High-resolution 13C NMR studies of the tetragonal two-dimensional polymerized C60 phase

We present NMR data of tetragonal (tet-2D) two-dimensional polymerized C60 obtained under high pressure. By using 13C MAS NMR, we were able to identify two resonances, a broad and intense resonance around 146 ppm and a small one at 73.5 ppm. The former line has several components due to inequivalent sp2 carbons on the C60 molecules which were distorted by the transformation under high pressure. We attribute the latter line to the sp3 carbons of the interball bondings. The 13C MAS NMR line-shape simulation of the obtained spectrum is compatible with the suggested polymeric structure where the C60 molecules are connected by [2+2] cycloadditions. We also report on 13C MAS NMR measurements of tet-2D at ambient pressure and at temperature ranging from 298 to 500 K. We verified that the FCC structure of the pristine C60 is recovered by annealing the sample above 200°C.