μ-Acetato-di-μ-phenolato-metal(II)cobalt(II) (metal = Fe, Co, Ni, Cu, Zn) complexes with low-spin Co(II): Synthesis, structures, and magnetism

The dinucleating macrocyclic ligand (L^2;2)^2-, prepared by the [1:1] cyclic condensation of N,N′-dimethyl-N,N′- ethylenedi(5-bromo-3-formyl-2-hydroxybenzylamine) and ethylenediamine, has dissimilar N(amine)₂O₂ and N(imine)₂O ₂ metal-binding sites sharing two phenolic oxygen atoms. It has afforded μ-acetato-di-μ-phenolato-metal(II)cobalt(II) complexes (metal(II) = Fe^II, Co^II, Ni^II, Cu^II, Zn ^II). X-ray crystallographic studies indicate that the M^II is bound to the N(amine)₂O₂ site and has a square-pyramidal geometry with an acetate oxygen at the axial site. The Co ^II bound to the N(imine)₂O₂ site has a square-pyramidal geometry with an acetate oxygen at the apex or a distorted octahedral geometry with further coordination of a methanol molecule. The Co^II in the N(imine)₂O₂ site is of low-spin and has one unpaired electron in its d_z2 orbital. Magnetic studies indicate an antiferromagnetic interaction in the FeCo and CoCo complexes whereas a ferromagnetic interaction in the NiCo and CuCo complexes. The magnetic properties of the complexes are discussed in terms of the electronic structure of the M_II ion and the dinuclear MCo core structure.