Simple and efficient: Gold nanoparticles from triphenylphosphane gold(I) carboxylates without addition of any further stabilizing and reducing agent

Article abstract of DOI:10.1016/j.inoche.2011.02.003

An innovative and straightforward methodology for the generation of gold nanoparticles (= NP) from [(Ph₃P)-AuO₂CCH ₂(OCH₂CH₂)₂OCH₃] without addition of any further stabilizing and reducing reagents is reported; particles of size 3-6 nm (average diameter 4 nm) with narrow size distribution are obtained.

Full text of DOI:10.1016/j.inoche.2011.02.003

Inorganic Chemistry Communications 14 (2011) 676–678
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Simple and efficient: Gold nanoparticles from triphenylphosphane gold(I)
carboxylates without addition of any further stabilizing and reducing agent
André Tuchscherer a, Dieter Schaarschmidt a, Steffen Schulze b, Michael Hietschold b, Heinrich Lang a,
⁎
a
Faculty of Natural Sciences, Department of Inorganic Chemistry, Chemnitz University of Technology, Straße der Nationen 62, 09111 Chemnitz, Germany
b
Faculty of Natural Sciences, Department of Solid Surfaces Analysis, Chemnitz University of Technology, Reichenhainer Strasse 70, 09126 Chemnitz, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
An innovative and straightforward methodology for the generation of gold nanoparticles (= NP) from
[(Ph3P)-AuO2CCH2(OCH2CH2)2OCH3] without addition of any further stabilizing and reducing reagents is
reported; particles of size 3–6 nm (average diameter 4 nm) with narrow size distribution are obtained.
© 2011 Elsevier B.V. All rights reserved.
Received 19 January 2011
Accepted 12 February 2011
Available online 19 February 2011
Keywords:
Gold
Nanoparticle
Thermolysis
Carboxylate
Transition metal nanoparticles (= NP) are of high interest in many
applications [1], due to their unique optical [2,3], electrical [4],
magnetical [5], and catalytical [6] properties depending on the size,
shape, and size distribution [7]. In particular, group-11 metal NP allow
the design of new generations of nanodevices and smart materials [8–
10]. Nanostructured metal colloids can be obtained by top-down or
bottom-up methodologies [11–13]. The latter method includes mainly
electrochemical [14] and photochemical [7,15] pathways. The most
common and efficient synthesis strategy in this field is the chemical
reduction of metal ions to zerovalent metal NP in aqueous [16,17] or
organic solvents [18]. As stabilizing components mostly ethylene
glycols [19,20] and polymers/co-polymers [21] or dendrimers [22]
with donating functionalities including N, P, S, and O donor atoms are
used.
We here discuss a novel methodology to form gold NP with size
diameter of 3–6 (+/-1) nm using [(Ph3P)AuO2CCH2(OCH2CH2)2-
OCH3] (3) [23] as starting material. The formation of the NP was
carried out by thermolysis at relative low temperature, whereas no
further stabilizing and even reducing agent was necessary.
Molecule 3 is accessible by the reaction of [(Ph3P)AuCl] (1) with
the silver carboxylate [AgO2CCH2(OCH2CH2)2OCH3] [24] (2) in tolu-
ene at ambient temperature (Scheme 1). Compound 3 was charac-
terized by elemental analysis, IR and NMR spectroscopy and mass-
spectrometry [23]. Complex 3 crystallized in the triclinic space group
ethoxy]acetato ligand do not show any distinctive features (Fig. 1)
[25].
The thermal decomposition of 3 was studied by thermogravimetric
and differential scanning calorimetric experiments to obtain first infor-
mation of the decomposition behavior of 3 (Fig. 2). Decomposition of 3 is
observed at 232 °C, the overall mass diminution with 68.8% corresponds
to the formation of elemental gold (Δm/m0=69.0%, theoretical). The
melting point of 3 was determined by DSC experiments (133 °C). The
decomposition of 3 shows an overlay of various exothermic and
endothermic processes (Fig. 2). From TG–MS coupling experiments the
formation of CO2, PPh3 and ethylene glycol fragments were observed
which indicated the cleavage of the Au―O bond. Most probably, the in-
situ formed organic and inorganic species are responsible for the narrow
size distribution of the Au NP. Obviously, the thermal induced
decomposition of 3 follows a similar mechanism as found for akin silver
species [26].
Based on these studies we choose mesitylene as organic solvent for
the thermal decomposition of 3 to generate Au NP, due to its high
boiling point and non-coordinating behavior. In a typical experiment a
6.3×10−3 mol/l mesitylene solution containing 3 was heated to reflux
for 10 min. The color of the solution turned from colorless to intensive
purple which indicates the formation of gold NP. The UV-vis spectrum
shows a plasmon band at 523 nm (Fig. 3). This result evinces that
metal-organic 3 decomposes in solution at much lower temperature as
found in the solid state (vide supra). TEM analyses gave an average size
diameter of 4.0 (+/-1) nm with a sharp size distribution (Fig. 4). In
addition, we carried out further thermolysis experiments at lower
temperatures. At 138 °C (para-xylene) the reaction time increased to
1 h and at 111 °C (toluene) to 24 h, which shows that NP generation
decelerates with decreasing reaction temperature. The received NP size
P1̄. The P1―Au1―O1 unit is almost linear (177.5°), the Au―P, Au―O
as well as the C―C and C―O distances of the 2-[2-(2-methoxyethoxy)
⁎
Corresponding author. Tel.: +49 371 531 21210; fax: +49 371 531 21219.
E-mail address: heinrich.lang@chemie.tu-chemnitz.de (H. Lang).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.02.003

A. Tuchscherer et al. / Inorganic Chemistry Communications 14 (2011) 676–678
677
O
Ag
O
O
O
O
3
3
- AgCl
3
3
- CO2
Scheme 1. Synthesis of 3 and thermal induced generation of Au-NP; schematic view of stabilized Au-NP by the in-situ generated organic/inorganic matrix.
Fig. 1. ORTEP diagram (50% probability level) of the molecular structure of 3 with the atom-numbering scheme. All hydrogen and disordered atoms are omitted for clarity. Bond
distances (Å) and angles (°): Au1―P1 2.214(3), Au1―O1 2.079(7), C1―O1 1.307(13), C1―O2 1.210(14); P1―Au1―O1 177.5(3), O1―C1―O2 125.3(11), C1―O1―Au1 113.3(7).
diameters are with 3.9 (+/-1) and 4.0 (+/-1) nm similar to the results
obtained at 168 °C. The formation of gold NP at lower temperatures
(benzene, 80 °C) could not be observed, which indicates that for NP
formation from 3 a certain temperature is required. The thus formed NP
are stable about several weeks in solution. The removal of the solvent
gives a deep purple viscous residue which is able to re-disperse.
The NP size and size distribution are obviously not influenced by the
reaction temperature but probably by the glycol chain and its decompo-
sition products. Changing the concentration from 7.8⋅10-4 mol/l (3.8
(+/-0.6) nm) to 1.6⋅10-2 mol/l (4.4 (+/-0.5) nm) shows a slightly
enlargement of the average NP size.
Transmission electron microscopy (TEM) data show that homo-
geneous, conformal NP were formed (Fig. 4).
Most likely after thermal induced decarboxylation of 3 the thus
formed organic species recombine to form the ethylene glycols which
acts as stabilizing component for the in-situ formed gold colloids. The
formation of ethylene glycol derivatives could be determined by 1H
NMR studies, where it was found that during decomposition the in-
situ generated Au NP are stabilized by ethylene glycol fragments as
well as non-decomposed [(Ph3P)AuO2CCH2(OCH2CH2)2OCH3] as
evidenced by a deep field shift of the signals of the ethylene glycol
Fig. 2. TG (black) and DSC (gray) traces for the thermal heating of 3 in argon (flow rate
40 ml⋅min−1, heating rate 5 K⋅min−1).
Fig. 3. UV–vis spectra of Au NP obtained by thermolysis of 3 (c=6.3×10−3 mol/l) in
mesitylene.

678
A. Tuchscherer et al. / Inorganic Chemistry Communications 14 (2011) 676–678
We have developed a straightforward and efficient way to
generate gold nanoparticles by thermolysis of a phosphane gold
ethylene glycol carboxylate in organic solvents (toluene, para-xylene
and mesitylene) at low temperatures. The advantage of this
preparation methodology is that no reducing and stabilizing agents
have to be added. The generated NP are of narrow size distribution
and are stabilized by a small organic/inorganic matrix.
Actually, we are using the methodology described above for the
formation and stabilization of various metal and metal oxide NP from
further transition metal and main-group element carboxylates.
Acknowledgments
We gratefully acknowledge the Deutsche Forschungsgemeinschaft
(IRTG, Materials and Concepts for Advanced Interconnects, GRK 1215)
and the Fonds der Chemischen Industrie for generous financial support.
Appendix A. Supplementary material
CCDC-793568 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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