"Ferric ammonium oxalate" - (NH4)3Fe(C2O4)3
This compound is often called "ferric ammonium oxalate", but this name actually is wrong. There is no free ferric ion in this compound, but the complex trisoxalatoferrate (III). The correct name is ammonium trisoxalatoferrate (III).
A solution of this compound in water is lime-green and contains ions NH4+ and Fe(C2O4)33-. The compound does not contain free Fe3+ ions.