Synthesis and Crystal Structure of Maricite and Sodium Iron(III) Hydroxyphosphate John. N. Bridson Sean E. Quinlan Peter R. Tremaine 10.1021/cm9704847.s001 https://acs.figshare.com/articles/journal_contribution/Synthesis_and_Crystal_Structure_of_Maricite_and_Sodium_Iron_III_Hydroxyphosphate/3594963 Maricite and sodium iron hydroxyphosphate (SIHP) are recently discovered iron(II) and iron(III) compounds that play a major role in phosphate “hideout” and corrosion in high-pressure boilers. This paper reports a novel method for synthesizing maricite by thermally decomposing the complex of aqueous iron(III) nitrilotriacetic acid at 200 °C and methods for the hydrothermal synthesis of SIHP from Fe<sub>3</sub>O<sub>4</sub> or FePO<sub>4</sub>. The crystal structure of maricite is identical to the impure natural mineral (Le Page Y.; Donnay G. <i>Can. </i><i>Mineral.</i> <b>1977</b>, <i>15</i>, 518−521). The X-ray diffraction pattern of SIHP is consistent with an orthorhombic unit cell containing 8 units of formula Na<sub>3</sub>Fe(PO<sub>4</sub>)<sub>2</sub>·(Na<sub>2(1</sub><sub>-</sub><i><sub>x</sub></i><sub>)</sub>H<sub>2</sub><i><sub>x</sub></i>O), with <i>x</i> = 0.226 ± 0.025. This is similar, but not identical, to the formula Na<sub>4</sub>Fe(OH)(PO<sub>4</sub>)<sub>2</sub>·<sup>1</sup>/<sub>3</sub>NaOH proposed by Ziemniak and Opalka (<i>Proc. Sixth Int. Symp. on Environmental </i><i>Degradation of Materials in Nuclear Power </i><i>Systems</i><i>Water Reactors</i>; Gold, R. E., Simonen, E. P., Eds.; Mater., Metals, Minerals Soc., 1993; pp 929−935.). The main structural feature is a chain of iron(III) ions linked by bridging oxygens and phosphate bridges. The iron phosphate chains are held together by sodium ions in the ratio 3Na/Fe/2(PO<sub>4</sub>). Charge balance with the O<sup>2-</sup> bridge between each iron ion is maintained by Na<sup>+</sup> and H<sup>+</sup> ions located in a relatively open cage in the phosphate lattice. The structure is significant in that it explains the variable stoichiometry observed in powder diffraction patterns, and it identifies the stoichiometry of H and O, which cannot be determined from solubility studies. 1998-02-12 00:00:00 Crystal Structure phosphate lattice phosphate bridges paper reports SIHP 8 units solubility studies sodium iron hydroxyphosphate FePO 4 powder diffraction patterns synthesizing maricite hydrothermal synthesis Environmental Degradation Sixth Int Na Charge balance sodium ions iron ion Fe 3 O 4 iron phosphate chains crystal structure unit cell novel method