In this paper, we combine synchrotron powder x-ray diffraction, 7 Li nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) experiments to study the structural evolution of Li 4 C 60 and how its electronic ground state depends on the crystal symmetry. The compound in the two-dimensional polymer phase with mixed interfullerene bonding motifs is a band gap insulator. EPR, however, reveals the presence of intrinsic centers originating from broken C 60–C 60 bonds and local Li off-stoichiometry that create states in the band gap and account for the complex temperature dependence of the spin susceptibility as well as the residual temperature dependence of the 7 Li NMR shift. At low temperatures, the Li+ ions are statically disordered on the 7 Li NMR timescale. The observed 7 Li NMR line narrowing at T> 200 K is ascribed to the Li+ diffusion dynamics and above room temperature the …