Interaction between gold (III) chloride and potassium hexacyanoferrate (II/III)—Does it lead to gold analogue of Prussian blue?

Prussian blue analogues are a class of compounds formed by the reaction between metal salt and potassium hexacyanoferrate (II/III). In our earlier report, the formation of Au@Prussian blue nano-composite was noticed on potential cycling the glassy carbon electrode in a medium containing gold (III) chloride and potassium hexacyanoferrate (III). Hence in this work, the formation of gold hexacyanoferrate was attempted by a simple chemical reaction. The reaction of gold (III) chloride with potassium hexacyanoferrate (II/III) was examined by UV–Vis spectroscopy and found that there is no redox reaction between gold (III) chloride and potassium hexacyanoferrate (III). However, the redox reaction occurs between gold (III) chloride and potassium hexacyanoferrate (II) leading to the formation of charge transfer band and the conversion of hexacyanoferrate (II) to hexacyanoferrate (III) was evidenced by the emergence of new absorption peaks in UV–Vis spectra. The oxidation state of gold in Au–Fe complex was found to be +1 from X-ray photoelectron spectroscopy. The stability of the Au–Fe complex was also studied by cyclic voltammetry. Cyclic voltammetric results indicated the presence of high spin iron in Au–Fe complex. Hence ‘as formed’ Au complex may be KFex[Au(CN)2]y. The results revealed that the formation of gold hexacyanoferrate was not feasible by simple chemical or electrochemical reaction in contrast to other Prussian blue analogues.

► In group IB, Cu and Ag form Prussian blue analogues but similar formation of gold hexacyanoferrate was not found in the literature and non-existence of gold hexacyanoferrate remains a mystery.
► Potential cycling of gold chloride and potassium ferro/ferri cyanide was resulted in the formation of Au-PB nano-composite.
► Redox reaction between gold chloride and potassium ferrocyanide ion is spontaneous but no reaction occurs when gold chloride and potassium ferricyanide is mixed.
► We are proposing the formation of a compound with general formula ‘KFex[Au(CN)2]y’ and discussing the formation of gold hexacyanoferrate is not feasible by simple chemical or electrochemical reaction in contrast to other PB analogues.