Teaching Ferrocenium How to Relax: A Systematic Study on Spin-Lattice Relaxation Processes in tert-Butyl-Substituted Ferrocenium Derivatives

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• 作者：Matthias Reiners ; Dirk Baabe ; Peter Schweyen ; Matthias Freytag ; Peter G. Jones and Marc D. Walter
• 刊名：European Journal of Inorganic Chemistry
• 出版年：2017
• 出版时间：January 10, 2017
• 年：2017
• 卷：2017
• 期：2
• 页码：388-400
• 全文大小：2072K
• ISSN：1099-0682c

文摘

Sterically encumbered ferrocenium salts with four, five, or six tert-butyl substituents and a variety of counteranions ([BF₄]^–, [SbF₆]^–, and [PF₆]^–) were prepared. The electronic structures of these materials were investigated by various physical techniques including electron paramagnetic resonance (EPR) and Mössbauer spectroscopy and solid-state magnetic susceptibility measurements. Spin–orbit coupling and low-symmetry distortions split the electronic ground states (²E_2g) in these compounds into two Kramers doublet states (Ψ_a and Ψ_b); the energy difference between these states was evaluated by EPR spectroscopy and magnetic susceptibility measurements and decreases with increasing steric demand at the ferrocenium moiety. Further information on the first excited state (²A_1g) was obtained by solid-state magnetic susceptibility measurements, which also indicated that an increasing steric bulk resulted in a decreasing energy gap between the ²E_2g(Ψ_a) and ²A_1g states. The Mössbauer spectra revealed temperature-dependent line shapes attributed to unusually slow paramagnetic relaxation on the ⁵⁷Fe Mössbauer time scale. The pertinent spin–spin and spin–lattice (Orbach and Raman) relaxation parameters were determined for these materials and further substantiate the trends observed by our EPR spectroscopic and solid-state magnetic susceptibility studies.