Chemistry Reference
In-Depth Information
Fig. 9 (a) FCC unit cell; (b to c) construction of cuboctahedron from FCC; (d) icosahedron
transformed from cuboctahedron by corrugating the middle 6-atom (Au
6
) hexagon into a chair-like
configuration
phosphine ligands tend to simply adsorb on the surface gold atoms via a one-on-one
fashion (terminal bonding) [
16
-
29
], while thiolate ligands often form a chain-like
structure by incorporating some gold atoms [
7
-
13
,
75
-
81
]. The so far revealed
surface structure modes [
7
-
13
] of gold nanoclusters provide valuable information on
how the larger nanoclusters should be stabilized by the thiolate ligand and what
factors determine their stability.
The reported structures of thiolate-protected gold nanoclusters can be catego-
rized into FCC and non-FCC types (where FCC: face-centered cubic) [
7
-
13
]. Bulk
gold adopts an FCC structure (Fig.
9a
), and its unit cell comprises 8 vertices and
6 face centers. The 14-atom FCC unit cell is an empty structure (i.e., non-centered),
from which a cuboctahedron consisting of 13 atoms can be readily constructed
(Fig.
9b
). The cuboctahedron is faceted by 6 squares and 8 triangles, and the center
atom is coordinated to 12 first-shell atoms. Transformation of the 13-atom cubocta-
hedron gives rise to a 13-atom icosahedral structure (Fig.
9c
,d)[
82
], which
preserves the 12 coordination but the surface becomes exclusively triangular facets
(Fig.
9d
). Overall, the cuboctahedron is a fragment of FCC, but the icosahedron is
not, as the presence of fivefold rotation axis in the icosahedron breaks the
cubic symmetry.
Below we first discuss the non-FCC-type structures with increasing size, including
Au
25
(SC
2
H
4
Ph)
18
,Au
38
(SC
2
H
4
Ph)
24
,andAu
102
(SPh-COOH)
44
[
7
-
10
]. Examples of
FCC structures include Au
28
(S-Ph-
t
-Bu)
20
and Au
36
(S-Ph-
t
-Bu)
24
[
11
,
12
].
