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

Abstract

Ab initio MO calculations have been carried out on F 2  HF and Cl 2  HF complexes in order to shed light on the reactivities of elemental fluorine and chlorine with graphite. The results show that the F 2  HF and Cl 2  HF complexes are stabilized by 10.50 and 5.2kJ/mol respectively. A partial charge transfer from the halogen molecules (X 2) to HF occurs. The X 2 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 X 2 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 Cl 2 with HF and its smaller oxidizing ability.