Equilibrium and structural studies of copper(II) complexes with a tridentate ligand containing amide, pyrazyl and pyridyl nitrogen donors: Effect of anions coligands on crystal structures of copper(II) complexes

The stability constants of the Cu(II) chelates with the tridentate ligand 2-(N, 2-pyridylmethyl)pyrazinecarboxamide (Hpzpy), determined by potentiometry UV–Vis and mass spectrometries, show the formation of [Cu(pzpy)]+, [Cu(pzpy)(OH)], [Cu(pzpy)2] and [Cu(pzpy)2(OH)]− species (where pzpy is an amide-deprotonated ligand). In the solid state, the synthesis, crystal structures, and electronic and magnetic properties of three new CuII compounds containing the tridentate pzpy ligand with the general formula [CuII(pzpy)(L)(OH2)x] (where x = 1 for L = CH3CO2− and x = 0 for L = N3− or NC–N–CN−) are reported. The geometries of the CuII ions are described as a five-coordinate slightly distorted square pyramidal monomeric compound [Cu(pzpy)(OH2)(CH3CO2)] (1) and polymeric complexes, [Cu(pzpy)(N3)]n (2) and [Cu(pzpy)(N(CN)2)]n (3). Polymerization for complex 2 comes from equatorial–apical bridges of the “naked” pyrazine nitrogen atoms, while in compound 3, the copper centers were bridged by NC–N–CN− anions. These three compounds have been characterized in details by infrared, ligand field and EPR spectroscopy; the data are consistent with the single-crystal X-ray structures.