Chemistry Reference
In-Depth Information
Au
7
Xe
Au
20
Au
19
Fig. 9 Proposed structures of neutral Au
7
,Au
19
and Au
20
clusters of gold on the basis of FELIX
data. Krypton atoms interact weakly with the clusters through van der Waals' forces
planar edge capped triangle with C
s
symmetry and Au
19
and Au
20
have close-
packed structures based on a tetrahedron (see Fig.
9
)[
153
]. These structures have
been predicted as the global minima on the basis of DFT calculations. Recent
developments in this field are discussed in the chapter authored by Fielicke and
Woodham.
In the 1970s and 1980s, solution and solid-state NMR were used to study the
structures of molecular gold cluster compounds with 4-13 metal atoms. The
clusters whose structures had been unambiguously determined by single-crystal
X-ray crystallographic determinations were used to define the strengths and limi-
tations of the technique [
111
,
154
-
157
]. NMR studies on small clusters with
phosphine are structurally informative since their
31
P{
1
H}nuclei have the appro-
priate abundance and sensitivity to provide good high-resolution spectra. However,
many of the larger clusters have stereochemically non-rigid skeletal geometries in
solution (even at low temperatures) and consequently the structural information
obtained was not as helpful as originally anticipated [
111
,
154
-
157
].
31
P{
1
H}NMR
proved to be more helpful for studying clusters in the solid state, where their
stereochemical rigidity provides more structural information [
154
]. Since the
majority of stabilising ligands used in colloid and cluster syntheses are organically
based,
1
H NMR is very useful for confirming the presence of these molecules on the
