While the dimerization of imide D remains exothermic, its entropy change is positive and estimated to have similar magnitude (see Methods). This means that the free energy of the dimerization of D is not expected to be very low (Table ) and both dimers and monomers of D will exist in diluted solutions. Moreover, even if the dimer of D dominates in the solution, it appears that it can also cleave C -H bonds since its two active centers retain their structure and remains accessible to small CH 4 molecules. It should also be noted that bulky substituents in D do not affect the energetics of the methane activation compared to imide C (Table ).