A new continuous two-step molecular precursor route to rare-earth oxysulfides Ln2O2S

A continuous two-step molecular precursor pathway is designed for the preparation of rare-earth oxysulfides Ln2O2S (Ln=Y, La, Pr, Nd, Sm–Lu). This new route involves a first oxidation step leading to the rare-earth oxysulfate Ln2O2SO4 which is subsequently reduced to the rare-earth oxysulfide Ln2O2S by switching to a H2–Ar atmosphere. The whole process occurs at a temperature significantly lower than usual solid state synthesis (T≤650 °C) and avoids the use of dangerous sulfur-based gases, providing a convenient route to the synthesis of the entire series of Ln2O2S. The molecular precursors consist in heteroleptic dithiocarbamate complexes [Ln(Et2dtc)3(phen)] and [Ln(Et2dtc)3(bipy)] (Et2dtc=N,N-diethyldithiocarbamate; phen=1,10-phenanthroline; bipy=2,2′-bipyridine) and were synthesized by a new high yield and high purity synthesis route. The nature of the molecular precursor determines the minimum synthesis temperature and influences therefore the purity of the final Ln2O2S crystalline phase.