I searched for this onsite already, and also found the following answer on Quora:

In aqueous environment, iron(III) is bound by water molecules and exists as $\ce{[Fe(H2O)6]^3+}$. Due to strong interaction between Fe(III) and some of the aqua ligands, the complex can dissociate into $\ce{[Fe(OH)_n(H2O)6^{n-}]3^{n-}}$ and $\ce{H+}$. Carbonate is a base, so it will capture proton and further facilitate the formation of hydroxyl complexes so much that it will produce $\ce{H2CO3}$ and $\ce{Fe(OH)3}$, the former eventually decomposes into water and $\ce{CO2}$. Therefore, iron(III) carbonate cannot exist in water.

In solid state, most of iron(III) compounds are hygroscopic, which means that they have strong affinity for moisture. And of course, when water gets involved, the above processes start happening, which eventually decomposes iron(III) carbonate, if it could ever be formed as solid.

Therefore, the compound itself is not stable in solutions or in solid states.

Is this correct? What happens in the following equation then:

$$\ce{2 FeCl3(aq) + 3 Na2CO3(aq) -> Fe2(CO3)3 + 6 NaCl}$$

Will we get different end products? What will be solid? Hydroxides or oxides? Will there be carbon dioxide evolved? Are any of the products going to be hydrates?

  • $\begingroup$ Strongly related but not a dupe: chemistry.stackexchange.com/q/38916 $\endgroup$ – Gaurang Tandon Apr 24 '18 at 1:24
  • $\begingroup$ No, your equation is not correct. The correct equation is 2FeCl₃ + 3Na₂CO₃ + 3H₂O = 2Fe(OH)₃ + 6NaCl + 3CO₂ $\endgroup$ – شاهين حسن Feb 18 '19 at 16:08
  • 2
    $\begingroup$ It is not clear what do you mean stable. Iron(III) salts generally form an oxo-hydroxo precipitate unless some complexation or other tricks going on. From that point of view, it doesn't matter if carbonate or other non- or weakly complexing ion you have as a counter ion, they are not stable. $\endgroup$ – Greg Feb 18 '19 at 16:20

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