EFFECT OF 1,4-DIOXANE ON THE COMPLEXATION OF LANTHANIDES WITH α-HYDROXYISOBUTYRATE
Kriz, Maria Rebecca
MetadataShow full item record
Water has been described as the “universal solvent� because of its ability to dissolve many substances and its ubiquitous nature. The nature and properties of water as a solvent have been well studied. The main impetus for this work is to investigate the effect of a co–solvent containing ether groups on the properties of water as a solvent. The ether chosen for this work, 1,4–dioxane, is a non–polar aprotic solvent with a boiling point and density similar to water but possessing a dielectric constant significantly lower than that of water. Water and 1,4–dioxane are miscible in all proportions. Addition of 1,4–dioxane to water will disrupt the normal structure of water because of its relatively bulky structure and its ability to accept two hydrogen bonds without donating any hydrogen bonds. The effect of 1,4–dioxane on the properties of water can be probed by manipulating an already well–established system. The ligand α –hydroxyisobutyric acid (HIBA) is well known for its ability to separate adjacent trivalent lanthanides and actinides in chromatographic applications. When compared to other structurally similar ligands, HIBA works remarkably well for trivalent lanthanide separations. The lanthanides provide an ideal place to study electrostatic effects in chemical bonding, as the charge remains constant at +3 while the ionic radius decreases 20% across the 14 members of the lanthanide series. This dissertation will focus on the characterization of lanthanide complexation with HIBA in 1,4–dioxane/water media. A characterization of the HIBA complexation with the lanthanides in a 1,4–dioxane/water media includes a thorough investigation of the effect of the media on the ligand itself. The ligand was characterized by examination of the protonation constants and heat of protonation. A computational density functional theory study explored potential ways the ligand, water and 1,4–dioxane may interact in solution. The thermodynamic constants (δG, (δH, and (δS) of lanthanide–HIBA complexes were determined as a function of 1,4–dioxane and compared to a completely aqueous system. The effect of 1,4–dioxane on the residual hydration of metal–ligand complexes was investigated using laser–induced fluorescence studies of europium.