Why Are Polymorphism and Multiple Crystal Forms Important

The example of the polymorphs (allotropes) of carbon illustrate the key messages of this chapter different crystal forms of a substance can possess very different properties and behave as different materials. This concept has important implications in all fields of chemistry associated with the production and commercialization of molecules in the form of crystalline materials (drugs, pigments, agrochemicals and food additives, explosives, etc). The producer, in fact, needs to know not only the exact nature of the material in the production and marketing process, but also its stability with time, the variability of its chemical and physical properties as a function of the crystal form, etc. In some areas, e.g. the pharmaceutical industry, the search for and characterization of crystal forms of the API has become a crucial step for the choice of the best form for formulation, production, stability and for intellectual property protection. 

Physical and thermodynamic properties density and refractive index, thermal and electrical conductivity, hygroscopicity, melting points, free energy and chemical potential, heat capacity, vapor pressure, solubility, thermal stability 

Spectroscopic properties electronic, vibrational and rotational properties, nuclear magnetic resonance spectral features 

Kinetic properties rate of dissolution, kinetics of solid state reactions, stability 

Surface properties surface free energy, crystal habit, surface area, particle size distribution 

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