PHASE-CHANGES AND CHEMICAL-REACTIONS IN MOLECULAR-CRYSTALS

Changes in the attitude of crystallographers to phase changes and chem ical reactions in molecular solids over the last 50 years are sketched . Various ways of classifying polymorphic modifications and structural changes in solids are discussed, and examples are given. The methods applied include multi-temperature crystal structure analysis, analysis of anisotropic displacement parameters, differential scanning calorim etry, solid-state NMR and visual observation. The importance of defect s in influencing the kinetics of solid-solid phase changes is stressed .