Formula: Na3[Fe(C2O4)3]·3H2O Other names are: sodium oxalatoferrate and sodium ferrioxalate. Product of dissolving rust in oxalic acid (H2C2O4) in presence of sodium oxalate. Surprisingly for an iron (III) compound, has bright green color. A well-known example of coordination complex.
- Color: bright green
- Stability on air: not stable, dehydrate after a day on dry air. Store in tightly closed container.
I used the following procedure:
Prepare iron (III) hydroxide Fe(OH)3. Oxide Fe2O3, and intermediates between them are good too, though they are less reactive. Easiest way is reaction between FeCl3 and NaOH or soda NaHCO3. Or just get some rust.
Dissolve Fe(OH)3 in hot oxalic acid solution, taking 3 moles of acid per 1 mole of Fe(OH)3. This would produce dark greenish-brown solution of iron (III) oxalate
Neutralize excess of acid with NaOH or soda. Brown solution would turn bright green - color of the complex ion [Fe(C2O4)3]3+. Filter it and crystallize the compound from it.
Total equation is:
Fe(OH)3 + 3H2C2O4 + 3NaHCO3 → Na3[Fe(C2O4)3] + 6H2O + CO2
My samples were grown using slow evaporation method, growth time is 2 weeks. The compound crystallizes very well, large and transparent crystals are easy to get. Solubility is much bigger than of potassium analog, my rough estimate is about 60g/100ml.
According to the literature, the compound is light sensitive, decomposing on strong light. It appears to be stable under regular room light though.
It is not especially dangerous, though significant amounts of oxalates can be poisonous.