Structural Variations and Polymorphism of Some Derivatives of 6-Amino-2-phenylsulfonylimino- 1,2-dihydropyridine

Following up from a study of polymorphism in the title compound, 6-amino-2-phenylsulfonylimino-1,2-dihydropyridine, 12 phenyl-substituted derivatives were examined for polymorphism by recrystallization from
a large number of solvents. The title compound contains hydrogen bond donor (D) and acceptor sites (A) located in
a AADD juxtapositioning. Two structural families that differ in their use of the AADD hydrogen bond functionality
may be identified. Methyl and chloro substitution in the ortho position or fluoro substitution in the para position
leads to a catemer motif, which is related to the kinetic form of the title molecule. Meta Substitution by methyl and
larger substituents in the para position block this structural option. While meta-methyl and para-chloro substitution
lead to unique structures, two polymorphs of the para-methyl-substituted derivative could be crystallized and these
adopt the dimer arrangement. With the larger bromo, iodo, methoxy, and trifluoromethyl substituents in the para
position, dimers arranged into interconnected layers are obtained. These dimer structures are reminiscent of the
thermodynamic form of the title compound. It is noteworthy that the majority of derivatives of the title compound
fail to show polymorphic behavior, and this shows that our understanding of polymorphism is still far from complete.