ESR-Untersuchungen zu Struktur- und Bindungsverhältnissen von tri- und bicyclischen Cobalt(II)- und Kupfer(II)-Chelaten mehrzähniger Schiffscher Basen des Typs M(O N N O) und M(S N)2 sowie zur Sauerstoffadduktbildung der Cobalt(II) Chelate

Structural and Bonding Properties of Quadridentate and Bidentate Cobalt(II) and Copper(II) Schiff Base Complexes and Oxygenation Behavior of the Co^II Complexes. An ESR Study ESR investigations on the low-spin cobalt(II) chelates bis(benzoylacetaldehyde)-ethylendiimine-cobalt(II), bis(benzoylacetaldehyde)-1,2-cyclohexandiimine-cobalt(II) and bis(p-chlor-β-mercaptozimtaldanilato)-cobalt(II) as well as the corresponding copper(II) chelates are reported. The large anisotropy of the g tensor of the Co^II chelates caused by strong spin-orbit interactions, and the position of the maximum g tensor component g_x in the molecules obtained by comparison with the ESR spectra of the Cu^II complexes predicts a MO for the unpaired electron which consists mainly of the Co d_yz obital. In solution (CHCl₃/pyridine) the Co^II chelates react immediately with molecular oxygen forming CoL_n(O₂)(py)] species characterized by ESR spectra with strongly reduced g tensor anisotropy and small ⁵⁹Co hyperfine coupling constants. The unpaired electron appears to be mainly localized in the O₂-part of hte molecules. The CoN₂S₂ coordination sphere shows a lower affinity to oxygen than the CoN₂O₂ type complexes. In the CuN₂O₂ complexes the unpaired electron is found to be in a MO containing the Cu d_xy orbital. Due to remarkable covalency¹⁴ N and H hyperfine interactions are observed in the ESR spectra. Analyzing the hyperfine coupling constants the extent of unpaired spin density on the N donor atoms and the N-2s/2p hybridization degree is estimated.