| Potassium ferrioxalate | |
|---|---|
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| IUPAC name |
Potassium ferric(III) oxalate
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| Other names | Potassium ferrioxalate
Potassium trioxalatoferrate (III) |
| Identifiers | |
| CAS number | 5936-11-8 |
| Properties | |
| Molecular formula | K3[Fe(C2O4)3]
K3[Fe(C2O4)3].3H2O |
| Molar mass | 437.20 g/mol - anhydrous potassium trioxalatoferrate (III)
491.25 g/mol - hydrated potassium trioxalatoferrate (III) |
| Appearance | emerald green hydrated crystals |
| Density | 2.13 g/cm3, solid |
| Melting point |
230 °C, 503 K, 446 °F |
| Solubility in water | ?M (20 °C) |
| Structure | |
| Coordination geometry |
octahedral |
| Dipole moment | 0 D |
| Hazards | |
| R-phrases | R20 R21 R22 R34 R36 R37 R38 |
| Related compounds | |
| Related compounds | Fe(C2O4)2 |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
| Infobox references | |
Potassium ferrioxalate, is a chemical compound with the formula K3[Fe(C2O4)3], where iron is in the +3 oxidation state. It is an octahedral transition metal complex in which three bidentate oxalate ions are bound to an iron centre. Potassium acts as a counterion, balancing the 3- charge of the complex. Crystals of the trihydrated form of the complex, K3[Fe(C2O4)3].3H2O, are emerald green in colour. In solution the complex dissociates to give the ferrioxalate anion, [Fe(C2O4)3]3-, which appears fluorescent green in colour. Potassium ferrioxalate is often used in chemical actinometry.
Contents |
Preparation
The complex can be synthesised from the reaction between iron(III) sulfate, barium oxalate and potassium oxalate:
Fe2(SO4)3 + 3 Ba(C2O4) + 3 K2(C2O4) → 2 K3[Fe(C2O4)3] + 3 BaSO4
The reactants are dissolved in water and heated for around 1.5 hours. BaSO4 precipitates out leaving behind the newly formed complex in solution. The complex can then be obtained by filtering off the BaSO4 and cooling the solution so that it crystallizes out.
Isomerism
The ferrioxalate complex demonstrates optical activity since there are two non-superimposable stereoisomers of the complex. In accordance with the IUPAC convention, the isomer with the left-handed screw axis is assigned the Greek symbol Λ (lambda). Its mirror image with the right-handed screw axis is given the Greek symbol Δ (delta)[1].
Photoreduction
In solution the ferrioxalate complex is decomposed by light. The complex reacts with a photon of light to form Fe(C2O4)22- and CO2. Iron is reduced (gains an electron) from the +3 oxidation state to +2. This process is called photoreduction:
2 [Fe(C2O4)3]3- + hν → 2 [Fe(C2O4)2]2- + C2O42- + 2 CO2
If a solution of green K3[Fe(C2O4)3] is left in sunlight for a few hours it turns orange due to the formation of Fe(C2O4)22- ions.
References
- ^ Greenwood, Norman N.; Earnshaw, A. (1997), Chemistry of the Elements (2nd ed.), Oxford: Butterworth-Heinemann, ISBN 0-7506-3365-4
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