Chemistry Reference
In-Depth Information
Wu et al. [
75
] reported a one-pot process for the synthesis of 19 gold atom-
contained nanoclusters (Au
19
(SC
2
H
4
Ph)
13
) by the combination of both kinetic
control and thermodynamic selection principles. In a typical synthesis, Au
(I) aggregates were first formed by adding phenylethylthiol into a cold solution of
HAuCl
4
∙
3H
2
O(0
C) under constant stirring. In the next step, a freshly prepared
toluene solution of borane-
tert
-butylamine complex was added drop by drop. In
this reported method, the key point is that the usually used reducing agent NaBH
4
was replaced with a weaker one (borane-
tert
-butylamine complex). Under the
preparation conditions, the initially formed nanocluster mixture underwent size
convergence into a monodispersed 19-atom nanocluster after a prolonged aging
process (~60 h). The purity of the as-prepared clusters was characterized by the
SEC (Fig.
5a
), from which all of the spectra are superimposable, indicating the high
purity of the product. From the ESI-MS shown in Fig.
5b
, a dominant peak at
m/z
5,659.3 could be assigned to the Au
19
(SC
2
H
4
Ph)
13
Cs
+
. In addition, LDI-MS analy-
sis showed a core with a mass of 3-4 kDa, which is consistent with this formula.
This work clearly demonstrates the importance of both kinetic control and thermo-
dynamic selection in the synthesis of monodispersed metal nanoclusters and
provides idea for the synthesis of atomically precise nanoclusters.
3.9 Au
20
Nanoclusters
Since the synthesis of Au
55
(PPh
3
)
12
Cl
6
by Schmid et al. [
76
], many efforts have
been devoted to the syntheses and applications of phosphine-stabilized gold
nanoclusters. Compared to the thiol-capped Au nanoclusters, the syntheses of
phosphine-stabilized clusters need more tough reaction conditions, such as anaero-
bic atmosphere and diborane gas reducing agent. Hutchison and coworkers [
77
]
developed a safer, more convenient, and more versatile process for the synthesis of
phosphine-capped gold nanoclusters, which is analogous to those originally
reported by Schmid. Based on the synthesis strategy, Zhang et al. [
78
] synthesized
PPh
3
-protected Au
20
nanoclusters (Au
20
(PPh
3
)
8
). In the synthesis, AuCl(PPh
3
) and
tetraoctylammonium bromide (TOABr) were dissolved in a toluene/water mixture.
NaBH
4
dissolved in water was then added dropwise under vigorous stirring. Gold
nanoclusters were collected in dichloromethane after stirring the solution overnight.
The HRTEM measurements showed that the majority of the nanoclusters have
diameters of less than 1 nm and the cluster composition was determined to be
Au
20
(PPh
3
)
8
2+
by the accurate mass measurement of its doubly charged cation.
Recently, Wang and coworkers [
79
] successfully synthesized phosphine-
protected Au
20
nanoclusters with novel structure through the NaBH
4
reduction of
Au(PPhpy
2
)Cl (PPhpy
2
¼
bis(2-pyridyl)-phenylphosphine). With pyridyl phos-
phine as protecting ligand, the stability of the formed gold nanoclusters can be
improved because the P and N donors in the pyridyl phosphine could bridge two
