Spectral investigation of the products of reactions of cyanide ion with oxo-bridged binuclear iron(III) complexes of 1,10-phenanthroline and 2,2′-bipyridine

Abstract

Reactions of cyanide ion with aqueous solutions of oxo-bridged binuclear complexes of iron(III) and 1,10-phenanthroline or 2,2′-bipyridine, [L₂(H₂O)Fe–O–Fe(H₂O)L₂]⁴⁺(L = phen or bipy), are pH and temperature dependent. In the range 45–50 °C and pH 4·0, the complexes [Fe^III(phen)₂(CN)₂]CN and [Fe^III(bipy)₂(CN)₂]CN are formed, respectively. At room temperature and pH 1·2–1·5, the reduction products [Fe^II(phen)₂(CN)₂] and [Fe^II(bipy)₂(CN)₂] are obtained, respectively. Addition of cyanide ion to the binuclear complexes at pH 3·8–4·2 and room temperature results in a green solution, which rapidly becomes yellow. The green solution is believed to be due to the ion [L₂(CN)Fe–O–Fe(CN)L₂]²⁺, which in solution may undergo rapid decomposition to [Fe^IIIL₂(CN)₂]⁺.