Polymorphism, what it is and how to identify it: a systematic review†
This review on polymorphism is a personal, non-comprehensive view on the field of polymorphism – a term which is often misused. Indeed, the discussion about polymorphism and related terms is still ongoing in the area of crystal engineering. This is why we felt it timely to look into the historical development of its definition and to delimit it. A short introduction to thermodynamic aspects and characterization methods of polymorphs is given. One chapter is then dedicated to polymorphism of elements and inorganic compounds, before discussing the term for organic and organo-metallic compounds. Chosen examples are given each time to illustrate the cases of polymorphism. In the end, the conclusion yields three flow schemes useful in determining polymorphism for each compound class.