Structural evolution of atomically precise thiolated bimetallic [Au 12+ nCu32(SR)30+ n]4- (n = 0, 2, 4, 6) Nanoclusters

Article abstract of DOI:10.1021/ja501811j

A series of all-thiol stabilized bimetallic Au-Cu nanoclusters, [Au _12+nCu₃₂(SR)_30+n]^4- (n = 0, 2, 4, 6 and SR = SPhCF₃), are successfully synthesized and characterized by X-ray single-crystal analysis and density functional theory (DFT) calculations. Each cluster consists of a Keplerate two-shell Au₁₂@Cu₂₀ core protected by (6 - n) units of Cu₂(SR)₅ and n units of Cu₂Au(SR)₆ (n = 0, 2, 4, 6) motifs on its surface. The size and structural evolution of the clusters is atomically controlled by the Au precursors and countercations used in the syntheses. The clusters exhibit similar optical absorption properties that are not dependent on the number of surface Cu₂Au(SR)₆ units. Although DFT suggests an electronic structure with an 18-electron superatom shell closure, the clusters display different thermal stabilities. [Au_12+nCu₃₂(SR) _30+n]^4- clusters with n = 0 and 2 are more stable than those with n = 4 and 6. Moreover, an oxidation product of the clusters, [Au ₁₃Cu₁₂(SR)₂₀]^4-, is structurally identified to gain insight into how the clusters are oxidized.

Full text of DOI:10.1021/ja501811j

Communication
pubs.acs.org/JACS
Structural Evolution of Atomically Precise Thiolated Bimetallic
4
−
[
Au Cu (SR) ] (n = 0, 2, 4, 6) Nanoclusters
12+n 32 30+n
Huayan Yang, Yu Wang, Juanzhu Yan, Xi Chen, Xin Zhang, Hannu Hak
kinen,‡
†
,§
†,§
†
‡
†
̈
,†
and Nanfeng Zheng*
†State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials,
and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
‡
̈ ̈ ̈ ̈
Departments of Physics and Chemistry, Nanoscience Center, University of Jyvaskyla, FI-40014 Jyvaskyla, Finland
*
S Supporting Information
8
−14
well.
More recently, single-crystal analysis also demon-
ABSTRACT: A series of all-thiol stabilized bimetallic
strated that both the core and surface structures of thiol-capped
4−
Au−Cu nanoclusters, [Au Cu (SR)30+n] (n = 0, 2, 4,
1
2+n
32
Ag nanoparticles could be significantly different from those of
1
5−18
6
and SR = SPhCF ), are successfully synthesized and
3
thiolated Au nanoparticles.
In the case of
characterized by X-ray single-crystal analysis and density
functional theory (DFT) calculations. Each cluster consists
of a Keplerate two-shell Au @Cu core protected by (6
4−
[
Au Ag (SR) ] , Au and Ag were revealed to be distributed
12
32
30
in a core−shell fashion rather than a random fashion, with all
17
1
2
20
Ag atoms located on the surface of the clusters. In the
−
n) units of Cu (SR) and n units of Cu Au(SR) (n = 0,
, 4, 6) motifs on its surface. The size and structural
2 5 2 6
synthesis of Au Cu clusters, the use of pyridyl-bearing ligands
13
x
2
helped to control the number and location of Cu sites on the
surface of icosahedral Au13 core and manipulate the catalytic
evolution of the clusters is atomically controlled by the Au
precursors and countercations used in the syntheses. The
clusters exhibit similar optical absorption properties that
19
exposure of Au atoms.
In sharp contrast to the recent significant progress in
identifying the molecular structures of thiolated Au and Ag
nanoclusters, the synthesis and structure characterization of all-
are not dependent on the number of surface Cu Au(SR)6
2
units. Although DFT suggests an electronic structure with
an 18-electron superatom shell closure, the clusters display
thiol capped metallic nanoclusters containing Cu have been
4
−
different thermal stabilities. [Au12+nCu (SR)30+n] clus-
20,21
32
rarely reported.
We now report our success in preparing a
ters with n = 0 and 2 are more stable than those with n = 4
series of all-thiol capped bimetallic Au−Cu nanoclusters,
and 6. Moreover, an oxidation product of the clusters,
4
−
[
Au Cu (SR) ]
(n = 0, 2, 4, 6), and their crystal
4
−
12+n
32
30+n
[
Au Cu (SR) ] , is structurally identified to gain
13 12 20
4−
structures. Each [Au12+nCu (SR)30+n] cluster is consisting of
32
insight into how the clusters are oxidized.
a Keplerate two-shell Au @Cu core protected by (6 − n)
12
20
units of Cu (SR) and n units of Cu Au(SR) (n = 0, 2, 4, 6) on
2
5
2
6
its surface. The metal distribution and the surface structure of
the bimetallic nanoclusters were found to be highly sensitive to
the Au precursors and countercations [i.e., tetraphenyl-
imetallic nanocrystals have attracted increasing research
B
attention in recent years, mainly because of the complexity
of their compositions and structures, which creates more
opportunities to finely tune their physical and chemical
+
+
phosphonium (PPh ), tetrabutylammonium (NBu )] intro-
4
4
1
−5
duced in their syntheses. In the case of n = 2, 4, or 6, Au atoms
properties.
Currently, high-quality bimetallic nanocrystals
are located at both the core and the surface of the clusters. The
are mostly prepared by wet reduction chemistry assisted by the
4
−
6
,7
[Au12+nCu32 (SR)30+n
]
clusters exhibited similar optical
use of organic capping agents. It has been well-documented
that both the distribution of metals and the binding structure of
capping ligands are vital to the overall properties of organic-
absorption properties. Density functional theory (DFT)
calculations indicated an electronic structure with an 18-
electron superatom shell closure in the metal core of the
clusters and reproduced well the measured optical absorption
spectra for clusters with n = 0, 2. The stability of the clusters
was found to be highly dependent on their surface structures.
5
capped bimetallic nanocrystals. Nevertheless, until now there
has been a lack of effective methods that allow the precise
determination of molecular-level structures of bimetallic
nanocrystals. Recently, an effective route has been developed
to provide detailed molecular structures of metal nanoparticles
by synthesizing and crystallizing organic-capped, atomic-precise
metal nanoclusters into single crystals, followed by X-ray
4−
Synthesis of [Au12+nCu32 (SR)30+n
]
nanoclusters involved
the co-reduction of the Au(I) precursor [i.e., chloro(triphenyl-
phosphine)gold(I) (ClAuPPh ), chloro(diphenyl-2-pyridyl-
3
8
−18
phosphine)gold(I) (ClAuDPPy)] and Cu(ClO ) by aqueous
4
2
diffraction analysis.
This method has been extensively
NaBH in the presence of 4-(trifluoromethyl)thiophenol and
4
applied successfully to resolve the surface structure of thiol-
8
−14
countercations. The synthesis was carried out in a mixed
solvent of dichloromethane and methanol at 0 °C using an ice
capped Au nanoparticles.
Staple Au-thiol units (e.g., -RS-
Au-SR-, -RS-Au-SR-Au-SR-) are revealed on the surface of all
crystallographically determined thiol-capped Au nanoclusters
and have become gradually accepted as a common surface
structural feature for larger thiol-capped Au nanoparticles as
Received: February 20, 2014
Published: May 5, 2014
©
2014 American Chemical Society
7197
dx.doi.org/10.1021/ja501811j | J. Am. Chem. Soc. 2014, 136, 7197−7200

Journal of the American Chemical Society
Communication
Figure 1. Crystal structure of the [Au Cu (SR) ]4 cluster. (a)
−
Figure 2. Surface structures of Au Cu @Au (x = 0, 2, 4, 6)
12 32 x
12
32
30
4
−
4−
4
−
nanoclusters: (a) [Au Cu (SR) ] . (b) [Au Cu Au (SR) ] . (c)
Overall structure of the [Au Cu (SPhCF ) ] cluster. All hydrogen
and trifluoromethyl groups are omitted for clarity. (b) Two-shell
Au @Cu core of the cluster. (c) Structure of the cluster with the
Au @Cu two-shell cores in the space-filling style. (d) Structure of
the surface [Cu (SPhCF ) ] motif. Color legend: orange spheres, Au;
blue spheres, Cu; yellow spheres, S; gray sticks/spheres, C.
12 32 30 12 32 2 32
12
32
3 30
Schematic diagram of the formation of the Cu Au(SR) unit from
2
6
4
−
C u ( S R ) 5 u n i t . ( d ) [ A u 1 2 C u 3 2 A u ( S R ) ]
Au Cu Au (SR) ] . Color legend: gold spheres, Au; blue spheres,
. ( e )
2
4
3 4
12
20
4−
[
12 32 6 36
12
20
Cu; yellow spheres, S. All hydrogen, fluorine, and carbon atoms are
omitted for clarity.
2
3 5
4
−
bath (see Supporting Information for details). Crystallization of
the nanoclusters was performed by layering hexane into the
CH Cl solution of clusters at 4 °C. The overall synthetic
[Au Ag (SR) ] was averaged as 2.978 Å, only 3% longer
12 32 30
than the sum of Ag atomic radii (1.44 Å).
To our surprise, the absence of a strong Cu···Cu interaction
made the synthesis of [Au12+nCu (SR)30+n] (n = 0, 2, 4, 6)
highly sensitive to the synthetic conditions. Both the Au
precursor and the countercation used in the synthesis were
found critical in determining the final structure of the Au−Cu
bimetallic nanoclusters (see Supporting Information for
details). If ClAuPPh was used and PPh Br was substituted
2
2
4−
method was similar to that of Au Ag clusters which we
1
2
32
32
17
recently developed. However, in the synthesis of Au−Cu
bimetallic nanoclusters, the types of gold precursor and clusters’
charge-balancing countercations were revealed to play
important roles in determining the final structures of the
bimetallic nanoclusters.
3
4
All the structures of [Au12+nCu (SR) ]4 (n = 0, 2, 4, 6)
−
by NBu Br, the synthesis led to the formation of
32
30+n
4
4
−
4−
clusters were determined by X-ray single crystal analysis (Table
S1). When ClAuPPh3 and PPh4+ were used as the gold
precursor and the countercation, the obtained cluster was
Au Cu with n = 0. As illustrated in Figure 1a,
[Au Cu (SR) ]
instead of [Au Cu (SR) ] . The
12 32 30
1
4
32
32
4−
[Au Cu (SR) ] cluster can be better formulated as
14
32
32
4
−
[Au12+nCu (SR)30+n]
(SR)30+2] cluster also contains a two-shell Au @Cu Kepler-
with n = 2. The [Au12+2Cu32
32
4
−
1
2
32
12
20
4
−
[
[
Au1 2 Cu3 2 (SR)
]
has a structure similar to
ate core (Figure S2). However, in contrast to
3 0
17
4
−
4−
Au Ag (SR) ] . The −4 charge of each cluster is
[Au Cu (SR) ] (Figure 2a), the Au @Cu Keplerate
1
2
32
30
12
32
30
12
20
+
4−
balanced by four PPh4 countercations (Figure S1). The core
of the Au Cu cluster can be depicted as an Au @Cu
core in [Au12+2Cu32 (SR)30+2
Cu (SR) units and one pair of Cu Au(SR) units (Figure 2b),
]
is capped by two pairs of
12
32
12
20
2
5
2
6
Keplerate cage with a hollow Au icosahedron encapsulated in
not three pairs of Cu (SR) units. While the two Cu atoms in
the Cu (SR) unit are sharing a bridging thiolate, the two Cu
2 5
1
2
2 5
a pentagonal dodecahedral Cu shell (Figure 1b).
2
0
4
−
In the [Au Cu (SR) ] cluster, each Au @Cu Kepler-
atoms in the Cu Au(SR) unit are connected by a linear
12
32
30
12
20
2 6
ate cage is further surface-capped by six Cu (SR) units in an
octahedral symmetry to form the final structure (Figure 1c).
Au(SR) unit (Figure 2c). The surface Cu Au(SR) unit can be
2 2 6
2
5
thus structurally formulated as (SR) Cu-SR-Au-SR-Cu(SR) .
2
2
4−
The Cu (SR) unit can be better formulated as (SR) Cu-SR-
The −4 charge in [Au Cu (SR) ] clusters is well-balanced
2
5
2
14
32
32
Cu(SR) . Within the Cu (SR) unit, each Cu atom is three-
by four NBu4+ cations, as directly confirmed by the single-
2
2
5
−
−
coordinated by three SR groups, sharing one bridging SR
crystal analysis (see Table S1 for detailed crystal data).
−
+
4
with the other Cu (Figure 1d). While the bridging SR does
not bind to other Cu atoms, each of the other four thiolate
groups in the Cu (SR) unit further bind to two other Cu
More interestingly, if ClAuDPPy and PPh were respectively
used as the gold precursor and the countercation, the synthesis
4
−
resulted in the formation of [Au Cu (SR) ] , another
2
5
16
32
34
4
−
atoms on the dodecahedral Cu20 shell. Every two of the six
Cu (SR) units are equivalent, so they can be divided into three
member of the series of [Au12+nCu (SR)30+n] with n = 4
32
(Figure S3). As shown in Figure 2d, on the surface of
2
5
4
−
groups. The bridging angles of ∠Cu−SR−Cu are 76.1°, 75.2°,
and 74.7°, respectively. The average Cu···Cu distance in six
Cu (SR) units is 2.763 Å (2.761−2.781 Å), 8% longer than the
[Au Cu (SR) ] , two pairs of Cu Au(SR) units and one
16 32 34 2 6
Cu (SR) unit are capping the Au @Cu core. Moreover,
2
5
12
20
when the gold precursor was ClAuDPPy and the countercation
2
5
+
4−
sum of Cu atomic radii (1.28 Å), indicating that there is no
strong metal−metal interaction within the two Cu atoms of the
Cu (SR) units. In comparison, the surface Ag···Ag distance in
was NBu , the synthesis yielded [Au Cu (SR) ] , namely
4 18 32 36
4
−
[Au12+nCu (SR)30+n] with n = 6 (Figure S4). In [Au Cu
32
32
18
4−
(SR) ] , the Au @Cu core is protected by three pairs of
2
5
36
12
20
7
198
dx.doi.org/10.1021/ja501811j | J. Am. Chem. Soc. 2014, 136, 7197−7200

Journal of the American Chemical Society
Communication
prone to oxidation by air than Ag(0), [Au12+nCu (SR) ]4
−
32
30+n
(
[
n = 0, 2, 4, 6) clusters displayed much poorer stabilities than
4
−
Au Ag (SR) ] clusters. At room temperature, when
1
2
32
30
dissolved in solvents (i.e., DMF, CH Cl ), only the
2
2
4
−
[
Au Cu (SR) ] clusters were stable. The other three
12 32 30
clusters were partly oxidized in solution after storage in air
for 1 week. To better compare their stabilities, the single
crystals of the clusters were dissolved in DMF and subjected to
heat in air at 50 °C. UV−vis spectroscopy was applied to
monitor the degradation of the clusters. The studies showed
that all four clusters were degraded in DMF upon heating, with
the intensities of all characteristic absorption peaks decreased
with heating time (Figure S7). The peaks around 500 and 711
nm became broad gradually as the heating time was increased.
After 2 h of heating, while all the other characteristic absorption
peaks disappeared, the peak at 543 nm was still present.
Figure 3. Optical absorption spectra of [Au Cu (SPhCF ) ]·
1
2
32
3 30
+
+
4
4
PPh , [Au Cu (SPhCF ) ]·4NBu , [Au Cu (SPhCF ) ]·
4 14 32 3 32 4 16 32 3 34
+ +
PPh , and [Au Cu (SPhCF ) ]·4NBu in CH Cl and the
4−
4−
4
18
32
3
36
4
2
2
[Au Cu (SR) ] and [Au Cu (SR) ] exhibited better
1
2
32
30
14
32
32
4
−
computed absorption spectrum for [Au Cu (SR) ] . In the
4−
4−
1
2
32
30
stabilities than [Au Cu (SR) ] and [Au Cu (SR) ] .
For [Au Cu (SR) ] and [Au Cu (SR) ] , the peaks
1
6
32
34
18
32
36
theoretical spectrum, the individual optical transitions have been
folded into a smooth curve by using a Gaussian width of 0.1 eV.
4−
4−
12
32
30
14
32
32
around 500 and 711 nm did not show obvious change in the
4
−
4−
first 10 min. For [Au Cu (SR) ] and [Au Cu (SR) ] ,
16
32
34
18
32
36
the intensity of the peaks around 500 and 711 nm decreased
Cu Au(SR) units (Figure 2e). These results suggested the
2
6
4−
significantly. The poorer stabilities of [Au Cu (SR) ] and
important roles of reaction conditions, particularly the type of
reactants, in determining the size and structural evolution of
bimetallic nanoparticles.
16
32
34
4−
[
Au Cu (SR) ] might be explained by the presence of
18 32 36
more Cu Au(SR) units on their surfaces. The presence of
2
6
more Cu Au(SR)6 units would make the clusters more
Despite their different surface structures, the four
2
4
−
susceptible to oxidation by air. It should be noted that, in the
[
Au12+nCu (SR)30+n] (n = 0, 2, 4, 6) clusters exhibited
32
4
−
absence of O , all [Au Cu (SR)30+n] (n = 0, 2, 4, 6)
similar optical properties. As shown in Figure 3, the UV−vis−
2
12+n
32
clusters are stable at room temperature. No obvious change in
the optical absorptions of their solutions in CH Cl was
NIR absorption spectra of the four clusters in CH Cl all
2
2
displayed three obvious peaks at ∼500, 543, and 711 nm, and
one weak shoulder peaks at 600 nm. However, it should be
pointed out that the peak at ∼500 nm was slightly blue-shifted
as more Cu (SR) units were substituted by Cu Au(SR) . The
2
2
observed in 6 days (Figure S8).
To understand the degradation process of the
4
−
[Au12+nCu32(SR)30+n
]
clusters, much effort was made to
crystallize the degradation products by dissolving them in
CH Cl and diffusing the solution with hexane. We were
fortunate to obtain single crystals of the degradation products
2
5
2
6
electronic structures and optical properties of
4
−
[
Au12+nCu (SR)30+n]
clusters were studied via DFT
2
2
32
computations (see Supporting Information for technical
details). Structural details of the relaxed clusters are compared
to the crystal structure data in Table S2. As shown previously
4
−
of [Au16Cu32(SR)34
revealed the cocrystallization of [Au13Cu12(SPhCF ) ]
3 20
]
clusters. X-ray single-crystal analysis
4
−
4−
4−
17
+
4
for [Ag (SR) ] and [Au Ag (SR) ] clusters, all these
clusters with PPh
as countercations in the obtained single
44
30
12
32
30
systems have a shell-closing number of 18 valence electrons in
crystals (Figure S9). In contrast to its parent
2
2
4−
4−
the metal core. The calculated HOMO−LUMO energy gaps
are 0.72, 0.72, 0.79, and 0.93 eV for n = 0, 2, 4, and 6,
respectively. All clusters have the superatomic 1D states as
highest occupied orbitals, and the manifold of the first few
unoccupied orbitals shows the expected 1F and 2S symmetries
[Au16Cu32(SR)34
]
cluster, each [Au13Cu12(SPhCF ) ]
3 20
cluster has a solid icosahedral Au13 unit instead of a hollow
Au12 unit as its core (Figure 4a). The icosahedral Au12 shell is
protected by two Cu (SR)10 units at centrosymmetric positions
6
with respect to the central Au of the Au13 unit (Figure 4b).
Structurally, the icosahedral Au12 shell consists of two jointed
(
Figure S5).
The computed optical absorption spectrum of
C
Cu
Cu
3
-symmetric Au
6
6
units, each of which is capped by a
(SR)10 unit. The arrangement of the six Cu atoms in
(SR)10 resembles that of a C -symmetric Au unit on the
4−
[Au Cu (SR) ] (SR = SPh) is shown in Figure 3. It has
12
32
30
two peaks at about 716 and 493 nm and two shoulders at about
00 and 542 nm. These features agree very well with the
6
3
6
6
icosahedral Au12 shell (Figure 4c). However, the 12 Cu atoms
from the two Cu (SR)10 units are not enough to yield a close
corresponding four features in the experimental spectrum,
although the lowest-energy peak is more intense in the
calculation. The computed spectrum of [Au Cu (SR) ] is
6
shell on the Au13 core, due to the longer distance between Cu
and the central Au atom. The two Cu (SR) units are
4−
1
4
32
32
6
10
rather similar and is not shown here. We also analyzed the
nature of the transitions at 716, 542, and 493 nm (details not
shown here). This analysis showed that the lowest-energy peak
is caused dominantly by the superatomic 1D → 1F transitions
separated from each other. In each Cu (SR) unit, one thiolate
6 10
is face-capping the center Cu unit as a μ ligand. The other
3
3
nine thiolate groups are equally divided into three different
types (Figure 4c). Both μ and μ thiolate ligands, each bound
2
3
(
Figure S6), while the higher-energy peaks have significant
to only one Au, are identified between the Au12 shell and the
Cu shell. Each of the other three thiolate ligands serves as a μ2
ligand to joint two Cu outward at the edge of the Cu (SR)
contributions from mixed metal−ligand transitions, where also
the Au(5d) and Cu(3d) electrons contribute.
6
10
4
−
Although displaying little difference in their optical
unit. As a result, all Cu atoms in the [Au Cu (SPhCF ) ]
13
12
3 20
4−
absorption properties, the four [Au12+nCu (SR)30+n] (n =
0
cluster are planar-coordinated by three thiolates, similar to that
observed in Au Cu clusters. This situation makes the surface
32
, 2, 4, 6) clusters have different stabilities. As Cu(0) is more
13
x
7
199
dx.doi.org/10.1021/ja501811j | J. Am. Chem. Soc. 2014, 136, 7197−7200

Journal of the American Chemical Society
Communication
AUTHOR INFORMATION
Corresponding Author
nfzheng@xmu.edu.cn
■
Author Contributions
§
H.Y. and Y.W. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the MOST of China (2011CB932403) and the
NSFC of China (21131005, 21390390, 21333008) for financial
■
̈ ̈
support. The work in University of Jyvaskyla was supported by
the Academy of Finland. The computations were made at the
CSC computing center in Espoo, Finland, and at the HLRS
center in Stuttgart, Germany. X.C. thanks L. Lehtovaara for
discussions on DFT analysis of optical spectra.
4
−
Figure 4. Crystal structure of the [Au Cu (SPhCF ) ] cluster. (a)
13
12
3 20
Overall structure of the cluster. (b) Side view of the capping of two
Cu (SR) units on the Au13 core. (c) Top view showing how
Cu Au(SR) is sitting on the Au unit of the Au shell. Color legend:
6
10
2
6
6
12
gold spheres, Au; blue spheres, Cu; yellow spheres, S. All hydrogen
atoms and trifluoromethyl groups in (a) and fluorine and carbon
atoms in (b) and (c) are omitted for clarity.
REFERENCES
■
(
1) Ferrando, R.; Jellinek, J.; Johnston, R. L. Chem. Rev. 2008, 108,
8
45.
(2) Wang, D.; Li, Y. Adv. Mater. 2011, 23, 1044.
(
3) Pan, C.; Dassenoy, F.; Casanove, M.-J.; Philippot, K.; Amiens, C.;
4
−
structure of the [Au Cu (SPhCF ) ] cluster totally differ-
1
3
12
3 20
Lecante, P.; Mosset, A.; Chaudret, B. J. Phys. Chem. B 1999, 103,
10098.
ent from that of the Au (SR) cluster, in which the Au core
2
5
18
13
is evenly capped by six -RS-Au-SR-Au-SR- units although both
clusters contain the same number of metal atoms. Successful
structural determination of the degradation product of the
(4) Zhang, Y.; Huang, W.; Habas, S. E.; Kuhn, J. N.; Grass, M. E.;
Yamada, Y.; Yang, P.; Somorjai, G. A. J. Phys. Chem. C 2008, 112,
12092.
4
−
(
5) Hong, J.-W.; Kim, D.-H.; Lee, Y.-W.; Kim, M.-J.; Kang, S.-W.;
Han, S.-W. Angew. Chem., Int. Ed. 2011, 50, 8876.
6) Wu, B. H.; Zheng, N. F. Nano Today 2013, 8, 168.
(7) Niu, Z.; Li, Y. Chem. Mater. 2013, 26, 72.
8) Zeng, C.; Qian, H.; Li, T.; Li, G.; Rosi, N. L.; Yoon, B.; Barnett,
[
Au12+nCu (SR)30+n] clusters suggested that their instability
32
in solution was mainly due to the easy oxidation of low-valent
Cu by air. To our surprise, even with a nine-electron structure,
the oxidation product, [Au Cu (SPhCF ) ] , was much
more stable than its parent [Au Cu (SR) ] cluster. The
[
(
4
−
1
3
12
3 20
(
4−
1
6
32
34
R. N.; Whetten, R. L.; Landman, U.; Jin, R. Angew. Chem. 2012, 124,
13291.
4
−
Au Cu (SPhCF ) ] cluster exhibited a major absorption
13 12 3 20
at 540 nm (Figure S10). No obvious decay was observed, even
after its DMF solution was heated in air at 80 °C for 1.5 h.
To summarize, a series of all-thiol capped bimetallic Au−Cu
(9) Heaven, M. W.; Dass, A.; White, P. S.; Holt, K. M.; Murray, R. W.
J. Am. Chem. Soc. 2008, 130, 3754.
(10) Das, A.; Li, T.; Nobusada, K.; Zeng, C.; Rosi, N. L.; Jin, R. J. Am.
Chem. Soc. 2013, 135, 18264.
4−
nanoclusters, [Au Cu (SR) ]
(n = 0, 2, 4, 6), have been
1
2+n
32
30+n
(
11) Das, A.; Li, T.; Nobusada, K.; Zeng, Q.; Rosi, N. L.; Jin, R. J. Am.
Chem. Soc. 2012, 134, 20286.
12) Qian, H. F.; Eckenhoff, W. T.; Zhu, Y.; Pintauer, T.; Jin, R. C. J.
Am. Chem. Soc. 2010, 132, 8280.
13) Zeng, C. J.; Li, T.; Das, A.; Rosi, N. L.; Jin, R. C. J. Am. Chem.
successfully prepared. The metal distribution and the surface
structure of the bimetallic nanoclusters were found to be highly
sensitive to the Au precursors and countercations used in the
(
4−
syntheses. Each [Au12+nCu (SR)30+n] (n = 0, 2, 4, 6) cluster
32
(
consists of a Keplerate two-shell Au @Cu core protected by
1
2
20
Soc. 2013, 135, 10011.
(14) Jadzinsky, P. D.; Calero, G.; Ackerson, C. J.; Bushnell, D. A.;
Kornberg, R. D. Science 2007, 318, 430.
(
4
6 − n) units of Cu (SR) and n units of Cu Au(SR) (n = 0, 2,
2
5
2
6
, 6) on its surface. Different surface structures among the
clusters did not result in obvious differences in their absorption
properties but did lead to different stabilities.
(15) Yang, H. Y.; Lei, J.; Wu, B. H.; Wang, Y.; Zhou, M.; Xia, A. D.;
Zheng, L. S.; Zheng, N. F. Chem. Commun. 2013, 49, 300.
(16) Yang, H. Y.; Wang, Y.; Zheng, N. F. Nanoscale 2013, 5, 2674.
4−
4−
[
Au Cu (SR) ] and [Au Cu (SR) ] exhibited better
12 32 30 14 32 32
4−
4−
(17) Yang, H. Y.; Wang, Y.; Huang, H. Q.; Gell, L.; Lehtovaara, L.;
stabilities than [Au Cu (SR) ] and [Au Cu (SR) ] .
1
6
32
34
18
32
36
Malola, S.; Hakkinen, H.; Zheng, N. F. Nat. Commun. 2013, 4, 2422.
̈
Structural determination of the degradation product of the
4
−
(18) Desireddy, A.; Conn, B. E.; Guo, J.; Yoon, B.; Barnett, R. N.;
Monahan, B. M.; Kirschbaum, K.; Griffith, W. P.; Whetten, R. L.;
Landman, U.; Bigioni, T. P. Nature 2013, 501, 399.
[
Au12+nCu (SR)30+n] clusters clearly indicated that the poor
32
stability of thiolated Au−Cu bimetallic nanoclusters was mainly
due to the easy oxidation of zerovalent Cu by air.
(
19) Yang, H.; Wang, Y.; Lei, J.; Shi, L.; Wu, X.; Mak
Tang, Z.; He, J.; Hakkinen, H.; Zheng, L.; Zheng, N. J. Am. Chem. Soc.
2013, 135, 9568.
̈
inen, V.; Lin, S.;
̈
ASSOCIATED CONTENT
Supporting Information
Experimental details, detailed crystallographic data including
■
*
S
(20) Negishi, Y.; Munakata, K.; Ohgake, W.; Nobusada, K. J. Phys.
Chem. Lett. 2012, 3, 2209.
(21) Dhayal, R. S.; Liao, J.-H.; Lin, Y.-R.; Liao, P.-K.; Kahlal, S.;
the CIF files, computational details, UV−vis spectra of
4
−
Saillard, J.-Y.; Liu, C. W. J. Am. Chem. Soc. 2013, 135, 4704.
(22) Walter, M.; Akola, J.; Lopez-Acevedo, O.; Jadzinsky, P. D.;
[
Au Cu (SPhCF ) ]
(n = 0, 2, 4, 6) clusters, UV−vis
12+n
32
3 30+n
+
spectra of [Au Cu (SPhCF ) ]·4PPh , comparison of
1
3
12
3
20
4
Calero, G.; Ackerson, C. J.; Whetten, R. L.; Gronbeck, H.; Hak
̈
kinen,
computed and experimental bond lengths, analysis of the
electronic structure, and optical transitions of
H. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 9157.
4−
[
Au Cu (SR) ] . This material is available free of charge
12 32 30
via the Internet at http://pubs.acs.org.
7
200
dx.doi.org/10.1021/ja501811j | J. Am. Chem. Soc. 2014, 136, 7197−7200