The molecular structures of carbon and silicon tetrafluorides.

The tetrahedral structure of the halides of Group IV is well established. The relation of the molecular constants to the force field governing the motion of the atoms is less certain; in particular, some difficulty has been found in reconciling the interatomic distances obtained by electrons diffraction with those deduced by other means. We have obtained certain of these molecular constants from an examination of the infra-red absorption spectra of gaseous carbon and silicon tetrafluorides. Preparative Carbon tetrafluoride was formed by the direct action of fluorine on carbon. The halogen was generated by the electrolysis of fused potassium bifluoride in a copper vessel, the anode being a graphite rod; the gas was passed through a hard glass tube packed with sodium fluoride and then through charcoal. A stream of dry nitrogen had been passed through the absorbents and the molten electrolyte for some hours. The resulting gas was condensed in a liquid air trap, and separated; after evaporation through silver nitrate solution to remove oxygen and silicon fluorides, and through soda-lime to remove hydrogen fluoride and CO2, it was again condensed and fractionally distilled, as far as was possible with the small yields obtained, over a small temperature range at about - 130° C.