Carbonite (ion)

The carbonite ion is the double ionized ion of dihydroxymethylidene, with the chemical formula: CO2−
2. Alkali metal salts, Li
2CO
2, K
2CO
2, Rb
2CO
2 and Cs
2CO
2, have been observed at 15 K.[1][2] Interestingly, sodium does not form a carbonite. Due to the lone pair on the carbon atom, salts of the carbonite ion would be protonated to form formate and formic acid, rather than the carbene.

Carbonite (ion)
Identifiers
3D model (JSmol)
  • InChI=1S/CO2/c2-1-3/q-2
    Key: DEXSTXPKYXOQOB-UHFFFAOYSA-N
  • [C]([O-])[O-]
Properties
CO22−
Molar mass 44.010 g·mol−1
Related compounds
Related compounds
 Carbonate, Carbon monoxide, Carbon dioxide, Oxalate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

At lower metal concentrations, salts of the monovalent anions CO−
2 were favored over CO2−
2. Carbonite was not detected when sodium was used as the metal.[2] The alkali metal carbonites obtained in the cryogenic experiments decomposed to the corresponding carbonate (with release of carbon monoxide) or oxalate.[1][2] The carbonite ion is promptly converted to carbonate in the presence of oxygen.[3][4]

The presence of carbonite ions has been proposed to be relevant to the absorption of carbon monoxide on calcium oxide and magnesium oxide[3] and on ceria.[4] In the former, it has been suggested that the carbon atom attaches via a coordinate covalent bond to an oxygen atom from the substrate through its free bonds.[3] In these contexts, it appears that the carbonite ion reacts with excess carbon monoxide to form an anion with the ketene structure, O=C=CO2−
2.[3]

Infrared spectroscopy data confirm earlier theoretical studies that the carbonite anion has a bent structure, with the O−C−O angle varying between 120° and 130° depending on the context. The metal atoms interact with both oxygen atoms. However two geometrical arrangements for the lithium and caesium salts were detected, only one of them being symmetrical on the two oxygen atoms.[1][2]

References
  1. Kafafi, Zakya H.; Hauge, Robert H.; Billups, W. Edward; Margrave, John L. (1983). "Carbon dioxide activation by lithium metal. 1. Infrared spectra of Li+CO2–, Li+C2O4–, and Li22+CO22– in inert-gas matrices". Journal of the American Chemical Society. 183: 3886–3893. doi:10.1021/ja00350a025.
  2. Kafafi, Zakya H.; Hauge, Robert H.; Billups, W. Edward; Margrave, John L. (1984). "Carbon dioxide activation by alkali metals. 2. Infrared spectra of M+CO2– and M22+CO22– in argon and nitrogen matrices". Inorganic Chemistry. 23: 177–183. doi:10.1021/ic00170a013.
  3. Babaeva, M. A.; Tsyganenko, A. A. (1987). "Infrared spectroscopic evidence for the formation of carbonite CO2−
    2     ions in CO interaction with basic oxide surfaces". Reaction Kinetics and Catalysis Letters. 34 (1): 9–14. doi:10.1007/BF02069193.
  4. Binet, Claude; Ahmed Badri; Magali Boutonnet-Kizling; Jean-Claude Lavalley (1994). "FTIR study of carbon monoxide adsorption on ceria: CO22– carbonite dianion adsorbed species". Journal of the Chemical Society, Faraday Transactions. 90 (7): 1023–1028. doi:10.1039/FT9949001023.
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