A relationship between the size of
metal particles and their catalytic
activity has been established over a nanometer scale (2–10
nm). However, application on a subnanometer scale (0.5–2 nm)
is difficult, a possible reason being that the activity no longer
relies on the size but rather the geometric structure as a cluster
(or superatomic) compound. We now report that the catalytic activity
for the oxygen reduction reaction (ORR) significantly increased when
only one atom was removed from a magic number cluster composed of
13-platinum atoms (Pt<sub>13</sub>). The synthesis with an atomic-level
precision was successfully achieved by using a dendrimer ligand as
the macromolecular template strictly defining the number of metal
atoms. It was quite surprising that the Pt<sub>12</sub> cluster exhibited
more than 2-fold catalytic activity compared with that of the Pt<sub>13</sub> cluster. ESI-TOF-mass and EXAFS analyses provided information
about the structures. These analyses suggested that the Pt<sub>12</sub> has a deformed coordination, while the Pt<sub>13</sub> has a well-known
icosahedral atomic coordination as part of the stable cluster series.
Theoretical analyses based on density functional theory (DFT) also
supported this idea. The present results suggest potential activity
of the metastable clusters although they have been “missing”
species in conventional statistical synthesis