All-metal antiaromatic molecule:: Rectangular Al44- in the Li3Al4- anion

We report the experimental and theoretical characterization of antiaromaticity in an all-metal system, Li3Al4-, which we produced by laser vaporization and studied with the use of photoelectron spectroscopy and ab initio calculations. The most stable structure of Li3Al4- found theoretically contained a rectangular Al-4(4-) tetraanion stabilized by the three Li+ ions in a capped octahedral arrangement. Molecular orbital analyses reveal that the rectangular Al-4(4-) tetraanion has four pi electrons, consistent with the 4n Huckel rule for antiaromaticity.