Perovskite-like modification of Cs3Sb2I9 as a member of theOD family A3B2X9

The structure of the trigonal modification of Cs3Sb2I9was refined by XRD methods (Syntex {ie572-1} diffractometer, λMoKα at T = 285 K. The structure is ofperovskite type A3B3-xX9 with ordered vacancies in the B-sublattice. The unit cell with pseudo-R-centering has the following parameters: α = 8.435(7), c = 10.390(7) Å, V = 757.5 Å3, Z = 1; dx = 4.67 g/cm3. The centrosymmetric space group {ie572-2} was chosen based on the laser radiation second harmonic generation test. The parameters of the pseudo-rhombohedron corresponding to the perovskite cell are a’ = 5.976 å, α = 89.78°. The R-lattice of a perovskite structure is disturbed by ordered Sb vacancies in one of the three I6, octahedra. The structural modifications of the compounds A3B2X9 are analyzed in terms of Dornberger-Schiffs OD theory as the members of the family formed by the two-dimensional periodic fragments ofperovskite type structures.