Beschreibung:
<jats:p>The title structures of KScS<jats:sub>2</jats:sub>(potassium scandium sulfide), RbScS<jats:sub>2</jats:sub>(rubidium scandium sulfide) and KLnS<jats:sub>2</jats:sub>[Ln = Nd (potassium neodymium sufide), Sm (potassium samarium sulfide), Tb (potassium terbium sulfide), Dy (potassium dysprosium sulfide), Ho (potassium holmium sulfide), Er (potassium erbium sulfide), Tm (potassium thulium sulfide) and Yb (potassium ytterbium sulfide)] are either newly determined (KScS<jats:sub>2</jats:sub>, RbScS<jats:sub>2</jats:sub>and KTbS<jats:sub>2</jats:sub>) or redetermined. All of them belong to the α-NaFeO<jats:sub>2</jats:sub>structure type in agreement with the ratio of the ionic radii<jats:italic>r</jats:italic><jats:sup>3+</jats:sup>/<jats:italic>r</jats:italic><jats:sup>+</jats:sup>. KScS<jats:sub>2</jats:sub>, the member of this structural family with the smallest trivalent cation, is an extreme representative of these structures with rare earth trivalent cations. The title structures are compared with isostructural alkali rare earth sulfides in plots showing the dependence of several relevant parameters on the trivalent cation crystal radius; the parameters thus compared are<jats:italic>c</jats:italic>,<jats:italic>a</jats:italic>and<jats:italic>c</jats:italic>/<jats:italic>a</jats:italic>, the thicknesses of the S—S layers which contain the respective constituent cations, the sulfur fractional coordinates<jats:italic>z</jats:italic>(S<jats:sup>2−</jats:sup>) and the bond-valence sums.</jats:p>