The importance of C–H⋯N, C–H⋯π and π⋯π interactions in the crystal packing of the isomeric N1,N4-bis((pyridine-n-yl)methylene)-cyclohexane-1,4-diamines, n = 2, 3 and 4

Abstract

The molecular structures of the isomeric N¹,N⁴-bis((pyridine-n-yl)methylene)-cyclohexane-1,4-diamines, where n = 2 (1), 3 (2) and 4 (3), show the same effective conformation, in particular between the n-pyridine rings and the bridging cyclohexane rings. Theoretical structures of 1–3 are more symmetric and confirm that the pyridine residues are orthogonal to the plane through the four methylene groups of the bridging cyclohexyl groups. Crystal packing in 1–3 is dominated by C–H⋯N_pyridine interactions. In 1, these interactions lead to linear chains and, along with π⋯π contacts, give rise to a layer structure. In 2, the C–H⋯N_pyridine interactions extend in three dimensions and are complemented by C–H⋯N imine and C–H⋯π contacts. Finally, in 3, the C–H⋯N_pyridine interactions lead to layers that are connected by C–H⋯π interactions to give a 3D network. It appears that in the structures of 1–3, the relative disposition of the pyridine and imine groups allows for the participation of the former in intermolecular interactions owing to their accessibility compared with the latter.