These experimental findings are supported by a DFT study with the wB97XD/6-31+G(d) model chemistry: CB and protonated DABCO are able to form a coordination complex (with protonated DABCO located above a CB portal, see Figure ) as well as an inclusion complex (with protonated DABCO inside the CB cavity, see Figure ). The coordination complex exhibits a perfect C2 symmetry axis where the protonated hydrogens of the DABCO nitrogen atoms form distinct coordinative bonds with their neighboring CB portal oxygen atoms (Figure , right). The less symmetric inclusion complex also consists of distinct coordinative bonds between the protonated DABCO hydrogens and their neighboring upper and lower CB portal oxygens (Figure , right). The complex formation energy of the coordination complex (-619.7 kJ mol -1 ) is 39.4 kJ mol -1 more stable in comparison to the inclusion complex (-580.3 kJ mol -1 ) thus the overall DABCO binding of the coordination complex is stronger: This may be traced to the unfavorable charged DABCO nitrogen atoms inside the non-polar CB[6] cavity of the inclusion complex which do not occur in the coordination complex. If thermodynamic control is assumed for the complex formation reaction, a minimum energy difference of 39.4 kJ mol -1 leads to a coordination-to-inclusion-complex ratio of about ten million to one at room temperature so that the comparatively small concentration of the inclusion complex would be hardly detected under experimental conditions.