To confirm the bidentate coordination mode of the new halogen bond donors, which was likely observed in the titration studies presented above, and to confirm their structure, crystallization experiments of the compounds were performed. We then co-crystallized 3 with TBA-Br and obtained a monoclinic crystal structure. Strong tridentate binding towards the bromide guest is indeed present, with two symmetry-defined equal bond lengths of 3.206 Å and a third slightly elongated one of 3.286 Å (RXB = 0.84 and 0.86 respectively). These bonds also exhibit the characteristic high linearity with C-I-Br-angles of 170° and 173° respectively.