Chemistry Reference
In-Depth Information
Au
6
P
n
; and Au
7
P
n
. Several new Au
m
Te
n
(
m
¼
1-11;
n
¼
1-4) clusters were
identified.
3 Tools for Determining Structures and Their Application
to Gold Cluster Ions
Ever since the development of soft ionisation methods such as FAB, ESI and
MALDI, mass spectrometry has been applied to the analysis of gold cluster
compounds. The primary concern has generally been the assignment of cluster
formulae. For larger clusters where the stoichiometries of gold to ligand are
unknown, or which are polydisperse mixtures, or mixtures containing different
ligands, this can be challenging. Various approaches have been adopted to over-
come these problems. For example, Maity et al. have used [
168
] 50:50
phenylacetylene and para-tolylacetylene mixtures to assign the stoichiometry of
organogold clusters protected by phenylacetylene.
In this section we do not review all of the analytical applications of MS in gold
cluster chemistry. Rather we highlight the types of tools that have been developed
to study the structures of both bare and ligated cluster ions in the gas phase.
Quantum chemical calculations are an essential adjunct to experimental techniques,
which allow the gas-phase structures of many clusters to be obtained. A recent
interesting review by Kappes et al. highlights the techniques used to date to
determine the structures of bare gold clusters [
169
]. The experimental techniques
discussed below include (1) fragmentation methods (identify atom connectivity),
(2) ion mobility spectrometry (IMS) (identify the collision cross section), (3) infra-
red multiphoton dissociation (IRMPD) (identify IR absorption), (4) UV-Vis spec-
troscopy (identify the UV-Vis absorption spectra to investigate the clusters
structure), (5) trapped ion electron diffraction (TIED) (identify molecular scatter-
ing) and (6) photoelectron spectroscopy (PES) (identify the electron binding
energy).
3.1 MS-Based Fragmentation Methods
The most commonly used approach in mass spectrometry to gain structural infor-
mation is the use of activation methods to induce fragmentation of a mass-selected
precursor ion. Activation can occur, for example, via collision-induced dissociation
(CID, discussed in Sect.
3.1.1
), surface-induced dissociation (SID), laser-based
activation methods such as photodissociation (PD, discussed in Sect.
3.1.1
) and
ion-electron interactions (discussed in Sect.
3.1.2
). When tunable lasers are used,
this allows the spectroscopy of AuNCs to be examined, and this is discussed further
in Sects.
3.3
and
3.4
below.
