Alkali-earth metal fullerides Ca(C60)2 and Ba(C60)2: a new solution-phase method for the preparation and characterization with ESR, UV–NIR, IR and Raman spectroscopy

Ca(C60)2 and Ba(C60)2, prepared in a THF/H2O solution, were characterized by UV–NIR, ESI-MS, IR, ESR and Raman spectroscopy. ESR spectra of Ca(C60)2 and Ba(C60)2 are temperature-dependent: the linewidth increases abruptly at about the melting point of THF and the ESR signal diminishes gradually below 170 K. A possible explanation for this is that THF crystallization results in the exclusion of solute from the lattice and leads to C60− aggregation, which promotes line broadening and the formation of a diamagnetic dimer of (C60)22−. The oxidation of Ca(C60)2 and Ba(C60)2 in THF was monitored by UV–NIR. The oxidation rate of C60− was found to depend on the countercation.