Complexes of metals with paramagnetic 3-Imidazoline schiff bases

Abstract

Methods for the synthesis of intracomplex bischelates CuL₂, NiL₂, CoL₂, and the mixed- ligand complex NiL₂y₂, where L is a deprotonated derivative of the stable nitroxide 4- (2′- hydroxyphenyl)- 2,2,5,5tetramethyl- 3- imidazoline- 1-oxyl, were developed. In the solid state, the compounds have a molecular structure. The most significant difference in the structure of ML₂ molecules lies in the values of the angle between the chelate rings (56.9‡ for CuL₂, 78.8‡ for CoL₂, and 0‡ for NiL₂. In complexes with paramagnetic metal ions, the intramolecular exchange interactions are ferromagnetic in character and are close in the order of magnitude (5.7 cm^{− 1} for CuL₂ and 6.8 cm⁻ for NiL₂Py₂) to the values for complexes with deprotonated enaminoketone derivatives of 3- imidazoline. The NiL₂ molecules, having a square coordination of the central atom, are biradicals with antiferromagnetic exchange interactions between the unpaired electrons of nitroxyl groups (− 3.6 cm⁻). The transformation of NiL₂ into NiL₂Py₂ leads to a transition of Ni(II) from the low- to high- spin state and to ferromagnetic exchange between the unpaired electrons of the paramagnetic centers.