ESR study of the electronic structure and dynamic Jahn-Teller effect in nickelocenium cation

Abstract

The nickelocenium cation doped with the magnetic isotope ⁶¹Ni has been diluted into several diamagnetic host lattices and studied by EPR spectroscopy at low temperatures in polycrystalline samples. From the analysis of the ⁶¹Ni hyperfine tensor, supplemented by EHMO and MS-Xα calculations, a quantitative comparison of the covalency and the dynamic Jahn-Teller effects with the related d⁷ system cobaltocene has been possible. From line-width studies as a function of temperature we conclude that the line shape at low temperatures (4 K) is mainly due to inhomogeneous broadening effects; the spin-lattice relaxation increasing rapidly at higher temperatures cannot be explained solely by an Orbach mechanism via a closeby upper Kramers doublet in a satisfactory way.