Metallic properties of the ternary fullerides $A{\mathrm{Ba}}_2{\mathrm{C}}_{60}(A=\mathrm{K},\mathrm{R}\mathrm{b},\mathrm{C}\mathrm{s})$

Electronic properties and molecular dynamics of mixed alkali-alkaline earth fullerides $A{\mathrm{Ba}}_2{\mathrm{C}}_{60}\hspace{0.5em}(A=\mathrm{K},\mathrm{R}\mathrm{b},\mathrm{C}\mathrm{s})$ are investigated by NMR and compared to the isostructural alkali fullerides $A_3{\mathrm{C}}_{60}.$ Consistent with previous Raman investigations, our results indicate a fivefold charge transfer to the ${\mathrm{C}}_{60},$ a charge state that is not found in pure alkali fullerides. ${}^{13}\mathrm{C}$ NMR experiments reveal a metallic ground state for all compounds with an inhomogeneous charge distribution on the fullerene molecule. The importance of electron-electron correlations is discussed in terms of the Korringa enhancement factor. Correlation effects appear to be somewhat similar to the isostructural superconducting $A_3{\mathrm{C}}_{60}.$ Transverse relaxation experiments were performed to probe the reorientational dynamics of the ${\mathrm{C}}_{60}$ molecules. No dependence of the activation energy of the reorientational motion on the type of alkali ion is found.