C₇₈ Cage Isomerism Defined by Trimetallic Nitride Cluster Size:  A Computational and Vibrational Spectroscopic Study

Abstract

Molecular structures of Dy(3)N@C(78) and Tm(3)N@C(78) clusterfullerenes are addressed by the IR and Raman vibrational spectroscopic studies and density functional theory (DFT) computations. First, extensive semiempirical calculations of 2927 isomers of C(78) hexaanions followed by DFT optimization were applied to establish their relative stability. Then, DFT calculations of a series of M(3)N@C(78) (M = Sc, Y, Lu, La) isomers were performed which have shown that the stability order of the isomers depends on the cluster size. While the Sc(3)N cluster is planar in the earlier reported Sc(3)N@C(78) (D(3)h: 24,109) clusterfullerenes, relatively large Y(3)N and Lu(3)N clusters would be forced to be pyramidal inside this cage, which would result in their destabilization. Instead, these clusters remain planar in the nonisolated pentagon rule (non-IPR) C(2): 22,010 isomer making Y(3)N@C(78) and Lu(3)N@C(78) clusterfullerenes with this cage structure the most stable ones. Finally, on the basis of a detailed analysis of their IR and Raman spectra supplemented with DFT vibrational calculations, the recently isolated Tm(3)N@C(78) and the major isomer of Dy(3)N@C(78) are assigned to the non-IPR C(2): 22,010 cage structure. A detailed assignment of their experimental and computed IR and Raman spectra is provided to support this conclusion and to exclude other cage isomers.

Chemical, Electrochemical, and Structural Properties of Endohedral Metallofullerenes

“…The first reports of EMFs with carbon cages containing fused pentagon systems were those of Sc 2 @C 66 [115] and Sc 3 N@C 68 (D 3 :6140). [110] Other examples are [75b, 104,[116][117][118][119][120][121] On the other hand, spectroscopy along with DFT calculations strongly suggested that the major isomer of Dy 3 N@C 78 and Tm 3 N@C 78 both have the non-IPR carbon cage of symmetry C 2 :22 010 [122] and that Ce 2 @C 72 possesses a non-IPR carbon cage of D 2 symmetry, as in the case of La 2 @C 72 . [123] It is interesting to note that as the size of the fullerene increases, the number of fused pentagon systems decreases; for example, Sc 3 N@C 68 (D 3 :6140) has three fused pentagon systems while Gd 3 N@C 82 (C s :39 663) and M 3 N@C 84 (C s :51 365) (M = Gd, Tb, Tm) have only one ( Figure 5).…”

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

“…has been achieved during recent years. [24-26, 28-30, 32-37, 39, 40, 45, 49-53] Many of them have been structurally characterized by X-ray diffraction, the largest being Tb 3 N@C 88 . [54] The derivatization of MNEFs by means of typical organic reactions, such as Diels-Alder, [26,31,55,56] 1,3-dipolar cycloaddition of azomethine ylides, [25,27,[57][58][59] and BingelHirsch cyclopropanation, [60,61] has also been performed.…”

Review—The Beautiful Molecule: 30 Years of C60and Its Derivatives

“…One suggestion is that all free electrons from metal atoms should be localized in the carbon cage, therefore a metal atom and carbon cage would form an ionic model of bonding (as a ligand). The charge of the carbon cage has been confirmed by some theoretical [90][91][92][93][94][95] and experimental 87,[96][97][98][99] results. Other studies on various EMFs established that was a smaller charge on the metal atom than was expected in the anion-cation structure 88,[100][101][102][103][104][105][106] and pointed toward the hypothesis of covalent bonding.…”

“…In this case, the LUMO of EMFs is localized in the metal atom. 94,110,111 Fullerenols ( Figure 5) differ from other fullerene derivatives. These molecules behave as proton conductivity materials.…”