New Insights Into the Electronic-Structures of Solid-State Dioxygen Adducts of N,N′-Ethylenebis(Salicylaldiminato)Cobalt(II), Co(Salen), and of Active Precursors

Abstract

Oxygen-active forms of [Co( salen )], derived from solvated forms such as [Co( salen )].C₆H₆, [Co( salen )]CHCl₃ and Co( salen )(C₅H₅N), have long been known to bind dioxygen reversibly in the solid state. It has generally been accepted that the product of oxygenation is the diamagnetic peroxo -bridged species [Co( salen )]₂O₂. However, the present detailed study of temperature-dependent magnetic susceptibilities and of electron spin resonance spectra clearly shows that this is an oversimplification. The data show that the oxygenated species also contain the paramagnetic superoxo -like species [O₂Co( salen )] as well as dimeric 'inactive' [Co( salen )]₂ centres . Prolonged oxygenation produces also a second monomeric Co(salen) component although the e.s.r . spectra of both Co^IIspecies are diminished in intensity relative to the [O₂Co( salen )] signal. The magnetic properties of the oxygen-active Co( salen ) samples are compatible with ferromagnetically coupled pairs of Co( salen ) molecules, with further weak antiferromagnetic coupling between such sets of pairs. These magnetostructural features appear to be related to the solid-state oxygen reactivity. The solvated precursors also show weak magnetic interactions but different in detail to those in the desolvated materials.