Cesium and fluorine hook up in record-setting complex

Abstract

Among the elements, cesium, located in the lower left corner of the periodic table, and fluorine, in the upper right corner, are among the largest electropositive and smallest electronegative elements, respectively. When chemists look at possible ways to get the two elements together, something interesting is bound to happen. And it has. Klaus-Richard Pörschke, David Pollak, and Richard Goddard of the Max Planck Institute for Coal Research have prepared a molecule in which a central cesium atom is coordinated by 16 fluorine atoms, establishing a new precedent for chemical bonding. Pörschke announced the team’s discovery in a Division of Inorganic Chemistry symposium at the American Chemical Society national meeting last week in San Diego. Going beyond a coordination number of 12 is rare because of the limited space available around the central atom of a molecule and electrostatic repulsion between the ligands. Chemists have flirted with 16-coordinate compounds for years,