Computational Study On The Metal Sulfides And Metal Nitrides Fullerenes

Endohedral metallofullerenes（EMFs） are compounds with metal atom（s） or clusters encaged inside fullerene cages. To date, many kinds of endohedral metallofullerenes have been synthesized and isolated experimentally. However, due to limited experimental conditions and yield, there are some difficulties in the characterization of endohedral metallofullerenes. In order to determine the carbon cage structure, theoretical calculation has become an important means to such problems. One can predict the thermodynamically stable fullerene or endohedral fullerenes, analyze the properties of these stable structures by optimization calculations, and thus can provide a theoretical reference for experimental study. In this paper, systematical density functional theory（DFT） calculations were performed on metal sulfides and metal nitrides fullerenes, the structure and stability were analyzed. The following three parts are included:Density functional theory calculations were performed on the thermodynamic and kinetic stability of Sc₂S@C₉₀, and some other related properties. The calculations demonstrate that the two lowest-energy isomers of Sc₂S@C₉₀ are Sc₂S@C₉₀:99913 and Sc₂S@C₉₀:99915, respectively. To clarify the relative stabilities of the five lowest-energy isomers of Sc₂S@C₉₀ at high temperatures, we examined the relative concentrations of five lowest isomers between 0-4000 K; the calculations demonstrate that the two lowest-energy isomers of Sc₂S@C₉₀ may coexist in the soot at high temperatures. QTAIM analysis shows that there are strong interactions between encaged cluster and parent cage, molecular orbital and nature charge analysis demonstrate that the encaged cluster can transfer electron to cage. Additionally, the infrared spectra of the two lowest-energy isomers were simulated.Density functional theory calculations were performed on the structure and properties of Sc₂S@C₆₈ and Sc₂O₂@C₆₈. The calculated results demonstrate that Sc₂S@C₆₈ shares the same parent cage as Sc₂C₂@C₆₈:6073, the transferred electrons from the encaged Sc2 S and Sc₂O₂ clusters stabilize the active cages. Sc2 S is V-shaped inside the cage, whereas Sc₂O₂ is square-like. There’s no tendency to bond with the two fused pentagons of Sc₂O₂@C₆₈ for the two Sc atoms, however, they form an unusually Sc-Sc single bond. The calculations show that Sc₂O₂ embed in C₆₈:6094 is more favorable than in C₆₈:6073, and the HOMO-LUMO gaps of Sc₂O₂@C₆₈ is evidently broader than that of Sc₂S@C₆₈. These results suggest that the detected compounds is more likely to be Sc₂O₂@C₆₈, at least Sc₂O₂@C₆₈ is much readily to be produced under similar experimental conditions. Finally, we simulated MS and UV spectral of the two compounds, which can provide help to structure identification of the corresponding compounds in the future.Recent experiments indicated that fullerene isomers outside the classical definition can also encapsulate metallic atoms or clusters to form endohedral metallofullerenes. We here performed a systematic density functional study on MSc₂N@Cn（M=Sc, Y, La; n=78, 80, 82）. The calculations demonstrate that many heptagon-including non-classical trimetallic nitride template fullerenes are similar in stability to their classical counterparts and the conversion between low-energy non-classical and classical parent cages via Endo-Kroto insertion/extrusion of C₂ units and Stone-Wales isomerization may facilitate the formation of endohedral trimetallic nitride fullerenes. Close structural connections are found between favored isomers of trimetallic nitride template fullerenes from C₇₈ to C₈₂. It appears that the lower symmetry and local deformations associated with introduction of a heptagonal ring favor encapsulation of intrinsically less symmetrical mixed metal nitride clusters.