Sc2S@C68: an obtuse di-scandium sulfide cluster trapped in a C2v fullerene cage

Abstract

The spectrum-detected smallest sulfide clusterfullerene Sc₂S@C₆₈ has not been characterized yet. Herein, we explored a series of Sc₂S@C₆₈ species to determine which could be the most promising isomer. The results suggest that a sulfide cluster encapsulated in the C_2v(6073)-C₆₈ cage which violates the isolated pentagon rule (IPR) with two opposite pentalenes has the lowest energy and an overwhelming thermodynamic stability. Two scandium atoms coordinate with the two opposite pentalenes, leading to an obtuse Sc–S–Sc angle of 151°. The bond lengths of the two Sc–S bonds are equivalent. Frontier molecular orbital distributions exhibit substantial overlaps between metallic orbitals and cage orbitals, indicating that covalent interactions cannot be ignored, which have been unambiguously identified in terms of Mayer bond order and bonding critical point (BCP) indicator methods. Electrochemical properties as well as ¹³C NMR, UV-vis-NIR, and IR spectra of Sc₂S@C_2v(6073)-C₆₈ have been theoretically studied to assist further experimental characterization.