Magnetization Slow Dynamics in Ferrocenium Complexes.

The Single-Molecule Magnet (SMM) properties of a series of ferrocenium complexes, [Fe(η5-C5R5)2]+ (R = Me, Bn), are reported. In the presence of an applied dc field, the slow dynamics of the magnetization in [Fe(η5-C5Me5)2]BArF 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(η5-C5Bn5)2]BF4 and [Fe(η5-C5Bn5)2]PF6, also exhibit magnetization slow dynamics, however an additional relaxation process is clearly detected for these analogous systems.

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