On the structure and properties of iron halide–graphite intercalates: a comparison of the reactivity of free and graphite-intercalated iron(III) chloride

Abstract

Using different preparation procedures, distinctly different types of first-stage graphite intercalates of FeCl₃ have been synthesized in a routine manner. Amongst these is identified, for the first time, a charge-transfer complex containing [FeCl₄]^–, with the graphite host acting as the counter ion. Using results obtained from Mössbauer spectroscopy and X-ray powder diffractometry, a direct comparison is made between the sequence of events which accompany exposure to air of crystalline bulk FeCl₃ and intercalated FeCl₃. Whereas intercalated FeCl₃ slowly hydrolyses to yield both tetrahedrally and octahedrally co-ordinated complexes between the graphite layers, free FeCl₃ converts either, following slow exposure, into partially hydrated species, or when the reaction is rapid to a mixture of FeO(OH) and HFeCl₄. The overall expulsion of the metal halide from between the host sheets is considered to proceed via both ‘electronic’ and ‘physical’ de-intercalation steps.