Atomically Precise Gold Catalysis - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 92

d n 9 r 4 n g | 7

Figure 4.3 Breakdown of the X-ray crystal structure of [TOA 1 ][Au 25 (SCH 2 CH 2 Ph) 18 ]
as seen from [001]. (a) Arrangement of the Au 13 core with 12 atoms on the
vertices of an icosahedron and one in the center. (b) Depiction of gold
and sulfur atoms, showing six orthogonal Au 2 (SCH 2 CH 2 Ph) 3 'staples'
surrounding the Au 13 core (two examples of possible aurophilic bonding
shown as dashed lines). (c) [TOA 1 ][Au 25 (SCH 2 CH 2 Ph) 18 ] structure with
the ligands and TOA 1 cation (depicted in blue) (Legend: gold, yellow;
sulfur, orange; carbon, gray; hydrogen, off-white; the TOA 1 counter-ion
is over two positions with one removed for clarity).
(Reproduced with permission from ref. 21, Copyright American
Chemical Society, 2008).

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active sites on the gold particle at an atomic level. These fundamental
properties can also pave way for designing newer types of novel, highly
active, and selective gold cluster catalysts.
Generally, gold cluster catalysts are obtained using two different synthesis
approaches i.e., physical approach and the chemical approach. The differ-
ence between both approaches is that the clusters formed using physical
approach does not possess any stabilizing ligands whereas the clusters
formed through chemical approach have organic ligands stabilizing them.
Physical approaches normally include gas-phase deposition techniques such
as chemical vapor deposition (CVD) and physical vapor deposition (PVD) and
chemical approaches include solution-based reduction of metal salts in the
presence of organic ligands. Due to the absence of ligands on their surface,
the bare clusters formed using physical methods have large surface energy
and are highly reactive for catalytic applications. By controlling the size of