Though the simple cyanide Fe(CN)3 is unknown, the
thiocyanate is prepared as dark violet crystals by reaction of thiocyanogen with iron or by
extracting a mixture of potassium thiocyanate and an iron(III) salt with ether, followed by
evaporation of the ether. It is very soluble in water from which it crystallizes as the red
trihydrate Fe(SCN)3. 3H2O. The blood-red colour developed when dilute solutions of
iron(III) salts and thiocyanate ions are mixed is due largely to the [Fe(SCN(H2O)5]2+ ion;
this reaction finds extensive use in the qualitative and quantitative determination of iron.
