title: Observation of all-metal aromatic molecules.
abstract: Aromaticity is a concept invented to account for the unusual stability of an important class of organic molecules: the aromatic compounds. Here we report experimental and theoretical evidence of aromaticity in all-metal systems. A series of bimetallic clusters with chemical composition MAl4- (M = Li, Na, or Cu), was created and studied with photoelectron spectroscopy and ab initio calculations. All the MAl4- species possess a pyramidal structure containing an M+ cation interacting with a square Al4(2-) unit. Ab initio studies indicate that Al4(2-) exhibits characteristics of aromaticity with two delocalized pi electrons (thus following the 4n + 2 electron counting rule) and a square planar structure and maintains its structural and electronic features in all the MAl4- complexes. These findings expand the aromaticity concept into the arena of all-metal species.
authors.affiliation: Department of Physics, Washington State University, 2710 University Drive, Richland, WA 99352, USA.
authors.forename: X L
authors.initials: XL
authors.lastname: Li
authors.forename: A E
authors.initials: AE
authors.lastname: Kuznetsov
authors.forename: H F
authors.initials: HF
authors.lastname: Zhang
authors.forename: A I
authors.initials: AI
authors.lastname: Boldyrev
authors.forename: L S
authors.initials: LS
authors.lastname: Wang