Date of Award
Doctor of Philosophy (PhD)
William Pennington, Committee Chair
The halogen bond, XB, has been known since the nineteenth century. A XB involves the donation of electron density from a donor such as N, O, S, or Se to an electropositive region on another atom typically iodine or bromine. XB acceptors are Lewis bases and XB donors are Lewis acids keeping terminology hydrogen bonding. The highly directional characteristic of the halogen bond paired with phenyl embrace interactions provide very useful supramolecular synthons allowing for the engineering of cocrystals with specific directional bonding motifs.
Nitrogen electron acceptors such as quinoxaline, phenazine, 4,4’-bipyridine, and 4,4’-dimethyl-2,2’-bipyridine are cocrystallized with 1,4-diiodotetrafluorobenzene (1,4-F4DIB), 1,4-difluorotetraiodobenzine (1,4-F2TIB), or 4,4’-diiodooctofluorobiphenyl (4,4’-F8DIBPh). Structures form chain motifs with nitrogen atoms being located on opposite sides of the acceptor molecules.
Sulfur and selenium acceptors in bis(diphenylphosphino) alkane disulfide/diselenides. The alkane chain can have an even or odd number of carbon atoms. The even numbered alkane chains positions the sulfur or selenium acceptors in a staggered like conformation. The odd numbered alkane chains position the S or Se acceptors in a gauche-like conformation. The even alkyl chains prefer sheet motifs while the odd alkyl chains prefer 3D networks.
The phosphorous acceptor 1,2-bis(diphenylphosphino)ethane, dppe, is reported with chain motifs through XBs linked by phenyl embraces. Cocrystallization of dppe and 1,4-F4DIB results in two polymorphs and a 1:3 structure. All three structures can be synthesized by Mechanosynthesis which provides a mean to search for undiscovered cocrystals.
2,3,5,6-tetra(2′-pyridyl)-pyrazine (TPPZ) has been cocrystallized with 1,4-F2TIB, 4,4’-F8DIBPh, and 1,4-F4DIB forming chain motifs. TPPZ can have one of many conformations due to the pyridyl rings ability to rotate about the single carbon-carbon bond preferring only a few conformations observed in the structures reported here.
Tetraalkylammonium iodides are cocrystallized with diiodine and an organoiodide forming a variety of motifs. Sheets to 3D networks are observed increasing from methyl to butyl alkyl groups. The [N(alkyl)4]I3•organoiodide structures can provide XB enhanced iodine hopping in electrolyte for dye sensitized solar cells.
Siegfried, Adam Michael, "Development of Sulfur and Selenium Halogen Bonded Synthons and Mechanosynthesis of Halogen Bonded Cocrystals" (2016). All Dissertations. 2086.