13C MAS NMR investigation of two-dimensional polymerised C60 using paramagnetic O2 as a chemical shift agent

In this work, we present C-13 MAS NMR results of the rhombohedral (rh-2D) and tetragonal (tet-2D) two-dimensional polymerised C-60, under high pressure, using the paramagnetic O-2 as a chemical shift and relaxation agent. The C-13 MAS NMR spectrum of the rh-2D polymer (under Po-2 = 2400 Torr) shows two resonances, a broad and intense line around 152.8 and a small one at 78.3 ppm. The spectrum of the tetragonal tet-2D polymer (under Po-2 = 2500 Torr), shows two isotropic lines around 150.6 and 77.9 ppm. For both polymers, the intense Line around 150 ppm has several components, related to the deformation of the spherical shape of the C-60 molecules. We attribute the observed group of lines to the inequivalent sp(2) carbons on the C-60 molecules, and the small line around 78 ppm to the intermolecular sp(3) bonding carbons. NMR signals of C-13 nuclei in the vicinity of paramagnetic species are subjected to large paramagnetic shifts and short relaxation times T-1, the consequences of it on the NMR spectra will be discussed here. The method used allows a quantitative evaluation of the population of inequivalent carbons (sp(2) and sp(3)) of the studied polymers, in a significantly shorter time than the time needed in the absence of O-2. (C) 2000 Elsevier Science Ltd. All rights reserved.