New sesquisulfides of the lanthanides with the U2S3-type structure (M2S3, M = Tb and Dy) were prepared through the oxidation of TbClH0,67 and DyCl2, respectively, with appropriate amounts of sulfur in the presence of NaCl fluxes in silica protected sealed tantalum containers at 850 °C for at least seven days. The preparation from the elements (2M + 3S; M = Tb and Dy) under otherwise analogous reaction conditions and temperatures was also successful when equimolar fluxes of NaCl were applied. The crystal structure was determined from single crystal data for Tb2S3 and Dy2S3, both crystallizing with the U2S3-type structure (orthorhombic, Pnma, Z = 4; Tb2S3: a = 1067.87(8), b = 388.06(4), c = 1049.07(7) pm ; Dy2S3: a = 1062.45(7), b = 386.59(4), c = 1044.36(8) pm) when prepared under the above-mentioned conditions.
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