Title: Pristine isolation of sixfold-symmetric oblate C72 fullerene validating the isolated pentagon rule and the spherical-saturation principle

Authors: Zhou, Yuan-Biao; Wang, Wei; Chen, Zuo-Chang; Lin, Yao; Huang, Ling-Xi; Deng, Qing-Song; Wang, Yu-Xiang; Lai, Jin-Bin; Tian, Han-Rui; Hong, Wenjing; Li, Jing; Tan, Yuan-Zhi; Xie, Su-Yuan; Zheng, Lan-Sun

Abstract: Fullerenes satisfying the isolated pentagon rule (IPR) have been isolated across the C 60 –C 96 series, with the exception of C 72 , whose sole IPR isomer has remained elusive. Here we report the isolation and structural characterization of pristine D 6d -C 72 . Single-crystal X-ray diffraction and 13 C NMR spectroscopy establish its sixfold symmetry and highly oblate geometry, with a minor-axis length of only 5.79 Å, making it the flattest IPR fullerene and the shortest fullertube identified. To rationalize its formation despite its predicted thermodynamic instability, we introduce a spherical-saturation principle that quantitatively compares the experimental stability of fullerene cages and their derivatives through chlorination-based energetic indices. The analysis shows that D 6d -C 72 is sufficiently spherically saturated to survive in carbon soot, whereas lower-energy non-IPR C 72 isomers require derivatization for stabilization. Owing to its anisotropic structure, D 6d -C 72 forms single-molecule junctions with two distinct conductance states. Mechanical elongation over only 2.5 Å produces a conductance switching ratio of 147.9, corresponding to a switching efficiency of 59.2 Å −1 . These findings fill a long-standing gap in fullerene chemistry and identify D 6d -C 72 as a promising molecular component for mechanically controlled single-molecule electronic devices.

Full-Link: https://www.nature.com/articles/s41467-026-78886-y