Macrocyclic unsymmetrical binuclear copper(II) complexes as ligands: Spectral, structural, magnetic and electrochemical studies

A new series of macrocyclic unsymmetrical binuclear copper(II) complexes was prepared by using [CuLa,b] (L-a = [6,6'-piperazine-1,4-diyldimethylenebis(4-methyl-2-formyl)phenol] and L b = [6,6'-piperazine-1,4diyldimethylenebis(4-bromo-2-formyl)phenol]) and [Cu(oxen)](CLO4)(2) or [Cu(oxpn)](ClO4)(2), where oxen = N,N'-bis(2-aminoethyl)oxamide and oxpn = N,N'-bis(3-aminopropyl)oxamide. The binuclear copper(H) complexes contain three different compartments: the first compartment has two piperazinyl nitrogens and two phenolic oxygens (N2O2), the second compartment has two phenolic oxygens and two imine nitrogens (O2N2) and the third compartment has two imine nitrogens and two amide nitrogens (N-4) as coordinating sites. Apart from the three compartments the complex has two oxamide oxygen atoms for further coordination. The copper(II) ion in the complex is tetracoordinated with two tertiary nitrogen atoms and two phenoxy oxygen atoms coordinated in the equatorial plane to the copper(H) ion and the geometry around the copper nuclei is distorted square planar. The binuclear copper(H) complexes were characterized by elemental and spectral analysis. Electronic spectra of the complexes show a single broad band for the d-d transition in the region around 585-635 nm. The mono- and binuclear copper(II) complexes show four-line hyperfine splitting in the ESR spectra. For the mononuclear complexes the observed g(parallel to) values are in the range 2.21 to 2.31, g(perpendicular to) values vary from 2.10 to 2.11 and A(parallel to) values from 175 to 180 G. For the binuclear complexes the observed g(parallel to\) values are in the range 2.20 to 2.10, g, values vary from 2.06 to 2.01 and A(parallel to) values from 165 to 175 G. Room temperature magnetic moments of the mono- and binuclear copper(II) complexes show a mu(ef)f value around 1.72 BM, which is near to the spin-only value of 1.73 BM. Electrochemical studies of the mono- and binuclear copper(II) complexes are discussed. The mononuclear copper(II) complexes show one irreversible reduction wave in the region -0.54 to -0.89 V and the binuclear copper(H) complexes show two irreversible single-step one-electron transfer processes in the range E-pc(1) = -0.35 to 0.53, E-pc(2) = -0.62 to -0.78 at the cathodic potential region.