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.