page_title: Halogen bond
section_title: Preparation of poly(diiododiacetylene)
hierarchical_section_title: Halogen bond / Applications / Crystal engineering / Preparation of poly(diiododiacetylene)
caption_attribution_description: English: halogen bond picture one TL
context_page_description: A halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity.
context_section_description: Applications utilizing properties of conjugated polymers emerged from work done by Heeger, McDiaramid, and Shirakawa with the discovery that polyacetylene is a conducting, albeit difficult to process material. Since then, work has been done to mimic this conjugated polymer’s backbone (e.g., poly(p-phenylenevinylene)). Conjugated polymers have many practical applications, and are used in devices such as photovoltaic cells, organic light-emitting diodes, field-effect transistors, and chemical sensors. Goroff et al. prepared ordered poly(diiododiacetylene) (PIDA) via prearrangement of monomer (2) with a halogen bond scaffolding. PIDA is an excellent precursor to other conjugated polymers, as Iodine can be easily transformed. For instance, C−I cleavage is possible electrochemical reduction.
  Crystal structures of monomer (2) are disordered materials of varying composition and connectivity. Hosts (3–7) were investigated for their molecular packing, primarily by studying co-crystals of monomer (2) and respective host. Both (3) and (4) pre-organized monomer (2), but steric crowding around the iodines prevented successful topological polymerization of the monomer. Hosts (5–7) utilize hydrogen bonds and halogen bonds to hold monomer (2) at an optimal distance from each other to facilitate polymerization.
  In fact, when host 7 was used, polymerization occurred spontaneously upon isolation of the co-crystals. Crystal structures show the polymer strands are all parallel to the hydrogen-bonding network, and the host nitriles are each halogen-bonded to iodine atoms. Half of the iodine atoms in (1) in the crystal are in close contact to the oxalamide oxygen atoms. Oxygen atoms of host 7 are acting as both hydrogen and halogen bond acceptors.
caption: PIDA, monomer, and host scaffolds used.
exif: {}