On the other hand, C4Si2H6N12F12 and its dimers have much higher LUMO energies due to the presence of fluorine atoms. As a result, fluorine-containing cages possess higher HOMO-LUMO gaps and chemical hardness, and significantly lower electrophilicity. For all considered cages, dimers demonstrate lower HOMO-LUMO gaps and chemical hardness due to their large effective sizes. Such behavior is typical for the most cage-like molecules.
To evaluate the possible energy gain associated with the dimer formation, we consider hypothetical dimerization reaction in the following form
2M + 2CH2 → D + 4NX2 (X=O or F),
where M is a monomer (CL-20, CSi5H6N12O12 or C4Si2H6N12F12), and D is the corresponding dimer. Thermodynamic characteristics of these reactions are calculated for the low-energy dimers as a difference between the corresponding values of energies and Gibbs energies for the products and reactants. Obtained data are presented in Table 2. Negative values of ΔE and ΔG show that the dimerization reaction is energetically favorable. High temperature inhibits dimerization, especially for the CSi5H6N12O12 cage. However, ΔG remains negative for all considered dimers even at very high temperature of 3000 K.