Iron(II)oxalate Dihydrate—Humboldtine:<italic/> Synthesis, Spectroscopic and Structural Properties of a Versatile Precursor for High Pressure Research

• Main Authors: Harald Müller, Léa Bourcet, Michael Hanfland
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Minerals
• Subjects: iron(II)oxalate dihydrate FeC₂O₄ × 2 H₂O; iron(II)oxalate dideuterate FeC₂O₄ × 2 D₂O; ⁵⁷FeC₂O₄ × 2 H₂O; humboldtine; hydrothermal synthesis; single crystal diffraction
• Online Access: https://www.mdpi.com/2075-163X/11/2/113

Iron(II)oxalate dihydrate FeC₂O₄ × 2 H₂O—humboldtine is not only an important synthetic intermediate, but also a key building block for the preparation of various advanced materials. Interestingly, FeC₂O₄ × 2 H₂O can be transformed readily into phase-pure siderite FeCO₃. The importance of siderite for earth sciences, in particular for the understanding of the deep carbon cycle of our planet, is paramount. The availability of high-quality single crystals of FeC₂O₄ × 2 H₂O is crucial for diffraction or spectroscopic studies at high pressure. The present article describes a versatile synthetic approach to single crystals of FeC₂O₄ × 2 H₂O and its deuterated analogue starting from metallic iron together with a complete characterization of the products obtained. The same protocol has been employed successfully for the preparation of ⁵⁷FeC₂O₄ × 2 H₂O, as required for Möβbauer spectroscopy. In addition, the pressure-dependence of the crystal and molecular structure of the title compound was investigated up to <i>p</i> ≥ 20 GPa.