MONOMERIC AND DIMERIC COPPER(II) COMPLEXES OF A REDOX-ACTIVE SCHIFF-BASE LIGAND BIS(2,5-DIHYDROXYACETOPHENONE) ETHYLENEDIAMINE

Monomeric and dimeric copper(II) complexes with a tetradentate Schiff base, bis(2,5-dihydroxyacetophenone) ethylenediamine have been synthes ized and characterized by spectroscopic techniques. Solution EPR of th e complexes in DMSO shows less than four g(parallel-to) lines and a br oadening of the g(perpendicular-to) component suggesting a lowered sit e symmetry for the copper(II) ion. The g(perpendicular-to) component s hows nitrogen super-hyperfine structure. A clear five-line pattern eme rges with A(N) congruent-to 15 +/- 1 G, supporting the binding of a te tradentate ligand with two N and two O donor sites. For the monomeric complexes g(parallel-to) is in the range of 2.18-2.20, suggesting a ne ar square-planar arrangement of N2O2 donor groups (theta = 0). The com plexes exhibit a visible band with lambda(max) in the 500-600 nm regio n in solution. This is found to split into two components in the solid state reflectance spectra. The spectral data suggests a distorted tet ragonal geometry for copper(II) ions in the present complexes. The cop per complexes prepared by using CuCl2 analyses for the stoichiometry 2 Cu : 1 DAen, i.e. [Cu(DAen)CuCl2], suggesting the formation of a dime ric species. This is supported by low lambda(eff) of 1.49 B.M., implyi ng an exchange coupled complex. Further, the coupling constant evaluat ed for the peaks resolved in g(parallel-to) region is 118.75 G, a valu e which is nearly half of that found for the monomeric complexes.