Frustration of H-Bonding and Frustrated Packings in a Hexamorphic Crystal System with Reversible Crystal-Crystal Transitions.

The study of transitions between polymorphic phases is a less investigated chapter of the widely studied book of polymorphism. In this paper, we discuss the phase behavior of a new compound that has been rationally designed to show frustration of H-bonds for the strong amide N-H donor, which cannot be involved in H-bonding nor in van der Waals interactions. The compound () is a showcase of almost all possible cases of transitions between polymorphs [monotropic/enantiotropic, fast/slow, diffusive/displacive, and single-crystal-to-single-crystal (SCSC)] and of relation between polymorphs with different '.