Remarkable Stabilities of Trimetallic Nitride Clusterfullerenes MSc₂N@C₇₀ (M = Sc, Y, Dy) with Three Pentagon Adjacencies: A Theoretical Survey

A MSc₂N@C₇₀ (M = Sc, Y, Dy) family has been systematically investigated by density functional calculations in conjunction with statistical thermodynamic analyses for the first time. The results revealed that C₂ᵥ(7854)-C₇₀ is the most predominant carbon cage when encapsulating DySc₂N, YSc₂N, and Sc₃N clusters. In addition, endohedral structures based on C₁(7852)-C₇₀ and C₁(7851)-C₇₀ are also stable with large concentrations in the temperature region of fullerene formation. All these three isomers are non-IPR structures with three pentagon adjacencies (PA) and related by Stole-Wales transformation. The interaction energies (INT) of MSc₂N@C₂ᵥ(7854)-C₇₀, MSc₂N@C₁(7852)-C₇₀, and MSc₂N@C₁(7851)-C₇₀ are much more negative than those of the IPR structures MSc₂N@D₅ₕ(8149)-C₇₀, revealing a stabilizing effect of the MSc₂N (M = Sc, Y, Dy) clusters toward the PAs. On the basis of the ionic model of (MSc₂N)⁶⁺@C₇₀⁶–, which is confirmed by the frontier orbital analyses, the electron back-donation from C₇₀⁶– to (MSc₂N)⁶⁺ increases in the order of Sc₃N@C₇₀ < YSc₂N@C₇₀ < DySc₂N@C₇₀. Therefore, the INT value increases in the order of Sc₃N@C₇₀ < YSc₂N@C₇₀ < DySc₂N@C₇₀, suggesting that the stabilizing effect of the endohedral cluster is weakened by Y and Dy. Moreover, the UV–vis–NIR spectra of MSc₂N@C₂ᵥ(7854)-C₇₀ (M = Sc, Y, Dy) coincide with the experimental characterizations well, and simulations for other isomers will be helpful for further identification of those metal nitride clusterfullerenes.