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Access Type

WSU Access

Date of Award

January 2020

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Matthew J. Allen

Abstract

The research projects in this dissertation pertain to the properties of molecular divalent lanthanide complexes with a focus on luminescence properties in solution. Most available research in lanthanide chemistry focuses on either the trivalent oxidation state or the divalent oxidation state in solid inorganic host matrices. The results described herein contribute to the body of knowledge regarding the effects of coordination environment on the spectroscopic and electrochemical properties of divalent lanthanides in solvated molecular complexes.

The divalent-europium-containing complex Eu(II)23 was evaluated as a visible-light-excited photoredox precatalyst. Stoichiometric and catalytic carbon–carbon bond forming reactions of Eu(II)23 with benzyl chloride in the presence of blue light were performed. A substrate scope with organic substrates of varying reduction potentials was also explored to frame the electrochemical window within which the precatalyst can perform chemical reductions. Spectroscopic, electrochemical, and structural characterizations of the complex add insight to the mechanistic aspects of the reductive coupling reaction. The results of this study serve as foundational knowledge for future research endeavors focusing on Eu(II)-based photoredox chemistry.

The divalent-europium-containing complex Eu(II)25, a structurally modified variant of Eu(II)23, was synthesized to examine the electronic and steric effects of alkylated tertiary amines versus secondary amines on the luminescence of the coordinated Eu(II) ion. The steric bulk of the added methyl groups forced Eu(II)25 into a lower coordination number than Eu(II)23, invoking hypsochromic spectroscopic shifts that were not expected based strictly on the electronic character of the tertiary amine donors of 25. The steric hindrance of the methyl groups in 25 provided increased protection of the Eu(II) ion from nonradiative interactions with solvent molecules with respect to 23, providing a substantial increase in the luminescence quantum yield of the complex. The results of this study provide information for tuning the luminescence wavelength and intensity of Eu(II)-containing complexes in solution.

A series of Yb(II)-containing cryptates with varying electronic and steric character was synthesized and characterized. Structural, spectroscopic, and electrochemical trends among the complexes were observed. These trends were compared to the trends observed in the analogous series of Eu(II)-containing complexes, with differences and similarities between the trends being discussed. The results of this study serve as an imperative guide as to the translatability of ligand trends across the divalent lanthanide series

The results of these studies are expected to enhance the ability to selectively and rationally modulate the luminescence of divalent-lanthanide-containing complexes based on metal selection and coordination environment, ultimately improving the intrigue and impact of the field of divalent lanthanide luminescence in solution.

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