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Sodium tris(carbonato)cobalt(III)

Sodium tris(carbonato)cobaltate(III) is the inorganic compound with the formula Na<sub>3</sub>Co(CO<sub>3</sub>)<sub>3</sub>•3H<sub>2</sub>O. The salt contains an olive-green metastable cobalt(III) coordination complex. The salt, a homoleptic metal carbonato complex, is sometimes referred to as the “Field-Durrant precursor” and is prepared by the “Field-Durrant synthesis”. It is used in the synthesis of other cobalt(III) complexes. Otherwise cobalt(III) complexes are generated from cobalt(II) precursors, a process that requires an oxidant.

Synthesis

An aqueous solution of cobalt(II) nitrate and hydrogen peroxide is added to a solution of sodium bicarbonate, leading to precipitation of the olive solid. The reaction also generates lots of oxygen due to the decomposition of hydrogen peroxide. The method is a modification of the synthesis of what has been described as “Co<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>”.

Structure and synthetic applications

The identity of this complex anion has been established by X-ray crystallography of [Co(NH<sub>3</sub>)<sub>6</sub>][Co(κ<sup>2</sup>-CO<sub>3</sub>)<sub>3</sub>], which is also olive-green. This salt is prepared by the addition of [Co(NH<sub>3</sub>)<sub>6</sub>]Cl<sub>3</sub> to fresh solutions of sodium tris(carbonato)cobaltate(III). It is anhydrous. The anionic complex features three bidentate (κ<sup>2</sup>-) carbonate ligands. The structure of Na<sub>3</sub>Co(CO<sub>3</sub>)<sub>3</sub> or its hydrates, while probably featuring the same anion, is not absolutely certain. Thermal gravimetric analysis favors the presence of one aquo ligand, and infra-red spectroscopy indicates the presence of both bi- and unidentate carbonate ligands.

To some extent, the exact description of the title salt is unimportant since it is mainly used as a synthetic intermediate. Products include [Co(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup>, [Co(κ<sup>2</sup>-CO<sub>3</sub>)(H<sub>2</sub>O)<sub>4</sub>]<sup>+</sup>, and [Co(κ<sup>2</sup>-CO<sub>3</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>−</sup> and their derivatives where the aquo ligand has been displaced. The closely related potassium tris(carbonato)cobaltate(III) has also been used for the preparation of diverse complexes. These derivatives include [Co(NH<sub>3</sub>)<sub>2</sub>(κ<sup>2</sup>-CO<sub>3</sub>)<sub>2</sub>]<sup>−</sup> and [Co(CN)<sub>2</sub>(κ<sup>2</sup>-CO<sub>3</sub>)<sub>2</sub>]<sup>3-</sup>, rare examples of bis(carbonato) cobaltate(III) complexes. Other derivatives include the dinitrite [Co(NH<sub>3</sub>)<sub>2</sub>(κ<sup>2</sup>-CO<sub>3</sub>)(NO<sub>2</sub>)<sub>2</sub>]<sup>−</sup> and the oxalate [Co(NH<sub>3</sub>)<sub>2</sub>(κ<sup>2</sup>-CO<sub>3</sub>)(C<sub>2</sub>O<sub>4</sub>)]<sup>−</sup>.

References

Other literature

  • Fikru Tafesse, Elias Aphane, and Elizabeth Mongadi (2009): "Determination of the structural formula of sodium tris-carbonatocobaltate(III), Na3[Co(CO3)3]·3H2O by thermogravimetry". Journal of Thermal Analysis and Calorimetry, volume 102, issue 1, pages 91–97.
  • Thomas P. McCutcheon and William J. Schuele (1953): "Complex Acids of Cobalt and Chromium. The Green Carbonatocobalt(III) Anion". Journal of the American Chemical Society, volume 75, issue 8, pages 1845–1846.