C-13 MAS NMR investigation of two-dimensional polymerised C-60 using paramagnetic O-2 as a chemical shift agent

In this work, we present C-13 MAS NMR results of the rhombohedral (rh-2D) a nd tetragonal (tet-2D) two-dimensional polymerised C-60, under high pressur e, 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 To rr), 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 de formation of the spherical shape of the C-60 molecules. We attribute the ob served group of lines to the inequivalent sp(2) carbons on the C-60 molecul es, and the small line around 78 ppm to the intermolecular sp(3) bonding ca rbons. NMR signals of C-13 nuclei in the vicinity of paramagnetic species are subj ected to large paramagnetic shifts and short relaxation times T-1, the cons equences of it on the NMR spectra will be discussed here. The method used a llows a quantitative evaluation of the population of inequivalent carbons ( sp(2) and sp(3)) of the studied polymers, in a significantly shorter time t han the time needed in the absence of O-2. (C) 2000 Elsevier Science Ltd. A ll rights reserved.