Carboranes with endo substituents: to B or not to B, that is the question

The reported crystal structures for 8- endo -EMe 2 Cl-9-SMe 2 -7,8-C 2 B 9 H 10 (E = Si or Ge) contain the endo- substituent at the carbon atom of the open face. These geometries contrast with the universally accepted view that endo substituents are attached to boron atoms in carboranes. Here, hybrid DFT computations demonstrate that the two C atoms at 8 and 9 positions are the B atoms in the crystal structures. Endo -substituents are indeed attached to B not to C in carboranes containing the C 2 B 9 framework so far.