Introduction

The study of reactions involving solids is an important aspect of solid state chemistry from the point of view of understanding the influence of structure and imperfections on the chemical reactivity of solids. It is important to identify the factors governing solid state reactivity in order to be able to synthesize new solid materials with desired structure and properties. Solid state reactions differ from those in homogeneous fluid media in a fundamental respect; whereas reactions in the liquid or the gaseous state depend mainly on the intrinsic reactivity and concentration of the chemical species involved, solid state reactions depend to a large extent on the arrangement of the chemical constituents in crystals. The fact that the constituents are fixed in specific positions in crystals introduces a new dimension in the reactivity of solids, not present in other states of matter. In other words, chemical reactivity is determined more often by the crystal structure and defect structure of solids rather than by the intrinsic chemical reactivity of the constituents. This feature of solid state reactions is clearly brought out in topochemical and topotactic reactions. Most of the photochemical transformations of organic solids are controlled by crystal chemistry. We shall discuss organic solid state reactions in some detail and devote our attention to intercalation reactions of solids that have gained considerable importance recently. We shall briefly deal with some aspects of catalysis to point out how solid state chemistry plays a role in this crucial branch of chemical technology.