Date of Award
Doctor of Philosophy (PhD)
William T. Pennington
Colin D. McMillen
Scott T. Iacono
Joseph S. Thrasher
Halogen bonding, the attractive interaction of an electrophilic region on a halogen atom with a nucleophilic region on another atom or molecule, provides a highly directional tool in forming solid-state motifs. This interaction, along with the related chalcogen bonding interactions, forms powerful synthons, which, when combined with other typical intermolecular attractions such as hydrogen bonding, allow for the design of supramolecular structures and inputs to crystal engineering. This dissertation research serves two primary purposes: (1) to catalog halogen and chalcogen bonding interactions with various donor molecules and (2) to utilize these interactions to probe interesting organic transformations.
In order to more fully characterize these fundamental interactions, 2,5-diiodothiophene was combined with N-heterocyclic diamines and ammonium iodides. This thiophene molecule can serve as both a halogen and chalcogen bond donor. The analysis of 19 new co-crystalline structures revealed a significant preference for C–I···I over C–I···S interactions. Further, thiourea and 1,3-dimethylthiourea, combined with the common halogen bond donors 1,2-, 1,3-, and 1,4-diiodotetrafluorobenzene, as well as 1,3,5-trifluoro-2,4,6-triiodobenzene, to form chains, rings, and sheets through I···S halogen bonding.
The cyclic, sulfur-containing molecules, 1,3- and 1,4-dithiane provide the typical halogen bonding motifs with iodofluorobenzenes. The combination of 1,3-dithiane and 1,2-diiodotetrafluorobenzene yielded the first deep eutectic solvent based on halogen bonding, likely resulting from the steric frustration resulting from the intramolecular proximity of the donor and acceptor atoms in these molecules. Further, these dithianes provide a rich series of products from the reaction with diiodine and dibromine.
Finally, the utility of networks derived from the halogen bonding of iodide, polyiodide, and diiodine donor molecules to trap novel organic fragments was explored. Through the direct reaction of phenothiazine with diiodine at varying stoichiometries and in varying solvents allowed the study of the halogen bonding of the phenothiazine radical cation, as well its dimer, 10-(3-phenothiazinylidene)phenothiazinium, neither of which have been previously studied in the solid-state. Halogen bond-directed cocrystallization further revealed novel heterocycle formation from the reaction pyridine-thiocarboxamides with diiodine. This strategy provided structures of complex organic fragments derived from the addition of two, three, or four equivalents of the pyridine-containing molecule. These results highlight the importance of these fundamental intermolecular interactions in the study of solid-state motifs and the direction of organic transformations.
Peloquin, Andrew, "COMPETITION BETWEEN HALOGEN AND CHALCOGEN BONDING AND THEIR ROLE IN PROBING ORGANIC TRANSFORMATIONS" (2022). All Dissertations. 2969.
Author ORCID Identifier
Available for download on Thursday, May 18, 2023