A new iron(II) thiocyanato thiocyanogen complex

The reaction between Fe3+ and SCN−, in glacial acetic acid medium, gave a dark red solution which differs from the classical FeSCN2+, prepared in aqueous medium, with regard to stability and composition. In contrast to [FeSCN]2+ which undergoes photochemical decomposition and is bleached by light and reduced by hydroxylammonium chloride, the new complex is stable towards these agents, but it reacts with water. In addition to the charge transfer band at 480 nm exhibited by both solutions, the new complex exhibits a sharp strong band at 253 nm characteristic of the trithiocyanate ion, [SCN− + NCSSCN]; thiocyanogen being produced by oxidation of SCN− by Fe3+. The reaction with water is attributed to the hydrolysis of thiocyanogen mainly into sulphate. The presence of thiocyanogen in the new complex enhanced polymerixation and subsequent deposition of solid complex. On the basis of chemical, spectral, and thermal analyses the formula K2[Fe(SCN)4(NCSSCN)], is assigned to the new compound.