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 Cu-II compounds containing the tridentate pzpy ligand with the general formula [Cu-II(pzpy) (L)(OH2)(x)] (where x = 1 for L = CH3CO2 and x = 0 for L = N-3 or NC-N-CN ) are reported. The geometries of the Cu-II ions are described as a five-coordinate slightly distorted square pyramidal monomeric compound [Cu(pzpy)(OH2)(CH3CO2)] (1) and polymeric complexes, [Cu(pzpy)(N-3)](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. (C) 2011 Elsevier B. V. All rights reserved.