Chemistry Reference
In-Depth Information
structure (Au-ligands bonding modes) of Au NCs are still not very clear except for a
few of clusters. At present, X-ray crystallography is the most reliable approach used
for the determination of the structure of metal clusters. In order to study the crystal
structures, stable and high-quality single crystals have to be synthesized. The
crystal structure of several gold clusters has been crystallographically determined
so far, including [Au
25
(SR)
18
]
q
(
q
¼
1, 0) [
23
,
24
], [Au
38
(SR)
24
][
49
], and
[Au
102
(SR)
44
][
25
]. The studies showed that they did not show the face-centered
cubic (fcc) packing of the bulk metal and their cores exhibited unique molecule-like
atomic structures. For instance, Au
25
has a centered icosahedral Au
13
core capped
by an exterior shell composed of the remaining 12 Au atoms in the form of
six -RS-Au-RS-Au-RS- motifs. It should be noted that the crystal structures
may be fine tuned by changing the chemical environments, which is important for
manipulating the properties of gold nanoclusters.
3 Syntheses of Atomic Precise Au Nanoclusters with
Different Compositions
3.1 Au
5
Nanoclusters
Tan and coworkers [
50
] successfully prepared water-soluble fluorescent Au
5
nanoclusters through a robust photoreduction of HAuCl
4
in the presence of poly
(methacrylic acid) functionalized with pentaerythritol tetrakis 3-mercaptopropionate
(PTMP-PMAA). Under irradiation with an ultraviolet light source (8W, wavelength
¼
365 nm), the initial clear solutions gradually changed from yellow to orange,
accompanied by the evolution of emission peaks. The morphology and size of Au
5
nanoclusters were characterized using a TEM, which shows the Au nanoclusters
with a diameter of 0.6
0.4 nm. MALDI-TOF MS displayed that Au
5
nanoclusters
are the dominant Au-containing components in the colloidal solution.
3.2 Au
8
Nanoclusters
Zheng et al. [
51
] synthesized water-soluble, monodispersed, blue-emitting Au
8
nanoclusters encapsulated in biocompatible poly(amidoamine) PAMAM
dendrimer. Gold ions were first sequestered into internal core of dendrimers,
where the tertiary amines could form coordination bonds with the AuCl
4
ions.
Upon addition of NaBH
4
, gold atoms aggregate within the dendrimers to form small
nanoclusters and protected by the external shell of dendrimer which can prevent
cluster aggregation into large nanoparticles. From the electrospray ionization (ESI)
mass
spectrometry measurements, Au
8
was
found to be
the dominant
Au-containing component
in the fluorescent
solutions.
Interestingly,
the
