Electronic structure of peroxo and superoxo polyamine cobalt (III) complexes

Abstract

Electronic spectra of two mononuclear cobalt(III) superoxides, [Co(CN)₅O₂]³⁻ and [Co(s-Me₂en)₂0₂Cl] ⁺ where s-Me₂en is N,N'-dimethylethylenediamine, have been studied. An unusually low intensity for the low energy MLCT band may be indicative of highly covalent, though weak, pi bonding between the cobalt and the superoxide in both complexes. The electronic spectra and electron paramagnetic resonance (E.P.R.) of the latter indicate a cis configuration. Anisotropic E.P.R. spectra proved not to be simulable by computor methods assuming parallel g (spectroscopic splitting factor) and A (hyperfine coupling) tensors. Nor were the anisotropic A values compatable with the isotropic A value. Electronic spectral, E.P.R. and magnetic susceptibility studies indicate only about 20% initial oxygenation at room temperature for Co(s-Me₂en)₂Cl₂. Electronic spectral studies of [CoL0₂CoL]⁴⁺, where L = 1, 4, 7, 10,13-pentaazatridecane, "tetren", 2,5-bis(5-(1,4-diazahexyl)pyridine, "epyen” ; 1,9 -bis(2 -pyridyl)-2 ,5 ,8 -triazanonane, "pydien"; 1, 11 -bis(2 -pyridyl)-2,6,10-triazaundecane, "pydpt"; 1,9-bis(4-imidazolyl)-2,5,8- triazanonane, "imdien"; or 1 ,11-bis(imidazolyl)- 2, 6, 10-trizaundecane, "imdpt", indicate great lability in the position transaxial to the peroxide. The complexes in which L = pydien or pydpt are especially labile..