The present invention also relates a metal complex complexing with the fluoro-ponytailed bipyridine derivatives, which is represented by the general formula (2): ##STR00001## and each R.sub.f is the same or different and represents a fluoro-alkyl group having from 3 to 11 carbon atoms, preferably a perfluoro-alkyl group having from 9 to 11 carbon atoms; X.sup.- represents a halogenide such as fluoride, bromide, chloride, or iodide; and M represents a metal selected from the group consisting of Mo, Cr, Re, Ru, Fe, Rh, Ni, Pd, and Cu.