The capacity of LimB6H62- (m = 1, 2) as a hydrogen storage medium is studied using density functional theory. The binding strength of Li atom is sufficiently large to ensure the stability of LimB6H62-. Each Li atom can adsorb six H-2 molecules and the B6H6 moiety can adsorb four H-2 molecules. Li2B6H62- can bind up to 16 H-2 molecules with an average binding energy of 0.169 eV/H-2, leading to a hydrogen storage capacity of 27.1 wt%, which is much higher than that of the neutral Li2B6H6 system. The enhanced electrostatic field around the Li atom originates from the charge transfer from B6H62- to Li, accounting for the high adsorption capacity. The electrostatic field can be enhanced by controlling the charge state of the metal-organic complex, thereby significantly improving the hydrogen adsorption capacity. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.