Zur Kenntnis des Natriumthioferrates(III)

The mixed valency compound Na₃Fe₂S₄, which is also formed in iron-sodium polysulfide melts, is oxidized and hydrated to NaFeS₂·H₂O (x ≈ 2) on air. It is shown by TGA that this hydrate loses the water reversibly between 80–140 °C. A crystal structure model for the water free phase NaFeS₂ is proposed (space group I 222,a=6.25 Å,b=10.83 Å,c=5.40 Å). The formation of NaFeS₂·xH₂O from Na₃Fe₂S₄ and the reversible phase transformation between NaFeS₂·xH₂O and NaFeS₂ are topotactic. Na⁺ ions in NaFeS₂·xH₂O are easily exchanged against K⁺, Rb⁺, Cs⁺, Tl⁺, Ca²⁺, Sr²⁺, and Ba²⁺. The high chemical reactivity of the sodium thioferrates is discussed and their crystal structures are compared with the other alkali metal thioferrate structures.