Dinuclear Nickel (II) 2,2′-Bibenzimidazole Bridged Complexes: Synthesis, Structure, Magnetic, and Electrochemical Properties

The reaction of [NiBr2(bpy)2] (bpy = 2,2 '-bipyridine) with 2,2 '-bibenzimidazole or 5,5 ',6,6 '-tetramethyl-2,2 ' bibenzimidazole (bbim) in the presence of AgBF4 and Et3N results in the formation of dinuclear nickel(II) complexes with bridging bbim ligands. The crystal structures of the obtained complexes [Ni2(mu-bbim)(bpy)4] [(BF4)2] have been determined. Variable-temperature EPR as well as magnetometry experiments indicate antiferromagnetic interactions between the nickel atoms in the complex molecule at low temperatures. Density functional theory (DFT) calculations confirm these findings. Cyclic voltammetry and in situ EPR spectroelectrochemistry demonstrated that these complexes can be electrochemically reduced resulting in the formation of Ni(I) and Ni(0) derivatives. This can be considered as a strategy for controlling the electronic state of these dinuclear nickel complexes, thus providing a way to design magnetic materials with switchable properties.