Additional Steps toward Molecular Scale Wires:  Further Study of Ni510/11+ Chains Embraced by Polypyridylamide Ligands

This paper presents two advances in the development of the chemistry of extended metal atom chains (EMACs) that employ di(2-pyridyl)amide (dpa) and its higher homologues (loosely called polypyridylamides). As EMACs employing these ligands are extended to greater lengths, low solubility becomes an increasingly difficult problem. Also, increased stability would be desirable. We have employed a method, which is designed to be applicable to chains of any length, to introduce stabilizing substituents (ethyl groups) on some of the pyridyl rings. We illustrate this here by the synthesis and characterization of the pentanickel complexes Ni5(etpda)4Cl2·6CHCl3 and [Ni5(etpda)4](PF6)3·4Me2CO, etpda = the anion of N,N‘-bis(4-ethylpyridyl)-2,6-diaminopyridine. As we had previously predicted, on the basis of the behavior of Ni3(dpa)4Cl2 and [Ni3(dpa)4](PF6)3, oxidation causes marked changes in structure and magnetic behavior indicative of a change of electronic structure that would cause an insulator−conductor transformation. We now demonstrate that this is what occurs not only in the previously known Ni5 compounds but in the new ethyl-substituted ones.