Access Type

Open Access Embargo

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Matthew J. Allen

Abstract

Trivalent lanthanide (Ln3+)-containing complexes have a number of important applications in molecular imaging, catalysis, medical diagnosis, information storage, and environmental sensing. The properties of Ln3+-containing complexes that are useful for these applications are influenced by coordination chemistry, including the number of coordinated ligands and ligand-exchange rates. The coordination numbers for water molecules bound to Eu3+ and Tb3+ have been studied by luminescence-decay measurements; however, the coordination numbers of other important oxygen-containing functional groups such as ketones, esters, ethers, sulfonyls, amides, phosphine oxides, and aldehydes have not been as thoroughly studied in solution because of the lack of hydroxyl groups that quench the luminescence of Eu3+ or Tb3+. Therefore, there is a need to develop analytical methods to measure the coordination of different functional groups to Ln3+ ions. This thesis describes efforts to measure the number of solvent molecules coordinated to Dy3+ ions using 17O-NMR spectroscopy in acetone, ethyl acetate, tetrahydrofuran, dimethylsulfonate, dimethylformaldehyde, di-isopropyl ketone, hexamethyl acetone and 4-chlorobenzaldehyde. These solvents were selected because they contain a range of functional groups that have different electron-donating abilities and steric bulk. The measured coordination numbers were consistent with reasonable values, indicating that 17O-NMR spectroscopy is a useful tool for measuring the coordination number of non-hydroxyl oxygen-containing ligands.

In addition to coordination numbers of ligands, ligand-exchange rates are another important parameter that impacts the coordination chemistry of Ln3+ ions. This thesis describes the study of water-exchange rates of Ln3+ ions in room temperature ionic liquids. Room temperature ionic liquids were studied because they are important solvents for Ln3+ ions. Luminescence-decay measurements were used to measure the coordination number of Eu3+ and Tb3+ ions in water/1-ethyl-3-methylimidazolium ethylsulfate (1:19, v/v), and variable-temperature 17O-NMR spectroscopy was used to measure the water-exchange rates of Gd3+, Tb3+, Dy3+, Ho3+, and Er3+ ions in water/1-ethyl-3-methylimidazolium ethylsulfate (1:19, v/v). Water-exchange rates increased with increasing charge density of Ln3+ ions, except for Tb3+. This trend of water-exchange rates is opposite to the trend of Ln3+ aqua ions, indicating that the change of solvents can manipulate ligand-exchange rates of Ln3+ ions to the extreme case of inversing exchange-rate trends. For Tb3+ ions, the fast water-exchange rate was attributed to the presence of a trace amount of Tb4+ that was confirmed by X-ray absorption spectroscopy. These findings suggest variable-temperature 17O-NMR spectroscopy is a useful technique to study the ligand-exchange rates of Ln3+ ions in ionic liquids.

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