Periodic DFT calculations show that stability of binuclear cationic gallium-oxo clusters in high-silica zeolites is mainly controlled by the favorable geometrical environment of the Ga3+ ions, whereas the effect of the direct interaction with the charge-compensating framework anionic sites is less important. Extraframework cyclic Ga2O22+ cations are shown to be active for light alkane dehydrogenation. (C) 2008 Elsevier Inc. All rights reserved.