Study spin-off: a molecular 'ferric wheel.' (molecule that resembles a Ferris wheel)

Study spin-off: A molecular 'ferric wheel'

"Once in a while nature gives you a real beauty like this one," says Stephen J. Lippard, a chemist at the Massachusetts Insxitute of Technology in Cambridge.

The object of his admiration is a 200-atom molecule with a circular architecture resembling the famous amusement park ride invented in 1893 by engineer G.W.G. Ferris. The molecule's double entendre name reflects its chemical character: compounds containing iron -- or ferrum, in Latin -- often have the terms ferric or ferrous in their names depending on the number of positive charges that their iron atom brings into chemical bonds with the compound's other atomic or molecular components.

MIT graduate student Kingsley L. Taft serendipitously created the "ferric wheel" during routine studies of iron- and oxygen-containing complexes, which he and Lippard use as simple models of certain protein cores. Taft found that when one of these "iron-oxo" complexes reacts with ferric nitrate in a methanos solution, a green-brown color appears and then gives way to a yellow color when ether diffuses into the system. After several days, brown-gold crystals form. X-ray diffraction studies of the crystals reveal that the reaction produces circular molecules with 10 iron atoms linked via molecular bridges consisting mostly of carbon, hydrogen and oxygen; chlorine atoms cap the bridge groups that form the wheel's outer rim.

The chemists describe the evocative structure, which they say has no known use, in the Dec. 19, 1990 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.