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I have heard that the dianion of carbon dioxide, $\ce{CO2^{2-}}$ was named carbonite.

Does such a species really exist? Basically, is it stable enough to be a plausible molecule? If so, under what conditions is this true?

This question is very confusing to me, I understand the concept somewhat but I don't know what information I need in order to figure out the answer.

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The obvious Star Wars puns aside, I have never heard about the dianion of a carbon dioxide dianion and/or that it was named carbonite.

However, the carbon dioxide radical anion, $\ce{CO2^{.-}}$, is experimentally available.

Typically, it is generated by hydrogen atom abstraction from formate, $\ce{HCOO-}$, using $\ce{HO^.}$ radicals. The $\ce{HO^.}$ radicals, in turn, are obtained from vacuum ultraviolet (VUV) irradiation of water at a wavelength of $\lambda = 175~\mathrm{nm}$.


UPDATE

Apparently, I was wrong about the dianion! As Mithoron pointed out in his comment, species like $\ce{M2^{2+}CO2^{2-}}$, formed in the reaction carbon dioxide with alkali metals in argon or nitrogen matrixes, have been detected by IR spectroscopy. See Inorganic Chemistry, 1984, 23, 177-184 for details.

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    $\begingroup$ It looks dianion also was made researchgate.net/publication/… $\endgroup$ – Mithoron Dec 13 '16 at 19:59
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    $\begingroup$ $\ce{CO2^{\bullet -}}$ is also thought to be a key intermediate in the electrochemical reduction of carbon dioxide. (e.g., PDF link) $\endgroup$ – hBy2Py Dec 13 '16 at 20:20
  • $\begingroup$ @hBy2Py Brian, that's interesting :) Actually, I think that I cited one of the authors, Jean-Michel Saveant, more than once. I always went the other way: oxidation of carboxylates to the corresponding radicals, followed by decarboxylation. $\endgroup$ – Klaus-Dieter Warzecha Dec 13 '16 at 20:26
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    $\begingroup$ I'm sorry, @Mithoron, but that is just preposterously cool. $\endgroup$ – hBy2Py Dec 13 '16 at 20:44
  • $\begingroup$ Carbonite di-anion may exist not only in low temperature matrices. Wikipedia reports that it may be a surface species when carbon monoxide is adsorbed onto some oxide surfaces including line and magnesia. $\endgroup$ – Oscar Lanzi Jun 24 '18 at 21:33

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