The size of molecular wheels made from gallium ions can be controlled by changing the organic linker molecules
Metal ions can be linked together by small organic molecules to form clusters with well-defined structures and compositions. Of particular interest are complexes in which a number of metals are brought together to form a circle — the so-called molecular wheels. These highly symmetric structures have served as models with which to study magnetism at the molecular level.
Now, George Christou and colleagues1 at the University of Florida, Gainesville in the USA have prepared the first example of a molecular wheel made from gallium. This ‘gallic wheel’ comprises ten gallium ions linked together in a circle, with each pair of metals bridged by two different organic molecules. A simple change in the reaction recipe — replacing one set of bridging molecules with others that bind in a different way — led to an expanded wheel made from 18 gallium ions. Most significantly, however, the larger wheel could be converted directly into the smaller one by substituting the original bridges back into the structure. Similar behaviour was also observed with ‘ferric wheels’ made from iron.
Template-directed strategies do not work so well for larger molecular wheels (>10 metals) and generally require the central cavity to be occupied. Christou’s approach, however, suffers neither of these drawbacks, leading to large tubular structures that may have useful properties.
King, P., Stamatotos, T. C., Abboud, K. A. & Christou, G. Angew. Chem. Int. Edn (2006). 10.1002/anie.200602743