Synthesis and Characterization of an Eight-Membered Heterocyclic 1,3,5,7-Tetra(3-pyridyl)-1,3,5,7-tetrazacyclooctane

N,N′-Bis(3-pyridyl)methanediamine was prepared by treating 3-aminopyridine with formaldehyde in acetonitrile. By treating it with formaldehyde, the eight-membered heterocyclic ring compound 1,3,5,7-tetra(3-pyridyl)-1,3,5,7-tetrazacyclooctane was prepared. This could occur in a two-step manner in a [3+1+3+1] cycloaddition reaction. The compounds were characterized by X-ray crystallography, 1H and 13C NMR spectroscopy, and mass spectrometry. The powder XRD pattern of 1,3,5,7-tetra(3-pyridyl)-1,3,5,7-tetrazacyclooctane was also determined and revealed an uncommon twist-crown conformation, which was further confirmed by DFT calculations.