Imperial College London

Henry Rzepa

  
An [earlier
post](http://www.ch.ic.ac.uk/rzepa/blog/?p=439){target="_blank"}
described how a (spherical) halide anion fitted snugly into a cavity
generated by the simple molecule propanone, itself assembled by sodium
cations coordinating to the oxygen. A recent elaboration of this theme,
reminiscent of the children's toys where objects have to be fitted into
the only cavity that matches their shape, Nitschke and co-workers report
the creation of a molecule with a tetrahedral rather than a spherical
cavity (DOI:
[10.1126/science.1175313](http://dx.doi.org/10.1126/science.1175313) ),
into which another but much smaller tetrahedral molecule is fitted.  The
small molecule is P~4~, in which each of the three valencies of the P
atom is directed to a corner of the tetrahedron. The large molecule
 comprises four Fe atoms. These are each octahedrally coordinated with
six ligand sites, three of which mimic the P atoms in also being
directed towards the remaining three vertices of a tetrahedron.

![P4 inside a Tetrahedral cavity.
](http://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2009/07/P4.jpg "P4 inside a  Tetrahedral cavity. "){.aligncenter
.size-full .wp-image-550 loading="lazy" decoding="async"
onclick="jmolInitialize('../Jmol/');jmolSetAppletColor('yellow');jmolApplet([450,450],'load wp-content/uploads/2009/07/P41.mol;select atomno=7,atomno=6,atomno=5,atomno=8; cpk on; color atom orange;zoom 120;spin 3;');"
width="237" height="229"}

Needless to say, the properties of the P~4~ molecule when entrained into
this larger container are nothing like that of the free molecule. Now it
is quite inert, but this is due purely to the snug fit. For example, the
normal reaction of this molecule is to oxidize in air. But such
oxidation would now produce a molecule too big to fit into the cavity.
Hence no reaction!

So, now the search is on for a cubic container to include a cubic
molecule!

::: {.wp_orcid_field}
[https://orcid.org/0000-0002-8635-8390](https://orcid.org/0000-0002-8635-8390){target="_blank"
rel="author"}
:::


An earlier post described how a (spherical) halide anion fitted snugly into a cavity generated by the simple molecule propanone, itself assembled by sodium cations coordinating to the oxygen.

Messaggi di Rogue Scholar

Molecular toys: Tetrahedral cavities