Copper(II) complexes containing a CuN < inf > 4 < /inf > O < inf > 2 < /inf > coordination sphere assembled via pyridine-imine-amide coordination: Synthesis, structure and properties

Abstract

Copper(II) complexes [CuL2] of pyridine-N, imine-N and amide-O donor Schiff bases (HL) are reported. The Schiff bases Hpabh, Hpamh and Hpadh were prepared by condensation of 2-pyridinecarboxaldehyde with benzhydrazide, 4-methoxybenzhydrazide and 4-dimethylaminobenzhydrazide, respectively. The complexes were synthesized in MeOH media by reacting Cu(OAc)2·H2O with HL in a 1:2 mole ratio. The X-ray structure of [Cu(pabh)2] was determined. The rhombically distorted octahedral CuN4O2 coordination sphere is formed by two mononegative meridionally spanning pyridine-N, imine-N and deprotonated amide-O donor ligands. Electronic spectra of the complexes display two d-d bands at ca. 700 and ca. 1300 nm and two strong absorptions due to charge transfer transitions in the 450-268 nm range. Room temperature (298 K) solid state magnetic moments (1.90-2.08 μB) suggest an S = 1/2 spin state in each complex. The powder e.p.r. spectra of [Cu(pabh)2] and [Cu(pamh)2] at room temperature are consistent with a rhombic distortion of the N4O2 octahedron around the metal centre. However the spectrum of [Cu(padh)2] suggests a tetragonal elongation of the CuN4O2 octahedron.