Supramolecular structures formed by 2-aminopyridine derivatives. Part I. Hydrogen-bonding networks via N–H⋯N interactions and the conformational polymorphism of N,N′-bis(2-pyridyl)aryldiamines

Abstract

A family of N,N′-bis(2-pyridyl)aryldiamines were prepared and their solid state structures investigated by X-ray crystallography. Due to a low energy barrier to C–N rotation, the 2-arylaminopyridine system can adopt either Z or E conformations, which may lead to conformational polymorphism. The E,E conformers form designated hydrogen-bonded polymeric tapes with the dimeric R₂²(8) motif. In contrast, the Z,Z conformers assemble via N–H⋯N hydrogen bonds, generating the catemer motif that leads to complex 1D, 2D or 3D supramolecular structures. The two types of intermolecular hydrogen-bonding motifs observed in the crystal structures can be easily differentiated with the assistance of solid state IR spectroscopy.