Additional Steps toward Molecular Scale Wires:  Further Study of Ni₅^10/11+ 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.