Octamethonium iodide 1a self-assembles with 1,2-diiodotetrafluoroethane 2a into a 1:1 high melting discrete supramolecular complex. It is interesting to notice that the distance between the N's in 1a well matches the anion separation in I^-∙∙∙I(CF₂)₂I∙∙∙^-I.

In order to verify the role played by the size matching of interacting partners in the formation of the adducts, we challenged the higher congeners of 1b-c with the respective longer a,w-diiodoperfluoroalkanes 2b-c. All matching cations/superanions couples form the same discrete adducts, which melt invariably higher than the adducts obtained by mismatched couples, which, in turn show very different crystal packing (1a ∙ 2b and 1b ∙ 2d).

We proved the ability of bismethonium congeners to phase out selectively (100% yield, 100% recovery) the complementary partner from a solution containing equivalent amounts of the homologues a,w-diiodoperfluoroalkanes. This applied also to complex industrial mixtures with very long diiodoperfluorocarbons (m = 8-16).

Powder diffraction analysis demonstrated that the matching supramolecular adducts form also through a gas-solid reaction starting from the more volatile diiodoperfluorocarbons 2a,b. A comparison with the structure of pure decamethonium iodide 1b suggests a “sliding doors” mechanism to create room to the diiodoperfluorocarbon.