$\ce{CO_x}$ are part of the oxocarbon molecule class. Commonly known are $\ce{CO}$ and $\ce{CO2}.$ However, there are molecules in which $x$ is equal to or larger than $3.$ Those molecules are barely known, other than the fact that they're unstable.

$\ce{CO3}$ decomposes slowly enough that it may come into contact with other molecules (including biomolecules), but nothing is known of its possible oxidizing potential.

$\ce{CO4},$ $\ce{CO5}$ and $\ce{CO6}$ are very unstable, and could possibly be strong oxidants (though it may never be known since they're too unstable).

Other than that, any information?

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    $\begingroup$ Its hard to give (m)any solid facts about molecules which barely exist. ;) What would CO5 even look like? A ring structure? $\endgroup$
    – Karl
    Dec 26, 2019 at 8:07
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    $\begingroup$ What are the properties of two-headed people that live on an island beyond the ocean? $\endgroup$ Dec 26, 2019 at 8:49
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    $\begingroup$ The compounds do exist, however, they aren't stable above really cold temperatures (around 120 K for carbon tetroxide, to 106 K for carbon pentoxide and then 60 K for carbon hexoxide). $\endgroup$
    – JMRD
    Dec 26, 2019 at 10:09
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    $\begingroup$ Adding to previous comment, logically, carbon trioxide should be stable until an even higher temperature than carbon tetroxide. In the gas phase however, as noted, it still decomposes slowly enough to potentially encounter other molecules. $\endgroup$
    – JMRD
    Dec 26, 2019 at 10:16

1 Answer 1


At least the trioxide $\ce{CO3}$ exists, and it has even been detected in at least two isomeric forms. Wikipedia reports that it forms as a transient species in reactions between carbon dioxide and atomic oxygen or ozone, in irradiation of solid carbon dioxide, and even in oxidation of carbon monoxide by $\ce{O2}$.

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    $\begingroup$ If you have said A, you must also say B: $\ce{CO4}$; $\ce{CO5}$; $\ce{CO6}$. Don't leave Wikipedia half-milked:) $\endgroup$
    – andselisk
    Dec 26, 2019 at 17:41
  • $\begingroup$ Thus, "at least" the trioxide. Feel free to add more info! $\endgroup$ Dec 26, 2019 at 19:14

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