Intercalation compounds of graphite with nickel chloride: synthesis, structure, and mechanism of intercalation

The intercalation of nickel chloride into graphite in presence of chlorine gas has been studied in the temperature range 390 – 750 °C with an apparatus allowing the measurement of the chlorine pressure during intercalation. The results indicate that chlorine takes part in the reaction with a 600 mmHg threshold pressure below which no intercalation occurs. Between 495 and 690 °C, a second stage compound C 11.3 NiCl 2.13 , is obtained with the apparent activation energy of the intercalation being about 50 kcal/mole. X-ray investigations show that intercalated nickel chloride has a structure very close to the nickel chloride sandwich in free metal halide. However, intercalant layers are not complete, with the filling coefficient being at most 0.71. All of the data are consistent with an islandic nature of nickel chloride: islands of diameter 100 A allow explanation of the non integer stoichiometric coefficients given by chemical analyses and the amount of charge transferred from graphite to nickel, which is, moreover, consistent with a decrease of CC bond lengths as observed by X-ray diffraction.