Abstract Spectral and structural studies of N, N′-dimethyl-N, N′-bis (pyridin-2-ylmethyl)-1, 2-diaminoethane (L 1), N, N′-dimethyl-N, N′-bis (pyridin-2-ylmethyl)-1, 3-diaminopropane (L 2), and their copper (II) complexes were carried out by spectroscopic and DFT methods. The DFT results show that conventional and nonconventional H-bonds present in L 1 and L 2 influence the NMR chemical shifts at different pH values, which thus suggests that the ...