Chainlike Structure Formed in Iodine Monochloride Graphite Intercalation Compounds

The structure of iodine monochloride (ICl) intercalated into graphite (GIC) has been revisited, and a stage 1 stoichiometry of about 10 carbon atoms to 1 ICl molecule is determined. Intercalation proceeds readily at room temperature without additional energy input. A chainlike structure of alternating halogen species is proposed for the intercalation layer based on detailed Raman spectroscopic analysis and ab initio calculations. Long-range ordering is observed, reaching beyond one layer of carbon. The calculated density of states shows p-doping of the carbon layers upon intercalation, in agreement with Raman spectroscopic analysis. The intercalation is reversible upon heating and can be cycled several times. While iodine chains have been observed in other nanocarbons, ICl is the first example of extended halogen chains intercalated in graphite. Indeed, intercalant phases of acceptor GICs have rarely been studied to date, and the current findings are of potential interest in structural chemistry, materials science, solid-state batteries, and other areas.