Entirely unlike the aromatic closo B[n]H[n][2-] borane dianions, isoelectronic Si[6][2-] and Si[12][2-] are antiaromatic. Their O[h] and I[h] symmetries are responsible, as the other deltahedral silicon dianion clusters do not exhibit this behavior. These high symmetries prevent mixing among the degenerate lone pair and skeletal orbitals, leading to paratropic behavior.