Chemistry Reference
In-Depth Information
SEC
Size exclusion chromatography
SEM
Scanning electron microscopy
SERS
Surface enhanced Raman spectroscopy
SR
Organothiolato
t
-Bu
tert
-butyl
TEM
Transmission electron microscopy
TGA
Thermogravimetric analysis
Tio
Tiopronin
Tetra(
n
-octyl)ammonium bromide
TOAB
Tol
4-Methylphenyl
XRD
X-ray diffraction
1
Introduction
The introduction to the preceding volume defined more clearly the differences
between clusters, colloids and nanoparticles and highlighted the important synthetic
routes to these interesting materials and their characterisation. It also suggested that
there are grey areas in-between these classes, where the differences remain less
clearly defined. The original synthesis of gold cluster compounds, based on the
reduction of linear gold(I) phosphine complexes, originated in the late 1960s from
Malatesta's group in Milan [
1
-
5
] and was prompted by the contemporary charac-
terisation of related hydrido-complexes of platinum. The area was greatly extended
by Mingos [
6
-
15
] and Steggerda [
16
-
19
] in the 1970s and 1980s. The molecular
cluster compounds which they characterised unambiguously by single crystal X-ray
studies had 4-13 gold atoms. In the late 1990s Teo reported the larger
[Au
39
Cl
6
(PPh
3
)
14
] cluster [
20
,
21
] which had its origins in his related studies of
gold-silver clusters based on linked icosahedra. In 1981 Schmid et al. reported
[
22
-
26
] that if diborane B
2
H
6
was used rather than NaBH
4
to reduce gold
(I) triphenylphosphine complexes, then the resultant product was
[Au
55
(PPh
3
)
12
Cl
6
], which he formulated as a very stable closed shell and close-
packed cluster with 42 surface atoms, 12 of which are stabilised by triphenyl-
phosphine and 6 by chloro-ligands. Au
55
is the second of the series of the so-called
close-packed “full-shell clusters”. Although definitive and evidence-based single
crystal structural data were not obtained, it was proposed on the basis of spectro-
scopic data that it consists of a cuboctahedral fragment of the close-packed metallic
structure of bulk gold.
As the result of the synthetic work described above, which led to well-defined
molecular clusters, it was established that their nuclearities could be reduced or
increased by the addition of specific reagents. Typical degradation reactions of gold
cluster cations result in the loss of a few gold atoms and are induced by the addition
of phosphines or soft anionic ligands which shift the equilibrium by coordinating to
the outgoing AuPR
3
+
cation. Complementary aggregation reactions are encouraged
either by the addition of mononuclear gold(I) complexes or the replacement of
