Exohedrally stabilized C70 isomer with adjacent pentagons characterized by crystallography

All C70 isomers other than the well-known D5h-symmetric C70 (#8149) are highly elusive due to their defiance of the isolated pentagon rule (IPR), and, in turn, have long been underrated for years. Here we show a non-IPR hollow C70 (#8064) with C2-symmetry stabilized by exohedral chlorination as #8064C70Cl10. Its connectivity with two pairs of fused pentagons was determined unambiguously by single crystal X-ray diffraction analysis. Based on the geometric criterion in terms of the pyramidalization angle as well as theoretical computations on the Kekule structure and the negative nucleus independent chemical shift, the exohedral stabilization of the labile #8064C70 is rationalized by releasing the local strain relevant to the fused pentagons and achieving the aromaticity of the remaining sp2-hybridized carbon framework in the exohedral derivative of #8064C70. This new entrant in the C70 family, in addition to two previously reported non-IPR isomers (by Yang, Dunsch et al. for Sc3N@#7854C70 and by Echegoyen et al. for Sc2S@#7892C70), provides valuable opportunities for experimental and theoretical research involving non-IPR isomers of C70 beyond the common D5h-C70.