Forget Sonic. Molybdenum is the prickly element of the day, thanks to German
chemists who have designed and synthesised a super structure containing 368
molybdenum atoms with a rather spiky profile.
Achim Mueller and colleagues at the University of Bielefeld have for many
years been developing ways to make increasingly complexity and geometric
complexes. Previously, they synthesised a metal wheel with a mere 154 Mo
atoms. Then they moved on to spheres, which were highlighted in The
Alchemist in 1999. These metal "buckyballs" had some 500 atoms. Now, the
Bielefeld team has curled up what the whimsically call a nano-hedgehog.
This compound uses the team's increasingly well-known approach to building
structures from the molybdate (molybdenum oxide) building block. Mo has
several properties that make it easy to exploit in building new compounds
the size and shape of which can be tailored simply by changing the boundary
conditions under which it is made. For example, the bonding to Mo can be
altered readily as too can its coordination number. It readily exchanges
water as a ligand and Mo-O-Mo type bridging bonds can form, allowing for
split-and-link processes. In turn, the formation of terminal Mo-O groups
provides a boundary on the otherwise potentially unlimited growth of a
complex.
The new compound is a giant molybdenum oxide based nanocluster. It is
approximately the size of haemoglobin protein molecule (diameter
approximately 6 nm), which is far bigger than other structurally
well-defined synthetic species. It contains 368 metal (1880 non-hydrogen)
atoms formed by the linking of 64 {Mo1}-, 32 {Mo2}-, and 40 {Mo-(Mo5)}-type
sub-units. The team reveals how the cluster forms as a result of a
"remarkable symmetry-breaking process". This, they add is revealed by the
surface geometry of the compound, which takes on a spiked appearance. Hence
the whimsical monicker.
Mueller sees this unusual complex as a springboard from which chemists can
dive into the pool of similarly sized materials with tailorable properties.
Ref: Angew. Chem. 2002, 114(7).