Browsing by Subject "Supramolecular Chemistry"
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Item ITC and NMR spectroscopy binding studies of meso- octamethyl-calix[4]pyrrole and its derivatives(2009-05) Gross, Dustin Eugene; Sessler, Jonathan L.This dissertation reports on the recent discovery that calix[4]pyrrole not only functions as an anion receptor, but also has the ability to act as an ion pair receptor. It was discovered that in the solid state large diffuse cations, such as Cs+ and imidazolium, will occupy the electron-rich cone-like cavity that is formed upon anion binding to the NH region of the calix[4]pyrrole core. Also discussed are efforts devoted to improving the anion binding ability of calixpyrroles and fine-tuning their inherent selectivity. This has been probed through a variety of structural modifications. One of the most attractive of the modification strategies currently being explored involves expansion of the central binding cavity by using higher order β-fluorinated calix[n]pyrroles; n = 5, 6, and 8. An advantage of β-fluorinated calix[4]pyrrole is that it shows enhanced anion binding affinities toward several anions compared to the parent calix[4]pyrrole. Fluorinated calixpyrroles have also shown an ability to extract anions from aqueous environments into organic media. An alternative strategy has been to attach “straps” resulting in bicyclic systems, which further define the binding cavity achieving higher affinity and anion selectivity. The binding interactions of calixpyrrole and it derivative have been quantified using analytical techniques, such as nuclear magnetic resonance spectroscopy and isothermal titration calorimetry. The results of these latter studies will be discussed herein.Item The influence of anion-pi interactions between multi-atomic anions and pi-acidic ring systems on the self-assembly of coordination compounds(2009-05-15) Schottel, Brandi LeeAnion-? interactions, weak attractions between anions and ?-acidic ring systems, have become an important topic in supramolecular chemistry within the past five years. Although a variety of computational studies have been undertaken by several groups to investigate the nature of these interactions, no comprehensive experimental investigations had been performed until the completion of the work described herein. The results presented in this dissertation indicate that anion-? interactions involving large complex anions are controlling elements in self-assembly reactions with cations that involve ?-acidic ring systems. Syntheses performed with the ligand 3-6-bis(2?-pyridyl)-1,2,4,5-tetrazine, or bptz, with M(II) first row transition metal salts (M = Mn, Fe, Ni, Cu, and Zn), produced self-assembled complexes that varied in shape and M:ligand ratio based on the presence of particular anions. Through a series of solution and structural studies, it was determined that the cationic polygons are templated by the size and shape of the specific anions during self-assembly. A close inspection of the bptz complexes in the solid state indicated that the anions were participating in anion-? interactions with the ?-acidic central tetrazine ring of the ligand. To show that these anion-? interactions were indeed important, reactions of bptz ligand as well with 3,6-bis(2?-pyridyl)-1,2-pyridazine (bppn) with Ag(I) salts were performed to compare the effect that specific anions had on self-assembly interactions between similar ligands with different ?-acidities. The results indicate that the Ag(I) complexes that included the ?-acidic tetrazine ring are strongly influenced by the anion presence, while those complexes that were synthesized with the similarly shaped, but electroneutral bppn ligand only relied on the anions for charge-balance. To better understand the anion-? interactions in the obtained bptz complexes, a computational study was performed on systems with the polyatomic anions [BF4]- and [PF6]- interacting with simple heteroaromatic rings of varying degrees of ?-acidity. Based on the final optimized complex geometries and Atoms in Molecules (AIM) critical point analyses, it was determined that anion-? interactions involving multiatomic anions interact with ?-systems in different orientations based on the symmetry of the ring system in the complex.