Optical properties of βdoubleprime-(ET)2SF5RSO3 (R = CH2CF2, CHFCF2): Changing physical properties by chemical tuning of the counterion

The authors report the polarized infrared reflectance of Βdoubleprime-(ET)2SF5CHFCF2SO3 as a function of temperature. This salt is a derivative of the first fully organic superconductor, βdoubleprime-(ET)2SR5CH2CF2SO3, where the nature of the alkyl group has been modified to contain a chiral center. This small chemical modification has a dramatic effect on the spectral and charge transport properties. The βdoubleprime-(ET)2SF5CHFCF2SO3 complex displays highly anisotropic behavior compared with the superconducting material; the essential difference is observed in the perpendicularb direction where the interdimer interaction is weak, in agreement with recent theoretical calculations. The temperature dependence of key anion vibrational modes is discussed in terms of intermolecular hydrogen bonding within the anion pocket. That small chemical modifications of the anion template result in such striking changes in the physical properties suggests that the βdoubleprime-(ET)2SF5RSO3 system is quite close to a Mott phase boundary