A hidden rule in metal sulfide fullerenes: A case study of Sc2S@C88

Abstract

To elucidate the structure of a compound is a necessary step for its practical applications. To study the structure and properties of metal sulfide fullerene Sc2S@C88 detected by mass spectrometry, 11 194 isomers of C88 and 33 isomers of Sc2S@C88 were systematically examined by density functional theory calculations. The calculations show that the two lowest-energy isomers are Sc2S@C88:81 738 (IPR-35) and Sc2S@C88:81 735 (IPR-32), followed by Sc2S@C88:81 729 (IPR-26), Sc2S@C88:81 712 (IPR-9), and Sc2S@C88:81 733 (IPR-30). Structural analysis shows that the first two energetically favored isomers are bridged by the third and fifth energetically favored isomers, which can transfer into each other via direct Stone–Wales rotation. The calculations of temperature effect show that the first two favored isomers become dominant forms of Sc2S@C88 with decreasing temperature and may coexist in the soot. This structural convertibility among favored isomers of Sc2S@C88 suggest a hidden rule that birds of a feather flock together in metal sulfide fullerenes. This rule may decrease the range of candidate cages for the structural identification of a metal sulfide fullerene. IR spectra are simulated for helping the future experimental identification of Sc2S@C88.