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Structural and EPR Studies on Single-Crystal and Polycrystalline Samples of Copper(II) and Cobalt(II) Complexes with N2S2-Based Macrocyclic Ligands

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journal contribution
posted on 09.07.2007, 00:00 by Abel Tamayo, Jaume Casabó, Lluís Escriche, Pablo González, Carlos Lodeiro, Alberto C. Rizzi, Carlos D. Brondino, M. C. G. Passeggi, Raikko Kivekäs, Reijo Sillanpää
The properties of Cu(II) and Co(II) complexes with oxygen- or nitrogen-containing macrocycles have been extensively studied; however, less attention has been paid to the study of complexes containing sulfur atoms in the first coordination sphere. Herein we present the interaction between these two metal ions and two macrocyclic ligands with N2S2 donor sets. Cu(II) and Co(II) complexes with the pyridine-containing 14-membered macrocycles 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L) and 7-(9-anthracenylmethyl)-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1) have been synthesized. The X-ray structural analysis of {[Co(ClO4)(H2O)(L)][Co(H2O)2(L)]}(ClO4)3 shows two different metal sites in octahedral coordination. The EPR spectra of powdered samples of this compound are typical of distorted six-coordinated Co(II) ions in a high-spin (S = 3/2) configuration, with the ground state being S = 1/2 (g1 = 5.20, g2 = 3.20, g3 = 1.95). The EPR spectrum of [Cu(ClO4)(L)](ClO4) was simulated assuming an axial g tensor (g1 = g2 = 2.043, g3 = 2.145), while that of [Cu(ClO4)(L1)](ClO4) slightly differs from an axial symmetry (g1 = 2.025, g2 = 2.060, g3 = 2.155). These results are compatible with a Cu(II) ion in square-pyramidal coordination with N2S2 as basal ligands. Single-crystal EPR experiment performed on [Cu(ClO4)(L1)](ClO4) allowed determining the eigenvalues of the molecular g tensor associated with the copper site, as well as the two possible orientations for the tensor. On the basis of symmetry arguments, an assignment in which the eigenvectors are nearly along the Cu(II)−ligand bonds is chosen.