Characterization and structural determination of a new sodium lanthanum phosphate thiosulfate, Na2La[PO4][S2O3]

The reaction of La2O3 and Na3[PO3S] in a flux of Na2S4 at 400 °C for 10 days produced a pale yellow crystalline powder identified as Na2La[PO4][S2O3]. Powder X-ray diffraction analysis revealed a monoclinic unit cell with parameters a = 13.7789(3) Å, b = 5.3358(1) Å, c = 9.3558(2) Å, β = 89.972(3)°, V = 687.85(2) Å3 (Z = 4) in the space group P21/c. The crystal structure was determined using a Rietveld analysis of the powder diffraction data. The structure consists of two-dimensional anionic layers of [La[PO4][S2O3]]2− with charge-compensating Na+ cations between the layers. The new compound was characterized by thermal analysis (DSC, TG–MS), vibrational spectroscopy (FT-IR and Raman), and energy-dispersive spectroscopy (EDS). Thermal analysis shows that the compound is not stable at elevated temperatures in air, displaying two irreversible thermal events between 140 and 800 °C that lead to a mass loss of 2.2% and a new single-phase crystalline compound.