[Cu@Sn9]3− and [Cu@Pb9]3−: Intermetalloid Clusters with Endohedral Cu Atoms in Spherical Environments

Highest possible symmetry! Nine Sn atoms are arranged to give an almost perfect sphere around a Cu atom in the endohedrally filled Zintl ion [Cu@Sn9]3−. The rapid equilibration of the nine Sn atoms on the spectral NMR timescale leads to an exceptionally sharp 63Cu NMR signal. In contrast to the more common endohedrally filled fullerenes, the title complexes can be synthesized in macroscopic quantities as [K([2.2.2]crypt)]+ salts.