CsYbSe₂

Caesium ytterbium diselenide, CsYbSe₂, crystallizes in space group P6₃/mmc of the hexagonal system. It is isostructural with CsPrS₂, which has the β-RbScO₂ structure type. In the asymmetric unit, the site symmetries of atoms Cs, Yb and Se are m2, m and 3m, respectively. The structure comprises layers of edge-shared YbSe₆ octahedra perpendicular to [001], with Cs atoms between the layers in a trigonal-prismatic arrangement.

Dicerium disilicate, Ce₂[Si₂O₇]

Dicerium disilicate, Ce₂[Si₂O₇], crystallizes in space group P4₁ of the tetra­gonal system. It has isostructural analogues among the disilicates of the larger rare-earth elements, namely Ln₂[Si₂O₇] (Ln is La, Pr, Nd or Sm). The structure consists of discrete Ce³⁺ cations and [Si₂O₇]^6- anions; the asymmetric unit containing four cations and two anions. Each anion is formed from two SiO₄ tetra­hedra that share a vertex.