Browsing by Subject "supramolecular chemistry"
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Item Experimental and Theoretical Investigations of Anion-pi Interactions Metallacyclic Architectures of First-Row Transition Metals and N-Heteroaromatic Ligands(2012-07-16) Giles, IanResearch into anion-pi interactions has shifted from attempts to establish the legitimacy of the interaction to the incorporation of anion-pi interactions into supramolecular architectures. The research discussed in this dissertation explores the subtle effects of ligand, anion, and metal ion on supramolecular architectures of tetrazine-based ligands in the context of anion-pi interactions and their importance in the design and synthesis of supramolecular architectures. Computational studies highlight the importance of the arene quadrupole moment, molecular polarizability, and substituent effects on the strength of anion-pi interactions. More importantly, however, this work establishes that there is a distinct directionality inherent to the anion-pi interaction between polyatomic anions and N-heterocycles, which can be used to direct ligands in supramolecular architectures as demonstrated through the work of the Dunbar group in recent years, particularly that of the square and pentagonal metallacycles. The extension of metallacycles of bptz to CoII and FeII demonstrates the ability to tune the size of the metallacyclic cavity by simply changing the metal ion and results in the surprising encapsulation of two [SbF6]- anions in [Fe5(bptz)5(NCCH3)10][SbF6]10. 1H NMR spectroscopy and electrochemical studies reveal slight but significant differences characteristic of the square and pentagonal metallacycles and support the presence of anion-pi interactions in solution and highlight the importance of the encapsulated anion in the templation and stability of the metallacycles. A study of the interconversion between the square and pentagonal metallacycles via 1H NMR is presented for the first time. Increasing the pi-acidity of the chelating ligand from bptz to bmtz results in the encapsulation of only one [SbF6]- anion in [Fe5(bmtz)5(NCCH3)10][SbF6]10, maximizing anion-pi interactions with the ligand despite the tighter fit. A significant hurdle in the incorporation of different anions into the metallacyclic structures was overcome with the development of a new synthetic protocol for [Fe(NCCH3)6]2+ salts of a wide range of anions from sodium salts and Fe4Cl8(THF)6. Also, the nuclearity of the less stable [Fe5(bptz)5(NCCH3)10][PF6]10 metallacycle was established via a combination of MS, electrochemistry and 1H NMR experiments through comparisons with known FeII metallacycle solution behavior.Item Physical Models of Noncovalent Interactions Involving Aromatic Rings(2014-04-17) Bloom, Jacob Walter GoldsteinNoncovalent interactions involving ?-systems play a vital role throughout chemical and biological processes. These ?-interactions can be found in organic photovoltaics and electronics as well as govern many protein and DNA interactions. A fundamental and physically meaningful model of these interactions is necessary for the efficient exploitation of these materials and rational drug design. First, the role of aromaticity in ?-stacking, cation/?, and anion/? interactions is investigated. Aromaticity weakly hinders ?-stacking and greatly hinders anion/? interactions, while greatly enhancing cation/? interactions. Nonaromatics, therefore, present themselves as a new target in design for ?-stacking and anion/? interactions. The well-established local direct interaction model for ?-stacking that substituent effects are due solely to local electrostatic changes has also been expanded herein. First, we show that the local direct model for substituent effects in ?-stacking also applies to polar XH/? interactions. The nonpolar XH/? interactions vary little with substituent, depending only on changes in dispersion. The energetic changes of both sets of XH/? interactions follow well-known substituent constants. Next, the local direct interaction model is expanded to the use of electric fields to reconcile unusual similarity in the substituent effects between benzene, triazine, and borazine. Substituent effects for different rings are similar as long as the electric fields of those rings are similar in the location of the substituent. In fact, the substituent effect scales proportionally to the relative strength of those fields. Lastly, in an analysis on anion/? complexes with a variety of azines and benzene, it is shown that changes induced through the substitution of a carbon-hydrogen bond with nitrogen are almost exclusively from the nuclear charge differences. This reconciles well with the local direct interaction model.