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Encyclopedia of Physical Science and Technology EN010H-470 July 16, 2001 16:53

Nanosized Inorganic Clusters 309

A. Superfullerene Clusters
with Icosahedral Symmetry
It is possible to construct a giant species similar in size
and shape to spherical viruses with icosahedral symmetry
(i.e., having C 5 , C 3 , and C 2 axes) from a reaction system
in which pentagonal units with C 5 symmetry can first be
generated, then get linked and placed at the 12 corners
of an icosahedron. In the case of polyoxomolybdates,
these pentagonal units of the type {(Mo)Mo 5 } consist of a
central pentagonal bipyramidal MoO 7 unit sharing edges
with 5 MoO 6 octahedra. The {(Mo)Mo 5 } unit is itself a
constituent of the {Mo 8 }-type unit abundant in many giant
polyoxomolybdates (see below) in which two additional
MoO 6 octahedra are bound (sharing corners) to the
{(Mo)Mo 5 } unit. In the presence of linkers, units which
are capable of bridging two (or more) building blocks,
V
for instance, those of the classical [Mo 2 O 4 ] 2+ type
(typically formed in reduced molybdate solutions in the
FIGURE 11 Schematic representation of the icosahedron presence of bidentate ligands), an icosahedral molecular
spanned by the centers of the {(Mo)Mo 5 } subfragments of the system with 12 of the mentioned pentagons and 30 of
{Mo 132 }-type cluster. Two of the {Mo 11 } units each formed by the
{(Mo)Mo 5 } groups and the five related Mo centers of the five neigh- the mentioned linkers is formed with the stoichiometry
V
V 2+ [Mo VI 72 Mo 60 O 372 (CH 3 COO) 30 (H 2 O) 72 ] 42− ({Mo 132 }).
boring {Mo 2 O 4 } bridges are emphasized.

FIGURE 12 Comparison of the polyhedral representations of the {Mo 132 } (left-hand side) and
II
I
0
{(Mo) (Mo 5 ) (Fe 5/2 ) } 12 (right-hand side) spherical clusters. The pentagonal centers of the {Mo(Mo 5 )} are
shown in white, the {Mo 2 } groups and Fe-based octahedra are shown as light gray polyhedra, and the remaining
(Mo 5 ) as dark gray polyhedra.