Influence of ortho-substituent on the molecular and crystal structures of 2-(N-arylimino)coumarin-3-carboxamide: isotypic and polymorphic structures

Abstract

During a comprehensive study of a series of 2‐(N‐arylimino)coumarin‐3‐carboxamides with the aryl group substituted in the ortho‐position by either a halogen atom, a methyl group or a methoxy group, the existence of three groups of isotypic crystal structures has been revealed. The similarity of crystal structures belonging to the same groups was confirmed by the analysis based on the comparison of pairwise interactions energies obtained from quantum chemical calculations. Group I includes unsubstituted, methyl‐substituted and polymorphic modification 1 of fluoro‐substituted 2‐(N‐arylimino)coumarin‐3‐carboxamide. Structures of polymorphic modification 2 of fluoro‐substituted derivative, chloro‐substituted and polymorphic modification 1 of bromo‐substituted 2‐(N‐arylimino)coumarin‐3‐carboxamide may represent group II. Group III contains structures of polymorphic modification 2 of bromo‐substituted derivative, iodine‐ and methoxy‐substituted 2‐(N‐arylimino)coumarin‐3‐carboxamides. Structures of the same type group have extremely close parameters of the unit cell as well as those of molecular and crystal structures. But they are not identical. Polymorphic modifications of fluoro‐ and bromo‐substituted 2‐(N‐arylimino)coumarin‐3‐carboxamides belong to different crystal types mainly due to different arrangement of basic structural motifs separated out using quantum chemical calculations.

Usage of Quantum Chemical Methods to Understand the Formation of Concomitant Polymorphs of Acetyl 2-(N-(2-Fluorophenyl)imino)coumarin-3-carboxamide

“…The coumarine polymorphism has been thoroughly studied and five crystal forms have been found . In contrast to coumarine, the 2-iminocoumarine crystal structure has not been determined and only three pairs of polymorphic modifications has been found among its derivatives. , The two polymorphs of acetyl 2-( N -(2-fluorophenyl)­imino)­coumarin-3-carboxamide are of special interest for studying due to the fact that different forms were crystallized from the same solution . The comparison of structures formed under different conditions gives the opportunity to discuss the principles of crystal formation and forces influencing it.…”