Structural origin of inhomogeneous properties in (fluoranthene)2PF6 crystals

Twinned and untwinned (FA)2PF6 crystals are analysed by X-ray scattering at varied temperature. A rotation by 180° around the a axis (stacking axis) is identified as the typical twinning rule. The influence of twinning on the crystal quality in general is derived, as well as its irrelevance for the Peierls transition at TP = 180 K and for the high-temperature structural transition at TS = 200 K, accompanied by the loss of the FA-stack's mirror plane (space group A2/m to P21/c). These observations are discussed with respect to recent electron spin resonance imaging results. Differing concentration of localized defects in the different growth sectors of macroscopic single crystals is identified as an obvious explanation of inhomogeneous ESR properties.