Sodium ferrioxalate: Difference between revisions

| verifiedrevid = 373355817

| Name = Sodium ferrioxalate

| ImageFile = Sodium TrisoxalatoferrateIIIoct.jpg

| ImageName1 =

| ImageSize = 200px

| ImageName = Sodium ferrioxalate

| IUPACName = Sodium ferric(III) oxalate

| OtherNames = Sodium ferrioxalate

Sodium trisoxalatoferrate (III)

| Section1 = {{Chembox Identifiers

| CASNo = 5936-14-1

| RTECS =

}}

| Section2 = {{Chembox Properties

| Formula = Na₃[Fe(C₂O₄)₃]

Na₃[Fe(C₂O₄)₃].xH₂O

| MolarMass = 388.88 g/mol - anhydrous sodium trioxalatoferrate (III)<p>388.88 + x(18.01) g/mol - hydrated sodium trioxalatoferrate (III)</p>

| Appearance = lime green hydrated crystals

| Density = 1.97 g/cm³ at 17 °C

| Solubility = 32.5pts per 100pts solvent, cold water, 182pts per 100pts, boiling water<ref>C.R.C. Handbook of Chemistry and Physics, 62nd Ed., page B149, ISBN-0-8493-0462-8, 1981, CRC Press</ref>

| MeltingPtC =

}}

| Section3 = {{Chembox Structure

| Coordination = [[octahedral]]

| CrystalStruct =

| Dipole = 0 [[Debye|D]]

}}

| Section7 = {{Chembox Hazards

| ExternalMSDS =

| MainHazards = Corrosive. Eye, respiratory and skin irritant.

| RPhrases = {{R20}} {{R21}} {{R22}} {{R34}} {{R36}} {{R37}} {{R38}}

| SPhrases =

}}

| Section8 = {{Chembox Related

| OtherAnions =

| OtherCations =

| Function = compounds

| OtherFunctn = [[Iron(II)_oxalate|Fe(C₂O₄)₂]]

}}

'''Sodium ferrioxalate''', also known as '''sodium oxalatoferrate''', is a chemical compound with the formula Na₃[Fe(C₂O₄)₃], where iron is in the +3 oxidation state. It is an octahedral [[transition metal complex]] in which three [[bidentate]] [[oxalate]] ions act as [[ligands]] bound to an iron centre. Sodium acts as a [[counterion]], balancing the -3 charge of the complex. Crystals of the hydrated form of the complex, Na₃[Fe(C₂O₄)_x].xH₂O, are lime green in colour. In solution the complex dissociates to give the ferrioxalate anion, [Fe(C₂O₄)₃]^3-, which appears a deep apple green in colour.

==Bonding==

The bonds to the iron atom are dative covalent bonds where the ligands, (oxalate ions, blue), donate a lone pair into the empty p and d orbitals of the transition metal (iron, red), atom. The three oxalate ions donate 12 electrons in all and Fe-III has three electrons in the d orbitals leaving 13 empty places in the remaining d and p orbitals.

==Solubility==

This compound is very soluble in hot water, (182 parts per 100 parts solvent by mass), but a lot less soluble in cold water, (32 parts per 100 parts solvent), about the solubility of sodium chloride. It is not appreciably soluble in ethanol or ethanol water mixtures which are more than 50% ethanol by mass. It is somewhat more soluble in water than the corresponding [[Potassium ferrioxalate|potassium salt]].

[[Image:Na3FeOx3_01.JPG#filelinks|thumb|left|Sodium trisoxalatoferrate crystals]]

The crystals pictured were synthesised by mixing solutions of sodium oxalate and ferric oxalate and waiting a few hours for the brown colour of the ferric oxalate to be replaced with the green colour of the complex anion. This complex is relatively inert and the equlaibrium is attained only slowly at room temperature. The ferric oxalate was made by dissolving rust in [[oxalic acid]] and filtering off any residual insolubles. The solution was evaporated at just below boiling until small crystals appeared on the bottom indicating the solution was then hot and saturated. The solution was allowed to cool in a beaker sitting on a large aluminium block. The thermal mass of the block allowed sufficiently slow cooling over night to produce crystals a few milimetres long. These larger crystals are pictured at the upper left.

Fe₂(C₂O₄)₃ + 3 Na₂(C₂O₄) → 2 Na₃[Fe(C₂O₄)₃]

Stoichiometry was not worried about and an excess of sodium oxalate was added, this is a lot less soluble in hot water than the ferrioxalate and crystallizes out first. The intensity of the green colour was used as a guide to concentration of the solution with respect to the complex. A few drops of 100 vol hydrogen peroxide were periodically added during the evaporation to maintain the iron in the III oxidation state and any insoluble ferrous oxalate was removed if it precipitated out.

The smaller crystals were recovered from the solution by placing it in the freezer after the large crystals had been removed. The smallest crystals, pictured at the lower right were precipitated from the cold solution by addition of methylated spirit.

==Isomerism==

The ferrioxalate complex demonstrates optical activity since there are two non-superimposable [[stereoisomer]]s of the complex. This is described in more detail under [[potassium ferrioxalate]].

Theoretically the two stereoisomers could be separated by crystallization of a [[diastereomeric salt]] of the optically inactive racemic mixture of ferrioxalate ions with an optically active cation, such as methylethylpropylammonium ion which is one pure enantomer. Thus methylethylpropylammonium ferrioxalate should crystallize out to produce crystals which are non superimposable mirror images. These would be Λ-methylethylpropylammonium Λ-ferrioxalate and Λ-methylethylpropylammonium Δ-ferrioxalate.

==Photoreduction==

In solution the ferrioxalate complex is decomposed by light. This is described in more detail under [[potassium ferrioxalate]]. Some samples of the crystals were exposed to direct sunlight for a few hours, the larger crystals did not appear to be affected, however solutions and small crystals so exposed did change colour to a different shade of green.

{{DEFAULTSORT:Sodium Ferrioxalate}}

[[Category:Coordination compounds]]

[[Category:Iron compounds]]

[[Category:Oxalates]]