The isomers of B6O3, B6O3 and B6O32- were studied using DFT, MP2 and G3B3 methods. The dianion B-3(BO)(3)(2) possesses a perfect triangular D-3h form, that undergoes to lower symmetry in the anionic (C-2v) and neutral (C-s) states. The adiabatic electron affinity of B6O3 and vertical detachment energy of B6O3- amount to 3.97 and 4.07 eV, respectively. NBO and ELF analyses reveal that B6O32- possesses a global pi-aromaticity, a local sigma-electron delocalization, and a three-center-two-electron bond. The high stability of the dianion illustrates the growth mechanism of boron oxide clusters that is governed by formation of strong BO bonds and small boron cycles. (C) 2009 Elsevier B.V. All rights reserved.