Crystal structure of the new ternary silicides Dy18Pt50+xSi16−x (x = 0.28) and Y18Pt50+xSi16−x (x = 0.56)

The crystal structures of the compounds Dy18Pt50+xSi16−x (x = 0.28) (I) and Y18Pt50+xSi16−x (x = 0.56) (II) have been investigated by means of single crystal techniques (Nonius KappaCCD diffractometer, ω- and φ-scans, Mo Kα radiation). Both compounds belong to a new structure type (space group P4/mbm, Z = 1, a = 18.7778(2) Å, c = 4.0897(1) Å (I) and a = 18.7777(3) Å, c = 4.0891(1) Å (II)) closely related to the Er36Pt102−xSi32 (x = 2.6) type of structure (space group P42/mnm, Z = 1, a = 18.6723 Å, c = 8.1734 Å). Coordination numbers for three crystallographically independent Dy and Y atoms are 18, 15 and 12 and for Pt atoms range from 9 to 12, distorted cuboctahedra being typical for most of the Pt-atom polyhedra. Triangular prisms with three additional atoms are characteristic for coordination polyhedra of silicon atoms. The peculiarity of the defects of the Pt and Si atom positions as well as the relationship with the Er36Pt102−xSi32 structure is discussed.