 656 (ν Ge-O), 544 and 440 cm (O-Ge-O/Ge-O-Ge); found: C, 3.5±0.7; O, 31.0±3.7; Ge, 65.5±3.7; Raman
H
7 5
BrGeO : C, 30.72; H, 1.84; found: spectroscopy and PXRD confirmed the presence of hexagonal
2
2
ambient temperature of a saturated solution of
to give (
3
in 1,4-dioxane brittle monolith; Oxidation of: HM-2 (0.241 g) gave Ox-2
2
3
)
2
.
[0.117 g, single point BET-surface area: 9 m /g; CHN analysis (%)
found: C, 0.22; EDX analysis (%) found: C, 3.1±0.8; O, 28.7±3.9;
Ge, 68.2±4.1; Raman spectroscopy and PXRD confirmed the
General procedure for the synthesis of phenolic resin/germanium
oxide hybrid materials by thermally induced twin polymerization
presence of hexagonal and tetragonal GeO
2
]; HM-3 (0.306 g)
in melt - exemplified for compound
1
2
gave Ox-3 [0.082 g, single point BET-surface area: 20 m /g; CHN
analysis (%) found: C, 0.60; EDX analysis (%) found: C, 3.3±0.6;
O, 31.2±3.4; Ge, 65.5±3.3; Br, -; Raman spectroscopy and PXRD
Compound (0.507 g, 2.60 mmol) was polymerized at 200 °C
1
under Ar atmosphere and treated at this temperature for 3 h.
The obtained solid was washed with dichloromethane
2
confirmed only the presence of hexagonal GeO ].
-1
(
10 * 3 mL) and dried under reduced pressure (10 mbar) in
Single crystal X-ray diffraction analyses
order to remove volatile by-products. The product HM-1
[
0.471 g, 92 %, CHN analysis (%) found: C, 42.38; H, 3.38; EDX Crystallographic data of the compounds (
1
)
3
4
, 2·(1) · n-pentane,
analysis (%) found: C, 54.1±2.4; O, 18.7±0.9; Ge, 27.2±0.6] was
(2) and (3) · 1,4-dioxane were collected with an Oxford Gemini
2 2
a pale yellow phenolic resin/germanium oxide monolith; S diffractometer (CrysAlis RED Version 1.171.32.5 from Oxford
Polymerization of: (0.507 g, 2.04 mmol) at 220 °C gave HM-2 Diffraction Ltd.) using Mo-K (λ = 0.71073 Å) at 100 K [( ] or
0.417 g, 97 %, CHN analysis (%) found: C, 47.11; H, 4.44; EDX Cu-K radiation (λ = 1.54184 Å) at 110 K [2·( · n-pentane and
analysis (%) found: C, 55.9±2.3; O, 17.6±0.8; Ge, 26.5±0.5] as a ] or 100 K [( ]. The structures were solved by direct
yellow monolith; (0.876 g, 3.20 mmol) at 230 °C gave HM-3 methods using SHELXS-2013 and refined by full matrix least-
0.861 g, 98 %, CHN analysis (%) found: C, 30.10; H, 1.77; EDX square procedures on F using SHELXL-2013. Absorption
analysis (%) found: C, 33.4±3.1; O, 10.8±1.1; Ge, 27.8±0.9; Br, corrections were semi-empirical from equivalents. All non-
2
α
1)
3
[
α
1)
4
(2
)
2
3)
2
3
2
95
[
2
8.0±0.9] as colorless clumps.
hydrogen atoms were refined anisotropically and a riding model
was employed in the refinement of hydrogen atom positions.
General procedure for the synthesis of porous Ge@C materials -
exemplified for hybrid material HM-1
The crystallographic data for (
3 4 2
1) , 2·(1) · n-pentane, (2) and
(3)
2
· 1,4-dioxane have been deposited at the Cambridge
1
0 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
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Page 11 of 14
Jo uP rl ne aa sl eo fd oM na ot et r ai ad l jsu sCt hme am r gi si nt rs y A
Journal Name
ARTICLE
Crystallographic Data Centre as supplementary publications The resulting aqueous slurries were coated onto Cu foil (9 µm,
View Article Online
DOI: 10.1039/C5TA09891B
CCDC 1438301 [(
438302 [( ] and CCDC 1438300 [(
be obtained free of charge from the Cambridge Crystallographic in air tight coin-type cells assembled in an Ar-filled glove box (O
3 4
1) ], CCDC 1438303 [2·(1) · n-pentane], CCDC MTI Corporation) and subsequently dried at 80 °C for 12 hours
1
2
)
2
2
3) · 1,4-dioxane], they can under vacuum. Electrochemical measurements were conducted
2
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
< 0.1 ppm, H
counter and reference electrode. 1M LiPF
wt. of ethylene carbonate (EC) and dimethyl carbonate (DMC)
Merck, battery grade) with 3% fluoroethylene carbonate (FEC,
Hisunny Chemical Co., battery grade) served as electrolyte. As
separator glass fiber (GF/D, Whatman) was used. Galvanostatic
cycling tests were carried out at ambient temperature on MPG2
multi-channel workstation (BioLogic).
2
O < 0.1 ppm) using elemental lithium as both
6
in a 1:1 mixture by
Computational Details
The quantum chemical calculations have been carried out at the
(
DFT-D (B3LYP-D3/def2-TZVPP) level of theory using the
TURBOMOLE program package.9
6-103
All structure data given as
xyz-files in the Supporting Material were obtained by relaxing
all degrees of freedom and confirmed as minima by normal
mode analysis.
Table 3 Crystallographic and experimental data of the single crystal X-ray diffraction analyses of (1)
3
, 2·(1)
4
· n-pentane, (2)
2 2
and (3) · 1,4-
dioxane.
Compound
(1)
3
2·(1)
4
· n-pentane
(2)
2
(3) · 1,4-dioxane
2
Formula
C
21
H
18Ge
3
O
6
C
61
H
60Ge
8
O
16
C
16
H
16Ge
2
O
4
C
18
H
18Br
2
Ge
2
O
6
-
1
-1
-1
-1
Molecular mass
Temperature
Wavelength
Crystal system
Space group
Crystal size
584.12 g mol
100 K
1.54184 Å
monoclinic
1629.81 g mol
110 K
0.71073 Å
tetragonal
I-4
0.20 × 0.20 ×
0.18 mm
14.4998(3) Å
14.4998(3) Å
14.6335(6) Å
90°
417.47 g mol
110 K
0.71073 Å
triclinic
635.32 g mol
100 K
0.71073 Å
monoclinic
ꢃ
P2
0.2 × 0.2 ×
.16 mm
11.5755(3) Å
1
/n
P1
1
P2 /c
0.4974 × 0.4881 × 0.0897
mm
0.34 × 0.06 ×
0.04 mm
9.1184(6) Å
5.8156(4) Å
18.7848(10) Å
90°
91.848(5)°
90°
995.62(11) Å
0
a
b
c
α
β
γ
V
Z
5.0400(8) Å
5.7142(6) Å
13.393(2) Å
78.607(11)°
81.131(14)°
89.160(11)°
373.54(9) Å
1
1.856 Mg m
4.019 mm
16.1191(10) Å
11.8463(4) Å
90°
110.168(4)°
90°
2074.83(16) Å
4
1.870 Mg m
90°
90°
3
3
3
3
3076.61(18) Å
2
1.759 Mg m
2
-
3
-3
-3
-3
Density calculated
2.119 Mg m
7.066 mm
-
1
-1
-1
-1
-1
μ [mm ]
5.455 mm
3.920 mm
F (000)
1152
1620
208
616
Theta range for data collection
Index ranges
4.83 to 63.94°
-12 ≤ h ≤ 13
3.421 to 24.977°
-17 ≤ h ≤ 16
-17 ≤ k ≤ 12
-13 ≤ l ≤ 17
5657
3.141 to 24.991°
-5 ≤ h ≤ 5
-6 ≤ k ≤ 6
-15 ≤ l ≤ 15
1656
3.67 to 24.99°
-10 ≤ h ≤ 10
-6 ≤ k ≤ 6
-13 ≤ l ≤ 22
3242
-
-
17 ≤ k ≤ 18
13 ≤ l ≤ 8
Reflections collected
Independent reflections
6394
3365
2651
1656
1738
[
R(int.) = 0.0260]
[R(int.) = 0.0186]
2651
[R(int.) = 0.0612]
1656
[R(int.) = 0.0471]
1738
Data
3365
2
Goodness-of-fit on F
1.031
1.041
1.104
0.916
2
Final R indices [I>2σ(l)], ωR2 (F ) (all
data)
Largest diff. peak and hole
R1 = 0.0345,
wR2 = 0.0930
0.632 and
R1 = 0.0219,
wR2 = 0.0463
0.301 and
R1 = 0.0597,
wR2 = 0.1798
1.495 and
R1 = 0.0398,
wR2 = 0.0927
1.108 and
-3
-3
-3
-3
-
0.531 e.Å
-0.265 e.Å
-1.544 e.Å
-0.649 e.Å
Electrode fabrication, cell assembly and electrochemical
measurements
Acknowledgements
We gratefully acknowledge financial support by the DFG
Forschergruppe 1497 “Organic-Inorganic Nanocomposites
through Twin polymerization” and the Fonds der Chemischen
Ge@C samples, carbon black (CB, Super C65, TIMCAL), and
carboxymethyl cellulose (CMC, Grade: 2200, Daicel Fine Chem
Ltd.) were mixed in the ratio 8:1:1 with deionized water using a
Fritsch Pulverisette 7 classic planetary mill (1 hour at 500 rpm).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
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Page 12 of 14
ARTICLE
Journal Name
Industrie for a fellowship (P. K.). We thank N. Rüffer for TGA 24.
measurements and M. Weber for recording the Raman spectra.
A. Jana, V. Huch and D. Scheschkewitz, AngeVwiew. CAhrteicmle O.,nIlninte.
Ed., 2013, 52, 12179-12182.
P. S. Billone, K. Beleznay, C. R. Harrington, L. A. Huck and
W. J. Leigh, J. Am. Chem. Soc., 2011, 133, 10523-10534.
S. Yao, C. van Wüllen and M. Driess, Chem. Commun., 2008,
DOI: 10.1039/C5TA09891B
25.
26.
27.
5393-5395.
Keywords
U. Anandhi and P. R. Sharp, Inorg. Chim. Acta, 2006, 359,
3521-3526.
Germylenes ● twin polymerization ● X-ray diffraction analysis ●
germanium-containing porous materials ● organic-inorganic 28.
hybrid materials ● Li-ion batteries
K. Revunova and G. I. Nikonov, Dalton Trans., 2015, 44,
840-866.
S. B. Kim, P. Sinsermsuksakul, A. S. Hock, R. D. Pike and R.
G. Gordon, Chem. Mater., 2014, 26, 3065-3073.
F.-W. Yuan and H.-Y. Tuan, Chem. Mater., 2014, 26, 2172-
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
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Journal of Materials Chemistry A
Page 14 of 14
View Article Online
DOI: 10.1039/C5TA09891B
Table of content
Novel germylenes based on salicyl alcoholates were synthesized and their thermally induced
twin polymerization to give organic-inorganic hybrid materials was studied. Structural studies
including single crystal X-ray diffraction analysis, NMR spectroscopy and DFT-D calculations
revealed the formation of oligomers in the solid state and equilibriums in solution. Thermally
induced twin polymerization of germylenes gave hybrid materials based on germanium-
containing phenolic resins in a single step. Carbonization of these resins under reductive
conditions resulted in porous Ge@C materials, which were tested as potential anode materials
-1
for rechargeable Li-ion batteries. Reversible capacities of 540 mAhg were obtained at a
-1
current density of 346 mAg without apparent fading for 100 cycles, which demonstrates that
germanium is well accessible in the hybrid material.