ENDOR Evidence of Electron-H_2 Interaction in a Fulleride Embedding H_2

摘要

An endofulleropyrrolidine, with H_2 as a guest, has been reduced to a paramagnetic endofulleride radical anion. The magnetic interaction between the electron delocalized on the fullerene cage and the guest H_2 has been probed by pulsed ENDOR. The experimental hyperfine couplings between the electron and the H_2 guest were measured, and their values agree very well with DFT calculations. This agreement provides clear evidence of magnetic communication between the electron density of the fullerene host cage and H_2 guest. The ortho-H_2/para-H_2 interconversion is revealed by temperature-dependent ENDOR measurements at low temperature. The conversion of the paramagnetic ortho-H_2 to the diamagnetic para-H_2 causes the ENDOR signal to decrease as the temperature is lowered due to the spin catalysis by the paramagnetic fullerene cage of the radical anion fulleride.