The crystal structure of Mg₂(OH)₃(Cl,Br).4H₂O

Abstract

The triclinic structure of Mg~(OH)aC1.4H20 has been studied by the method of isomorphous replacement.Atomic positions were derived from a :Fourier (010) projection based on powder data, together with such information as could be gathered from the more or less diffuse (hkl) reflexions.The backbone of the structure is formed by puckered layers parallel to (100), consisting of infinite double chains of MgO 6 octahedra extending in the b direction.Each octahedron shares two opposite edges with neighbours from its own chain, and two more with the complementary chain.The oxygens in the corners shared by two oetahedra are exactly opposite the corresponding oxygens from adjacent double chains.That explains the linkage between them; half of these comers are occupied by H20 which is so strongly polarized that it forces the adjacent chain into a spatially uneconomical position.The anions, alternating with an equal number of water molecules so as to form rows lib, are situated between the layers.There is a tendency towards disorder in these rows, resulting in typical diffuse-scattering phenomena which are explained in a qualitative way.