A New Pyridine-Azacrown Compound Py3Am and Crystal Structures of Its Complexes with Zn2+ and Ni2+ Cations

The aza-macrocyclic ligand Py3Am based on a pyridine-azacrown compound containing three chelating acetamide groups is synthesized for the first time. Its complexes with nickel and zinc are characterized by NMR, mass, and IR spectroscopic techniques, and their crystal structures are determined by the single crystal X-ray diffraction analysis. In both complexes, the transition metal atom is completely encapsulated into the macrocycle cavity with the formation of a similar coordination environment. The presence of an additional outer-sphere Na⁺ cation in the structure of the zinc complex weakly affects the conformation of the complex. Despite that the geometric parameters indicate that the ligand is not ideal for the coordination of small cations of transition metals, a combination of these types of donor groups provides the efficient coordination of the ligand, which is important for the stability of complexes in a biological medium.