Chemistry Reference
In-Depth Information
3.16 Au
67
Nanoclusters
By using a variety of mass spectrometric techniques, the formulas of a series of gold
clusters with core sizes of 5, 8, 14, 22, and 29 kDa have been determined to be
Au
25
(SR)
18
[
19
], Au
38
(SR)
24
[
44
], Au
102
(SR)
44
[
25
], and Au
144
(SR)
60
[
104
,
105
],
respectively. However, the unambiguous composition identification of the cluster
with 14 kDa core mass has been largely impeded mainly due to the difficulty in
obtaining a high yield of the 14 kDa nanoclusters in the synthetic process. By using
single-phase method, Dass synthesized gold nanocluster enriched in 14 kDa mass
[
106
]. It was found that Au
68
nanoclusters in high yield could be specifically
obtained when the growth rate is effectively lowered at certain levels of aggrega-
tion. With MDLDI MS employing threshold laser fluence and DCTB as matrix, the
composition of the product was determined to be Au
68
(SR)
34
on the basis of the
detection of the parent molecular ion. However, due to lack of methods to produce
pure Au
68
nanoclusters in sufficient quantity and thus the incomplete character-
izations, the obtained Au
68
nanoclusters may be just an intermediate product
[
86
]. Recently, Dass and coworkers [
107
] not only synthesized and isolated the
pure species in high yield but also determined its composition of Au
67
(SR)
35
on the
basis of high-resolution ESI-MS on two different thiolate groups, i.e., 2-
phenylethanethiol and
n
-hexanethiol. In their work, a cluster mixture with 14 and
22 kDa compounds were synthesized in THF. In the second stage, through mild
thermochemical treatment of the polydispersed mixture in the presence of excess
thiol, samples characterized by distinct peaks at 14 and 22 kDa were obtained.
Finally, by using a THF-methanol mixture in appropriate ratios, pure Au
67
nanoclusters were obtained in high yield. The optical absorption characterization
of the purified Au
67
compounds was carried out with UV-Vis measurement. As
shown in Fig.
13
, different from the spectra of Au
38
and larger (~Au
300
) clusters, the
obtained Au
67
shows a nearly monotonically rising absorption. The spectrum is in
substantial agreement with that reported by Alvarez et al. [
108
]. Moreover, the
Au
67
(SR)
35
nanocluster was structurally considered to be the smallest one to adopt
the complete truncated-decahedral motif for its core with a surface structure bearing
greater similarity to the larger nanoparticles.
3.17 Au
102
Nanoclusters
The first structure of Au
102
(
p
-MBA)
44
(
p
-MBA
para
-mercaptobenzoic acid)
cluster was reported by Jadzinsky et al. in 2007 [
25
]. Based on the gold atomic
packing in the cluster core and the Au-S bonding on the surface, a chiral crystal
structure was proposed with the central gold atoms packed in a Marks decahedron
and surrounded by additional layers of gold atoms in unanticipated geometries.
Ackerson et al. [
109
] investigated effects of some synthetic conditions (e.g., ratios
ΒΌ
