Synthesis and characterization of germanium coordination compounds for production of germanium nanomaterials

Article abstract of DOI:10.1002/ejic.200900556

A series of novel germanium(II) precursors was synthesized to initiate an investigation between the precursors' structures and the morphologies of the resulting nanoparticles. The precursors were synthesized from the reaction of Ge[N(SiMe₃)

Full text of DOI:10.1002/ejic.200900556

FULL PAPER
DOI: 10.1002/ejic.200900556
Synthesis and Characterization of Germanium Coordination Compounds for
Production of Germanium Nanomaterials
Timothy J. Boyle,*[a] Louis J. Tribby,[b] Leigh Anna M. Ottley,[a] and Sang M. Han[b]
Keywords: Germanium / Nanomaterials / Alkoxides / Thiols / Amides / Solid-state structures
A series of novel germanium(II) precursors was synthesized
to initiate an investigation between the precursors’ structures
and the morphologies of the resulting nanoparticles. The
precursors were synthesized from the reaction of Ge[N-
(SiMe3)2]2 or [Ge(OtBu)2]2 and the appropriate ligand: N,NЈЈ-
dibenzylethylenediamine (H2-DBED), tert-butyl alcohol (H-
OtBu), 2,6-dimethylphenol (H-DMP), 2,6-diphenylphenol (H-
DPP), tert-butyldimethylsilanol (H-DMBS), triphenylsilanol
(H-TPS), triphenylsilanethiol (H-TPST), and benzenethiol
(H-PS). The products were identified as: [Ge(µc-DBED)]2 (1,
µc = bridging chelating), [Ge(µ-DMP)(DMP)]2 (2), Ge(DPP)2
(3), [Ge(µ-OtBu)(DMBS)]2, (4), [Ge(µ-DMBS)(DMBS)]2 (5),
Ge(TPS)3(H) (6), [Ge(µ-TPST)(TPST)]2 (7), and Ge(PS)4 (8).
The GeII metal centers were found to adopt a pyramidal ge-
ometry for 1, 2, 4, 5, 7, a bent arrangement for 3, and a tetra-
hedral coordination for the GeIV species 6 and 8. Using a
simple solution precipitation methodology, Ge0 nanomateri-
als were isolated as dots and wires for the majority of precur-
sors. Compound 7 led to the isolation of amorphous GexSy.
The nanomaterials isolated were characterized by TEM,
EDS, and powder XRD. A correlation between the precur-
sor’s arrangement and final observed nanomorphology was
proffered as part of the “precursor structure affect” phenom-
enon.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
preparatory routes.[22–36] For our method, GeII precursors
were selected since the reduction potential of GeII to Ge0 is
+0.247 V in comparison to the +0.124 V reported for GeIV
to Ge0.[37] Of particular note for this route was the fact that
the ligand set of the precursor appeared to influence the
final observed Ge0 morphology.[21] This phenomenon was
referred to as the “precursor structure affect” (PSA) and
has been investigated and confirmed for a number of other
systems.[38–40]
In order to further probe the PSA for this system, a
larger family of varied GeII precursors was necessary. How-
ever, a search of the literature[41,42] revealed that only a
handful of acceptable structurally characterized GeII pre-
cursors (i.e., amides, alcohols) for the production of Ge0
nanomaterials were available.[21,43–71] Since both the steric
bulk of the pendant chains of the alkoxide[72] and the bond
dissociation energies [Ge–N (55 kcal/mol),[73] Ge–O
(157),[73] Ge–S (128)][74] of a the GeII precursors were
shown to play a role in the PSA, the synthesis and charac-
terization of series of GeII coordination compounds bound
by a variety of ligands was warranted.
Introduction
Germanium has come to the forefront of a possible re-
placement material for silicon in such applications as tran-
sistors,[1–3] nonvolatile memories,[4–6] photovoltaic de-
vices,[7–9] long-wavelength photodetectors,[10] and biological
detection systems.[11,12] This fundamental materials change
is being explored since it is expected that Ge-based elec-
tronics will display:I enhanced electrical properties, owing
to higher electron and hole mobility than noted for Si,[13]
(ii) smaller band gap behavior[6] (even though bulk Ge is an
indirect band gap material),[14] and (iii) a more pronounced
quantum confinement in comparison to Si due to the larger
Bohr exciton radius of Ge.[15–19] Unfortunately, further de-
velopment of these devices has been hindered by the lack of
a simple, rapid, high purity route to Ge nanomaterials.[20,21]
Recently, we reported on the synthesis of Ge0 nano-dots
and -wires from the decomposition of select GeII precursors
(e.g., amide vs. alkoxide)[21] that avoided the use of high
temperatures, high pressures, seed catalysts, and retention
of competing salt by-products reported for other literature
These compounds were generated through either the
well-established transamination[66–71] reaction [Equation
(1)], where Ge(NR2)2 (R = SiMe3)[59,60,75] was substituted
with a series of amines, alcohols, thiols (collectively referred
to as H-L) or the often used alcoholysis exchange [Equation
(2)] involving [Ge(OtBu)2]2.[47,76] The H-L modifiers investi-
gated in this work included N,NЈ-dibenzylethylenediamine
(H2-DBED), tert-butyl alcohol (H-OtBu), 2,6-dimethyl-
[a] Sandia National Laboratories, Advanced Materials Laboratory,
1001 University Boulevard SE, Albuquerque, New Mexico
87106, USA
Fax: +1-505-272-7336
E-mail: tjboyle@Sandia.gov
[b] Department of Nuclear and Chemical Engineering,
1 University of New Mexico, Albuquerque, NM 87131-0001,
USA
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900556.
5550
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5550–5560

Germanium Nanomaterials
phenol (H-DMP), 2,6-diphenylphenol (H-DPP), tert-butyl-
Obviously, the systematic variation and the proper ligand
dimethylsilanol (H-DMBS), triphenylsilanol (H-TPS), tri- composition to investigate the PSA of Ge0 nanomaterials
phenylsilanethiol (H-TPST), and benzenethiol (H-PS). The were not available from this set of compounds.[21,38–40,43–65]
products were identified as: [Ge(µc-DBED)]2 (1, µc = bridg- Therefore, the syntheses of GeII precursors with ligands se-
ing chelating), [Ge(µ-DMP)(DMP)]2 (2), Ge(DPP)2 (3), lected for both electronic and steric considerations were ini-
[Ge(µ-OtBu)(DMBS)]2, (4), [Ge(µ-DMBS)(DMBS)]2 (5), tiated. Once isolated and characterized, an initial study on
Ge(TPS)3(H) (6), [Ge(µ-TPST)(TPST)]2 (7), and Ge(PS)4 the conversion of these precursors to Ge0 nanomaterials via
(8). Once isolated, these compounds were used for the gen- a solution precipitation route was undertaken.[21]
eration of Ge-based nanomaterials following established
solution precipitation protocols.[21] The characterization of
these precursors, the nanomaterials produced and the pre-
liminary PSA correlation are discussed.
Synthesis
The ligands of interest [H-L, Equation (1)] were individu-
[59,60,75]
ally reacted with Ge(NR2)2
in toluene [Equa-
tion (1)]; except for 4 which was isolated from the modifica-
[47,76]
tion of [Ge(OtBu)2]2
[Equation (2)]. After stirring for
10 min, each reaction mixture was set aside and the volatile
component was allowed to slowly evaporate. Over an ex-
tended period of time under an argon atmosphere, light yel-
low or colorless X-ray quality crystals were isolated. FTIR
data of the dried crystals indicated that the reactive proton
for each ligand had been removed. In particular, the H–N
stretch for the diamine at ca. 3300 cm–1 for compound 1,
the H–O stretch of the alcohols at 3200–3500 cm–1 for 2, 3
and for the silanols of 4–6, as well as the H–S stretch for
the thiols at ca. 2500 cm–1 for 7 and 8 were no longer pres-
ent. For 6, a new peak at 2130 cm–1 was tentatively assigned
to a Ge–H stretching band.[80–83] For 5, a peak at 2131 cm–1
was observed which was tentatively assigned to a Ge–H in-
teraction, possibly from the protons of the Si(CH3)3 group.
Results and Discussion
The utility of GeII amide [Ge(NR2)2] and alkoxide
[Ge(OR)2] derivatives for the production of Ge0 nanomater-
ials has been previously demonstrated.[21] In an effort to
garner additional morphological control over the Ge0 nano-
materials by exploiting the PSA phenomenon, a series of
well-characterized Ge(NR2)2 and Ge(OR)2 precursors was
necessary. A search of the crystallographically characterized
species[41,42] constrained to Ge(NR2)2 yielded a complex
Crystal Structures
In order to assist in the characterization of 1–8, single-
family of compounds[50,52–58] that typically employ chelat- crystal X-ray structures of each were obtained and shown
ing amide groups as well as a series of simple Ge[N- in Figures 1, 2, 3, 4, 5, 6, 7, and 8, respectively. The struc-
[59–62,75]
(SiR3)2]2
species. Further searches for Ge(OR)2 ture plot of compound 1 (Figure 1) shows the structure of
structures (when calixarenes and hydroxy ligated species the GeII diamine derivative. For 1, each pyramidal Ge metal
were removed due to inherent problems associated with center is fully coordinated by three N atoms – two from the
these compounds for materials production) yielded two chelating DBED and one from the N of the other DBED.
structure types: (i) monomeric Ge(OR)2 where OR = The ethane linkage of each DBED was found to be twisted
OC(tBu)3,[49] O(CH2)2NMe2,[63] (2,6-di-R)phenoxy [R = 24.3° out of the plane with respect to the core, which is
tert-butyl
(DBP),[21]
tert-butyl-Me-4,[51]
2,6-isopro- in good agreement with the 22.0° twist of the monomeric
pylphenyl,[43] phenyl (DPP)],[45] (2,3,5,6-tetraphenyl)phen- [CH2N(tBu)]c Ge.[54] The remainder of comparable metrical
2
[77]
oxy,[45] Ge(DPP)2(NMe2)2 and (ii) dinuclear [(OR)Ge(µ- data are also in agreement between 1 [Ge–N(1) 1.86 Å; N–
OR)]2 where OR = mesityloxo (OMes)[45] and 2,6-diisopro- Ge–N 84.6°] and [CH2N(tBu)]c Ge [Ge–N 1.83 Å; N–Ge–
2
pylphenoxide (DIP).[45] Additionally, for GeII siloxides, the N 87.9°].[54] The Ge2N2 core of 1 [Ge-(µ-N) av. 2.01 Å, (µ-
[47]
heteroligated [(TPS)Ge(µ-OtBu)]2
and Ge(TPS)2- N)–Ge-(µ-N) 80.0°] compares favorably to [C6H3-2,6(C6H3-
[41]
{[(TMS)N=P(PH)2]2(CH2)}[64] have been disseminated as 2,6-iPr2)2(µ-NH2)Ge]2
[Ge-(µ-N) 2.02 Å; (µ-N)–Ge-(µ-
well as the GeIV bis-OSiR3 complex (porph)Ge(TPS)2 N) angle of 81.5°].
{porph
=
5,10,15,20-tetrakis[(2-triisopropysilyl)ethynyl]-
The use of aryl alcohols in Equation (1), led to the isola-
porphyrinato-N,NЈ,NЈЈ,NЈЈЈ}.[78] We were also interested in tion of 2 (Figure 2) and 3 (Figure 3). For the smaller DMP
the utility of thiolate derivatives as precursors for Ge0 or ligand, the dinuclear compound 2 was isolated with a single
single-source precursor for GeSx. Only a handful of GeII bridging and terminal DMP ligand bound to each pyrami-
thiolates have been crystallographically reported, including dal coordinated Ge metal center. The terminal DMP li-
[Ge(µ-StBu)2(StBu)]2,[79] the hydrido Ge(SPh3)3(H),[45] and gands adopt a trans arrangement (above and below the
the salts [Ge(SPh)3][N(Et)4][65] or [(SCH2CH2S)cGe(µ- Ge2O2 plane), similar to what was reported for the OMes[45]
SCH2CH2S)2][P(Ph)4] (c stands for cyclic).[65]
and DIP[45] derivatives. As is often noted for metal alk-
Eur. J. Inorg. Chem. 2009, 5550–5560
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5551

T. J. Boyle, L. J. Tribby, L. A. M. Ottley, S. M. Han
FULL PAPER
Figure 4. Structure plot of 4. Thermal ellipsoid plots are drawn at
30% level. Carbon atoms drawn as ball and stick and hydrogens
omitted for clarity.
Figure 1. Structure plot of 1. Thermal ellipsoid plots are drawn at
30% level. Carbon atoms drawn as ball and stick and hydrogens
omitted for clarity.
Figure 5. Structure plot of 5. Thermal ellipsoid plots are drawn at
30% level. Carbon atoms drawn as ball and stick and hydrogens
omitted for clarity.
Figure 2. Structure plot of 2. Thermal ellipsoid plots are drawn at
30% level. Carbon atoms drawn as ball and stick and hydrogens
omitted for clarity.
Figure 3. Structure plot of 3. Thermal ellipsoid plots are drawn at
30% level. Carbon atoms drawn as ball and stick and hydrogens
omitted for clarity.
Figure 6. Structure plot of 6. Thermal ellipsoid plots are drawn at
30% level. Carbon atoms drawn as ball and stick and hydrogens
omitted for clarity.
oxides,[66–71] the Ge–O terminal distances (av. 1.82 Å) are
shorter than the Ge-(µ-O) bridging bond lengths (av.
1.98 Å). The internal Ge2O2 core has angles of (µ-O)–Ge-
(µ-O) (av. 72.5°) and Ge-(µ-O)–Ge (av. 107.4°). These data Rothwell and co-workers;[45] however, for this crystal solu-
are in agreement with the literature Ge(OR)2 distances and tion, 3 was solved in the higher-ordered orthorhombic
angles[45,84] Ge–O (av. 1.82 Å), Ge-(µ-O) (av. 1.98 Å), and space group. The Ge–O bond length of 1.81 Å and O–Ge–
(µ-O)–Ge-(µ-O) (av. 72.2°) Ge-(µ-O)–Ge (av. 107.5 Å). For O angle of 90.2° are in good agreement with previously re-
the more sterically hindering DPP ligand, monomeric 3 was ported Ge–O bond lengths of av. 1.82 Å and O–Ge–O
isolated in a bent arrangement as previously reported by angles of av. 91.6°.[45]
5552
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5550–5560

Germanium Nanomaterials
distances
of
(TPS)2Ge{[(TMS)N=P(Ph)2]2(CH2)}2,[64]
[47]
(porph)Ge(TPS)2, and [(TPS)Ge(µ-OtBu)]2
av. 1.80,[78]
1.86,[64] and 1.81[47]Å, respectively are significantly longer
in comparison to those noted for 5 (av. 1.78 Å). This varia-
tion is most likely a reflection of the dinuclear, homoleptic
nature of 5 in comparison to the other compounds. Further
comparisons were made only to the dinuclear heteroleptic
[(TPS)Ge(µ-OtBu)]2.[47] The internal core distances and
angles of 5 [Ge-(µ-O) av. 1.98 Å, with O–Ge-(µ-O) angles
av. 96.0° and (µ-O)–Ge-(µ-O) av. 78.0°] appear to be
[47]
roughly in agreement with [(TPS)Ge(µ-OtBu)]2
[Ge-(µ-
O) av. 1.96 Å, with O–Ge-(µ-O) angles av. 96.3° and (µ-O)–
Ge-(µ-O) av. 74.7°]. In contrast to what was noted in the
FTIR, there were no CH2–H···Ge interactions observed in
the solid-state structure of 5.
Figure 7. Structure plot of 7. Thermal ellipsoid plots are drawn at
30% level. Carbon atoms drawn as ball and stick and hydrogens
omitted for clarity.
For 6, a monomer was isolated with three TPS groups,
which suggests that either one of the TPS ligands is proton-
ated or a hydride formed. The FTIR spectrum (vide infra)
and 1H NMR (vide supra) data indicated that the latter
interpretation was the most appropriate. Further analysis
of the electron density map of 6 revealed the presence of a
proton located as part of the tetrahedral geometry around
the Ge metal center (Figure 6). While the formation of the
unusual compound 6 is not fully understood, a potential
mechanism would include the initial formation of the
homoleptic Ge(TPS)2 species, followed by additional coor-
dination of free H-TPS, subsequent β-hydrogen transfer,
and conversion to the GeIV hydride species 6. This is consis-
tent with previously disseminated mechanisms of Ge–H for-
mation for other siloxide systems.[45,80,85] The Ge–H bond
length was resolved at 1.26 Å, which is shorter than the
recently published [Ge(H)(µ-O3SiR)]4, R = N(2,6-iPr2C6H3)-
(SiMe3), where the av. Ge–H bond length was 1.39 Å.[80]
The short Ge–H bond length is attributed to the decreased
electron donation capability of the attached TPS ligands;
Figure 8. Structure plot of 8. Thermal ellipsoid plots are drawn at
30% level. Carbon atoms drawn as ball and stick and hydrogens
omitted for clarity.
1
this is further evidenced in the Ge–H increased H NMR
It was of interest to determine what effect siloxide ligands shift downfield. The remainder of the metrical data (Ge–O
would have on the final structure of GeII species. The first av. 1.73 Å, O–Ge–O angles av. 107.5°, H–Ge–O angles of
attempt to generate a homoleptic precursor following an av. 111.3°) are in agreement with [Ge(H)(µ-O3SiR)]4 (Ge–O
alcoholysis exchange [Equation (2)] yielded the heteroleptic av. 1.74 Å, for O–Ge–O av. 108.8°, H–Ge–O av. 109.9°).[80]
structure of 4 (Figure 4). For this compound only the ter-
Attempts to expand the ligand set to include thiolates
minal OtBu groups were substituted by DMBS ligands, were undertaken following Equation (1), which yielded 7
leaving the original dinuclear pyramidal arrangement (see Figure 7). Compound 7 was found to be dinuclear with
around the Ge metal centers intact. The two bridging OtBu two bridging and two terminal cis TPST ligands, arranged
groups had a (µ-O)–Ge-(µ-O) angle of av. 74.5° with Ge- in a pyramidal geometry around the Ge cations. While four
(µ-O) distance of av. 1.96 Å, and terminal Ge–O distance GeIV–S–Si species are available in the literature,[86–89] 7 is
of av. 1.80 Å, similar to the metrical data of [Ge(µ-O- the first report of a GeII–S–Si complex, which complicates
tBu)(TPS)]2:[47] (µ-O)–Ge-(µ-O) av. 74.8°; Ge–OTPS av. metrical comparisons. The TPST species has a Ge2S4 core
1.81 Å; Ge-(µ-OtBu) av. 1.96 Å.
that is significantly distorted from planarity (56.2°) with
Attempts to generate homoleptic siloxides were realized angles of av. 78.4° (µ-S)–Ge-(µ-S) and av. 93.0° (S)–Ge-(µ-
following the transamination methodology [Equation (1)]. S) and distances of av. 2.32 Å for Ge–S and av. 2.47 Å Ge-
Using two equivalents of H-DMBS or H-TPS led to the (µ-S). These distances and angles do not compare favorably
fully substituted species 5 (Figure 5) and 6 (Figure 6), with the only appropriate model [Ge(µ-StBu)(StBu)]2:[79]
respectively. Interestingly, the DMBS derivative 5 adopted 27.6° twist of the Ge2S4, angles of av. 85.5° (µ-S)–Ge-(µ-S),
a dinuclear arrangement where the terminal DMBS ligands 92.1° (S)–Ge-(µ-S), and distances of 2.43 Å for Ge–S. The
of the pyramidal Ge were found in a cis conformation. This metrical variations must be due to changes in the steric bulk
unusual arrangement for GeII species forces a small out-of- and electron donation of the SSiR3 group of 7 to the SR
plane twist (4.22°) of the Ge2O2 core. The terminal Ge–O group of [Ge(µ-StBu)(StBu)]2.[79]
Eur. J. Inorg. Chem. 2009, 5550–5560
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5553

T. J. Boyle, L. J. Tribby, L. A. M. Ottley, S. M. Han
FULL PAPER
The use of the thiol H-PS in Equation (1) produced 8 tains its nuclearity upon dissolution, with rapid exchange
(Figure 8), a monomeric species that has four PS ligands of the bridging and terminal ligands.[45] Unfortunately, the
arranged in a distorted tetrahedral geometry around the Ge lowered solubility of 2 favors precipitation at reduced tem-
metal center. Since both the IR and 1H NMR spectroscopic peratures, which prevents similar studies and therefore defi-
data indicate the removal of the protons from the PS li- nite statements concerning its nuclearity in solution, cannot
gands and the metrical aspects of 8 were comparable to the be made. In CDCl3, 3 revealed a complex multiplet ranging
GeIV thiol species,[65,90–93] 8 is considered to be in the +4 from δ = 7.56–7.04 assigned to the numerous phenyl pro-
oxidation state instead of coordination of two H-PS ligands. tons associated with the DPP ligand. Since it appears that
In particular, the av. Ge–S distance of 8 was found to be a monomer may be structurally favored for 2 in solution, it
2.21 Å which favorably compares to the GeIV–S literature would also follow that the more sterically demanding DPP
distances (av. 2.24 Å; range 2.19–2.412 Å)[65,94] and not with ligand of 3 would also favor a monomeric species in solu-
GeII–S terminal distances (av. 2.32 Å; range 2.26– tion.
2.37 Å).[65,79]
The mixed alkoxide/siloxide species 4, in CDCl3, pre-
sented an NMR spectra with singlets at δ = 1.41, 0.90, and
0.06 ppm, assigned to the OC(CH3)3, OSi(CH3)2[C(CH3)3],
and OSi(CH3)2[C(CH3)3] moieties, respectively. Two com-
plete set of 13C NMR resonances and a single 29Si NMR
resonance at δ = 15.5 ppm were found for 4. Combined it
is not possible to determine the nuclearity of 4; however,
since the previously reported [Ge(µ-OtBu)(TPS)]2 deriva-
tive[47] was reported to be dinuclear in solution, it is reason-
able to think 4 maintains the same central core in solution,
with the sterically less demanding DMBS in place of the
TPS. For compound 5 dissolved in CDCl3, the 1H (δ = 1.81
and 1.01 ππµ), 13C, and 29Si peak (δ = 15.5 ppm) revealed
only one set of DMBS tBu and methyl group resonances.
This indicates that 5 is a monomer in solution.
Elemental analyses of samples 1–8 revealed that the dried
bulk crystalline materials are in agreement with the single
crystal structures obtained for 1–8. For 6, it was necessary
to subtract the lattice toluene molecule from the elemental
composition to obtain an acceptable analysis.
Solution Behavior
Since these compounds are dissolved prior to nanocrys-
tal processing, it is of interest to understand the solution
behavior of these compounds. Therefore, crystalline materi-
als of 1–8 were individually dissolved in either [D8]tol or
CDCl3, flame-sealed in an NMR tube, and variable tem-
perature 1H NMR spectra (VT-NMR range –20 to +45 °C)
Compound 6 displayed a sharp singlet at δ = 6.49 ppm
1
obtained for each sample. No significant changes were which is farther upfield in comparison to the reported H
noted in the NMR spectra over this temperature range for shift of [Ge(H)(µ-O3SiR)]4 at δ = 5.83 ppm;[80] however, this
all of the samples, unless specifically discussed below.
data combined with the other analytical data and crystal
For 1, two sets of resonances were expected for the ethyl- structure solution, leads to the assignment of 6 as the hy-
ene and methylene protons based on the asymmetry gener- dride. Examination of 7, in CDCl3, lead to the identifica-
ated by the µc-DBED ligand. Upon dissolution in [D8]tol, tion of multiplets in the expected range of δ = 7.39–7.22.
singlets at δ = 4.00 and δ = 2.92 tentatively assigned to the Attempts to distinguish between mononuclear and dinu-
ethylene and methylene moieties, respectively were ob- clear species was undertaken using VT NMR; however, the
served. This indicates a monomer exists in solution; how- lack of dynamic behavior noted for 7 indicates that a single
ever, the 13C NMR spectroscopic data revealed two sets of species is most likely present in solution. While the 13C
resonances that substantiates that the solid-state structure NMR spectroscopic data was complex and did not add any
of 1 is maintained in solution. The dinuclear 2 in [D8]tol significant structural information, the 29Si singlet at δ
also displayed a broad singlet for the 2,6-methyl groups of –13.5 ppm argues for the presence of a monomer in solu-
the aryloxide at δ = 2.25 but in contrast to 1, the 13C spec- tion. Mononuclear 8 was found to have multiplets in the
trum revealed only one set of resonances, suggesting 2 fa- range of δ = 7.36–7.20 with no indication of a hydride reso-
vored a monomer in solution. However, VT-NMR studies nance. Table 1 lists the observed NMR solution behavior
on [Ge(µ-DIP)(DIP)]2 indicate that this compound main- for these precursors.
Table 1. Structural[a] and analytical data for 1–8.
Ligand type
Solid-state structure
Solution behavior Dec. temp. [°C] Nano morph. AR
EDS
PXRD
1
2
3
4
5
6
7
8
NR2
OR
OR
OR/OSiR3
OSiR3
OSiR3
SSiR3
SR
di
di
mono
di
di
180
200
200–300
130
110
200–280
260–400
230
ND
NW
NW
–
NW
NW
amorphous
–
1
Ge
Ge
Ge
–
Ge
Ge
Ge/S
–
Ge0/cubic
Ge0/cubic
Ge0/cubic
–
mono
mono
di
mono
mono
mono
mono
20
13
–
50
50
NA
–
[b]
di
Ge0/cubic
Ge0/cubic
amorphous
–
mono (+4)
di
mono (+4)
[a] AR = aspect ratio, ND = nanodot, NW = nanowire. [b] Not used as a precursor (–).
5554
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5550–5560

Germanium Nanomaterials
Thermal Gravimetric Analysis
The PXRD pattern of the products isolated from the re-
action of 1–3, and 5 were collected and found to be consis-
tent with Ge0 with a preferred crystalline cubic structure
(PDF # 04–0545), see Figure 10. Since the materials are
nanopowders, the resulting patterns were broad and due to
this fact, it is not possible to rule out the potential inclusion
of amorphous Ge nanomaterials in the resulting pow-
ders.[35,36] Transmission electron microscopy analyses were
obtained on these materials and their images are shown in
Figure 11 (a–e) for 1, 2, 3, and 5, respectively. The results
obtained in this work are consistent with the previously dis-
seminated efforts for production of Ge0.[10,11,21] For 1, the
nanoparticles isolated appear to be 5 nm in diameter and
agglomerated (Figure 11, a). In contrast compounds 2, 3,
and 5 formed nanowires with a diameter (d) and aspect ra-
tio (AR) for the compound given [d (nm)/AR]: 2 (14/20,
Figure 11, b); 3 (7/13, Figure 11, c); 5 (5–17 up to 50, Fig-
ure 11, d). EDS analyses confirmed that Ge was formed in
each sample. Additional powder XRD and EDS patterns
concerning these compounds can be found in the Support-
ing Information.
In order to gain insight into the decomposition tempera-
ture differences for these precursors and their suitability for
nanomaterials production, TGA data were collected for
each compound, values given in parentheses are temp.,
%wt.-loss/calcd. %wt.-loss: 1 (180 °C, 76/ 76), 2 (200 °C,
82/77), 3 (200–300 °C, 87/87), 4 (130 °C, 85/74), 5 (110 °C,
88/78), 6 (200–280 °C, 60/61), 7 (260 °C, 81/89), and 8
(230 °C, 83/86). In general, the data for 1–8 (see Figure 9)
indicated that the initiation of the organic decomposition
occurred at temperatures that were acceptable for the pre-
paratory routes of interest. It should also be noted that for
7, a lower than expected weight loss was observed which
may be explained by the cleavage of the Si–S linkage [i.e.,
loss of Si(C6H5), 79% weight loss], forming a Ge–S com-
plex, which gradually loses sulfur as the temperature, ex-
ceeds 400 °C. The metrical listing of the decomposition
temperature of these compounds is included in Table 1.
Figure 9. TGA of compounds 1–8.
Figure 10. Powder XRD of Ge0 nanocrystals from 1 and nanowires
from 5 showing the characteristic cubic germanium crystal struc-
ture.
Nanomaterials
With a set of acceptable precursors that were amenable
to our processing routes, the production of Ge0 nanomater-
ials was undertaken. The use of a simple solution route em-
With the successful production of Ge0 nanomaterials it
ploying the non-coordinating octadecene as the main sol- was of interest to compare these results with the previous
vent was selected for the ease of interpretation of any pos- GeII precursors[10,11,21] to elucidate any PSA influences. Un-
sible PSA phenomenon. The Ge precursors 1–8 isolated for der identical conditions, Ge[N(SiMe3)2]2 was found to pro-
this study varied in both structural and electronic configu- duce 5 nm Ge0 nanodots, whereas Ge(DBP)2 (DBP = 2,6-
ration, which made these a reasonable set of compounds to dibutylphenol) formed Ge0 nanowires av. 20 nm in diameter
begin our study. Compound 4 was removed from consider- (AR = 20).[21] It is of note that Ge[N(SiMe3)2]2 has been
ation, since a heteroleptic ligand set would lead to confu- reported to form ca. 60 nm wires from a chemical vapor
sion in what ultimately determined the final nanomaterial route when a SiCxNy shell is employed.[19] Compound 1
properties. Since both 6 and 8 were GeIV species, they were allowed for a direct comparison to the previous amide re-
not investigated in the initial study. Compounds 1–3 and 5– sults. High resolution TEM revealed that the resulting
7 were thought to be acceptable precursors and used for nanomaterials from 1 were a conglomerate of nanoparticles
Ge0 nanomaterials production. For each reaction, dried that were similar in shape and size of those generated by
crystalline powders of the respective precursors were used Ge[N(SiMe3)2]2.[21] Therefore, the diamine did not drasti-
to minimize any contamination of the final nanomaterials cally alter the morphological properties of the resultant
generated.
nanomaterials.[59,60,75]
Eur. J. Inorg. Chem. 2009, 5550–5560
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5555

T. J. Boyle, L. J. Tribby, L. A. M. Ottley, S. M. Han
FULL PAPER
Figure 11. TEM images of Ge-based nanomaterials synthesized from: (a) 1, (b) 2, (c) 3, (d) 5, (e) 6, (f) 7.
For the alkoxy ligated compounds 2 and 3, the decompo-
The thiol derivative 7 was also processed to determine
sition results were also found to be in-line with the previous how these thiol precursors would behave in our system.
Ge(DBP)2 complex.[21] The smaller wire diameters and Based on the TGA data, the silanethiolate 7 was expected
lengths noted for 3 suggests that the sterically demanding to follow a similar decomposition route as the previous
DPP ligand slows the nucleation and growth of the wires compounds and yield either a Ge0 or a Ge–S nanomaterial.
as compared to the DMP ligand of 2 or the DBP ligand After processing, a broad PXRD pattern of the materials
of Ge(DBP)2.[21] This slower nucleation and growth could generated from 7 indicated that an amorphous material had
reasonably be attributed to the two-step decomposition been formed. TEM analysis revealed no distinguishable
pathway of the DPP ligands noted in the TGA (Figure 9).
morphology (Figure 11, f) but EDS analysis indicated that
For 5, a significant difference in decomposition tempera- both Ge and S were present in the nanomaterials; therefore,
ture was noted for the homoleptic siloxide precursors. For the material is thought to be an amorphous GexSy material.
5, the GeII precursor’s low decomposition temperature and A higher processing temperature is obviously required to
lack of steric bulk would suggest that a dot morphology complete the decomposition/crystallization of 7.[95] These
should prevail. However, significant amounts of nanowires results also indicate that 7 was not suitable for Ge0 nanom-
were noted in the various TEM images which indicates that aterial syntheses.
the lower thermal decomposition temperatures noted in the
TGA (Figure 9) does not play a significant role in the final
morphological properties of these compounds in this sys-
tem. The nanowires’ lengths were under a micron but were
Summary and Conclusions
much longer than those formed from 2 and 3. Again, the
This study increased the number of structurally charac-
differing factor was the DMBS ligand, which suggests that terized GeII precursors synthesized from either a transami-
siloxides favor longer growth times based on slower decom- nation or alcoholysis metathesis reaction, including diamide
position, forming nanowires.
(1), alkoxide (2, 3), siloxide (4, 5), silanethiolate (7), as well
Due to the success of high AR nanowires formed by the as GeIV hydride-siloxide (6), and thiolate (8) derivatives.
siloxide of 5, coupled with the presence of the hydride, com- Upon thermal decomposition of these compounds, it was
pound 6 became of interest to determine if this GeIV pre- found that nanodots were observed for 1, while the majority
cursor could be converted in our system and how this ef- (2, 3, 5, and 6) of compounds formed nanowires (alkoxides:
fected the final morphologies observed. The GeIV siloxane AR = 20; siloxides: AR = 50). The variation between the
precursor 6, was expected to result in a wire-like material alkoxide and siloxide nanowire AR is of interest and further
due to the similar decomposition temperature and bulky work to understand the factors behind this phenomenon
alkoxy ligands of Ge(DBP)2. The PXRD pattern indicated are underway. The results from this study in general indicate
that Ge0 had indeed been produced and TEM analyses re- the PSA plays a role in the resulting nanoparticle mor-
vealed nanowires with widths that ranged from 5–25 nm phology;[21] however, it is also obvious from these results
with the larger diameter wires having an AR of up to 50 that additional parameters and experimental approaches
(Figure 11, e) had been formed. These AR are significantly are required to garner the desired control to generate tai-
longer than the nanowire lengths of 2 and 3, and indicate lored Ge0 nanomaterials. Studies are currently underway to
that there may be a significant advantage using siloxide pre- determine how further system adjustments (i.e., tempera-
cursors for nanowire production.
ture, reaction time, concentration, sterics, electronics, etc.)
5556
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5550–5560

Germanium Nanomaterials
[47,76]
[Ge(µ-OtBu)(DMBS)]2 (4): Used [Ge(OtBu)2]2
(0.440 g,
influence the decomposition of the prescribed precursors
and subsequent evolution of crystalline Ge-based nanomat-
erials.
1.00 mmol), H-DMBS (0.266 g, 2.01 mmol), in hexanes (≈ 5 mL);
yield 86.2% (0.480 g). FTIR (KBr pellet): ν = 2958 (w), 2931 (w),
˜
2894 (m), 2857 (m), 1467 (m), 1388 (m), 1365 (m), 1251 (w), 1177
(m), 952 (w), 891 (w), 833 (w), 775 (w), 727 (m), 673 (s), 603 (w)
cm–1. 1H NMR (250.0 MHz, CDCl3): δ = 1.41 [s, 9 H, OC(CH3)3],
0.90 [s, 9 H, OSi(CH3)2C(CH3)3], 0.06 [s, 6 H, OSi(CH3)2C(CH3)3]
ppm. C20H48Ge2O4Si2 (553.94): calcd. C 43.36, H 8.73; found C
43.08, H 8.71.
Experimental Section
General: All compounds described below were handled with rigor-
ous exclusion of air and water using standard Schlenk line and
glove box techniques. All solvents were stored under argon and
used as received (Aldrich) in SureSeal bottles, including hexanes
(hex), toluene (tol), [D8]toluene ([D8]tol), [D6]acetone, and [D]chlo-
roform (CDCl3). The following chemicals were used as received
(Aldrich): GeCl2·dioxane, LiN(SiMe3)2, H2-DBED, H-OtBu, H-
DMP, H-DPP, H-DMBS, H-TPS, H-TPST, H-PS, oleylamine, and
[Ge(µ-DMBS)(DMBS)]2 (5). Crystals were obtained by reduction
of solvent and subsequent refrigeration (–30 °C) over 24 h. Used
H-DMBS (0.232 g, 1.75 mmol), Ge(NR2)2 (0.345 g, 0.877 mmol),
in tol (≈ 5 mL); yield 97.0% (0.285 g). FTIR (KBr pellet): ν = 2954
˜
(w), 2933 (w), 2890 (w), 2859 (w), 2131 (m), 1468 (m), 1408 (s),
1391 (s), 1361 (s), 1255 (w), 956 (w), 836 (w), 805 (w), 779 (w), 725
(w), 679 (m), 593 (m), 541 (s) cm–1. 1H NMR (250.0 MHz, CDCl3):
δ = 1.81 [s, 9 H, OSi(CH3)2C(CH3)3], 1.01 [s, 6 H, OSi(CH3)2-
C(CH3)3] ppm. 29Si NMR (49.66 MHz, [D8]tol): δ = 15.5 [OSi-
(CH3)2C(CH3)3] ppm. 13C NMR (62.86 MHz, [D8]tol): δ = 25.9
[OSi(CH3)2C(CH3)3], 18.5 [OSi(CH3)2C(CH3)3], –2.50 [OSi(CH3)2-
C(CH3)3] ppm. C24H60Ge2O4Si4 (670.26): calcd. C 43.01, H 9.02;
found C 42.81, H 8.64.
[59,60,75]
[47,76]
octadecene. Ge[N(SiMe3)2]2
and [Ge(OtBu)2]2
were
synthesized according to literature reports.
General Synthesis: Due to the similarity of the following reactions
a general preparation is presented with specific details presented
for each reaction below. In a glovebox, the appropriate ligand was
dissolved in a minimum amount of toluene and added via pipette
to a stirring mixture of Ge(NR2)2 dissolved in toluene. After stir-
ring for 10 min, the resulting reaction mixture was set aside and
the volatile portion was allowed to slowly evaporate until light yel-
low or colorless X-ray quality crystals were isolated.
Ge(TPS)3(H) (6). Used H-TPS (1.98 g, 7.16 mmol), Ge(NR2)2
(0.939 g, 2.39 mmol), in tol (≈ 20 mL); yield 93.1% (2.00 g). FTIR
(KBr): ν = 3067 (m), 3050 (m), 3022 (w), 3012 (w), 2998 (w), 2130
˜
(m), 1588 (w), 1425 (s), 1115 (s), 971 (s), 721 (s), 696 (s), 591 (m),
510 (s) cm–1. H NMR (250.0 MHz, CDCl3): δ = 7.37 [d, JH,H
=
1
[Ge(µc-DBED)]2 (1): Used H2-DBED (0.198 g, 0.824 mmol),
Ge(NR2)2 (0.324 g, 0.824 mmol), in tol (≈ 5 mL); yield 55.0%
3.75 Hz, 2 H, OSiC(C6H5)3], 7.13 [m, 2 H, OSiC(C6H5)3], 6.49 (s,
1 H, H-Ge) ppm. C54H46GeO3Si3 (899.79): calcd. C 72.08, H 5.15;
found C 72.18, H 5.51.
(0.258 g). FTIR (KBr pellet): ν = 3064 (s), 3025 (m), 2912 (m),
˜
2885 (m), 2850 (w), 2821 (m), 2793 (m), 2770 (w), 1599 (s), 1491
(m), 1450 (w), 1356 (m), 1304 (m), 1211 (m), 1153 (w), 1065 (w),
1010 (m), 872 (w), 745 (w), 701 (w), 635 (w) cm–1. 1H NMR
(250.0 MHz, [D8]tol): δ = 7.13–7.23 [m, 10 H, (C6H5)CH2N(CH)2-
NCH2(C6H5)], 4.00 [s, 2 H, (C6H5)CH2N(CH)2NCH2(C6H5)], 2.92
[Ge(µ-TPST)(TPST)]2 (7). Colorless crystals were obtained by re-
duction of solvent and subsequent refrigeration (–30 °C) over 24 h.
Used H-TPST (0.931 g, 1.59 mmol), Ge(NR2)2 (0.313 g,
0.796 mmol), in tol (≈ 5 mL); yield 75.2% (0.392 g). FTIR (KBr
[s,
4
H, (C6H5)CH2N(CH)2NCH2(C6H5)] ppm. 13C NMR
pellet): ν = 3357 (w), 3072 (m), 3048 (m), 3024 (w), 3013 (w), 2998
˜
(62.86 MHz, CDCl3): δ = 141.5, 129.0, 128.5, 128.4, 128.3, 127.1,
126.8 (C6H5)CH2N(CH)2NCH2(C6H5), 54.4, 54.1, 52.4, 49.4,
(C6H5)CH2N(CH)2NCH2(C6H5) ppm. C32H36Ge2N4 (621.83):
calcd. C 61.81, H 5.84, N 9.01; found C 62.14, H 5.72, N 9.16.
(w), 2958 (m), 2896 (w), 2855 (w), 1429 (s), 1116 (s), 736 (m), 702
(s), 534 (s), 514 (s), 503 (s), 486 (m) cm–1. H NMR (250.0 MHz,
1
CDCl3): δ = 7.39 [d, JH,H = 3.75 Hz, 6 H, SSi(C6H5)3], 7.31 [m, 6
H, SSi(C6H5)3], 7.22 [m, 3 H, SSi(C6H5)3] ppm. 29Si NMR
(49.66 MHz, CDCl3):
C72H60Ge2S4Si4 (1310.98): calcd. C 65.96, H 4.61; found C 65.33,
H 4.57.
δ
=
–13.50 [SSi(C6H3)3] ppm.
[Ge(µ-DMP)(DMP)]2 (2): Used H-DMP (0.191 g, 1.56 mmol),
Ge(NR2)2 (0.308 g, 0.782 mmol), in tol (≈ 5 mL); yield 90.8%
(0.224 g). FTIR (KBr pellet): ν = 3038 (m), 3019 (m), 2978 (m),
˜
2951 (m), 2914 (m), 2856 (m), 1590 (m), 1468 (w), 1262 (w), 1195
(w), 1168 (w), 1091 (w), 840 (w), 830 (w), 773 (w), 761 (w), 741
(w), 693 (w), 680 (w), 611 (m), 584 (w), 535 (m), 525 (m), 437 (w)
Ge(PS)4 (8): After mixing, the solution produced a deep red oil
with a light red solution. The light red solution was decanted off
and allowed to dry in the glovebox atmosphere to produce X-ray
quality crystals. Used H-PS (0.445 g, 5.12 mmol), Ge(NR2)2
(0.503 g, 1.28 mmol), in tol (≈ 10 mL); yield 62.3% (0.407 g). FTIR
1
cm–1. H NMR (250.0 MHz, [D8]tol): δ = 7.00 [d, JH,H = 3.75 Hz,
2 H, OC6H3(CH3)2], 6.73 [m, 1 H, OC6H3(CH3)2], 2.25 [s, 6 H,
OC6H3(CH3)2] ppm. 13C NMR (62.86 MHz, CDCl3): δ = 152.2,
129.8, 129.0, 123.7 [OC6H3(CH3)2], 17.4 [OC6H3(CH3)2] ppm.
C32H36Ge2O4 (629.79): calcd. C 61.03, H 5.76; found C 60.57, H
5.96.
(KBr): ν = 3072 (w), 3053 (w), 2961 (m), 2924 (m), 2853 (w), 1577
˜
(m), 1474 (m), 1466 (m), 1437 (m), 1095 (s), 1079 (s), 1022 (s), 737
(s), 688 (s) cm–1. 1H NMR (250.0 MHz, CDCl3): δ = 7.36–7.20 (m,
5 H, SC6H5) ppm. C24H20GeS4 (509.23): calcd. C 56.61, H 3.96;
found C 56.69, H 3.64.
Ge(DPP)2 (3): Used H-DPP (0.623 g, 2.53 mmol), Ge(NR2)2
(0.498 g, 1.27 mmol), in tol (≈ 5 mL); yield 80.6% (0.575 g). FTIR
Precursor Characterization: Fourier Transform Infrared (FTIR)
(KBr pellet): ν = 3080 (s), 3060 (m), 3051 (m), 3034 (s), 1595 (m), spectroscopic data were obtained on a Bruker Vector 22 Instrument
˜
1493 (m), 1455 (w), 1439 (m), 1408 (w), 1276 (m), 1241 (m), 1216 using KBr pressed pellets with bulk material, under an atmosphere
(w), 1085 (m), 1071 (m), 1028 (m), 842 (w), 761 (w) 746(w), 701 of flowing nitrogen. Elemental analyses were performed on a Per-
(w), 637 (w), 625 (m), 609 (w), 586 (m) cm–1. 1H NMR (250.0 MHz,
kin–Elmer 2400 CHN-S/O Elemental Analyzer. Reported nuclear
CDCl3): δ = 7.56 [d, JH,H = 3.75 Hz, 4 H, OC6H3(C6H5)2], 7.45 [m,
magnetic resonance (NMR) spectroscopic data were collected on a
4 H, OC6H3(C6H5)2], 7.36 [m, 2 H, OC6H3(C6H5)2], 7.28 [d, JH,H 250 MHz Bruker instrument using crystalline material dissolved in
1
= 3.75 Hz, 2 H, OC6H3(C6H5)2], and 7.04 [m, 1 H, OC6H3-
(C6H5)2] ppm. C36H26GeO2 (563.16): calcd. C 76.78, H 4.65; found
C 77.36, H 4.92.
[D8]tol or CDCl3. The H and 13C NMR spectroscopic data were
referenced against the residual protonated solvent, and 5% TMS
in [D6]acetone for 29Si NMR spectroscopy. Thermogravimetric
Eur. J. Inorg. Chem. 2009, 5550–5560
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5557

T. J. Boyle, L. J. Tribby, L. A. M. Ottley, S. M. Han
FULL PAPER
analyses (TGA) were collected by a TA Instruments SDT Q600 on
crystalline materials from room temperature to 700 °C at a 10 °C/
min heating rate, under a flowing atmosphere of nitrogen.
bic space group. In the case of 8, it should be noted that the sele-
nium analog Ge(SePh)4, where Ph = C6H5, also shares the same
non-centrosymmetric orthorhombic space group Pba2.[96] For com-
pound 6, a toluene molecule was located in the crystal lattice but
due to significant disordering it was squeezed out to improve re-
finement values using the Platon (v. 1.11, 2007) program.
General Single Crystal X-ray Structure Information: Crystals were
mounted onto a glass fiber from a pool of Fluorolube and imme-
diately placed in a cold N2 vapor stream, on a Bruker AXS dif-
fractometer equipped with a SMART 1000 CCD detector using
graphite monochromatized Mo-Kα radiation (λ = 0.7107 Å). Lat-
tice determination and data collection were carried out using
SMART Version 5.054 software. Data reduction was performed
using SAINTPLUS Version 6.01 software and corrected for ab-
sorption using the SADABS program within the SAINT software
package.
CCDC-705319 to -705326 contain the supplementary crystallo-
graphic data for 1–8, respectively. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Nanoparticle Synthesis: The dried crystalline precursor (1.00 mmol)
was dissolved in oleylamine and then rapidly injected into a solu-
tion of octadecene (10.0 mmol) preheated to 315 °C. The reaction
temperature was maintained at 315 °C for 30 min and allowed to
cool to room temperature. An aliquot of the Ge nanomaterial solu-
tion was dissolved in CHCl3 and precipitated using MeOH, which
was collected by centrifugation. After washing in this manner a
minimum of three times, the collected Ge nanomaterials were dis-
persed in CHCl3 and a drop was placed onto a TEM grid for subse-
quent analyses. It should be noted that size-selective precipitation
methods were not utilized for TEM analyses.
Structures were solved by direct methods that yielded the heavy
atoms, along with a number of the lighter atoms or by using the
PATTERSON method, which yielded the heavy atoms. Subsequent
Fourier syntheses yielded the remaining light-atom positions. The
hydrogen atoms were fixed in positions of ideal geometry and re-
fined using SHELXS software. The final refinement of each com-
pound included anisotropic thermal parameters for all non-hydro-
gen atoms. All final CIF files were checked at http://www.iucr.org/.
Data collection parameters for 1–8 are given in Table 2. It is of note
that crystal structures of M(OR)x often contain disorder within
the atoms of the pendant hydrocarbon chain, causing higher final
correlations than is typically observed for other metalorganic struc-
ture solutions.[66–71] The structures of 2 and 8 were solved with
well-behaved thermal ellipsoids in the non-centrosymmetric ortho-
rhombic space groups Pca21 and Pba2, respectively. For 2, the ar-
rangement of DMP ligands in a trans fashion prohibits a mirror
plane from bisecting the bridging DMP ligands in the orthorhom-
Nanoparticle Characterization: Powder X-ray diffraction (XRD)
was performed by a PANalytical X’Pert Pro XRD in the 2θ range
of 15–75° at a scan rate of 0.06°/s on drop-deposited Ge nanomat-
erials using a zero background holder. Transmission electron mi-
croscopy (TEM) analyses were performed on a JEOL JEM-2010
electron microscope equipped with an Oxford Instruments Energy
Dispersive X-ray Spectroscopic (EDS) detector.
Supporting Information (see also the footnote on the first page of
this article): Powder XRD patterns for 2, 3, 4, and 6.
Table 2. Crystal structure determination data collection parameters for 1–8.
Compound
1
2
3
4
Empirical formula
Formula weight
Temperature [K]
Space group
a [Å]
b [Å]
c [Å]
C32H36Ge2N4
621.83
144(2)
monoclinic, P21/n
8.7362(8)
9.1574(8)
18.7120(16)
95.9070(10)
1489.0(2)
2
1.386
2.045
6.02 (6.32)
11.47 (11.59)
C32H36Ge2O4
629.79
203(2)
orthorhombic, Pca21
17.014(5)
10.879(3)
C36H26GeO2
563.16
203(2)
orthorhombic, Pccn
22.0568(19)
11.0189(9)
11.6412(10)
C20H48Ge2O4Si2
553.94
173(2)
monoclinic, C2/c
23.361(3)
14.455(2)
16.994(2)
90.344(2)
5738.5(14)
8
1.282
2.198
3.41 (4.97)
8.25 (9.18)
16.282(5)
β [°]
V [Å3]
3013.7(15)
4
1.388
2.028
6.15 (7.74)
11.78 (12.37)
2829.3(4)
4
1.324
1.115
2.85 (3.36)
7.41 (7.74)
Z
Dcalcd. [mg/m3]
µ(Mo-Kα) [mm–1]
[a]
R1 (%) (all data)
[b]
wR2 (%) (all data)
Compound
5
6
7
8
Empirical formula
Formula weight
Temperature [K]
Space group
a [Å]
b [Å]
c [Å]
C24H60Ge2O4Si4
670.26
203(2)
monoclinic, P21/c
10.948(4)
14.225(5)
23.645(8)
90.336(5)
3682.0(2)
4
1.209
1.786
7.71 (11.91)
19.49 (21.60)
C54H46GeO3Si3
899.79
203(2)
monoclinic, P21/n
21.580(3)
9.9527(11)
24.529(3)
113.988(2)
4813.4(9)
4
1.242
0.753
4.80 (7.02)
10.69 (11.54)
C72H60Ge2S4Si4
1310.98
203(2)
monoclinic, C2/c
31.370(3)
9.2183(9)
23.357(2)
105.996(2)
6492.7(11)
4
1.341
1.170
5.59 (6.80)
11.27 (11.77)
C24H20GeS4
509.23
203(2)
orthorhombic, Pba2
8.595(5)
16.852(10)
8.142(5)
β [°]
V [Å3]
1179.3(12)
2
1.434
1.661
4.69 (6.35)
7.10 (7.65)
Z
Dcalcd. [mg/m3]
µ(Mo-Kα) [mm–1]
[a]
R1 (%) (all data)
[b]
wR2 (%) (all data)
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|ϫ100. [b] wR2 = [Σw(Fo – Fc ) /Σ (w|Fo|2)2]1/2 ϫ100.
2
2 2
5558
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5550–5560

Germanium Nanomaterials
[29] R. S. Wagner, W. C. Ellis, Appl. Phys. Lett. 1964, 4, 89–90.
[30] N. Zaitseva, J. Harper, D. Gerion, C. Saw, Appl. Phys. Lett.
2005, 86, 053105.
Acknowledgments
This work was partially funded by the National Science Founda-
tion (NSF) under Grant NSF CBET-0756776, the Office of Basic
Energy Sciences of the Department of Energy, and the National
Institutes of Health (NIH) through the NIH Roadmap for Medical
Research Grant #1 R21 EB005365-01. Information on this RFA
(Innovation in Molecular Imaging Probes) can be found at http://
[31] D. W. Wang, H. J. Dai, Angew. Chem. Int. Ed. 2002, 41, 4783–
4786.
[32] H. Gerung, S. D. Bunge, T. J. Boyle, C. J. Brinker, S. M. Han,
Chem. Commun. 2005, 1914–1916.
[33] Y. N. Xia, P. D. Yang, Y. G. Sun, Y. Y. Wu, B. Mayers, B. Gates,
Y. D. Yin, F. Kim, Y. Q. Yan, Adv. Mater. 2003, 15, 353–389.
J. Heath, F. Legoues, Chem. Phys. Lett. 1993, 208, 263–268.
[35] B. R. Taylor, S. M. Kauzlarich, H. W. H. Lee, G. R. Delgado,
grants.nih.gov/grants/guide/rfa-files/RFA-RM-04-021.html. Sandia [34]
is a multiprogram laboratory operated by Sandia Corporation, a
Lockheed Martin Company, for the United States Department of
Energy under contract DE-AC04-94AL85000.
Chem. Mater. 1998, 10, 22–24.
[36] M. Xuchu, W. Fengyi, S. M. Kauzlarich, J. Solid State Chem.
2008, 181, 1628–1633.
[37] A. J. Bard, R. Parsons, J. Jordan, in: Standard Potentials in
Aqueous Solutions, IUPAC, New York, 1985.
[1] X. An, R. Huang, X. Zhang, Y. Wang, Semicond. Sci. Technol.
2005, 20, 1034–1038.
[2] A. Khakifirooz, D. A. Antoniadis, Electron Device Lett. 2004,
25, 80–82.
[3] L. J. Lauhon, M. S. Gudiksen, C. L. Wang, C. M. Lieber, Na-
ture 2002, 420, 57–61.
[4] C. H. Tu, T. C. Chang, P. T. Liu, C. F. Weng, H. C. Liu, L. T.
Chang, S. K. Lee, W. R. Chen, S. M. Sze, C. Y. Chang, J. Elec-
trochem. Soc. 2007, 154, H435–H439.
[5] K. Gacem, A. El Hdiy, M. Troyon, I. Berbezier, P. D. Szkutnik,
A. Karmous, A. Ronda, J. Appl. Phys. 2007, 102, 093704–
093707.
[6] M. Kanoun, C. Busseret, A. Poncet, A. Souifi, T. Baron, E.
Gautier, Solid State Electron. 2006, 50, 1310–1314.
[7] A. D. Pasquier, D. D. T. Mastrogiovanni, L. A. Klein, T. Wang,
E. Garfunkel, Appl. Phys. Lett. 2007, 91, 183501–183503.
[8] R. Wang, Z. L. Guo, G. P. Wang, Sol. Energy Mater. Sol. Cells
2006, 90, 1052–1057.
[38] T. J. Boyle, B. A. Hernandez-Sanchez, C. M. Baros, M. A. Rod-
riguez, L. N. Brewer, Chem. Mater. 2007, 19, 2016–2026.
[39] T. J. Boyle, S. D. Bunge, T. M. Alam, G. P. Holland, T. J. Head-
ley, G. Avilucea, Inorg. Chem. 2005, 44, 1309–1318.
[40] T. J. Boyle, S. D. Bunge, N. L. Andrews, L. E. Matzen, K. Sieg,
M. A. Rodriguez, T. J. Headley, Chem. Mater. 2004, 16, 3279–
3288.
[41] C. Stanciu, M. Stender, A. F. Richards, M. M. Olmstead, P. P.
Power, Inorg. Chem. 2005, 44, 2774–2780.
[42] F. H. Allen, Acta Crystallogr., Sect. B 2002, 58, 380–388.
[43] C. Stanciu, A. F. Richards, M. Stender, M. M. Olmstead, P. P.
Power, Polyhedron 2006, 25, 477–483.
[44] L. W. Pineda, V. Jancik, K. Starke, R. B. Oswald, H. W. Roesky,
Angew. Chem. Int. Ed. 2006, 45, 2602–2605.
[45] C. S. Weinert, A. E. Fenwick, P. E. Fanwick, I. P. Rothwell,
Dalton Trans. 2003, 532–539.
[46] P. Bazinet, G. P. A. Yap, D. S. Richeson, J. Am. Chem. Soc.
2001, 123, 11162–11167.
[47] M. Veith, C. Mathur, V. Huch, J. Chem. Soc., Dalton Trans.
1997, 995–999.
[48] A. Meller, G. Ossig, W. Maringgele, M. Noltemeyer, D. Stalke,
R. Herbst-Irmer, S. Freitag, G. M. Sheldrick, Z. Naturforsch.
B: Chem. Sci. 1992, 47.
[49] T. Fjeldberg, P. B. Hitchcock, M. F. Lappert, S. J. Smith, A. J.
Thorne, J. Chem. Soc., Chem. Commun. 1985, 939–941.
[50] M. F. Lappert, M. J. Slade, J. L. Atwood, M. J. Zaworotko, J.
Chem. Soc., Chem. Commun. 1980, 621–622.
[51] B. Cetinkaya, I. Gumrukcu, M. F. Lappert, J. L. Atwood,
R. D. Rogers, M. J. Zaworotko, J. Am. Chem. Soc. 1980, 102,
2088–2089.
[52] F. E. Hahn, A. V. Zabula, T. Pape, A. Hepp, Eur. J. Inorg.
Chem. 2007, 2405–2408.
[53] M. Driess, S. Yao, M. Brym, C. van Wullen, Angew. Chem. Int.
Ed. 2006, 45, 4349–4352.
[54] W. A. Herrmann, M. Denk, J. Behm, W. Scherer, F.-R. Klin-
gan, H. Bock, B. Solouki, M. Wagner, Angew. Chem. Int. Ed.
Engl. 1992, 31, 1485–1488.
[55] I. L. Fedushkin, A. A. Skatova, V. A. Chudakova, N. M.
Khvoinova, A. Y. Baurin, S. Dechert, M. Hummert, H. Schum-
ann, Organometallics 2004, 23, 3714–3718.
[9] M. P. Deshmukh, J. Nagaraju, Sol. Energy Mater. Sol. Cells
2005, 89, 403–408.
[10] H. Gerung, T. J. Boyle, Y. Zhao, L. Wang, R. K. Jain, S. M.
Han, Appl. Phys. Lett. 2006, 89, 111107–111109.
[11] T. N. Lambert, N. L. Andrews, H. Gerung, T. J. Boyle, J. M.
Oliver, B. S. Wilson, S. M. Han, Small 2007, 3, 691–699.
[12] B. A. Hernandez-Sanchez, T. J. Boyle, T. N. Lambert, S. D.
Daniel-Taylor, J. M. Oliver, B. S. Wilson, D. S. Lidke, N. L. An-
drews, IEEE Trans. Nanobiosci. 2006, 5, 222–230.
[13] S. M. Sze, in: Physics of Semiconductor Devices, 2nd ed., John
Wiley & Sons, New York, 2002.
[14] R. Rosetti, R. Hull, J. M. Gibson, L. E. Brus, J. Chem. Phys.
1985, 83, 1406–1410.
[15] T. Takagahara, K. Takeda, Phys. Rev. B 1992, 46, 15578–15581.
[16] D. V. Melnikov, J. R. Chelikowsky, Solid State Commun. 2003,
127, 361–365.
[17] C. Bostedt, T. van Buuren, T. M. Willey, N. Franco, L. J. Term-
inello, C. Heske, T. Moller, Appl. Phys. Lett. 2004, 84, 4056–
4058.
[18] J. H. Warner, R. D. Tilley, Nanotechnology 2006, 17, 3745–
3749.
[19] S. Mathur, H. Shen, N. Donia, T. Rugamer, V. Sivakov, U. Wer-
ner, J. Am. Chem. Soc. 2007, 129, 9746–9752.
[20] D. Gerion, N. Zaitseva, C. Saw, M. F. Casula, S. Fakra, T.
Van Buuren, G. Galli, Nano Lett. 2004, 4, 597–602.
[21] H. Gerung, T. J. Boyle, L. J. Tribby, S. D. Bunge, C. J. Brinker,
S. M. Han, J. Am. Chem. Soc. 2006, 128, 5244–5250.
[22] Y. Y. Wu, P. D. Yang, Chem. Mater. 2000, 12, 605.
[23] S. Mathur, H. Shen, V. Sivakov, U. Werner, Chem. Mater. 2004,
16, 2449.
[24] A. M. Morales, C. M. Lieber, Science 1998, 279, 208–211.
[25] T. Hanrath, B. A. Korgel, J. Am. Chem. Soc. 2002, 124, 1424–
1429.
[26] T. Hanrath, B. A. Korgel, Adv. Mater. 2003, 15, 437–440.
[27] P. S. Shah, T. Hanrath, K. P. Johnston, B. A. Korgel, J. Phys.
Chem. B 2004, 108, 9574–9587.
[56]
[57]
[58]
O. Kuhl, P. Lonnecke, J. Heinicke, Polyhedron 2001, 20, 2215–
2222.
T. Gans-Eichler, D. Gudat, K. Nattinen, M. Nieger, Chem. Eur.
J. 2006, 12, 1162–1173.
A. V. Zabula, F. E. Hahn, T. Pape, A. Hepp, Organometallics
2007, 26, 1972–1980.
[59]
[60]
A. Schnepf, Z. Anorg. Allg. Chem. 2006, 632, 935–938.
R. W. Chorley, P. B. Hitchcock, M. F. Lappert, W.-P. Leung,
P. P. Power, M. M. Olmstead, Inorg. Chim. Acta 1992, 198, 203.
M. Veith, A. Rammo, Z. Anorg. Allg. Chem. 2001, 627, 662–
668.
Y. Q. Ding, Q. J. Ma, H. W. Roesky, R. Herbst-Irmer, I. Uson,
M. Noltemeyer, H. G. Schmidt, Organometallics 2002, 21,
5216–5220.
[61]
[62]
[28] T. Hanrath, B. A. Korgel, J. Am. Chem. Soc. 2004, 126, 15466–
15472.
Eur. J. Inorg. Chem. 2009, 5550–5560
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5559

T. J. Boyle, L. J. Tribby, L. A. M. Ottley, S. M. Han
FULL PAPER
[63] N. N. Zemlyansky, I. V. Borisova, M. G. Kuznetsova, Organo-
metallics 2003, 22, 1675–1681.
[64] W.-P. Leung, K.-W. Kan, C.-W. So, T. C. Mak, Appl. Or-
ganomet. Chem. 2007, 21, 814–818.
[65] B. Kersting, B. Krebs, Inorg. Chem. 1994, 33, 3886–3892.
[66] D. C. Bradley, Chem. Rev. 1989, 89, 1317–1322.
[67] D. C. Bradley, R. C. Mehrotra, D. P. Gaur, Metal Alkoxides,
Academic Press, New York, 1978.
[68] K. G. Caulton, L. G. Hubert-Pfalzgraf, Chem. Rev. 1990, 90,
969–995.
[69] C. D. Chandler, C. Roger, M. J. Hampden-Smith, Chem. Rev.
1993, 93, 1205–1241.
[70] L. G. Hubert-Pfalzgraf, New J. Chem. 1987, 11, 663–675.
[71] N. Y. Turova, E. P. Turevskaya, V. G. Kessler, M. I. Yanov-
skaya, The Chemistry of Metal Alkoxides, Kluwer Academic
Publishers, Boston, 2002.
[72] T. J. Boyle, L. J. Tribby, S. D. Bunge, Eur. J. Inorg. Chem. 2006,
4553–4563.
[73] M. F. P. Lappert, P. P. Sanger, A. R. Srivastava, R. C. in: Metal
and Metalloid Amides, Halsted Press, Chichester, U. K., 1980.
[74] P. A. G. O’Hare, L. A. Curtiss, J. Chem. Thermodynamics 1995,
27, 643–662.
[81]
S. Patai, Z. Rappoport, in: The Chemistry of Organic Germa-
nium, Tin and Lead Compounds, vol. 1–2, John Wiley & Sons,
New York, 1995–2002.
M. F. Lappert, J. L. Atwood, M. J. Zaworotko, A. J. Carty, J.
Organomet. Chem. 1981, 212, C4–C6.
M. Lesbre, P. Mazerolles, J. Satgé in The Organic Compounds
of Germanium, Wiley-Interscience, New York, 1971, p. 702.
A. E. Weatherby Jr., L. R. Goeller, A. G. DiPasquale, A. L.
Rheingold, C. S. Weinert, Inorg. Chem. 2007, 46, 7579–7586.
C. S. Weinert, Main Group Met. Chem. 2007, 30, 93–100.
G. Ossig, A. Meller, C. Bronneke, O. Muller, M. Schafer, R.
Herbst-Irmer, Organometallics 1997, 16, 2116–2120.
U. Herzog, U. Bohme, E. Brendler, G. Rheinwald, J. Or-
ganomet. Chem. 2001, 630, 139–148.
U. Herzog, G. Rheinwald, Organometallics 2001, 20, 5369–
5374.
U. Herzog, H. Borrmann, J. Organomet. Chem. 2003, 675, 42–
47.
H. A. Klasens, H. J. Backer, Recueil Trav. Chim. Pays-Bas
1939, 58, 941–947.
J. Pfeiffer, M. Noltemeyer, A. Meller, Z. Anorg. Allg. Chem.
1989, 572, 145–150.
D.-H. Chen, H.-C. Chiang, C.-H. Ueng, Inorg. Chim. Acta
1993, 208, 99–101.
R. R. Holmes, R. O. Day, A. C. Sau, J. M. Holmes, Inorg.
Chem. 1986, 25, 600–606.
J. E. Drake, A. G. Mislanker, J. Yang, Inorg. Chem. 1992, 31,
5543–5548.
A. Perakis, I. P. Kotsalas, E. A. Pavlatou, C. Raptis, Phys. Stat.
Sol.. B 1999, 211, 421–427.
H. J. Gysling, H. R. Luss, Organometallics 1989, 8, 363–368.
[82]
[83]
[84]
[85]
[86]
[87]
[88]
[89]
[90]
[91]
[92]
[93]
[94]
[95]
[96]
[75] P. J. Davidson, D. H. Harris, M. F. Lappert, J. Chem. Soc., Dal-
ton Trans. 1976, 2268–2274.
[76] M. Veith, J. Hans, L. Stahl, P. May, V. Huch, A. Sebald, Z.
Naturforsch., Teil B 1991, 16, 403–424.
[77] G. D. Smith, P. E. Fanwick, I. P. Rothwell, Inorg. Chem. 1990,
29, 3221–3226.
[78] A. Krivokapic, H. L. Anderson, G. Bourhill, R. Ives, S. Clark,
K. J. McEwan, Adv. Mater. 2001, 13, 652–656.
[79] M. Veith, P. Hobein, R. Rosler, Z. Naturforsch. B: Chem. Sci.
1989, 44, 1067–1081.
[80] U. N. Nehete, V. Chandrasekhar, H. W. Roesky, J. Magull, An-
gew. Chem. Int. Ed. 2005, 44, 281–284.
Received: June 18, 2009
Published Online: November 9, 2009
5560
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5550–5560