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) MF@C(CF) (M = Gd and Y). The molecular structure of GdF@C(CF) was unambiguously determined by single-crystal X-ray analysis to show a μ-fluoride-bridged Gd-F-Gd cluster with short Gd-F bonds of 2.132(7) and 2.179(7) Å. The F NMR spectrum of the diamagnetic YF@C(CF) confirms the existence of the endohedral F atom, which exhibits a triplet with a large F-Y coupling constant of 74 Hz and a high temperature sensitivity of the F 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 [YF]@[C] with an open-shell carbon cage, which thus necessitates the stabilization of FCFs by exohedral trifluoromethylation.