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Description:
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Anion -π interactions , weak attractions between anions and π -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 -π interactions involving
large complex anions are controlling elements in self -assembly reactions with cations
that involve π -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 -π interactions with the π -acidic
central tetrazine ring of the ligand .
To show that these anion -π 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 π -acidities . The results indicate that the Ag (I )
complexes that included the π -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 -π 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 π -acidity .
Based on the final optimized complex geometries and Atoms in Molecules (AIM )
critical point analyses , it was determined that anion -π interactions involving multiatomic
anions interact with π -systems in different orientations based on the symmetry of
the ring system in the complex . |