Entirely unlike the aromatic closo B_nH_n^2- borane dianions, isoelectronic Si₆^2- and Si₁₂^2- 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.