Supramolecular Organization via Halogen Bonds

Significance

Goroff and co-workers report that diiodobutadiyne in a co-crystal with nitrile-terminated oxalamides undergoes spontaneous 1,4-poly­merization to form poly(diiododiacetylene) (PIDA). The authors have previously demonstrated that weak, non-covalent halogen bonds between Lewis acidic iodine and Lewis basic pyridine in combination with oxalamide hydrogen bonding are sufficient for solid-state organization (N. S. Go­roff, S. M. Curtis, J. A. Webb, F. W. Fowler, J. W. Lauher Org. Lett. 2005, 7, 1891-1893). However, the critical C1-C4 distance (d ˜ 3.5 Å) and monomer repeat distance (r ˜ 4.9 Å) necessary for 1,4-polymerization were not realized. Here, the authors discover the optimal supramolecular scaffold by utilizing an iodine-nitrile halogen bond and altering the length of the oxalamide linker. For example, PIDA is not observed for a shorter oxal­amide (n = 3). Consistent with the SEM images and X-ray diffraction measurements, the absorption spectra indicate an ordered polydiacetylene with fully planar, s-trans conformation.