A series of Rb4Ln2(P2S6)(PS4)2 (Ln = La, Ce, Pr, Nd, Sm, Gd) rare earth thiophosphates with two distinct thiophosphate units [PVS4]3− and [PIV2S6]4−

Abstract

A series of rubidium rare earth thiophosphates with the formula Rb₄Ln₂(P₂S₆)(PS₄)₂ (Ln = La, Ce, Pr, Nd, Sm, and Gd) were synthesized using the high temperature molten flux crystal growth method utilizing a RbBr flux. Single crystals of all title compounds, as well as phase pure powders of the La-, Ce-, and Sm-containing compositions, were obtained. Single crystals of the title compounds were characterized by single crystal and powder X-ray diffraction for structure and phase identification. Rb₄Ln₂(P₂S₆)(PS₄)₂ crystallizes in the monoclinic crystal system adopting the P2₁/n space group for the large rare earths (Ln = La, Ce, Pr) and the C2/c space group for the smaller rare earths (Ln = Nd, Sm, Gd). This Rb₄Ln₂(P₂S₆)(PS₄)₂ series is a rare example of thiophosphates containing both tetrahedral [P^VS₄]³⁻ and dimeric [P^IV ₂S₆]⁴⁻ thiophosphate units that, in this structural family, link corrugated rare earth sulfide chains into sheets. The band gaps of the materials were determined from UV–Vis data and the fluorescence spectrum of Rb₄Ce₂(P₂S₆)(PS₄)₂ was collected. Optical band gaps were estimated to be 2.9 and 2.4 for the Nd and Sm analogues, respectively.