Capturing Metal Fluoride inside a Carbon Cage

We report here a new type of metal fluoride cluster that can be stabilized inside fullerene via in situ fluorine encapsulation followed by exohedral trifluoromethylation, giving rise to rare-earth metal fluoride clusterfullerenes (FCFs) M2F@C80(CF3) (M = Gd and Y). The molecular structure of Gd2F@C80(CF3) was unambiguously determined by single-crystal X-ray analysis to show a μ2-fluoride-bridged Gd–F–Gd cluster with short Gd–F bonds of 2.132(7) and 2.179(7) Å. The 19F NMR spectrum of the diamagnetic Y2F@C80(CF3) confirms the existence of the endohedral F atom, which exhibits a triplet with a large 19F–89Y coupling constant of 74 Hz and a high temperature sensitivity of the 19F chemical shift of 0.057 ppm/K. Theoretical studies reveal the ionic Y–F bonding nature arising from the highest electronegativity of the F element and an electronic configuration of [Y2F]5+@[C80]5–with an open-shell carbon cage, which thus necessitates the stabilization of FCFs by exohedral trifluoromethylation.