Chemistry Reference
In-Depth Information
Fig. 17 Total structure of Au
36
(SPh-
t
-Bu)
24
. The carbon tails (-Ph-
t
-Bu) are omitted for clarity.
(a) The view of kernel structure based on polyhedron fusion and shell-by-shell mode, respectively.
(b) Surface thiolate-protecting modes and the total structure of Au
36
(SR)
24
[
11
]. Color labels:
yellow
ΒΌ
sulfur, all the
other colors
are gold atoms
structure. The overall structure of Au
28
(SR)
20
has a quasi-
D
2
symmetry (Fig.
16c
).
The formula of Au
28
(SR)
20
may be represented as Au
20
[Au
2
(SR)
3
]
4
(SR)
8
. Note that
the structure of Au
28
(SR)
20
is also chiral as the case in Au
38
(SR)
24
and Au
102
(SR)
44
,
due to the rotation arrangement of the dimeric staples and bridging thiolates. A pair
of enantiomers exists in the unit cell of the Au
28
(SR)
24
single crystals.
5.2.2 The Case of Au
36
(SPh-t-Bu)
24
The Au
36
(SPh
-t-
Bu)
24
nanocluster was converted from Au
38
(C
2
H
4
Ph)
24
by reaction
with excess HSPh
-t-
Bu at 80
C[
11
]. It has a 28-gold-atom kernel. Unlike the
icosahedron-based kernel in the Au
38
(SR)
24
nanocluster, the 28-gold-atom kernel
in Au
36
is based on cuboctahedral building blocks and thus can be viewed as a
fragment of the FCC structure. From the view of polyhedron fusion, the Au
28
kernel
is composed of four interpenetrating cuboctahedra, with two cuboctahedra on the
top, the other two on the bottom (Fig.
17a
). The four center atoms of the four
cuboctahedra assemble into a tetrahedron. The other way to appreciate the kernel is
to view it as a two-shelled structure. In the center of Au
28
kernel, four gold atoms
pack into an Au
4
tetrahedron. Onto each facet of the Au
4
tetrahedron, a six-atom
Au
6
triangle is close-packed. Hence, there are 24 gold atoms on the second shell,
forming a vertex/edge-truncated tetrahedron. Since this Au
28
kernel has an FCC
structure, one can identify a-b-c-a cubic-close-packing layers (Fig.
17a
). The Au
28
gold kernel exposes four {111} and six {100} facets. The four {111} facets
