Cyclic carbon cluster dianions and their aromaticity

Cyclic carbon cluster dianions (CC2)(n)(2-) (n = 3-6) are investigated by ab initio methods with regard to their geometric properties, electronic stability, and aromaticity. The unique wheel-like structures of these dianions consist of a n-membered carbon ring, where a C-2 unit is attached to each carbon atom. All investigated dianions represent stable gas-phase dianions. While the smallest member of this family (CC2)(3)(2-) is clearly aromatic, the aromatic character decreases rapidly with increasing ring size. The geometries and the aromaticity of the cyclic clusters (CC2)(n)(2-) (n = 3-6) can be nicely explained using resonance structure arguments.