Vanadium 0 , dibenzene

In most paramagnetic sandwich complexes the proton hf structure is not resolved in low temperature powder or single crystal EPR spectra. In vanadium dibenzene, a typical example of this type of compound, the poor resolution is due to the fact that the aromatic rings are rigidly frozen at T < 50 K and thus the proton hfs tensors of the benzene rings are no longer magnetically equivalent. 

EI-EPR has also been applied in powder samples, where single crystal-like EPR spectra can be obtained for B0 observer fields which correspond to the orientations of principal values of ligand hfs tensors37. This is illustrated in Fig. 15 for a powder sample of dibenzene vanadium diluted into polycrystalline ferrocene. The hfs tensors of the twelve geometrically equivalent benzene protons are not coaxial with the g and the... 

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