Magnetic resonance of intercalation compounds of graphite: Questions of ionicity and mobility of inserted species

Abstract

Graphite will react at room temperature with Lewis acids as PF 5 and BF 3 in the presence of the oxidant C1F to form intercalation compounds containing closed-shell anions. In the case of “C 16BF 4”, the chemical shifts of both 11B and 19F nuclear magnetic resonances point to the existence of BF − 4, rather than the initial BF 3, within the graphite planes. The existence of second order quadrupolar coupling of the 11B resonance suggests, however, possible hybrid BF 3 BF − 4 character, as in B 2F − 7, a known dimeric anion of BF 4 and BF 3. NMR results on 19F and 31P in the two compounds “C 14PF 6” and “C 28PF 6” support this hypothesis, as “C 28PF 6” shows only the presence of PF − 6, but the more concentrated “C 14PF 6” shows composite PF 5 PF − 6 character. Our claim for intercalated anions in these systems is reinforced both by radical cation-type signals in the ESR and by deshielding effects in the 13C NMR. The narrow linewidths of the nuclear magnetic resonance absorptions of the intercalated species are suggestive of “liquid-like” behavior.