Refinement of the Crystal Structures of Strontium Cobalt Oxychlorides by Neutron Powder Diffraction

The crystal structures of strontium cobalt oxychlorides of general formula Sr 2 CoO 3 Cl (Co-1L), Sr 3 Co 2 O 5 Cl 2 (Co-2L), and Sr 4 Co 3 O 7.5 Cl 2 (Co-3L) have been determined from neutron powder data. The compounds crystallize in tetragonal symmetry, space group P 4/ nmm (Co-1L) or I 4/ mmm (Co-2L and Co-3L). Their structures are analogous to the Ruddlesden−Popper phases of general formula Sr n +1 M n O 2 n +1 . All three structures contain layers of highly distorted CoO 5 Cl octahedron. The Co-3L structure, in addition, has a layer of regular CoO 6 octahedra. Because the in-plane oxygen position of the latter is partially occupied, some of the Co atoms adopt pyramidal coordination, with their basal planes parallel to the c -axis. The temperature dependence of the magnetic susceptibility is also reported. The moment per mole of Co atom decreases with increasing number of (CoO 2 ) layers.