To identify the structures and understand the stability mechanism of the detected metal sulfide fullerene Sc2S@C-74, we performed a systematic density functional theory study on the isomers of C-74 with 0-3 B-55 bonds and 35 candidate isomers of Sc2S@C-74. The results demonstrate that Sc2S@C-74 violates the isolated pentagon rule and its cage has two B-55 bonds, the transferred electrons from Sc2S cluster stabilize the active cage (C-74:13333). Sc2S is linear inside the cage and significantly different from those of Sc2S@C-72 and Sc2S@C-82. The calculations demonstrate that it is highly favored for Sc2S cluster to be encaged inside (C-74:13 333). (C) 2013 Elsevier B.V. All rights reserved.