LATTICE-DYNAMICS OF FULLERENES PROBED BY ORGANOMETALLIC INTERCALATES

The 14.4 keV nuclear gamma-ray resonance in Fe-57 has been used as a p robe of the hyperfine interactions and lattice dynamics of the bisferr ocene (Fc) intercalates of C-60 and C-70. Over the temperature range 9 0 less than or equal to T less than or equal to 350 K the isomer shift is a smooth function of T and is very similar for neat Fc and the two intercalates. In contrast, the T-dependence of the quadrupole hyperfi ne interaction undergoes a marked change in slope at similar to 300 K in C(60)Fc(2), but not in C(70)Fc(2). A similar discontinuity at simil ar to 300 K is observed in the temperature dependence of the recoil-fr ee fraction in C(60)Fc(2), but not in C(70)Fc(2). These observations c an be related to the known phase change and onset of fullerene rotatio n in the former (as contrasted to the latter) and are supported by DSC measurements in the interval 240 less than or equal to T less than or equal to 380 K for both intercalates.