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

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@C_88:81 712 (IPR-9), and Sc₂S@C_88:81 733 (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. [ABSTRACT FROM AUTHOR]