It's A Metallic Aromatic

Abstract

They may not smell like aromatics, says Lai-Sheng Wang, but some new planar metal clusters appear to have the characteristics necessary to extend that appellation to them. The molecules consist of a square planar aluminum anion, Al 4 2- , capped by a cation of lithium, copper, or sodium. The anions have two delocalized π electrons, following the [4 n + 2) rule for aromaticity. Their flat shapeborne out by theoretical calculations—and unusual stability are also aromatic traits [ Science , 291 ,859 (2001)] Wang, an associate physics professor at Washington State University, and collaborators created the gas-phase metal molecules by vaporizing aluminum alloy targets with a laser and gleaning the structures via photoelectron spectroscopy. Metal aromatics are a relatively new chemical curiosity. Beginning in the mid-1990s, a group led by research chemist Gregory H. Robinson at the University of Georgia found good evidence for aromaticity in cyclic gallium compounds, which had organic ligands and were synthesiz...