Pentapotassium Sodium Bis[Trioxalatoferrate(III)]

Potassium Sodium Trioxalatoferrate(III) · Potassium Sodium Ferrioxalate · Potassium Sodium Iron(III) Oxalate Complex

Logo

Description

Pentapotassium Sodium Bis[Trioxalatoferrate(III)] is a striking coordination compound best known for its intense emerald-green color. In its pure form, it typically crystallizes as a well-defined octahedron with sliced edges. The vivid green coloration arises from the Iron(III)–Oxalate complex and can range from yellow-green to deep emerald depending on crystal thickness.

Requirements


  • Distilled Water
  • Iron(III) Chloride
  • Sodium Hydroxide
  • Potassium Hydroxide
  • Oxalic Acid
  • A few drops of a strong mineral acid (such as Sulfuric Acid or Hydrochloric Acid) (optional)
  • Protective gear (neoprene rubber gloves, protective goggles, lab coat)
  • Fishing Line

Synthesis and Crystal Growth Procedure


Begin by wearing protective gear (neoprene rubber gloves, protective goggles, lab coat).


Preparing saturated aqueous solutions of approximately 120 grams of Iron(III) Chloride, 40 grams of Sodium Hydroxide, 80 grams of Potassium Hydroxide, and 150 grams of Oxalic Acid. In a large beaker, slowly combine the Iron(III) Chloride solution with the Sodium Hydroxide and Potassium Hydroxide solutions. Then add the Oxalic Acid solution gradually while stirring continuously.


For reference, the reactions involved are as follows:


FeCl3 + 3NaOH = Fe(OH)3 + 3NaCl

FeCl3 + 3KOH = Fe(OH)3 + 3KCl

Fe(OH)3 + 3H2C2O4 + 3NaOH = Na3[Fe(C2O4)3] + 6H2O

Fe(OH)3 + 3H2C2O4 + 3KOH = K3[Fe(C2O4)3] + 6H2O

Na3[Fe(C2O4)3] + 5K3[Fe(C2O4)3] = 3K5Na[Fe(C2O4)3]2

Insert a fishing line into the solution and leave the system undisturbed until seed crystals begin to form. Once the crystals reach a suitable size, carefully remove excess crystals so that only one or two remain attached to each line. Transfer the saturated solution into a clean vessel, collect any residual precipitate (which may be redissolved to produce additional solution), and place the fishing line with the selected crystals into the fresh solution to continue growth. Inspect the crystals periodically and remove any new growth that forms on the line to prevent unwanted fusion with the main crystal.


After approximately one to two months, large, stable crystals will form. Carefully detach the crystal from the fishing line. Pentapotassium Sodium Bis[Trioxalatoferrate(III)] is stable under normal atmospheric conditions; therefore, no protective coating (such as nail polish) is required.


It is worth mentioning that Pentapotassium Sodium Bis[Trioxalatoferrate(III)] is considered photosensitive and should therefore be stored in a dark place. If mold happens to develop in the solution (which may occur), filter it and add a few drops of a strong mineral acid (such as Sulfuric Acid or Hydrochloric Acid) to suppress further mold growth.