The radical anions of two C60 Nteg-fulleropyrrolidine (teg = 3,6,9-trioxadecyl) adducts, the monoadduct and
the trans1-bisadduct have been studied in liquid solution and glassy matrix of 2-MeTHF by continuous wave
(cw) and pulsed X-band EPR and cw high-frequency EPR. The hyperfine coupling constants of the 14N nuclei
and of the 13C nuclei in natural abundance have been determined and discussed, also in relation with the spin
density distribution on the fullerene sphere obtained by restricted Hartree−Fock half-electron approximation
(RHF-HE), and the hyperfine coupling constants obtained with the density functional method. The calculation
results show a reasonable agreement with the experimental data. The g tensors have been determined by
HF-EPR in frozen matrix at low temperature, the monoadduct showing a rhombic tensor and the bisadduct
an axial one. The temperature dependence of the EPR line widths and of the electron spin−lattice relaxation
times measured by Inversion Recovery of the magnetization have been studied. The radical anion of the
bisadduct shows line widths decreasing on increasing the temperature, as usually expected, whereas the radical
anion of the monoadduct shows the opposite behavior. The electron spin−lattice relaxation times at room
temperature are respectively T
1 = 2.8 μs and T
1 = 200 ns. The relaxation behavior has been discussed and
compared with that of the C60 monoanion and of other fulleropyrrolidine adducts, taking into account the
time modulation of the parameters of the spin Hamiltonian due to the reorientation in solution, and the coupling
between rotational and electron spin magnetic moments. This spin-rotational mechanism gives rise to the
short T
1 and anomalous temperature dependence of the line widths in the monoadduct, whereas the larger
stiffness of the bisadduct reduces this effect.
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