Magnetization Slow Dynamics in Ferrocenium Complexes

Abstract

The Single-Molecule Magnet (SMM) properties of a series of ferrocenium complexes, [Fe($\eta^5$-C$_5$R$_5$)$_2$]+ (R = Me, Bn), are reported. In the presence of an applied dc field, the slow dynamics of the magnetization in [Fe($\eta^5$-C$_5$Me$_5$)$_2$]BAr$_{\textrm{F}}$ are revealed. Multireference quantum mechanical calculations show a large energy difference between the ground and first excited states, excluding the commonly invoked, thermally activated (Orbach-like) mechanism of relaxation. In contrast, a detailed analysis of the relaxation time highlights that both direct and Raman processes are responsible for the SMM properties. Similarly, the bulky ferrocenium complexes, [Fe($\eta^5$-C$_5$Bn$_5$)$_2$]BF$_4$ and [Fe($\eta^5$-C$_5$Bn$_5$)$_2$]PF$_6$, also exhibit magnetization slow dynamics, however an additional relaxation process is clearly detected for these analogous systems.