Interstitial iron(II)-chloride compounds with graphite—I.: Formation by reduction of iron(III)-compounds with Fe(CO)5

A graphite intercalation compound of FeCl₂ with a composition of 1 Fe:4.7 C, closely approaching the theoretically limiting stoichiometry FeCl₂C_4.22, is obtained by the reduction of the intercalation compound FeCl₃C_7.1 with Fe(CO)₅ under 150 atm of CO at 150°C. The FeCl₂-compound is characterized by its X-ray powder pattern and Mössbauer spectra. The distance between carbon layers increases from 9.40 Å in FeCl₃C_7.1 to 9.56 in FeCl₂C_4.73 by this reduction reaction. Carbon monoxide reduces FeCl₃C_7.1 at 150°C in a sluggish reaction which occurs under removal of iron chlorides from the intercalation compound in contrast to the reduction by Fe(CO)₅, which increases the Fe:C ratio.