CB7−: Experimental and Theoretical Evidence against Hypercoordinate Planar Carbon

Changing the wheel: Replacing one B− unit by C in B82− is predicted to yield a CB7− molecular wheel, which has now been produced by laser vaporization. Ab initio calculations show that CB7− has an extremely stable planar C2v structure in which C replaces B− at the rim of the B82− molecular wheel (see picture). The D7h structure with a heptacoordinate C atom lies 63 kcal mol−1 above the C2v structure.