Synthese,Charakterisierung und EPR-spektroskopische Untersuchung von Heteropolyverbindungen mit tetraedrisch bzw. oktaedrisch koordiniertem Eisen(III)

Synthesis, Characterization, and EPR Studies of Heteropoly Compounds with Iron(III) in Tetrahedral and Octahedral Coordination The heteropoly compounds H₅FeO₄W₁₂O₃₆] · 6 H₂O (a₀ = 1216 pm), H₃Fe(OH)₆Mo₆O₁₈] · 4 H₂O, Na₅FeO₄W₁₂O₃₆] · nH₂O and FeH₂FeO₄W₁₂O₃₆] · 17 H₂O, for the first time obtained in this work by freeze-drying and characterized by means of chemical analysis, i.r. and u.v. spectroscopy, X-ray powder-photographs, and magnetic measurements, appear as suitable model systems for EPR investigations. They contain, like a number of known Fe^III-heteropoly compounds, Fe^III in FeO₄ or/and FeO₆ units, which are isolated from each other by structural reasons. In the Keggin-compounds M₅E^IIIO₄W₁₂O₃₆] · nH₂O ( I ) (M = Na, Rb, TMA, TEA; E = Fe, Al, B) Fe^III occupies slightly distorted tetrahedral positions (g′ ≈? 2), which are characterized by zfs-values of ≈? 10 mT and line widthes ΔB of 2.0 ?15 mT. Unlike as for I cations with different physico-chemical characteristics have only little effect on the Fe^III-zfs. This holds for the Anderson-complexes M₃Fe(OH)₆Mo₆O₁₈]·nH₂O, (M = H, K, NH₄, TMA; g′ ≈? 4.3 ΔB ≈? 67 mT) and for M5SiO₄W₁₁O₃₅FeO₅(OH₂)]·nH₂O, (M = K, TMA; g′ = 4.3 ΔB = 26.5 mT). The FeO₆ octahedra are more distorted than the FeO₄ tetrahedra in I and therefore less susceptible for structural changes.