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

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 (G_calc(r)’s) to those experimentally observed for the compounds (G_obs(r)’s). Since the G_obs(r) of (C₂F)_n better fits to the G_calc(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).