Steering the Geometry of Butterfly-Shaped Dimetal Carbide Cluster within a Carbon Cage via Trifluoromethylation of Y2C2@C82(6)

As one of the largest sub-branches of endohedral clusterfullerenes, dimetal carbide clusterfullerene (CCF) in the form of M2C2@C2n is quite intriguing since an alternative structure of M2@C2n+2 as conventional dimetallofullerene may exist as well. Herein, by using high-temperature trifluoromethylation followed by HPLC separation and single-crystal X-ray diffraction study, we report for the first time the unambiguous structural determination of yttrium (Y)-based CCF as its trifluoromethyl derivatives, Y2C2@C82(6)­(CF3)16. Four isomers of Y2C2@C82(6)­(CF3)16 with different addition patterns of 16 CF3 groups are successfully isolated, and two Y atoms of the butterfly-shaped Y2C2 cluster are coordinated by two cage pentagons in each isomer. The butterfly geometry of Y2C2 cluster varies significantly in the four Y2C2@C82(6)(CF3)16 isomers, with Y···Y distances ranging from 3.544 to 4.051 Å dependent on the relative positions of the two yttrium-coordinated pentagons on the carbon cage.