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 (L2;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)2O2 metal-binding sites sharing two phenolic oxygen atoms. It has afforded μ-acetato-di-μ-phenolato-metal(II)cobalt(II) complexes (metal(II) = FeII, CoII, NiII, CuII, ZnII). X-ray crystallographic studies indicate that the MII is bound to the N(amine)2O2 site and has a square-pyramidal geometry with an acetate oxygen at the axial site. The CoII 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 CoII in the N(imine)2O2 site is of low-spin and has one unpaired electron in its dz2 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 MII ion and the dinuclear MCo core structure.