Structural connectivity and formation mechanism of monometallic cluster fullerenes YCN@C_n (n = 68–84)

Abstract

Excited by the recently experimental reports of monometallic cluster fullerenes, we examined the electronic and geometrical properties of monometallic cluster fullerenes YCN@C n with size from C 68 to C 84 by density functional theory and statistical thermodynamic calculations. The calculations demonstrate that the thermodynamically favored isomers of YCN@C n are in good agreement with available experimental results. Morphology analysis shows that the lowest-energy YCN@C n species are structurally connected by C 2 insertion/extrusion and Stone-Wales rotation, which can be promoted under high temperature; enthalpy-entropy interplay can change the relative abundances of low-energy isomers significantly at high temperature. All the results suggest that there is a structural evolution among these metallic cluster fullerenes in discharge condition, and thus, can rationalize their structural diversity in the soot and partly disclose their formation mechanism. The geometrical structures, electronic properties of these endohedral fullerene were discussed in detail. K E Y W O R D Sformation mechanism, monometallic cluster fullerenes, Stone-Wales rotation, structural evolution 1 | I N TR ODU C TI ON Fullerene molecules are hollow closed carbon cages containing 12 pentagons and n/2-10 hexagons. [1] The stability of bare fullerenes is usually determined by the isolated pentagon rule (IPR). [2] So far, all reported bare fullerenes have been known to satisfy the IPR. However, the parent cages of endohedral metallofullerenes (EMFs) can be non-IPR mainly due to the strong electron transfer interaction between encapsulated metallic atom (s)/cluster and the fullerene cages. [3] EMFs have attracted much attention owing to their unique geometrical structures, novel electronic properties, and potential applications. [4][5][6][7][8] It has long been thought that monometallofullerenes are only in the form of M@C 2n[9] and cluster fullerenes always encapsulate multiple metal atoms (two or more) inside. However, monometallic cluster fullerenes MCN@C n were successively reported since 2013. [10][11][12][13] The properties and applications of monometallic cluster fullerenes are different from both monometallic fullerenes and multimetallic cluster fullerenes due to the different geometrical and electronic structures of the encaged species. To our knowledge, the structural connectivity and formation mechanism of monometallic cluster fullerenes has not yet been clarified, although important progress has been made for empty fullerenes. [14] Therefore, it is of great interest to explore this new endohedral fullerene family. We, here, make a systematic computational study on monometallic cluster fullerenes YCN@C n (n 5 68-84). Interestingly, we find strong structural connectivity among the low-energy YCN@C n isomers in the form of C 2 insertion/extrusion and Stone-Wales transformations. [15] Our results provide clues to find new monometallic cluster fullerenes from the as-reported ones and partly disclose their formation mechanism.2 | C OM P UT ...

The formation mechanism of Sc-based metallofullerenes: a molecular dynamics simulation study

“…These Sc atoms can move along the surface of the growing carbon clusters and can be encapsulated within the cage. Our group systematically examined Sc 3 N@C n , 21 Sc 2 S@C n 22 and YCN@C n , 23 revealing that the energetically favored members are structurally interchanged through the insertion, extrusion, or rotation of a C 2 unit and thus suggest the crucial role of the C 2 unit in the formation of fullerenes and metallofullerenes. Experimentally, Kimura et al found that the formation of metal ion nuclei is crucial for the formation of metal-carbon clusters in metallofullerenes.…”

Theoretical Study on the Structure and Spectral Properties of Several Classical C84 Isomers and Their Newly Synthesized Derivatives

“…According to prior research, ,, the triplet states of U@ C s (15)-C 84 and U@ C 2 (8)-C 84 are the most energetically beneficial, while the singlet states of the other systems are more common in energy. Table shows the statistics over bond lengths, the HOMO–LUMO gaps of studied species, the relative energies of the three fullerene isomers and endohedral fullerenes as well as the sum of Mulliken charges on all carbon atom (ρ c ) for embedded derivatives.…”

“…This indicates that in some cases there is a strong interaction between the embedded metal and the carbon cage. 84 According to prior research, 41,85,86 the triplet states of U@ C s (15)-C 84 and U@C 2 (8)-C 84 are the most energetically beneficial, while the singlet states of the other systems are more common in energy. Table 1 shows the statistics over bond lengths, the HOMO−LUMO gaps of studied species, the relative energies of the three fullerene isomers and endohedral fullerenes as well as the sum of Mulliken charges on all carbon Compared with the original carbon cage and the shortest bond length of the C−C bond of the embedded derivatives increased, the longest bond length decreased, while the bond length of the YCN derivative changed more significantly.…”