Trapping a C₂ Radical in Endohedral Metallofullerenes:  Synthesis and Structures of (Y₂C₂)@C₈₂ (Isomers I, II, and III)

Abstract

Three isomers of yttrium carbide (Y 2 C 2 ) endohedral metallofullerenes, i.e., (Y 2 C 2 )@C 82 (I, II, III), have been synthesized and chromatographically isolated for the first time. The structures of (Y 2 C 2 )@C 82 (I, II, III) metallofullerenes have been characterized by 13 C NMR measurements, whose molecular symmetries have been determined to be C s , C 2V , and C 3V , respectively. In addition, a pure diyttrium metallofullerene, Y 2 @C 82 (III), has also been synthesized and structurally characterized. The 13 C NMR structural analyses indicate that (Y 2 C 2 )@C 82 (III) has exactly the same fullerene cage as that of Y 2 @C 82 (III). On the basis of the results, we propose a C 2 -trapping and loss of growth mechanism of dimetallofullerenes of (M 2 C 2 )@C 82 and M 2 @C 82 from M 2 @C 84 , respectively.

Chemical, Electrochemical, and Structural Properties of Endohedral Metallofullerenes

“…[97] In a similar way, theoretical calculations as well as 13 C NMR spectroscopy and refined X-ray structural analyses have revealed over the past years other metallic carbide EMFs such as Y 2 C 2 @C 82 (isomers C s , C 2v , and C 3v ), Ti 2 C 2 @C 78 (D 3h ), Sc 2 C 2 @C 68 (C 2v ), Sc 2 C 2 @C 82 (C 3v ), Sc 3 C 2 @C 80 (I h ), and Gd 2 C 2 @C 92 (D 3 ). [36,37,[98][99][100][101][102][103][104][105][106] Interestingly, among all of these EMFs, only Sc 2 C 2 @C 68 (C 2v ) was found to have a non-IPR carbon cage. [104] Crystallographic data together with calculations have strongly suggested that the metallic carbide unit is more stable in the bent geometry.…”

Electrochemistry of Carbon Nanoparticles

“…This would be consistent with a separate 13 C NMR study that showed that Y 2 C 2 @C 82 and Y 2 @C 82 have the same C 82 [C 3v ] cage. 67 The electronic structure of this compound was established by DFT calculations 64 to be (Sc 2 C 2 ) 4 þ C 82…”

Electronic Structure and Redox Properties of Metal Nitride Endohedral Fullerenes M3N@C2n (M=Sc, Y, La, and Gd; 2n=80, 84, 88, 92, 96)

“…[2][3][4] EMFs are stabilized by charge transfer from the internal metal cluster to the carbon cage, which becomes negatively charged. Apart from encapsulating single metal atoms, EMFs are also found with more than one metal atom (M 2 and M 3 ), [5][6][7][8][9][10][11][12][13][14] metal carbides (M 2 C 2 and M 3 C 2 ), [15][16][17][18][19][20][21][22][23] metal nitrides (M 3 N), [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] or even metal oxides (Sc 4 O 2 ), [41] in which M is a Group 3 or lanthanide metal atom. Interestingly, the carbon cages present in EMFs are different from those observed as empty fullerenes and in some cases they do not fulfill the isolated pentagon rule (IPR).…”