The solid-state structures of a butadiynylene-linked bidentate halogen bond donor, both as a single component and as a co-crystal with tetra-n-butylammonium iodide, are discussed. Solution-phase binding data indicate that this donor, which possesses only a single degree of conformational freedom, interacts with halides in a 1 : 1 stoichiometry through a convergent binding mode. In contrast, it forms a zigzag-type chain with iodide in the solid state. The X-ray crystallographic data enable detailed studies of the changes in molecular structure and supramolecular organization that accompany the formation of a halogen-bonded network.