Hydrolytic decomposition of tetramethylammonium bis(trifluoromethyl) aurate(I), [NMe4][Au(CF3)2]: A route for the synthesis of gold nanoparticles in aqueous medium

Article abstract of DOI:10.1002/ejic.201000863

Monodisperse gold nanoparticles (AuNPs) were obtained by hydrolytic decomposition of a new molecular precursor, tetramethylammonium bis(trifluoromethyl)aurate(I), [NMe₄][Au(CF₃) ₂], which has been characterised by spectroscopic and single-crystal X-ray diffraction analyses. On account of the simple and high-yield synthesis, the title compound represents a versatile synthon and an alternative to the commonly used chloroauric acid (HAuCl₄). Time-dependent NMR and UV/Vis spectroscopic studies revealed the chemical species and reaction cascade involved in the decomposition of a molecular species into gold clusters. The size and stability of the naked AuNPs was modulated simply by changing the precursor concentration. Copyright

Full text of DOI:10.1002/ejic.201000863

FULL PAPER
DOI: 10.1002/ejic.201000863
Hydrolytic Decomposition of Tetramethylammonium Bis(trifluoromethyl)-
aurate(I), [NMe4][Au(CF3)2]: A Route for the Synthesis of Gold Nanoparticles
in Aqueous Medium
David Zopes,[a] Silke Kremer,[a] Harald Scherer,[b] Lhoussaine Belkoura,[c]
Ingo Pantenburg,[a] Wieland Tyrra,[a] and Sanjay Mathur*[a]
Keywords: Gold / Nanoparticles / Hydrolysis / Plasmons
Monodisperse gold nanoparticles (AuNPs) were obtained by
single-crystal X-ray diffraction analyses. On account of the
hydrolytic decomposition of a new molecular precursor, tetra- simple and high-yield synthesis, the title compound repre-
methylammonium bis(trifluoromethyl)aurate(I), [NMe4][Au-
(CF3)2], which has been characterised by spectroscopic and
sents a versatile synthon and an alternative to the commonly
used chloroauric acid (HAuCl4).
Introduction
the reduction of the precursor HAuCl4.[6–8] Interestingly, a
majority of the efforts deal with the modulation of growth
parameters (reaction time, nature and concentration of re-
ductants and so on) and growth kinetics (addition of cap-
ping agents, seed-mediated growth and so on) of AuNPs;[8]
however, the development of new precursors for chemically
controlled generation of gold nanoparticles has received
somewhat less attention.[9] We report herein the synthesis
and structural characterisation of (perfluoroalkyl)aurates(I)
as potential synthons for the production of gold nanopar-
ticles in aqueous media, which can be seen as a viable exten-
sion of the well-known HAuCl4 routes.[5]
The efficient use of the reagent combination comprising
a fluoride source plus trimethyl(perfluoroalkyl)silane has
allowed us in recent years to prepare numerous perfluoro-
alkyl-metalate complexes of late transition metals as well as
main-group elements that are characterised by their extreme
reactivity[10–13] or stability.[14–16] (Trifluoromethyl)gold com-
pounds, whereby the predominant numbers of the charac-
terised derivatives contain gold in the trivalent oxidation
state, have generally been known for more than 30 years.[17]
The number of trifluoromethyl gold(I) compounds is lim-
ited to the examples of AuCF3·RPF2,[18] AuCF3·PR3[19] and
AuCF3·CϵNMe;[20] however, no (perfluoroalkyl)aurate(I)
has hitherto been described to the best of our know-
ledge.
Gold nanoparticles (AuNPs) attract a fascination in the
field of nanotechnology,[1] mainly due to their appealing
optical properties and the simplicity of the synthesis pro-
cedure, which have already been the focus of historical re-
search on metal colloids.[1,2] Furthermore, these nanopar-
ticles have already been transformed into commercial goods
by incorporating them into glass matrices to obtain a dis-
tinct red coloration Ϫ caused by the plasmon resonance in
nanoscopic gold clusters Ϫ seen in the stained glass win-
dows of churches (e.g., “Purple of Cassius”, made from
gold in the presence of tin[3]). The tremendous interest in
the applications of gold particles in modern nanotechnol-
ogy emerges from their fundamentally new properties; for
instance, AuNPs can act as carriers for the targeted delivery
of drug and biomolecules inside cells. Similarly, their strong
interaction with light enables a sensory mechanism in which
the optical properties may change upon binding to certain
molecules for the detection and quantification of analytes.[4]
The most commonly used synthesis of gold nanoparticles
involves the aqueous reduction of HAuCl4 by sodium cit-
rate.[5] The quest for a synthetic recipe that enables repro-
ducible syntheses of Au nanoparticles with a precise control
over size and shape has led to numerous modifications of
The reagent combination Me3SiCF3/F– efficiently allows
access to the synthesis of bis(trifluoromethyl)aurates(I) and
avoids the use of alkylzinc or cadmium compounds.[18–22]
We report here on the synthesis and structural characterisa-
tion of some bis(trifluoromethyl)aurates(I) and their reac-
tivity in aqueous solutions, which has led to formations of
monodisperse nanoparticles of Au, remarkably as aqueous
dispersions.
[a] Department für Chemie, Lehrstuhl für Anorganische und
Materialchemie, Universität zu Köln,
Greinstrasse 6, 50939 Köln, Germany
E-mail: sanjay.mathur@uni-koeln.de
[b] Institut für Anorganische und Analytische Chemie, Albert-
Ludwigs-Universität Freiburg,
Albertstrasse 21, 79104 Freiburg i. Br, Germany
[c] Department für Chemie, Institut für Physikalische Chemie,
Universität zu Köln,
Luxemburger Strasse 116, 50939 Köln, Germany
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S. Mathur et al.
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Table 1. Comparison of the NMR spectroscopic data (δ in ppm, J
Results and Discussion
in Hz) of isoelectronic species [Au(CF3)2]– and Hg(CF3)2.[a]
δ(19F)
1J(F,C)
3J(F,C) 4J(F,F)
δ(13C)
Synthesis and Characterisation of Bis(perfluoroalkyl)-
aurates(I)
[Au(CF3)2]–
Hg(CF3)2
–28.5
–37.5
347
355
19
16
Ͻ2
4.5
163.0
159.8
[a] CD3CN, room temperature.
(Trifluoromethyl)gold(I) compounds are formed either as
decomposition products of methyl(trifluoromethyl)gold(III)
derivatives[17] or selectively formed through halide exchange
reactions between AuX and Cd(CF3)2 complexes in the
presence of suitable ligands such as phosphanes,[19] fluoro-
phosphanes[18] or methyl isocyanide.[20]
The use of Me3SiCF3 as a reagent for the synthesis of
AuCF3·PR3 complexes has been reported in reactions of
synthetically challenging alkoxy- or aryloxy-gold(I) com-
pounds, AuORЈ·PR3 [RЈ = CH(CF3)2, Ph].[23]
The synthesis of the bis(trifluoromethyl)aurates(I),
[Au(CF3)2]–, proceeds similar to the procedure reported for
argentates,[15] platinates[14] and bismutates[11] (Scheme 1).
Mechanistically, the hypercoordinated (hypervalent) tri-
methyl(trifluoromethyl) fluorosilicate anion that is formed
in the elementary step[10] substitutes the chloride in AuCl
to form highly volatile trimethylfluorosilane and sparingly
soluble tetramethylammonium chloride. The intermediate
species {[Au(CF3)Cl]–, AuCF3·EtCN} then undergo a nu-
cleophilic attack by a second equivalent of the trifluorome-
thyl nucleophile, thereby replacing either the chlorido or the
propionitrilo ligand to finally yield [NMe4][Au(CF3)2]
(Scheme 1).
Figure 1. 13C NMR spectrum of the [Au(CF3)2]– ion [CD3CN; dis-
tortionless enhancement by polarization transfer, non decoupled,
30° pulse (deptnd30)].
An unexpected aurate(I), 1,1,1,4,5,5,5-heptafluoro-2,4-
bis(trifluoromethyl)pent-2-ene-3-(trifluoromethyl)aurate(I)
(Scheme 2), was identified with the help of correlated spec-
troscopy (19F,19F and 19F,13C), when a larger excess amount
(Ͼ20%) of Me3SiCF3 was used, thus implying a similar re-
action sequence as investigated for the formation of the
1,1,1,4,5,5,5-heptafluoro-2,4-bis(trifluoromethyl)pentide
ion[25] in fluoride-mediated reactions of Me3SiCF3 with
itself.
[NMe4][Au(CF3)2] was obtained as a colourless solid in
high yield and exhibited low sensitivity towards air and day-
light. After storage in daylight for several months, the de-
composition into elemental gold and gold(III) species was
evident (by means of NMR and UV/Vis spectroscopic data)
from which the tetrakis(trifluoromethyl)aurate(III) could be
unambiguously identified. Quartets and septets in the 19F
NMR spectra Ϫ although of very low intensity Ϫ indicated
tris(trifluoromethyl)gold(III) species of so far unknown
composition.[24]
The 13C NMR spectroscopic chemical shift of the bis(tri-
fluoromethyl)aurate(I) anion in solution (CD3CN) corre-
lated well with the value reported for the isoelectronic deriv-
ative Hg(CF3)2. The coupling constants 1J(19F,13C),
4
3J(19F,13C) and J(19F,19F) were also found to be compar-
able with those known for Hg(CF3)2 (Table 1). The quartet
of quartet splitting caused by the 1J(19F,13C) and
3J(19F,13C) couplings of the [Au(CF3)2]– moiety is depicted
in Figure 1.
Scheme 2. Formula of 1,1,1,4,5,5,5 heptafluoro-2,4-bis(trifluoro-
methyl)-pent-2-ene-3-(trifluoromethyl)aurate(I) with 19F and
13C NMR spectroscopic chemical shifts (13C data printed in italics).
Scheme 1.
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Hydrolytic Decomposition of [NMe4][Au(CF3)2]
+
The NMe4 cation was exchanged in a facile reaction aurate(I) may be added as a new candidate to the growing
with [PNP]I [PNP
= bis(triphenylphosphoranylidene)- family of weakly coordinating anions (WCAs) that show no
ammonium] or [K(18-crown-6)]I to yield the corresponding cation–anion interactions either in solution or in the solid
aurates in nearly quantitative amounts.
state.[28]
Within the accessible range, the compound exhibited two
irreversible oxidation waves at +0.73 and +1.05 V, which
were tentatively assigned to AuI/AuII and AuII/AuIII cou-
ples, respectively. No cathodic wave was detected up to
–3.2 V, which indicated that within a large range of about
4 V the compound is stable (Figure 4).
Molecular Structure of Bis(triphenylphosphoranylidene)-
ammonium Bis(trifluoromethyl)aurate(I), [PNP][Au(CF3)2]
The ion pair [PNP][Au(CF3)2] (Figure 2) [C1–Au–C2
178.9(2)°; Au–C1 2.059(6) Å, Au–C2 2.072(6) Å] showed a
quasilinear coordination for gold. These values and atomic
arrangements are in good agreement with data for dimeth-
ylaurate(I), [N(nBu)4][Au(CH3)2] [mean value of Au–C
bond length 2.075 Å; C–Au–C angle 178.2(2)°][26] and
trifluoromethyl(triphenylphosphane)gold(I),
[Au(CF3)-
(PPh3)][27] [Au–C bond length 2.045(4) Å; C–Au–P angle
178.56(11)°].
Figure 4. Cyclic voltammogram of [NMe4][Au(CF3)2] in MeCN/
[N(nBu)4]PF6 at 100 mVs–1 scan rate; T = 298 K. The small cath-
odic wave at about –2.7 V is due to an impurity in the solvent.
Kochi et al. reported an anodic oxidation wave for
[AuI(CH3)2]– of +0.498 V (converted into the ferrocene/
ferrocenium couple) and a value of +0.822 V for the corre-
sponding AuIII compound [Au(CH3)4]–.[26] Thus the first
oxidation potential observed for [Au(CF3)2]– is about
0.23 V higher and reflects the electron-withdrawing effect
of the CF3 ligands in [NMe4][Au(CF3)2]. A second anodic
wave for [AuI(CH3)2]– was not reported.
Figure 2. Molecular structure of the [PNP][Au(CF3)2] ion pair.
In the crystal structure, anions are layered in channels
formed by the bulky [PNP] cations without any significant
F–H contacts (Figure 3). Thus, the bis(trifluoromethyl)-
Hydrolysis of [NMe4][Au(CF3)2]
Although [NMe4][Au(CF3)2] is soluble in CD3OD with-
out exhibiting any significant decomposition, the same at-
tempt in D2O or H2O led to a rapid decomposition with
evolution of bubbles (CO2) accompanied by a colour
change of the reaction mixture from grey through pale pur-
ple to red, which is characteristic of the formation and
growth of gold nanoparticles.[2,5] After 30 min, no 19F
NMR spectroscopic evidence was found for any trifluoro-
methylgold(I) species in the solution. The decomposition
products were identified to be CO2 [precipitation of BaCO3
upon bubbling the gas through a Ba(OH)2 solution], F– that
–[29]
subsequently turned to HF2
followed by [SiF6]2– [δ(19F)
= –129.1 ppm; δ(29Si) = –188 ppm; J(29Si,19F) = 108 Hz]
and [BF4]– [δ(19F) = –150.2 ppm; δ(11B) = –1.4 ppm;
1J(19F,11B) Ͻ 1 Hz], the latter presumably being generated
by the reaction with the glass wall of the NMR spec-
troscopy tube (Scheme 3). A further signal in the 19F NMR
spectrum that consisted of four lines of equal intensity as
1
Figure 3. View of the unit cell along the crystallographic a axis.
Eur. J. Inorg. Chem. 2011, 273–280
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well as a quartet in the 11B NMR spectrum suggested the (CF2OCOCF3)]– [δ(CF3) = –28.6 ppm, t, 4J(19F,19F) ≈
1
formation of BF3·solvent adduct [δ(19F) = –143.0 ppm; 1.5 Hz, J(19F,13C) = 346 Hz, 3 F; δ(CF2) = –43.0 ppm, q,
1
δ(11B) = +0.3 ppm; J(19F,11B) = 15 Hz]. No evidence was 4J(19F,19F) ≈ 1.5 Hz, 1J(19F,13C) = 337 Hz, 2 F; δ(OCOCF3)
1
found for the formation of CF3H. To decelerate the decom- = –77.2 (–77.17) ppm, s, J(19F,13C) = 293 Hz, 3 F] and
position reaction and to elucidate the decomposition pro- bis[difluoro(trifluoroacetato)methyl]aurate(I) [Au(CF2OC-
cess, the hydrolysis was performed in a CD3CN/H2O mix- OCF3)2]– [δ(CF2) = –42.8 ppm, s, 1J(19F,13C) = 336 Hz,
ture (v/v ≈ 3:1), which revealed a singlet in the 19F NMR 4J(19F,13C) ≈ 2 Hz, 4 F; δ(OCOCF3) = –77.2 (–77.21) ppm,
1
spectra (δ = –21.0 ppm) and a quartet in the 13C NMR (δ = s, J(19F,13C) = 293 Hz, 6 F].
145 ppm) spectra, assignable to AuCF3·CD3CN or possibly
After prolonged reaction periods, the resonances of
AuCF3·H2O, although the formation of the latter appears trifluoromethyl[difluoro(trifluoroacetato)methyl]aurate(I)
to be unlikely. After a period of 5 d, a third signal that [Au(CF3)(CF2OCOCF3)]– vanished, whereas the signal in-
corresponded to trifluoromethylgold derivative was ob- tensities of CF3COF and bis[difluoro(trifluoroacetato)-
served in the 19F and 13C NMR spectra, which upon com- methyl]aurate(I) [Au(CF2OCOCF3)2]– increased. Therefore,
parison with published NMR spectroscopic data[24] sug- 13C NMR spectroscopic chemical shifts for the latter could
gested the formation of a mono(trifluoromethyl)gold(III) be provided [19F,13C heteronuclear single-quantum coher-
compound that was not characterised further. The forma- ence (HSQC) experiments, optimised for 340 Hz; 19F,13C
tion of a formal AuII species with an Au–Au bond also heteronuclear multiple-bond correlation (HMBC) experi-
cannot be excluded at this stage. These results denoted a ments, optimised for 30 Hz] to be δ = 159.4 (CF2), 153.1
selective hydrolysis by stepwise cleavage of F–C bonds and (OCO) and approximately 111.5 ppm (OCOCF3). On the
retention of one Au–CF3 bond. An intermediately formed basis of above observation, we suggest that intermediately
shortlived species AuCF3·CO would be directly converted formed CO acts as a reducing reagent under the influence
into the CD3CN adduct and CO2, on account of the strong of water, whereas ammonia became the reagent of choice
catalytic activity of gold (and its compounds) to oxidise to eliminate unwanted byproducts (Scheme 3).
CO.[30] A comparable conversion of a CF3 group into a CO
ligand has been recently reported for [Pt(CF3)4]2–, which
transformed under the influence of moisture into [Pt-
(CF3)3(CO)]–.[31] A selective substitution of one fluorine
atom of the CF3 group with retention of the carbon–metal
bond has been reported by D. Naumann et al.[32] in the
treatments of Cd(CF3)2 complexes with Lewis acid–base
Formation of AuNPs
In addition to the described and characterised byprod-
couples. The consecutive reactions of the in situ generated ucts, colloidal gold was obtained after the hydrolysis of
HF with common glassware are also well documented.[29]
[NMe4][Au(CF3)2]. The purple-coloured solution that con-
tained AuNPs was investigated by UV/Vis spectra to eluci-
date time-dependent particle growth. The scanning and
transmission electron micrographs provided insight into
particle morphology and size distribution. Figure 5 (a)
shows the kinetic behaviour of the UV/Vis absorption
measurement for
a
2.0 mm aqueous solution of
[NMe4][Au(CF3)2]. The spectroscopic data showed that nu-
cleation of the AuNPs began after 20 min with a maximal
absorption around λmax = 515 nm and a low intensity (ca.
0.5). The absorption maxima gradually showed a redshift
that indicated the particle growth by ripening processes.[33]
The reaction was found to be over after approximately
120 min, as no further shift or colour change was observed.
Figure 5 (b) shows SEM image of particles formed after
Scheme 3. Possible mechanistic pathways for the formation of
AuNPs upon hydrolysis of [NMe4][Au(CF3)2] with aqueous ammo-
nia.
To support these results, the reaction of [NMe4][Au- 120 min with an average particle size of around 28.7 nm (σ
(CF3)2] and trifluoroacetic acid anhydride (TFAA) was con- ≈ 17.7%). As expected, the unprotected particles (no sur-
ducted to obtain further evidence for the proposed reaction face coating) tend to assemble and agglomerate. The ag-
mechanism. Upon treatment of
a
solution of glomeration of NPs was augmented at higher precursor
[NMe4][Au(CF3)2] in CD3CN with an excess amount of concentration, which was corroborated by the observed red-
TFAA, 19F NMR spectroscopic control exhibited after shift of the absorption maxima in the UV/Vis spectra and
10 min, besides the signal of the starting materials those of the increase in the polydispersity (Figure 6). Initially, mono-
trifluoroacetyl fluoride CF3COF [δ(CF3) = –75.5 ppm, d, disperse AuNPs with an average size of 12.0 nm and a size
3J(19F,19F) = 6.5 Hz, 1J(19F,13C) = 283 Hz, 2J(19F,13C) = distribution of around 12.5% are formed (Figure 7), which
3
51 Hz, 3 F; δ(COF) = +14.7 ppm, q, J(19F,19F) = 6.5 Hz, grew in size in concentrated (4.0 mm) solutions to produce
2
1J(19F,13C) = 372 Hz, J(19F,13C) = 96 Hz, 1 F], trifluoro- AuNPs of average particle size (52.5 nm) with a substan-
methyl[difluoro(trifluoroacetato)methyl]aurate(I) [Au(CF3)- tially broader size distribution of 25.5% (Figure 6).
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Hydrolytic Decomposition of [NMe4][Au(CF3)2]
Figure 5. Time-dependent UV/Vis measurements (a) and SEM image (120 min) (b) including size distribution to control the kinetic of
the growth of the AuNPs starting from 2.0 mm solution of [NMe4][Au(CF3)2] precursor.
two weeks and only very slow agglomeration process was
observed in the UV/Vis measurements (Figure 7). This pre-
cursor concentration is comparable to the procedure re-
ported by Turkevich and co-workers when using HAuCl4 as
starting material.[5]
The formation of HF over the course of the decomposi-
tion reaction and its further reaction with the glass to gen-
erate [SiF6]2– and [BF4]– prompted us to use NH3 as a scav-
enger for HF. As expected, the addition of a small amount
of NH3 induced the formation of NH4F (19F NMR spectro-
scopic evidence), thereby accelerating the decomposition re-
action and reducing the reaction time from 120 to 20 min.
Figure 6. Influence of the precursor concentration on the resulting
Figure 8 shows the AuNPs obtained after this modifica-
size of AuNPs monitored by UV/Vis absorption spectra. The
tion for
a
concentration of 0.5 mm solution of
average particle size obtained from the TEM and SEM analyses of
the corresponding samples are given in the boxes shown along the
plotted numerical values.
[NMe4][Au(CF3)2]. Evidently, a chemically controlled (for-
mation of NH4F) decomposition of precursor due to the
addition of NH3 led to a fast nucleation step, thereby in-
hibiting particle growth by ripening and aggregative mecha-
The stability of AuNP dispersions could be enhanced by nisms. As a result, the obtained particles were nearly mono-
reduction of the precursor concentration. For instance, NPs dispersed (size distribution, 8.3%) with an average particle
obtained from 0.5 mm aliquots were stable for more than size of 9.7 nm.
Figure 7. TEM images and analysed size dispersion in AuNPs (at two different magnifications) obtained by a reduced precursor concentra-
tion of 0.5 mm [NMe4][Au(CF3)2].
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Figure 8. TEM images and analysed size distribution of AuNPs (at two different magnifications) obtained by a precursor concentration
of 0.5 mm and few amounts of NH3.
Tetramethylammonium Bis(trifluoromethyl)aurate(I): Solid [NMe4]-
F (0.77 g; 8.28 mmol) was added to a well-stirred solution of
Conclusion
We have reported a room-temperature synthesis of
monodisperse AuNPs by the hydrolysis of a new gold pre-
cursor, [NMe4][Au(CF3)2]. Mechanistic investigations by
time-dependent NMR and UV/Vis spectroscopic data re-
vealed that the precursor-to-nanoparticle transformation is
governed by a cascade of chemical reactions that can be
explained at the molecular level. The simplicity of the pre-
cursor activation and the possibility of controlling its de-
composition kinetics by addition of, for example, NH3 to
scavenge in situ formed HF, enabled a size-controlled syn-
thesis of gold nanoparticles.
Me3SiCF3 (1.487 mL, 9.93 mmol) in dry dimethoxyethane (15 mL)
at –60 °C, and the reaction mixture was slowly warmed to –30 °C.
At this temperature, AuCl (0.85 g, 4.14 mmol) was added. After a
while, [NMe4]Cl together with traces of elemental gold begin to
precipitate as a pale grey solid. The reaction mixture was allowed
to reach room temperature overnight. All volatile components were
removed in vacuo to obtain a waxy residue, which was washed
several times with small portions of n-pentane and dried in vacuo.
[NMe4][Au(CF3)2] was extracted from the powdery ochre raw mate-
rial by using dichloromethane with a Soxhlet apparatus and a bath
temperature that did not exceed 80 °C. Extraction was terminated
after 9 h. After removing the main quantity of the solvent by use
of a rotary evaporator, the colourless remainder was dried in vacuo
to give 1.02 g (2.48 mmol) [NMe4][Au(CF3)2] in 60% yield as
colourless crystals; m.p. 174–178 °C (glass capillary). 19F NMR
(282.4 MHz, CD3CN, 298 K, CCl3F): δ = –28.5 [s, 1J(F,C) =
347 Hz, 3J(F,C) = 19 Hz, 4J(F,F) = 2 Hz] ppm. 13C{1H} NMR
(75.5 MHz, CD3CN, 298 K, TMS): δ = 163.0 {qq, 1J(F,C) =
Experimental Section
General: All experiments were carried out in a dry nitrogen or ar-
gon atmosphere in carefully dried reaction vessels using Schlenk
techniques. Solvents were purified by reported methods.[34]
AuCl,[35] [NMe4]F[36] and [PNP]I[37] were synthesised according to
literature procedures. [K(18-crown-6)]I was prepared from a 1:1 re-
action of KI and the crown ether in an acetone dichloromethane
mixture. NMR spectra were recorded with a Bruker AVANCE II
300 spectrometer at 298 K; NMR spectrosopic frequencies (exter-
nal standards): 13C: 75.5 MHz (TMS), 19F: 282.4 MHz (CCl3F),
1H: 300.1 MHz (TMS); positive shifts denote downfield resonances.
Data collection to solve the structure of 1,1,1,4,5,5,5-heptafluoro-
3
1
347 Hz, J(F,C) = 19 Hz, [Au(CF3)2]–}, 55.3 {“t”, J(C,N) = 4 Hz,
[NMe4]+} ppm. 1H NMR (300.1 MHz, CD3CN, 298 K, TMS): δ =
2
3.12 {“t”, J(H,N) = 0.6 Hz, [NMe4]+} ppm. NMR spectroscopic
data recorded in CD3OD did not differ significantly. MS (ESI)–:
m/z (%) = 335.0 (100) [Au(CF3)2]–. C6H12AuF6N (409.12): calcd. C
17.61, H 2.96, N 3.42; found C 18.22 , H 3.45, N 3.55.
Bis(triphenylphosphoranylidene)ammonium
Bis(trifluoromethyl)-
aurate(I) [PNP][Au(CF3)2] and Potassium(18-crown-6) Bis(trifluoro-
2,4-bis(trifluoromethyl)pent-2-ene-3-(trifluoromethyl)aurate(I) methyl)aurate(I) [K(18-crown-6)][Au(CF3)2]: [PNP]I (0.67 g,
were carried out with a Bruker Avance 400 spectrometer at ambient
temperature. Electrochemical experiments were carried out in 0.1 m
[N(nBu)4]PF6 solutions with a three-electrode configuration (glassy
carbon electrode, Pt counter electrode, Ag/AgCl reference) and an
Autolab PGSTAT30 potentiostat and function generator. The fer-
rocene/ferrocenium couple (FeCp2/FeCp2+) served as internal refer-
ence. Negative ESI mass spectra in MeCN solutions were carried
out with a Finnigan MAT 900 apparatus with a flow rate of
2 μLmin–1. Visible decomposition points were determined with a
HWS Mainz 2000 apparatus. C, H and N analyses were carried out
with a HEKAtech Euro EA 3000 apparatus. The obtained AuNPs
were characterised by UV/Vis spectroscopy (Perkin–Elmer), trans-
mission electron microscopy (Zeiss) and a scanning electron micro-
scope (FEI).
1.0 mmol) and [K(18-crown-6)]I} (0.43 g, 1.0 mmol) dissolved in
10 mL of EtCN were added to a solution of [NMe4][Au(CF3)2] (ca.
1.0 mmol) that was prepared as described above. [NMe4]I precipi-
tated spontaneously after mixing both solutions; it was filtered off
and the resulting solution was evaporated to dryness. After washing
with n-pentane, colourless crystals of [PNP][Au(CF3)2] {[K(18-
crown-6)][Au(CF3)2]} were grown upon storing a CH2Cl2/Et2O
mixture for several days at –20 °C. The crystals were isolated in
better than 95% yield in both cases. C38H30AuF6NP2 (873.56):
calcd. C 52.25, H 3.46, N 1.60; found C 52.07, H 3.99, N 1.63;
m.p. 198–200 °C (glass capillary). C14H24AuF6KO6 (638.39): calcd.
C 26.34, H 3.79, N 0.00; found C 26.91, H 4.51, N 0.75; m.p. (onset
of decomposition) 194 °C (glass capillary). 19F and 13C NMR spec-
tra of the anion matched with those of [NMe4][Au(CF3)2] described
278
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Eur. J. Inorg. Chem. 2011, 273–280

Hydrolytic Decomposition of [NMe4][Au(CF3)2]
above. 1H and 13C NMR spectroscopic data of the [PNP] and
[K(18-crown-6)] cations matched with previously published val-
ues.[38]
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Single-Crystal X-ray Diffraction Study: Single crystals of
[PNP][Au(CF3)2] were obtained upon cooling saturated CH2Cl2
solutions to approximately –25 °C over several weeks. Data collec-
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a STOE IPDS II diffractometer using graphite-monochromated
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CCDC-785918 contains the supplementary crystallographic data
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Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Crystal
873.56 gmol–1; diffractometer IPDS-II, T = 170(2) K; 2θmax
54.8°; 0°ՅωՅ180°, φ = 0°, 0°ՅωՅ58°, φ = 90°, Δω = 2°, 119
images; –12ՅhՅ12, –13ՅkՅ13, –21ՅlՅ21; ρcalcd.
1.689 gcm–3; 16920 measured reflections of which 7502 were sym-
metrically independent; Rint 0.0526; F(000) 856; μ =
Data
for
[PNP][Au(CF3)2]:
C38H30NP2F6Au:
=
[17]
[18]
[19]
=
=
=
–1
¯
4.437 mm ; triclinic, P1 (no. 2), a = 990.7(1) pm, b = 1081.6(1) pm,
c = 1717.5(2) pm, α = 85.31(1)°, β = 74.83(1)°, γ = 75.28(1)°, V =
1717.7(7)ϫ106 pm3, Z = 2; R1/wR2 for 6033 reflections with
[Io Ͼ2σ(Io)]: 0.0367/0.0866, for all data: 0.0506/0.1004; Sall = 1.032.
[20]
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Acknowledgments
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The authors would like to thank the University of Cologne and the
European Union (EU), project “NANOMMUNE” funded within
the framework of the NMP call of the seventh framework pro-
gramme (FP7-NMP-2007-SMALL-1, grant number 214281) for
providing the infrastructure and financial assistance. Thanks are
due to Professor Dr. Dieter Naumann for valuable discussions. We
express our gratitude to our advanced students Gulara Hamidova,
Iana Sterman, Sabine Grupe and Stefan Schüller for doing some
part of the experimental work. We are indebted to Professor Dr.
Axel Klein for interpreting the cyclic voltammetry data, to Dr. Ma-
thias Schäfer (Institut für Organische Chemie) for recording the
ESI mass spectra and to Osman Arslan for the TEM measure-
ments.
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Received: August 10, 2010
Published Online: November 23, 2010
280
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Eur. J. Inorg. Chem. 2011, 273–280