EPR and solid-state NMR studies of poly(dicarbon monofluoride) (C2F)n

Poly( dicarbon monofluoride) (C2F)(n) was studied by electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (NMR). The effects of physisorbed oxygen on the EPR and NMR relaxation were underlined and extrapolated to poly( carbon monofluoride) (CF)(n) and semi-covalent graphite fluoride prepared at room temperature. Physisorbed oxygen molecules are shown to be an important mechanism of both electronic and nuclear relaxations, resulting in apparent spin-lattice relaxation time and line width during NMR and EPR measurements, respectively. The effect of paramagnetic centers on the F-19 spin-lattice relaxation was underlined in accordance with the high electron spin density determined by EPR. F-19 magic angle spinning (MAS) NMR, C-13 MAS NMR, and C-13 MAS NMR with F-19 to C-13 cross polarization (CP) underline the presence of two types of carbon atoms, both sp(3) hybridized: some covalently bonded to fluorine and the others linked exclusively to carbon atoms. Finally, a C-F bond length of 0.138 +/- 0.002 nm has been determined thanks to the re-introduction of dipolar coupling using cross polarization.