Are there any compounds with pentavalent carbon?

1 Answer
Ernest Z.
Apr 20, 2015

Scientists first prepared methanium ion in 1950.

Explanation:

Methanium ion

Fluoroantimonic acid #"HSbF"_6# reacts with methane to form methanium ion, #"CH"_5^"+"#.

It is a fluxional ion, in which the #"C-H"# bonds are continually breaking and re-forming even at 4 K.

https://phys.org/news/2015-03-shrew-scientists-decipher-spectrum-ch5.html

In the animation above, the black ball in the middle is the carbon atom, and the red and white ones are hydrogen atoms. The blue clouds represent the electron pairs.

A theoretical pentacoordinate carbon

Theoretical chemists have predicted that #"CBe"_5^(4-)# would have a planar pentacoordinate carbon and might even be stable in the gas phase.

mappingignorance.org

The bonds are not ordinary σ bonds. Instead, they involve various σ and π orbitals involving the whole molecule.

#"CAl"_4"Be"# and #"CAl"_3"Be"_2^-# are also theoretical possibilities.

pubs.rsc.org

Heptacoordinate carbon?

Another theoretical possibility is #"CTi"_7^(2+)#, with a #"C"# atom at the centre of a pentagonal bipyramid — a heptacoordinate #"C"# atom!

ACS Publications - American Chemical Society

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