Cobalt(II) complexes of o-hydroxyaryl aldehydes and ketones

Abstract

Cobalt(11) complexes of the types CoL₂, CoL₂B₂ have been prepared, where LH is an o-hydroxyaryl aldehyde or ketone and B = water or 4-methylpyridine. The compounds CoL₂B₂ have magnetic and spectroscopic properties typical of octahedral cobalt(11) complexes. The solid complexes CoL₂ have μ_eff 4.7-5.0 and spectra typical of octahedral cobalt(11). They are soluble and monomeric in toluene, and these solutions also have spectra typical of octahedral cobalt(11) and quite distinct from those of tetrahedral cobalt(11) complexes. It is concluded that these monomeric, 4-coordinate species are probably examples of high-spin square-planar cobalt(11) complexes, the planar structure being stabilized by d_π  → p_π back-coordination from the metal atom to the anti-bonding orbitals of a localized C=O double bond.