Spin-leakage of the fullerene shell of endometallofullerenes: EPR, ENDOR and NMR evidences Original Research Article

On embedding in the poly(bisphenol A carbonate) film, the lanthanum paramagnetic endometallofullerene, La-EMF, has featured stability against oxygen for more than 1 yearʹs storage of the film on air. Furthermore, an intense H-ENDOR signal was discovered in this system. Since there are no protons in La-EMF, the matrix H-ENDOR testifies permeability of the fullerene shell for the electron spin density. The EPR signals of La-EMF with unusually small hyperfine splitting constants aLa which were revealed in DMF and some other polar solvents, also suggest the partial transfer of the unpaired electron outside the fullerene cage. Moreover, for liquid solutions of La-EMF in hexamethylphosphoramide (HMPA), molecules of which contain the NMR active phosphorus-31, the paramagnetic shift of the 31P NMR signal of bulk HMPA molecules in the presence of La-EMF was revealed. Thus, the area of localization of the unpaired electron is not restricted by the fullerene shell but a runoff of the electron spin density beyond the fullerene cage takes place. The spin-leakage of the fullerene shell is worth consideration in sight of possible applications of fullerenes as the basis of novel magnetic materials.