Chemistry Reference
In-Depth Information
Recently, Jin's group [
93
] synthesized another Au
36
nanocluster with 24 thiol
ligands and reported the face-centered cubic (FCC)-type core structure of
Au
36
(SR)
24
(SR: 4-
tert
-butylbenzenethiolate (SPh-
t
Bu)). In this synthesis, pure
Au
38
(SCH
2
CH
2
Ph)
24
obtained by a size-focusing method was used as precursor
[
94
]. In spite of the high thermal and redox stability of Au
38
(SCH
2
CH
2
Ph)
24
nanoclusters, new clusters could been obtained when reacting with HSPh-
t
Bu at
appropriate conditions. From both ESI-MS and TGA analyses, the formula of the
nanocluster was determined to be Au
36
(SR)
24
, which is different from the previ-
ously reported composition of Au
36
(SPh)
23
[
92
]. X-ray crystallography was also
used to analyze the crystal structure of Au
36
(SPh-tBu)
24
rhombic single crystal. The
total structure of the as-synthesized Au
36
(SPh-tBu)
24
nanoclusters is shown in
Fig.
10
. The Au
36
nanocluster displays an unusual FCC-type core structure
consisting of an Au
28
kernel with a truncated FCC tetrahedron exposing (111)
and (100) facets. More interestingly, different from the previously reported Au
clusters, a new type of thiolate-binding mode was discovered, that is, 12 of the
24 ligands bind to the underlying Au atoms in a simple bridging mode, with the
remaining 12 thiolates forming the known dimeric staple motifs.
3.13 Au
38
Nanoclusters
While tremendous work has been done on the atomically precise Au
25
nanoclusters,
thiolate ligands passivated gold nanoclusters with other specific number of gold
atoms have also been pursued over the past years. Through controlled etching
process, Schaaff et al. [
95
] first reported the synthesis of Au
38
nanoclusters by
heating larger Au:SR clusters (~Au
75
, 1.1 nm in diameter) in neat dodecanethiol
solution under inert atmosphere. Subsequently, Chaki et al. [
44
] successfully
isolated the alkanethiolate-protected Au
38
nanoclusters and determined the compo-
sition of Au
38
(SC
n
H
2
n
+1
)
24
by ESI-MS analysis. Different from the commonly used
two-phase synthesis, unique etching process was used for the preparation of Au
38
nanoclusters. In 2008, Toikkanen et al. [
96
] reported a facile synthesis strategy to
obtain monodispersed hexanethiolate-protected Au
38
(SC
6
)
22
nanoclusters based on
the highly thermodynamic stability of Au
38
in excess thiol. Firstly, hexanethiolate-
capped gold nanoclusters were synthesized according to the Brust-Schiffrin
two-phase method. After phases separated and precipitated by acetonitrile (ACN).
The dichloroethane (DCE) solution of nanoclusters was then exposed to excess
hexanethiol under stirring for different times. Finally, Au
38
nanoclusters fully
passivated by the thiol monolayer were formed as the only product. It was found
that the Au
38
nanoclusters behave like molecules with a wide energy gap between
HOMO and LUMO and undergo quantized charging at room temperature in
electrochemical experiments. Cyclic voltammetry and scanning electrochemical
microscopy measurements demonstrated that
the Au
38
nanoclusters could be
reversibly oxidized to charge states
z
¼
+1 or +2; however, reduction to
z
¼
1
leads to desorption of the protecting thiolate monolayer.
