Polymorphism and Pseudopolymorphism of an Aromatic Amide: Spontaneous Resolution and Crystal-to-Crystal phase Transition

1,2-Bis(N-p-fluorobenzoyl-N-methylamino)benzene (1) afforded 13 types of crystals upon crystallization from various solvents. Eleven of them are pseudopolymorphs that have crystallizing solvents in the crystalline lattice, whereas the others are polymorphs. Both the polymorphs and pseudopolymorphs included conformational polymorphs based on cis/trans isomerization of the amide bonds. Three of the pseudopolymorphs showed spontaneous resolution (total asymmetric transformation), belonging to the chiral space group P31 or P32. The absolute configuration of each chiral crystal was determined by single crystal X-ray analysis. Solid-state CD spectrum was also measured in the KBr matrix for the same crystal used for X-ray analysis. Phase transition between the polymorphs and pseudopolymorphs was observed by simultaneous measurement of DSC and X-ray powder diffraction.