Phenoxido mediated antiferromagnetic and azide mediated ferromagnetic coupling in two dinuclear ferromagnetic nickel(ii) complexes with isomeric Schiff bases: a theoretical insight on the pathway of magnetic interaction

Abstract

Two new dinuclear nickel(II) complexes, [(H₂O)Ni(N₃)(L¹)(μ_1,1-N₃)Ni(L¹)] and [(H₂O)Ni(N₃)(L²)(μ_1,1-N₃)Ni(L²)]·MeOH, derived from two isomeric Schiff base ligands, HL¹ [2-{(2-(ethylamino)ethylimino)methyl}-6-ethoxyphenol] and HL² [2-{(2-(dimethylamino)ethylimino)methyl}-6-ethoxy-phenol], have been synthesized and characterized. Variable temperature (2–300 K) magnetic susceptibility measurements indicate the presence of moderate ferromagnetic exchange coupling between nickel(II) centers. In each complex, antiferromagnetic exchange takes place through the phenoxido bridge and ferromagnetic through the μ_1,1-azido bridge. The competitive interactions therefore reduce the overall magnetic coupling. In a theoretical complex, where the bridging azido ligand has been eliminated and the rest of the geometry is kept frozen, the magnetic coupling becomes antiferromagnetic which suggests that the ferromagnetic exchange occurs via the μ_1,1-azido bridge. Mulliken population analysis and spin density plots clearly show that the spin distributed spherically in the Ni centers is due to the presence of one unpaired electron in both the and orbitals. The shape of the spin density at the bridging O-atom and azide evidences the participation of their p orbitals in the magnetic coupling. The SOMO is basically constituted by the orbital of one nickel(II) center with the participation of the azide π-system. The SOMO−1 is constituted by the orbital of the other nickel(II), an oxygen atom and the azide π-system.