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.

Graphical abstractA continuous two-step molecular precursor pathway was designed for the preparation of rare-earth oxysulfides Ln2O2S (Ln=Y, La, Pr, Nd, Sm–Lu), starting from heteroleptic dithiocarbamate complexes. The influence of the nature of the molecular precursor on the minimum synthesis temperature and on the purity of the final Ln2O2S crystalline phase is discussed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A new high yield and high purity synthesis route of rare earth dithiocarbamates is described. ► These compounds are used as precursors in a continuous process leading to rare-earth oxysulfides. ► The oxysulfides are obtained under much more moderate conditions than previously described.