A simple aqueous metathesis reaction yields new lanthanide monothiophosphates

This paper describes the synthesis and characterization of two, new rare earth monothiophosphate materials, LaPO3S·xH2O and NdPO3S·yH2O, and their properties in comparison to the corresponding orthophosphates prepared by a similar aqueous metathesis reaction. Each of these new materials was found to exist in an amorphous phase similar to a corresponding orthophosphate mineral. The new rhabdophane-type oxythiophosphates were found to display reversible dehydration and rehydration under mild conditions. The materials were found to be thermally unstable. Disproportionation was found to occur at less than 450 °C under vacuum. Sulfur is lost during heating in air between 450 and 650 °C, according to thermogravimetric analysis (TGA) experiments, yielding the orthophosphate. The monothiophosphate hydrates display broad photoluminescence in the visible under excitation by a 325 nm laser. The compounds were also analyzed using differential thermal analysis, FT-IR and UV/vis/NIR spectroscopy.