Isomorphous crystal structures of chlorodi­acetyl­ene and iododi­acetyl­ene derivatives: simultaneous hydrogen and halogen bonds on carbon­yl

The crystal structures of tert-butyl (5-chloro­penta-2,4-diyn-1-yl)carbamate, C10H12ClNO2 (II), and tert-butyl (5-iodo­penta-2,4-diyn-1-yl)carbamate, C10H12INO2 (IV), are isomorphous to previously reported structures and accordingly their mol­ecular and supra­molecular structures are similar. In the crystals of (II) and (IV), mol­ecules are linked into very similar two-dimensional wall organizations with anti­parallel carbamate groups involved in a combination of hydrogen and halogen bonds (bifurcated N—H⋯O=C and C≡C—X⋯O=C inter­actions on the same carbonyl group). There is no long-range parallel stacking of diynes, so the topochemical polymerization of di­acetyl­ene is prevented. A Cambridge Structural Database search revealed that C≡C—X⋯O=C contacts shorter than the sum of the van der Waals radii are scarce (only one structure for the C≡C—Cl⋯O=C inter­action and 13 structures for the similar C≡C—I⋯O=C inter­action).