[Jorge Stolfi]

Does the compound iron(III) tris(hydrogenoxalate)  = Fe(HC₂O₄)₃ exist? 

It could be seen as the conjugate acid of the trisoxalatoferrate(III) ion, which is well known as its potassium and sodium salts.

I imagine that it could be obtained by treating iron hydroxide FeOOH.nH₂O with a solution of excess oxalic acid, and evaporating to crystallize.  Makes sense?

edit: fixed compound name

[chenbeier]

It will be I think Iron-III-oxalate.  Fe₂(C₂O₄)₃

[Jorge Stolfi]

It will be I think Iron-III-oxalate.  Fe₂(C₂O₄)₃

That is a real compound.  But I wonder whether one can get the "biolxalate" too. 

Compare sodium carbonate Na₂CO₃ with sodium bicarbonate NaHCO₃. Both are stable in normal conditions, but heating the latter yields the former with release of water:

  2 NaHCO₃  Na₂CO₃  + CO₂ + H₂O

The only bicarbonates that are stable as solids at normal conditions are basically the alkali and ammonium ones.  However, oxalic acid is stable while carbonic acid is unstable. So perhaps bi-oxalates (hydrogen oxalates) of other cations, like iron(III) are stable too.

Calcium bicarbonate does exists in solution; rather, one can have a solution with Ca²⁺ and HCO₃^-.  Likewise, in a solution that is acid enough (pH 2.5 - 3) one can have Fe³⁺ and HC₂O₄^- with little oxalate.  The question is whether one can evaporate that solution without losing the hydrogen-oxalate.

[AWK]

Does the compound iron(III) tris(hydrogenoxalate)  = Fe(HC₂O₄)₃ exist? 

Probably it does not exist. I do hope you searched over internet and found that this compound  is used for nomenclature and stoichiometry testing only.

It could be seen as the conjugate acid of the trisoxalatoferrate(III) ion, which is well known as its potassium and sodium salts.

This statement is not true. The conjugate of Fe(C₂O₄)₃^3- is H[Fe(C₂O₄)₃]^2-

I imagine that it could be obtained by treating iron hydroxide FeOOH.nH₂O with a solution of excess oxalic acid, and evaporating to crystallize.  Makes sense?

If people would not have dreams, the world would be uninteresting, but scientific dreams without knowledge lead rarely to the goal.
In fact, the hydrated iron oxide can be dissolved in oxalic acid but evaporation of its solution gives Fe₂(C₂O₄)₃·3H₂O.
One may try a very narrow range of pH rather below 2.9 or mixed solvents but you cannot exactly estimate the strength of chelating by oxalate on the solubility of your compound.

[Jorge Stolfi]

Thanks for the reply...

I do hope you searched over internet

Yes, of course. 

but scientific dreams without knowledge lead rarely to the goal.

The number of real 16-atom compounds so vastly exceeds the number of chemists that many of them surely have never been studied and described.  Especially if one includes compounds that are stable only under non-standard conditions, or can be made only by non-obvious routes.  I have seen a few notable examples.

I once asked a chemist friend of mine whether dodecahedrane existed.  He laughed at me.  That was a few years before it became headline news in science magazines.

True copper carbonate CuCO₃ was obtained only recently.  It seems that it will be more stable than the basic carbonate in water only under 4 atm of CO₂, or something like that.

This oxide of carbon has been known for almost 200 years, but cannot be produced by oxidizing carbon, which may explain why it is never mentioned in textbooks.   (By the way, does the oxygen analog of this exist?)

In fact, the hydrated iron oxide can be dissolved in oxalic acid but evaporation of its solution gives Fe₂(C₂O₄)₃·3H₂O.
One may try a very narrow range of pH rather below 2.9 or mixed solvents but you cannot exactly estimate the strength of chelating by oxalate on the solubility of your compound.

OK.  Maybe some day, someone... 

[AWK]

Concerning other unexpected discoveries.
Your statement for one of your previous posts is not quite true

while carbonic acid is unstable

- of course in water is unstable (but this is not stated in your post).
In the anhydrous conditions at RT, H₂CO₃ is quite a stable solid, soluble in ethyl ether and even can sublime on heating without decomposition. Traces of water catalyze its decomposition.
Many interesting syntheses are carried out now in anhydrous conditions; CuCO₃ mentioned by you is also the case although not so recently (almost 50 years ago).
I would try some reaction with known (NH₄)₃Fe(C₂O₄)₃·3H₂O.

[Jorge Stolfi]

Thanks again!