Polymorphism

Polymorphisme (Fr). Polymorphie (Ge). Polimorfismo (It). Polimorfismo (Sp). Полиморфизм (Ru).

The phenomenon in which the same solid chemical compound can adopt different forms and crystal structures. In 1969, Rosenstein & Lamy propose a definition: ‘‘When a substance can exist in more than one crystalline state it is said to exhibit polymorphism.’’[1] Polymorphs can provide valuable insights into crystal packing and structure-property relationships.[2]

For the Pharmaceutical industry, it is very important to know which polymorph(s) has been produced. Not only because of the different physical properties, but due to IP protection. Polymorphs are normally studied on nano-powders and are characterized by using XRPD techniques. Electron diffraction is a powerful tool than can detect different polymorphic crystalline systems even on the nanoscale. A dedicated electron diffractometer for such experiments will change in the future the way such systems are characterized, and it could change the way IP protection is done.

Examples:

· Diamond and graphite are polymorphs of each other: they have the same composition but different structures and properties.[3]

· 5-Methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, known as ROY for its red, orange, and yellow crystals, has seven polymorphs with solved structures, the largest number in the Cambridge Structural Database.[4]

Fig. 7 Polymorphs of ROY

References:

1 J.-P. Brog, C.-L. Chanez, A. Crochet and K. M. Fromm, RSC Advances, 2013, 3, 16905–16931.

2 L. Yu, Accounts of Chemical Research, 2010, 43(9), 1257-1266.

3 Ibid.

4 Ibid.