The influence of anion-pi interactions between multi-atomic anions and pi-acidic ring systems on the self-assembly of coordination compounds



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Anion-? 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.