Gas Phase Formation, Structure and Reactivity of Gold Cluster Ions - Gold Clusters, Colloids and Nanoparticles - page 187

Þ þ þ Au x þ RNH 2 ! Au x 1 RNH 2 ð Au ð 22 Þ

Þ þ þ Þ 2 þ ð

RNH 2 !

ð ð Þ

Au 3 RNH 2 Au RNH 2 Au 2 23

Reactions with the Sulphur Compounds H 2 S and CH 3 SSCH 3

Sugawara et al. examined the reactions of gold cluster cations Au n + 1-12)

with H 2 S in an FT-ICR mass spectrometer [ 67 ]. Four types of primary reaction
channels were observed: (1) adduct formation (Eq. ( 24 )), a reaction that occurs for
clusters where n

( n ¼

¼ 9, 11 and 12; (2) HS abstraction (Eq. ( 25 )), a reaction that only

2; (3) sulphuration to yield Au n S + occurs for n

¼

(Eq. ( 26 )), which occurs for

n ¼

4-8 and 10 and (4) Au displacement (Eq. ( 27 )), a reaction that only occurs for

2. Au 3 + was unreactive towards H 2 S and even n cluster cations were found to
be more reactive than adjacent odd n clusters. Subsequent sulphuration reactions of
Au n S + proceeded to give Au n S m + but stopped at Au n S m + x H 2 + when H 2 loss did not
occur. The maximum number of sulphur atoms, m , observed in Au n S m + increased
with the cluster size up to n

n ¼

¼ 7 and 8 (where m ¼ 5), while the sulphuration

reaction stopped at early stages for n > 9:

Au x þ Þ þ H 2 S ! Au x SH 2 ð ð 24 Þ

! Au x S ð þ þ H ð 25 Þ

Au x S þ þ ! H 2 ð 26 Þ

Þ þ þ ! Au x 1 SH 2 ð Au ð 27 Þ

Using FT-ICR mass spectrometry, H¨ckendorf et al. have shown that small odd
electron gold cluster anions Au x ( x 2 and 4) react with dimethyldisulphide via

S-S (Eq. ( 28 )) and S-C bond activation (Eq. ( 29 )) [ 283 ]. Au 2 also reacts via
displacement of a gold atom (Eq. ( 30 )) or anion (Eq. ( 31 )):

¼

Þ Au x þ

CH 3 SSCH 3 ! Au x SCH 3 ð ð 28 Þ

Þ ! ð ð Þ

Au x SSCH 3 29

Þ þ ! Au x 1 CH 3 SSCH 3 ð Au ð 30 Þ

! Au þ Au x 1 CH 3 SSCH 3 ð Þ ð 31 Þ

Reactions with H 2 and CH 4

The co-adsorption of hydrogen and methane on small bare cationic gold clusters
Au x + ( x 3, 5) has been proposed to occur on the same adsorption site of the gold

cluster (i.e. the same gold atom) [ 284 ], termed permissive co-adsorption. For these
experiments Bernhardt et al. used a variable-temperature ion trap. For short reaction
times, at 300 K, Au 3 CH 4 + is observed as a single product. Increasing the reaction
time to 1 and 2 s results in formation of Au 3 (CH 4 ) 2 (H 2 ) 2 + . When the ion-trap
temperature is reduced to 200 K, the formation of the CH 4 and H 2 adsorption

¼