Octacoordinated Carbon in a Boron-Carbon Cage

Carbon Flatland: Planar Tetracoordinate Carbon and Fenestranes

“…Also, evaluation of aromaticity in π systems surrounding and including the key carbon atom is appropriate. This property may be identified in terms of the (4 n + 2)-Hückel rule or the magnetic properties extracted from nucleus-independent chemical shift (NICS) parameters. − The electron localization function (ELF) has been developed for inspection of the electron distribution. , Determination of the coordination number is of particular interest for those clusters where the number of ligands surrounding the planar tetracoordinate carbon exceeds four …”

“…27,28 Determination of the coordination number is of particular interest for those clusters where the number of ligands surrounding the planar tetracoordinate carbon exceeds four. 29 If not stated otherwise, the structures discussed in the sections below were obtained by high-level ab initio and DFT calculations, in many cases corrected by the zero-point vibrational energy (ZPE).…”

Octacoordinate Carbons Encaged Inside Carborane Clusters: A Density Functional Theory Investigation

“…For example, isomer 3b can be rearranged into 6a through the transition state 8a with an energy barrier of 22.9 kcal mol -1 . This energy barrier is obviously higher than the barriers for the rearrangements of hydrocarbons 1a and 1b (15 and 6 to 7 kcal mol -1 , respectively) 26 and much higher than the barrier for the rearrangements of the octacoordinate boroncarbon C@C 4 B 4 43 (1.2 and 1.4 kcal mol -1 at the B3LYP/6-311+G** and MP2/6-311+G** level, respectively). For the hydrocarbons 1a and 1b, the rearrangements lead to the exohedral isomers with much lower energy (120-140 kcal mol -1 lower), indicating that these rearrangements are almost irreversible.…”

“…In all these carborane cages, the central carbon atom and the surrounding carbon and boron ligands are supposed to form multicenter bonds. Like the case for boroncarbon cluster C@C 4 B 4 , the formation of the multicenter bonds can be understood as follows. First, the central carbon forms C cen −C lig covalent bonds with the four carbon ligands since the C cen −C lig bonding interaction is generally much stronger than the C cen −B lig interaction as we have shown above.…”

“…Furthermore, from the theoretical point of view, it would be very helpful if some general strategies ,, are proposed for discovering possible hypercoordinate carbon structures. It is also interesting to see that many hypercoordinate carbons are obtained in boroncarbon ,,– ,,, or carborane ,,, compounds. The reasons may be as follows.…”