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 R3m: a ¼ 5.716(2) A° , c ¼ 45.01(3) A° for Ba2Co4ClO7 and a ¼ 5.7434(5) A° , c ¼ 46.151(9) A° 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)2þ or (Ba2Br2)2þ. The main difference between Ba2Co4ClO7 and Ba2Co4BrO7 is due to the fluorite-type layers: (Ba2Cl2)2þ double layers are perfectly ordered while (Ba2Br2)2þ blocks are affected by a structural disorder through the bromine atoms