Short-range structures of poly(dicarbon monofluoride) (C₂F)n and poly(carbon monofluoride) (CF)n

Abstract

The short-range structures of the so-called graphite fluorides, poly(dicarbon monofluoride) ((C2F)n) and poly(carbon monofluoride) ((CF)n), have been discussed, based on the neutron diffraction data. The C–C and C–F bond lengths in these compounds are determined to be 0.157–0.158 and 0.136 nm, respectively, which slightly differ from those previously evaluated and coincide with those found in polytetrafluoroethylene (PTFE). The structure models of (C2F)n (both AB-type and AA′-type) and (CF)n have been refined so as to give the best fit of the atomic pair distribution functions calculated for them (Gcalc(r)’s) to those experimentally observed for the compounds (Gobs(r)’s). Since the Gobs(r) of (C2F)n better fits to the Gcalc(r)’s of AB-type model rather than those for AA′-type model, the latter model is ruled out. The a-lattice parameter and the C–C–C bond angle in the refined structure model of (CF)n (0.260–0.261 nm and 111°, respectively) are slightly larger than those of (C2F)n (0.256–0.257 nm and 109–110°, respectively).