A Trinickel Dipyridylamido Complex with Metal−Metal Bonding Interaction: Prelude to Polynickel Molecular Wires and Devices?

The molecule Ni3(dpa)4Cl2 (1) can be oxidized by AgPF6 to give crystalline Ni3(dpa)4(PF6)3 (2) (dpa is the anion of di(2-pyridyl)amine). This reversible oxidation occurs at a potential of 0.908 V vs Ag/AgCl electrochemically. The X-ray structure of 2 shows that the oxidation causes a major structural change (even though it is reversible), namely, a contraction of the Ni−Ni distances from ca. 2.43 Å to 2.284[1] Å. In addition, the electronic structure changes so that from four unpaired electrons in 1 there is only one in 2. From these remarkable results, it is inferred that while 1, and all higher homologues with 5, 7, 9, ..., nickel atoms are poor electronic conductors, the cations obtainable from them may be much better ones. This in turn means that by controlling the oxidation state electrochemically, these molecules may be able to function as nanoscale diodes.