The identity of this complex anion is uncertain, suggestions include [Co(κ-CO)], [Co(κ-COH)(OH)], and [Co(κ-CO)(κ-CO)(OH)]. Thermal gravimetric analysis favors the presence of one aquo ligand,  and infra-red spectroscopy indicates the presence of both bi- and unidentate carbonate ligands.  The addition of [[hexaamminecobalt(III) chloride|[Co(NH)]Cl]] to fresh solutions of sodium tris(carbonato)cobalt(III) precipitates anhydrous salt [Co(NH)] [Co(κ-CO)]. This salt has been characterized by X-ray crystallography, which established that the anionic complex features three bidentate (κ-) carbonate ligands.
To some extent, the exact description of the title salt is unimportant since it is only used as a synthetic intermediate, it has no intrinsic value. Products include [Co(HO)], [Co(κ-CO)(HO)], and [Co(κ-CO)(HO)] and their derivatives where the aquo ligand has been displaced.  The closely related potassium tris(carbonatocobalt(III) has also been used for the preparation of diverse complexes.  These derivatives include [Co(NH)(κ-CO)] and  [Co(CN)(κ-CO)], rare examples of biscarbonato cobalt(III) complexes. Other derivatives include the dinitrite [Co(NH)(κ-CO)(NO)] and the oxalate [Co(NH)(κ-CO)(CO)].