O carbono, não é mais tetravalente? Um átomo de carbono faz seis ligações.

sexta-feira, janeiro 13, 2017

Crystal Structure Determination of the Pentagonal-Pyramidal Hexamethylbenzene Dication C6(CH3)62+


M. Sc. Moritz Malischewski, Prof. Dr. K. Seppelt

First published: 25 November 2016Full publication history

Molecular structure of C6(CH3)62+ in C6(CH3)62+ (SbF6)2⋅HSO3F, ellipsoids are shown at 50 % probability, C grey, H white; counteranions and co-crystallized HSO3F omitted for clarity.


In contrast to the well-known 2-norbornyl cation, the structure of which was a matter of long debate until its pentacoordinated nature was recently proven by an X-ray structure, the pentagonal-pyramidal dication of hexamethylbenzene has received considerably less attention. This species was first prepared by Hogeveen in 1973 at low temperatures in magic acid (HSO3F/SbF5), for which he proposed a non-classical structure (containing a hexacoordinated carbon) based on NMR spectroscopy and reactivity studies, but no X-ray crystal structure has been reported. C6(CH3)62+ can be obtained through the dissolution of hexamethyl Dewar benzene epoxide in HSO3F/SbF5 and crystallized as the SbF6− salt upon addition of excess anhydrous hydrogen fluoride. The crystal structure of C6(CH3)62+ (SbF6−)2⋅HSO3F confirms the pentagonal pyramidal structure of the dication. The apical carbon is bound to one methyl group (distance 1.479(3) Å) and to the five basal carbon atoms (distances 1.694(2)–1.715(3) Å).

Dedicated to Professor Karl Otto Christe on the occasion of his 80th anniversary


This work was supported by the Free University Berlin, Verband der Chemischen Industrie (VCI) and Deutsche Forschungsgemeinschaft (GRK 1582 (Fluorine as a Key Element)). Computing time was made available by High-Performance Computing at ZEDAT/FU Berlin.

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Agradeço ao meu filho Ariel Eugênio Salgueiro de Almeida por chamar minha atenção para o significado científico desta pesquisa.