New cobaltite materials containing CdI2-type layers: Synthesis and structures of Ba2Co4ClO7 and Ba2Co4BrO7

Single crystals of the title compounds were prepared by solid-solid reaction using BaCl2 or BaBr2 flux at 1100 °C. The structures of these two new cobaltites were solved and refined in the trigonal symmetry with space group R3¯m: a = 5.716(2) Å, c = 45.01(3) Å for Ba2Co4ClO7 and a = 5.7434(5) Å, c = 46.151(9) Å for Ba2Co4BrO7. The two compounds are isostructural and their structures can be considered as the intergrowth along [001] of hexagonal blocks (Ba2Co8O14)2− built from a close-packing of [O4] and [BaO3] layers with octahedral and tetrahedral cobalt, separated by fluorite-type double layers (Ba2Cl2)2+ or (Ba2Br2)2+. The main difference between Ba2Co4ClO7 and Ba2Co4BrO7 is due to the fluorite-type layers: (Ba2Cl2)2+ double layers are perfectly ordered while (Ba2Br2)2+ blocks are affected by a structural disorder through the bromine atoms.

Two- and three-dimensional electron density (ED) images calculated by Maximum Entropy Method for (a) Cl atom, (b) Br atom in Ba2Co4XO7 compounds (X = Cl or Br).Figure optionsDownload as PowerPoint slide