Structurally Diverse Copper(II) Complexes of Polyaza Ligands Containing 1,2,3-Triazoles: Site Selectivity and Magnetic Properties

Copper­(II) acetate mediated coupling reactions between 2,6-bis­(azidomethyl)­pyridine or 2-picolylazide and two terminal alkynes afford 1,2,3-triazolyl-containing ligands L1–L6. These ligands contain various nitrogen-based Lewis basic sites including two different pyridyls, two nitrogen atoms on a 1,2,3-triazolyl ring, and the azido group. A rich structural diversity, which includes mononuclear and dinuclear complexes as well as one-dimensional polymers, was observed in the copper­(II) complexes of L1–L6. The preference of copper­(II) to two common bidentate 1,2,3-triazolyl-containing coordination sites was investigated using isothermal titration calorimetry and, using zinc­(II) as a surrogate, in 1H NMR titration experiments. The magnetic interactions between the copper­(II) centers in three dinuclear complexes were analyzed via temperature-dependent magnetic susceptibility measurements and high-frequency electron paramagnetic resonance spectroscopy. The observed magnetic superexchange is strongly dependent on the orientation of magnetic orbitals of the copper­(II) ions and can be completely turned off if these orbitals are arranged orthogonal to each other. This work demonstrates the versatility of 1,2,3-triazolyl-containing polyaza ligands in forming metal coordination complexes of a rich structural diversity and interesting magnetic properties.