New series of hybrid fluoroferrates synthesized with triazoles: various dimensionalities and Mössbauer studies

Abstract

The solvothermal reactions of an equimolar mixture of FeF₂ and FeF₃ with Htaz (1,2,4-triazole), aqueous HF and DMF (dimethylformamide) at 120 °C yielded a series of new hybrid fluoroferrates (1–5). Their structures were characterized by either single crystal or powder X-ray diffraction data analysis. Both classes of hybrid networks were observed according to the Feⁿ⁺/Htaz/HF starting ratio: class I for 1 and 2 and class II for 3, 4 and 5. Four compounds, [Hdma]·(Fe₂(H₂O)₄F₆) (1), [Hdma]·(Fe₂(H₂O)₄F₆)·0.5H₂O (2), Fe₂F₅(Htaz) (3) and [Hdma]·(Fe₂F₅(H₂O)(Htaz)(taz)) (4), exhibit both Fe(II) and Fe(III) oxidation states while [Hdma]·(Fe₂F₅(taz)₂) (5) contains only Fe(III) cations. [Hdma]·(Fe₂(H₂O)₄F₆) (1) and [Hdma]·(Fe₂(H₂O)₄F₆)·0.5H₂O (2) contain anionic inorganic chains of alternating corner-sharing Fe(II) and Fe(III) octahedra; they are weakly hydrogen bonded to dimethylammonium cations [Hdma]⁺ which are formed by the in situ hydrolysis of DMF. The structure of Fe₂F₅(Htaz) (3) exhibits a three dimensional inorganic network resulting from the association of HTB planes of corner sharing Fe^IIF₄N₂ and Fe^IIIF₆ octahedra. [Hdma]·(Fe₂F₅(H₂O)(Htaz)(taz)) (4) and [Hdma]·(Fe₂F₅(taz)₂) (5) reveal two original two-dimensional sheets. In 4, the deprotonated and neutral amines connect trinuclear Fe₃F₁₀N₆ units of corner-sharing octahedra and mononuclear FeN₄(H₂O)₂ octahedra. Infinite Fe₂F₅(taz)₂ layers in 5 are built up from dinuclear species connected by deprotonated amines along two perpendicular directions. The thermal behavior and Mössbauer spectrometry results are detailed for the first tridimensional mixed valence hybrid fluoroferrate (3).