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 ar e reported. Two of the complexes contain chloride as a coligand and the oth er two contain acetate as a coligand. In each complex, the planar tridentat e monoanionic ligand binds the metal ion via the pyridine-N, the imine-N an d the amide-O atoms. The fourth site is satisfied by the chloride or the ac etate-O to form a square-plane. In the solid state, both complexes containi ng the acetate as the coligand exist as centrosymmetric dimeric species wit h 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 spec ies via equatorial-apical chloride bridges. The electronic spectra of the c omplexes in methanol solutions display a ligand-field band in the visible r egion (687-713 nm). The complexes are redox active and, in each case, two r eduction 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 studi es revealed that no significant spin-spin interaction is operative between the metal ions in any of these four complexes. (C) 2000 Elsevier Science Lt d. All rights reserved.