Ab initio MO calculations and experimental observations on the reactivities of elemental fluorine and chlorine with graphite in the presence of HF

Ab initio MO calculations have been carried out on F₂ HF and Cl₂ HF complexes in order to shed light on the reactivities of elemental fluorine and chlorine with graphite. The results show that the F₂ HF and Cl₂ HF complexes are stabilized by 10.50 and 5.2kJ/mol respectively. A partial charge transfer from the halogen molecules (X₂) to HF occurs. The X₂ molecules are polarized and the X atoms which are not hydrogen-bonded to HF carry a partial positive charge, making the complexes suitable for the dipole-induced dipole interaction with graphite. Furthermore, the X₂ molecules interacting with HF can be regarded as easily polarizable, large "soft oxidants", facilitating the subsequent charge transfer from graphite. HF plays a catalytic role both in intercalation and deintercalation processes. In contrast with fluorine, the reaction of chlorine with graphite in the presence of liquid HF barely yielded a stage-two compound after a prolonged reaction time, which was in agreement with the results of calculation. The lower reactivity of chlorine is attributed to the weaker interaction of Cl₂ with HF and its smaller oxidizing ability.