PH Driven Hydrothermal Syntheses of Neodymium Sulfites and Mixed Sulfate-Sulfites

A family of four new neodymium(III) compounds containing either sulfite or a mixture of hydrogen-sulfate and sulfite ligands has been hydrothermally synthesized. The low solubility of lanthanide sulfite compounds has, in the past, made the isolation of single-crystalline products difficult. To obtain these phases, sodium sulfite (Na₂SO₃) and sodium bisulfite (NaHSO₃) were employed as both anion sources and pH regulators. The in situ oxidation of sulfite to sulfate was controlled by dictating the pH of the starting solutions with these ligands. Sulfites were found to form at a neutral pH, whereas, when the pH was increased, the oxidation of sulfite to sulfate was observed in the crystalline products. The products discussed herein reveal the pH controlled process of in situ oxidation in these hydrothermal reactions.