Rodalquilarite Revisited: The Hydrothermal Synthesis and Structural Reinvestigation of H₃Fe₂(TeO₃)₄Cl

The known mineral rodalquilarite, H₃Fe₂(TeO₃)₄Cl, was obtained as high quality single crystals via hydrothermal reactions. This material crystallizes in the triclinic space group,P1, with cell constants ofa=5.103(2) Å,b=6.653(2) Å,c=9.012(3) Å,α=73.40(2)°,β=78.03(2),γ=76.76(2),V=282.1(2) ųand was obtained from an NH₄Cl solution that was heated at 375°C for 4 days. A detailed structural characterization was performed (R=0.039,R_w=0.050) and showed that this material is based on layers consisting of edge-sharing FeO₆octahedra which are interconnected by TeO₃pyramids which are completed by the presence of a terminal hydrogen atom. Additionally, a second set of TeO₃pyramids attached to the FeO₆octahedra are linked across the layers by a shared hydrogen atom. The layers are held together only through these O-H-O interactions and additional weak Te-Cl interactions. In this study, we compare this structure to a previous report of rodalquilarite and a reported triclinic form of Fe₂Te₄O₁₁, which may have been misidentified and is also the title compound. In addition, we have obtained the band gap of this material by diffuse reflectance spectroscopy and find it to be a wide band gap (E_g=2.51eV) material. The DC magnetic susceptibility was also obtained and showed that the title compound is antiferromagnetic with aT_Nof 29 K.