Chemistry Reference
In-Depth Information
of neutral gold carbonyl clusters by O
2
and N
2
O[
46
] together with the reviews on
neutral metal clusters by Knickelbein [
47
] and Shi and Bernstein [
48
].
Finally, while there are a growing number of reports on the use of gold
nanoparticles as a co-additive in the analysis of low molecular weight compounds
by laser desorption ionisation MS [
49
-
53
], these are not reviewed here.
2 MS-Based Analysis of Gold Nanoclusters Synthesised
in the Condensed Phase
Historically, mass spectrometry-based analysis of gold cluster compounds has
lagged behind other methods such as X-ray crystallography due to traditional
ionisation methods such as electron ionisation or chemical ionisation being incom-
patible with compounds of low volatility. It appears that the first analytical studies
of gold cluster compounds had to wait until the advent of fast atom bombardment
(FAB) [
54
], which allowed transfer of gold cluster cations such as [Au
6
(PPh
3
)
6
]
2+
to the gas phase [
55
].
2.1 The Need for Net Charge to Allow for Analysis of Gold
Nanoclusters via MS
While MALDI-MS and ESI-MS have been a boon for the analysis of metal
complexes and clusters, these ionisation methods are challenged by compounds
that have no net charge. For inorganic and organometallic complexes, a number of
strategies have been developed to overcome this limitation: (1) neutral metal
halides can have a halide anion replaced with a neutral ligand such as pyridine,
resulting in a MS detectable cationic complex [
36
]; (2) neutral ligands can be
swapped for related fixed charge analogues [
56
]; (3) addition of acids or bases
can allow protonation or deprotonation of coordinated ligands, thereby providing a
positive or negative charge [
36
]; (4) oxidation to form a charged complex in which
the metal centre is in a higher oxidation state [
36
]; (5) addition of a metal ion such
as Ag
+
to form a coordination complex [
36
] and (6) carbonyl derivatisation of
neutral metal carbonyls by alkoxides, azides and hydrides [
36
].
Gold NCs that have been synthesised in solution and then subjected to analysis
via ESI or MALDI can be considered to have the following general formula given
in Eq. (
5
):
h
i
z
Au
ð
a
Au
þðÞ
L
c
A
ðÞ
d
n
H
þ
ð
5
Þ
b
where L is a neutral ligand such a phosphine or bisphosphine and A is an anionic
ligand such as a thiolate or halide.
