Spin-transfer complexes of endohedral metallofullerenes: ENDOR and NMR evidences

The aim of this research was to answer the question whether the area of localization of unpaired electron in a paramagnetic endohedral metallofullerene is restricted by the fullerene shell or a “spin-leakage” beyond the fullerene cage is possible. Herein, we report an ENDOR investigation of La@C82 embedded into the polycarbonate films. The intensive 1H-ENDOR signal has been revealed. Since the La-EMF does not contain hydrogen atoms, this result testifies to the contact hyperfine interaction of the unpaired electron of La-EMF with the matrix hydrogen atoms, i.e. electron spin density on the polymer protons. We also report a NMR investigation of a liquid solution of the same La-EMF in hexamethylphosphoramide (HMPA), molecules of which contain the NMR active nucleus, phosphorus-31. The paramagnetic shift of the 31P NMR signal of bulk HMPA molecules in the presence of La-EMF has been revealed. Thus, much as the charge-transfer complexes, the paramagnetic EMF molecules can form the spin-transfer complexes in which the electron spin density partially localizes beyond the fullerene cage on atoms of the matrix in which the EMF molecules are embedded.