Synthesis and Spectroscopic Characterization of Manganese(II), Iron(III) and Cobalt(III) Complexes of Macrocyclic Ligand. Potential of Cobalt(III) Complex in Biological Activity

Abstract

A new series of manganese(II), iron(III) and cobalt(III) complexes of 14-membered macrocyclic ligand, (3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane-1,8-diamine) have been prepared and characterized by elemental analyses, IR, UV-VIS, <TEX>$^1H$</TEX>- and <TEX>$^{13}C$</TEX>- NMR spectra, magnetic susceptibilities, conductivities, and ESR measurements. Molar conductance measurements in DMF solution indicate that the complexes are electrolytes. The ESR spectrum for cobalt(III) complex in <TEX>$CD_3OD+10%D_2O$</TEX> after exposure to <TEX>$^{60}Co-{\gamma}$</TEX>-rays at 77 K using a 0.2217 M rad <TEX>$h^{-1}$</TEX> vicrad source showed <TEX>$g_{\perp}$</TEX> > <TEX>$g_{\parallel}$</TEX> > <TEX>$g_e$</TEX>, indicating that, the unpaired electron site is mainly present in the <TEX>$d_z2$</TEX> orbital with covalent bond character. In this case, the ligand hyperfine tensors are nearly collinear with <TEX>${\gamma}$</TEX>-tensors, so there is no major tendency to bend. Therefore, little extra delocalization via the ring lobe of the <TEX>$dz^2$</TEX> orbital occurs. However, the ESR spectrum in solid state after exposure to <TEX>$^{60}Co-{\gamma}$</TEX>-rays at 77 K showed <TEX>$g_{\parallel}$</TEX> > <TEX>$g_{\perp}$</TEX> > <TEX>$g_e$</TEX>, indicating that, the unpaired electron site is mainly present in the <TEX>$d_x2_{-y}2$</TEX> ground state as the resulting spectrum contains a large number of randomly oriented molecules provided that, the principle directions of g and A tensors. Manganese (II) complex 2, <TEX>$[H_{12}LMn]Cl_4.2H_2O$</TEX>, showed six isotropic lines characteristic to an unpaired electron interacting with a nucleus of spin 5/2, however, iron(III) complex 3, <TEX>$[H_{12}LFe]Cl_5.H_2O$</TEX>, showed spectrum of a high spin <TEX>$^{57}Fe$</TEX> (I=1/2), <TEX>$d^5$</TEX> configuration. The geometry of these complexes was supported by elemental analyses, IR, electronic and ESR spectral studies. Complex 1 showed exploitation in reducing the amount of electron adducts formed in DNA during irradiation with low radiation products.