Synthesis and characterization of fluorinated metal arsenates with a layer structure: (C₄H₁₂N₂)1.5[M₃F₅ (HAsO₄)₂(AsO₄)] (M=Fe, Ga)

Two fluorinated metal arsenates, (C₄H₁₂N₂)1.5[M₃F ₅(HAsO₄)₂(AsO₄)] (M=Fe, Ga), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, magnetic susceptibility, Mössbauer spectroscopy, and ⁷¹Ga NMR spectroscopy. The two compounds are isostructural and crystallize in the monoclinic space group P2₁/c (No. 14) with a=8.394(1) Å, b=21.992(3) Å, c=10.847(1) Å, β=96.188(2)°, and Z=4 for the Fe compound, and a=8.398(1) Å, b=21.730(3) Å, c=10.679(1) Å, β=95.318(2)°, and Z=4 for the Ga compound. The structure consists of infinite chains of corner-sharing MX₆ (X=O, F) octahedra and dimers of edge-sharing MO₃F₃ octahedra, which are linked into two-dimensional sheets through arsenate tetrahedra with diprotonated piperazinium cations between the sheets. Magnetic susceptibility and Mössbauer spectroscopy confirm the presence of Fe(III). The ⁷¹Ga MAS NMR spectrum clearly shows a line shape consisting of three components, corresponding to three crystallographically distinct Ga sites.