X-ray diffuse scattering and magnetic resonance: a study of structural phase transitions in perylene radical cation salts

The quasi-one-dimensional organic conductors di-perylene hexafluorophosphate and -antimonate undergo three and two structural phase transitions below room temperature, respectively. The unequivocal structural proof of the Peierls transition at Tp in both compounds is provided by X-ray diffuse scattering experiments. The characterization of the structural phase transitions above Tp is done using the analysis of X-ray patterns together with previously known ESR results. The combined techniques offer new insight into the relative displacements and rotations of the perylene stacks. The relationship between the Peierls transition and the precursor transitions is discussed.