ORTHORHOMBIC SYMMETRY COMPONENTS IN THE LIGAND-FIELD OF A MACROCYCLIC TETRAIMINE COPPER(II) COMPLEX

The single-crystal EPR spectrum of the tetraimine macrocyclic Cu(II) complex [Cu(C10H20N8)Cl]Cl has been measured, both in the lattice of the pure compound and of the isomorphous Ni(II) compound. The crystal structure of the Cu(II) complex has also been determined. The space group is P1BAR, with a = 7.574(1), b = 9.548(1), c = 11.469(1) angstrom, alpha = 96.32(1), beta = 107.19(1), gamma = 99.67(2)-degrees and Z = 2. The Cu-63-doped [Ni(C10H20N,)Cl] compound has an anisotropic EPR spectrum with g, = 2.178, g2 = 2.066, g3 = 2.048 and A1 = 175,A2 = 48,A3 = 22 G. Superhyperfine interactions with the nitrogen ligators were also observed. The g values for the pure compound are almost the same as for the diluted compound. The axial g1 and A1 vectors are nearly collinear, whereas the equatorial g2, g3 and A2, A3 components are at about 45-degrees from each other, the g eigenvectors lying approximately along the bond directions. These features of the spectrum indicate the presence of orthorhombic symmetry components in the ligand field of the macrocycle. These components have been studied with the aid of a detailed ligand field model, taking into account the anisotropic pi-bonding of unsaturated chelates.