Beschreibung:
<jats:p>The title structures NaGdS<jats:sub>2</jats:sub>(sodium gadolinium sulfide), NaLuS<jats:sub>2</jats:sub>(sodium lutetium sulfide) and NaYS<jats:sub>2</jats:sub>(sodium yttrium sulfide) were redetermined in order to improve the structural information available for the family of group 1 and thallium rare earth sulfides, which are isostructural with the rhombohedral α-NaFeO<jats:sub>2</jats:sub>structure type. In particular, the present investigation has been directed at the rhombohedral sodium rare earth sulfides. The observed dependence of the fractional coordinate<jats:italic>z</jats:italic>(S<jats:sup>2−</jats:sup>) on the identity of the rare earth element in the newly determined structures is in agreement with the known structures of the potassium and rubidium analogues. Crystals of NaGdS<jats:sub>2</jats:sub>and NaLuS<jats:sub>2</jats:sub>display obverse–reverse twinning.</jats:p>