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.

The coordination of Cu2+ ion with a tridentate pyrazinamide ligand (pzpy), followed by potentiometry UV–Vis and mass spectrometries show the formation of only mononuclear complexes in aqueous solution. In solid state, mononuclear and two polynuclear copper(II) complexes and coordinating anions as coligands have been fully characterized.Figure optionsDownload as PowerPoint slideHighlights
► In aqueous solution, Cu2+ and tridentate pyrazinecarboxamide ligand form only mononuclear species.
► The stoichiometries of these species (1:1 and 1:2) depends on metal:ligand ratio.
► In solid state, mono and polynuclear Cu(II) complexes with additional anionic coligand have been characterized.
► In all solid complexes, the geometry around Cu2+ ion is distorted square pyramidal.