Tuning the coordination properties of chiral pseudopeptide bis(2-picolyl)amine and iminodiacetamide ligands in Zn(ii) and Cu(ii) complexes

Seven bis(2-picolyl)amine (bpa) and five iminodiacetamide (imda) ligands were prepared with different modifications in their side chain structure. The coordination properties of the ligands (L) were influenced by changes in the aliphatic linker length (C1, C2, or C3), amide group isomers and type of chiral terminal group. Complexation with Cu(ii) afforded two polymorphs of a ML complex which features tetradentate coordination of a ligand with C2 linkers, while crystal structures of three trans-fac ML2 complexes with Cu(ii) and Ni(ii) show tridentate coordination of ligands with a C3 linker. The stoichiometry and stereochemistry of Zn(ii) and Cu(ii) complexes was further studied in solution by NMR and UV-Vis spectroscopy. DFT calculations gave an insight into the relative stability of isomers, as well as potential hydrogen bonding between two ligands in a ML2 complex. Furthermore, ML complexes of Cu(ii) exhibited DNA cleavage activity.