Sterically encumbered ferrocenium salts with four, five, or six tert-butyl substituents and a variety of counteranions ([BF 4 ] -, [SbF 6 ] -, and [PF 6 ] -) 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 ( 2 E 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
Adducts [Cp′FeI(NHC)] exhibit a highly anisotropic magnetic Ms = ±2 ground state resulting in unusual large spin–lattice (Orbach) relaxation barriers observed by zero-field 57Fe Mössbauer spectroscopy.
Open-metallocenes of the heavy alkaline-earth metals [(η(5)-Pdl')2M(thf)n] (M = Ca (1), Sr (2), n = 1; M = Ba (3), n = 2; Pdl' = 2,4-tBu2C5H5) are readily prepared by salt-metathesis between MI2 and KPdl' and characterized by NMR spectroscopy and X-ray diffraction studies.
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