Twinning and disorder in zinc perchlorate hexahydrate crystals

Abstract

The crystal structure of zinc Perchlorate hexahydrate resembles that of lithium Perchlorate trihydrate (space group: P 6 3 mc ) as far as the perchlorate-water arrangement is concerned. The distribution of zinc atoms among twice their number of available sites gives rise to orthorhombic symmetry (space group: Pmn 2 1 ), and crystals of this salt grow as three-component twins, in which the perchlorate-water arrangement is continuous throughout a crystal, discontinuity at the twin boundaries being only in the distribution of zinc atoms. Moreover, in the odd-layer Weissenberg photographs from rotation about the c axis, certain spots containing contributions from zinc atoms only streak out to form a hexagonal network. This observation has been explained in terms of mistakes in repetition along the b axis of the orthorhombic cell of each of the three twin components; the probability of such mistake has been estimated quantitatively from the intensity distribution of a suitable diffuse streak.