Quantum chemical insight of the dimetallic sulfide endohedral fullerene Sc₂S@C₇₀: Does it possess the conventional D_5h cage?

Like C₆₀, C₇₀ is one of the most representative fullerenes in fullerene science. Even though there are 8149 C₇₀ isomers, only two of them have been found before: the conventional D _5h and an isolated pentagon rule (IPR)-violating C _2v(7854). Through the use of quantum chemical methods, we report a new unconventional C₇₀ isomer, C₂(7892), which survives in the form of dimetallic sulfide endohedral fullerene Sc₂S@C ₇₀. Compared with the IPR-obeying C₇₀ and the C _2v(7854) fullerene with three pairs of pentagon adjacencies, the C₂(7892) cage violates the isolated pentagon rule and has two pairs of pentagon adjacencies. In Sc₂S@C₂(7892)-C₇₀, two scandium atoms coordinate with two pentalene motifs, respectively, presenting two equivalent Sc-S bonds. The strong coordination interaction, along with the electron transfer from the Sc₂S cluster to the fullerene cage, results in the stabilization of the non-IPR endohedral fullerene. The electronic structure of Sc₂S@C₇₀ can be formally described as [Sc₂S]⁴⁺[C₇₀]^4-; however, a substantial overlap between the metallic orbitals and cage orbitals has also been found. Electrochemical properties and electronic absorption, infrared, and ¹³C NMR spectra of Sc₂S@C₇₀ have been calculated theoretically.