Chemistry Reference
In-Depth Information
with the Au
3
+
cluster is accelerated. At a reaction time as short as 0.1 s, minute
amounts of Au
3
(CH
4
)
2
(H
2
)
2
+
are observed, and the dominant peaks correspond to
Au
3
(CH
4
)
x
(H
2
)
y
+
,(
x
,
y
3, 0; 3, 3). At reaction times greater than 0.5 s, the only
product observed is Au
3
(CH
4
)
3
(H
2
)
3
+
.
Mass-selected Au
5
+
stored in an ion trap under similar conditions reacts in a
similar way to Au
3
+
. At an ion-trap temperature of 300 K and a reaction time of
0.1 s, only one CH
4
molecule is adsorbed. Increasing the reaction time from 0.5 to
2 s results in the addition of a second adsorbate being H
2
to give Au
5
(CH
4
)(H
2
)
+
.
Reducing the temperature to 200 K enhances the reactivity of the cluster consider-
ably. At 0.1 s Au
5
(CH
4
)
2
+
is the dominant peak. Increasing the reaction time to 0.5 s
shows Au
5
(CH
4
)
3
(H
2
)
+
as the dominant peak with Au
5
(CH
4
)
2
(H
2
)
+
and
Au
5
(CH
4
)
3
(H
2
)
4
+
. Further increasing the reaction time from 0.5 up to 2 s results
in mainly Au
5
(CH
4
)
4
(H
2
)
4
+
.
¼
¼
Reactions with H
2
and CH
3
CH
CH
2
The mass-selected bare gold cluster cations, Au
3
+
and Au
5
+
, were reacted with
propylene (CH
3
CH
CH
2
) comparable to the reactions discussed above, however
replacing CH
4
with CH
3
CH
¼
¼
CH
2
. Both clusters appear to immediately react with
CH
3
CH
CH
2
. At a reaction time of 0.1 s and an ion-trap temperature of either
300 K or 200 K, the main peak is solely Au
3
(CH
3
CH
¼
CH
2
)
3
+
for the mass-selected
¼
the Au
5
+
trimer.
In comparison,
cluster at 300 K forms predominantly
CH
2
)
3
+
is the predominant
peak observed. In contrast to CH
4
, only trace amounts of CH
3
CH
CH
2
)
4
+
Au
5
(CH
3
CH
¼
and at 200 K Au
5
(CH
3
CH
¼
CH
2
are required
to react with and completely saturate the gold clusters which then also inhibit the
co-adsorption of molecular H
2
.
¼
Reactions with CH
3
X
Koszinowski et al. showed that the reaction of Au
2
+
with methyl halides could be
used to 'synthesise' the gold carbene, Au
2
CH
2
+
, in the gas phase (Eq. (
32
)) [
282
]:
Au
2
þ
Au
2
CH
2
þ
CH
3
X
!
HX
ð
32
Þ
Lang and Bernhardt studied bare gold cluster cation Au
3
+
and Au
5
+
reaction with
CHCl
3
and H
2
O[
285
]. With the ion trap at room temperature (300 K), it was found
that the reactions of Au
x
+
(
x
3, 5) proceeded quickly. For the trimer, the number
of adsorbate molecules of CHCl
3
and H
2
O never exceeds the number of gold atoms.
The distribution of the adsorbate molecules also suggests that there is an equilib-
rium constraint to direct the reaction channels. The Au
5
+
cluster exhibits an
X-shaped, D
2h
symmetry, with 4 equiv. gold corner atoms around the central gold
atoms. Hence, the number of adsorbate molecules does not exceed 4. The reaction
behaviour is comparable to Au
3
+
.
¼
