On the basis of the energies and B-11 NMR chemical shifts computed at the BP86/AE1(*) and GIAO-B3LYP/II' levels of density functional theory, respectively, the structure of the long-known protonated iron(II) bis(dicarbollide) can be assigned to a staggered isomer with a cisoid conformation of the carborane ligands. In the unprotonated species, in contrast, these ligands adopt the usual trans orientation, suggesting that suitable control of protonation/deprotonation equilibria could induce rotary motion at the molecular level.