DFT TPSSh/6-311+G(d) calculations are carried out on a series of 2D and 3D forms of B-n, n = 20, 22 and 24 in different charge states. For a certain size, the relative energy within a pair of two-dimensional quasi-planar (2D) and three-dimensional staggered double-ring (3D) boron cluster isomers may shift the sign as they reach a certain charge state. Specifically, electron addition tends to enhance the stability of the 2D over the corresponding 3D isomer irrespective of the available electrons. Linear correlations between 2D-3D relative energy and net charge are established. Along with 2D-to-3D geometry hopping at critical size, our results suggest a local 2D-3D geometry hopping via critical charge. (c) 2013 Elsevier B.V. All rights reserved.