Isomorphous crystal structures of chlorodi-acetyl-ene and iododi-acetyl-ene derivatives: simultaneous hydrogen and halogen bonds on carbon-yl.

The crystal structures of -butyl (5-chloro-penta-2,4-diyn-1-yl)carbamate, CHClNO (), and -butyl (5-iodo-penta-2,4-diyn-1-yl)carbamate, CHINO (), are isomorphous to previously reported structures and accordingly their mol-ecular and supra-molecular structures are similar. In the crystals of () and (), mol-ecules are linked into very similar two-dimensional wall organizations with anti-parallel carbamate groups involved in a combination of hydrogen and halogen bonds (bifurcated N-H⋯O=C and C≡C-⋯O=C inter-actions on the same carbonyl group). There is no long-range parallel stacking of diynes, so the topochemical polymerization of di-acetyl-ene is prevented. A Cambridge Structural Database search revealed that C≡C-⋯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 inter-action and 13 structures for the similar C≡C-I⋯O=C inter-action).