Dimeric and polymeric square-pyramidal copper(II) complexes containing equatorial-apical chloride or acetate bridges

Syntheses, crystal structures and physical properties of four new copper(II) complexes of deprotonated aroylhydrazones of 2-pyridine-carboxaldehyde are reported. Two of the complexes contain chloride as a coligand and the other two contain acetate as a coligand. In each complex, the planar tridentate monoanionic ligand binds the metal ion via the pyridine-N, the imine-N and the amide-O atoms. The fourth site is satisfied by the chloride or the acetate-O to form a square-plane. In the solid state, both complexes containing the acetate as the coligand exist as centrosymmetric dimeric species with the metal ion in a distorted square-pyramidal coordination sphere and the acetate group acting as a monoatomic equatorial-apical bridge. One of the complexes containing chloride is a similar centrosymmetric dichloro-bridged dinuclear species. However, the other one exists as a polymeric chain species via equatorial-apical chloride bridges. The electronic spectra of the complexes in methanol solutions display a ligand-field band in the visible region (687-713 nm). The complexes are redox active and, in each case, two reduction responses are observed in the potential range - 0.06 to - 0.29 and - 0.60 to - 0.70 V (vs. Ag/AgCl) in methanol solutions. Cryomagnetic studies revealed that no significant spin-spin interaction is operative between the metal ions in any of these four complexes. (C) 2000 Elsevier Science Ltd. All rights reserved.