Solid state 19F NMR study of acceptor-doped fullerenes (MF6)2C60 (M=As, Sb)

Abstract We report on temperature-dependent 19 F NMR measurements of solid C 60 intercalated with AsF 5 and SbF 5 acceptor species. Structure, molecular dynamics and possible phase transitions in the compounds are studied. The temperature dependence of the second moment, S 2 , of (AsF 6 ) 2 C 60 is typical for activation of molecular mobility on heating. The reorientation of the (AsF 6 ) − complex is random and lasts at least down to 67 K. The temperature dependence of S 2 for (SbF 6 ) 2 C 60 showing significant change in the range of 200–270 K is discussed. Further narrowing of the 19 F spectra of (SbF 6 ) 2 C 60 on heating occurs around 320 K. 19 F spectra at 7.04 T resolve two resonances corresponding to different fluorine species. Suggesting that these species randomly occupy two different interstitial sites, we give reasons for the absence of superconductivity down to 5 K in the compounds under study.