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

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 Fe(n+)/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(II)F4N2 and Fe(III)F6 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).