At the onset of our study, orientating computational investigations into monodentate model systems and the bidentate halogen bond donors m-1 and p-1 were performed, in order to get a preliminary estimate on their Lewis acidity in solution. The wellestablished M06-2X-D3/def2-TZVP(D) level of theory was employed, which has been shown to provide good results for halogen bonding, and solvent effects were treated with the SMD18 solvation model (see SI ǂ for further details). The strong monodentate XB donor C6F5I was first compared to a monoiodinated carborane, with pyridine acting as Lewis base, and at least comparable binding strengthsif not a slightly larger one for the carboranewere obtained in toluene (Table , see entries 1 and 2). A stronger XB-acceptor, trimethylamine, highlighted the stronger binding by the carborane even more (Table , entries 3 and 4).