CAl 11 - : a molecular rotor with a quasi-planar tetracoordinate carbon.

In this work, we analyzed the bonding and fluxional character of the global minimum of CAl 11 - . Its structure is formed by two stacked layers, one of them resembles the well-known planar tetracoordinate carbon CAl 4 on top of a hexagonal Al@Al 6 wheel. Our results show that the CAl 4 fragment rotates freely around the central axis. The exceptional stability and fluxionality of CAl 11 - derive from its particular electron distribution.