Chemistry Reference
In-Depth Information
to formaldehyde was predicted via DFT calculations. Each formaldehyde is formed
at a different end of the gold dimer, and they are formed in the following related
steps: oxygen absorbs at a gold site to form a peroxo intermediate, (CH
4
)Au-Au
(O-O)(CH
4
)
+
, which then abstracts a hydrogen atom to yield an organogold-
hydroperoxide intermediate, (CH
4
)Au-Au(O-OH)(CH
3
)
+
, which then loses water
to form a oxo-gold-carbene, (CH
4
)Au-Au(O)(CH
2
)
+
, that can then rearrange to
the O bound formaldehyde complex, (CH
4
)Au-Au(OCH
2
)
+
. The final step involves
absorption of the third methane molecule onto the bisformaldehyde complex,
(CH
2
O)Au-Au(OCH
2
)
+
, which acts as a trigger to release both formaldehydes:
2CH
4
þ
2O
2
!
2CH
2
O
þ
2H
2
O
ð
79
Þ
5 From the Gas Phase to Materials
Mass spectrometry-based studies offer exciting opportunities to direct the synthesis
of new materials, as dramatically highlighted by the discovery and subsequent
isolation of bulk fullerenes. Initial studies using a cluster beam source coupled to
a mass spectrometer led to the discovery of the magic number of C
60
[
328
]. Subse-
quently Kroto et al. proposed the Buckminsterfullerene structure [
329
]. These
exciting results inspired other researchers to devise synthetic strategies aimed at
isolating samples of C
60
in order to structurally characterise them, but it was not
until 5 years later that bulk samples became available [
330
].
Within the context of AuNCs, mass spectrometry has had an impact in the
generation of materials in two main ways: (1) the use of MS to 'direct' the synthesis
of gold NCs and (2) the use of MS as a preparative tool to mass select gold NCs and
soft land them onto surfaces. Both of these approaches are briefly described below.
5.1 MS-Directed Synthesis of Gold Clusters
As noted in Sect.
2
, mass spectrometry has been used to monitor the growth and
processing of gold clusters. In several cases, MS had been used to direct the synthesis
and isolation of bulk material of the gold cluster for subsequent structure and property
studies. Recent cases include work from the group of Konishi et al. [
58
,
59
]. For
example, the isolation of [Au
11
(Ph
2
P(CH
2
)
2
PPh
2
)
6
]
3+
[
59
], as the SbF
6
salt, was
found to be composed of an Au
9
core with two gold atoms located at the
exo
position.
In brief, the gold complex [Au
2
(Ph
2
P(CH
2
)
2
PPh
2
)]Cl
2
[
331
,
332
](200
mol) in 75mL
ethanol was treated with a 5 mL ethanolic solution of sodiumborohydride (400
ʼ
mol).
After 1 h of stirring crude material was precipitated using excess NaSbF
6
. ESI-MS
analysis of the crude precipitate revealedmonodispersed [Au
11
(Ph
2
P(CH
2
)
2
PPh
2
)
6
]
3+
,
m/z
ʼ
1519. The isolation of crystalline material suitable for structural studies by
X-ray crystallography was prompted by ESI-MS analysis of the crude material and
crystals successfully grown from ethanol/dichloromethane.
¼
