Date of Award
12-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
Committee Chair/Advisor
William T. Pennington
Committee Member
Colin D. McMillen
Committee Member
Stephen E. Creager
Committee Member
Joseph S. Thrasher
Committee Member
Apparao M. Rao
Abstract
Halogen bonding is a noncovalent intermolecular interaction analogous to hydrogen bonding that occurs between an electrophile and a nucleophile. This is often observed in compounds containing heavy halogens such as iodine and bromine. When these halogens are covalently bonded to another atom or molecule, preferably to an electron-withdrawing moiety, an electrophilic region called a sigma hole is created on the halogen atom on the extension of the covalent bond.
The first study of this dissertation presents a comprehensive characterization of eight newly synthesized triiodide salts using single-crystal X-ray diffraction, powder X-ray diffraction, thermal analysis (DSC and TGA), and Raman spectroscopy. This study aimed to establish baseline values for the structural and physical properties of triiodide salts as starting materials that may be used in triiodide salt-organoiodine cocrystals development and deep eutectic solvent (DES) formation. Establishing benchmark data for the parent triiodide salts is essential to assess how halogen bonding influences these systems. Three of these triiodides, NPe₄I₃, NMeBenzoSI₃, and 2-ClMePyrI₃, exhibited polymorphism, with each polymorphic pair displaying distinct crystal packing patterns. In each case, one polymorph contained an asymmetric triiodide anion, while the other featured a symmetric triiodide, illustrating the significant influence of cation identity on triiodide asymmetry and crystal packing.
The second study of this dissertation examined the cocrystallization of triiodide salts with organoiodine molecules and the formation of halogen-bonded DESs. This study revealed that organoiodines with triiodide salts form diverse supramolecular architectures, ranging from 1D chains to 3D frameworks, depending on the donor symmetry and the degree of iodination of the organoiodine molecules. Triiodide salts with longer alkyl chains favored the formation of both cocrystals and DESs. In contrast, triiodide salts with shorter alkyl chains predominantly formed cocrystals. Thermal and Raman analyses confirmed the retention of the triiodide entity across both crystalline and eutectic phases. Seven new type III halogen-bonded DESs were developed and characterized rigorously using thermal analysis and Raman spectroscopy. Low Transition Temperature Mixtures (LTTMs) were identified in systems where only the glass transition was observed in thermal analysis.
The third study of this dissertation investigated interactions between sulfur- and selenium-containing halogen bond acceptors and organoiodine molecules. Halogen bonding, such as I⋯S, I⋯Se, I⋯N, and I⋯I, and chalcogen bonding, such as Se⋯I, in these systems produced a wide variety of architectures, including 1D chains, 2D layers, and 3D frameworks. These findings highlight the identity of the chalcogen atom (S and Se) and the choice of the halogen bond donor as critical factors in determining the strength and geometry of halogen or chalcogen bonding.
These cocrystal findings advance crystal engineering principles toward rational synthon design and materials design. DES systems have found broad applications in areas such as metal deposition and synthesis, and an emerging area of DES study is biotransformations, which convert absorbed drugs into active agents or convert toxins into less harmful substances in the body. Traditionally, biotransformations are performed in aqueous solvents because polar organic solvents denature enzymes. Hence, replacing polar solvents with DESs could allow the substrate to dissolve without denaturing the enzymes.
Recommended Citation
Bandara, Madhushi, "Exploring Halogen Bonding Interactions in Cocrystals and Deep Eutectic Solvents" (2025). All Dissertations. 4101.
https://open.clemson.edu/all_dissertations/4101
Author ORCID Identifier
https://orcid.org/0000-0002-9237-0871