CRYSTALLOGRAPHY OF TOPOTACTIC REACTION

Abstract

Many reactions in solids are known to be governed purely by structural considerations. In these reactions one generally finds that a single crystal of the startling material is converted into a psedomorph containing one or more products in a definite crystallographic orientation and the conversion takes place throughout the volume o of the crystal. These observations can be made with the help of suitable diffraction techniques. The reason why there is no breakup of the lattice in such cases is because the crystal structures are to a large extent preserved. These reactions known as Topotacitic reactions, can therefore be adequately explained only if the relevant structures are taken into consideration. Topotaxy has been observed in a variety of reactions, such as polymorphic transformations, oxidations, dehydrations, decompitions, isomerisations, etc., both in organic and inorganic systems. The interest in these studies, the experimeentatl techniques employed and some examples in this field are discussed.