  The temperature dependences of the electric-transport properties of the
two-dimensional organic conductors beta"-(BEDT-TTF)2SF5CH2CF2SO3,
beta"-(d8-BEDT-TTF)2SF5CH2CF2SO3, and beta"-(BEDT-TTF)2SF5CHFSO3 are measured
by dc methods in and perpendicular to the highly-conducting plane. Microwave
measurements are performed at 24 and 33.5 GHz to probe the high-frequency
behavior from room temperature down to 2 K. Superconductivity is observed in
beta"-(BEDT-TTF)2SF5CH2CF2SO3 and its deuterated analogue. Although all the
compounds remain metallic down to low-temperatures, they are close to a
charge-order transition. This leads to deviations from a simple Drude behavior
of the optical conductivity which become obvious already in the microwave
range. In beta"-(BEDT-TTF)2SF5CH2CF2SO3, for instance, charge fluctuations
cause an increase in microwave resistivity for T < 20 K which is not detected
in dc measurements. beta"-(BEDT-TTF)2SF5CHFSO3 exhibits a simple metallic
behavior at all frequencies. In the dc transport, however, we observe
indications of localization in the perpendicular direction.
