Trapping an unprecedented TiC unit inside the icosahedral C fullerene: a crystallographic survey.

The sub-nanometer cavity of fullerene cages is an ideal platform to accommodate otherwise unstable species for accurate structural characterization with, for example, rather accurate single crystal X-ray diffraction (XRD) crystallography. Herein, we report the successful entrapment of an isolated TiC moiety inside the icosahedral-C cage to form TiC@I-C an arc-evaporation process in the gas phase. The single crystal XRD crystallographic results unambiguously reveal that the C-unit adopts an unprecedented cyclopropane-like structure which coordinates with the three titanium atoms in an unexpected fashion where the triangular C-unit is nearly perpendicular to the Ti-plane. The intercalation of a cyclopropanated C-unit into the titanium layer is thus unambiguously confirmed. The theoretical results reveal that the TiC cluster transfers six electrons to the I-C cage so that each titanium atom has a positive charge slightly above +2 and the C-unit is negatively charged with about -1. It is noteworthy that this is the first observation of the cyclopropane-coordination fashion in any reported organometallic complex, providing new insights into coordination chemistry.