The First Example of a True “Turnbull’s Blue” Family Compound with Trapped Iron Oxidation States

Abstract

The first compound of a true Turnbull′s Blue family [i.e. an iron(II) hexacyanoferrate(III)] complex with valence-trapped states of iron − [Fe([9]ane-S3)2]3[Fe(CN)6]2·2H2O (Ukrainian Red, UR) was synthesized. It crystallizes in the trigonal space group P3, a = 12.038(8) A, b = 12.038(8) A, c = 14.342(7) A, α = 90.00°, β = 90.00°, γ = 120.00°. The unit cell of UR consists of separate [Fe([9]ane-S3)2]2+ cations, [Fe(CN)6]3− anions and 5.3 molecules of water. Encapsulation of the FeII in the homoleptic thioether environment plays the dual role of stabilizing FeII and protecting the central metal ion from direct bridging with hexacyanoferrate(III) anions. The absence of such interactions and trapping of iron oxidation states in the cations and anions was demonstrated by X-ray diffraction and magnetic susceptometry. Magnetic measurements are consistent with diamagnetic FeII inside the macrocyclic moieties and S = 1/2 for FeIII in the hexacyanoferrate(III) anions.