ABSTRACT
Ubbelohde and co-workers [2,3] clearly showed that the intercalation of graphite by closed-shell anions, such as CIO4 and HSO4, increased the resistiv ity perpendicular to the carbon sheets, thus enhancing the two-dimensional char acter of the electrical conductivity. This anisotropy justifies the view, also held by Hennig [4], that the carbon sheets are positively charged, this charge being stabilized by the closed-shell anions. Such closed-shell guest species cannot provide for band formation via the pir frontier orbitals of the carbon atoms. Additionally, the relatively large size of these guest species (of effective diameter of more than 4 A) prevents effective carbon sheet/carbon sheet interaction. Graphite acceptor compounds as different as graphite-bromine [1,5] and graph ite bisulfate [1,4] can be modeled as salts composed of anions in the galleries between positively charged graphitic-carbon sheets. The application of a modi fied Born-Haber cycle to such salts was first made by Hennig [6]. That such an approach is of predictive value is nicely illustrated by the fluoroanion salts.
