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Access Type

WSU Access

Date of Award

January 2011

Degree Type

Thesis

Degree Name

M.S.

Department

Chemistry

First Advisor

Matthew J. Allen

Abstract

The magnetic and optical properties of divalent europium are of interest for catalysis, materials, magnetic, diagnostic-medical, and luminescence applications. Use of the aqueous Eu⊃II⊃ ion in these applications is limited due to the instability of Eu⊃II⊃ in the presence of air. To increase the use of Eu⊃II⊃ in these applications, it is desirable to increase the oxidative stability of the Eu⊃II⊃ ion in aqueous solution. Many attempts have been made to increase the oxidative stability of aqueous Eu⊃II⊃ with little success. The most stable aqueous Eu⊃II⊃ complex, before my research, was reported with the ligand [2.2.2]cryptand. My specific research strategy involved modifying this previously most stable ligand for aqueous Eu⊃II⊃ using principles of coordination chemistry. Four strategies were used based on principles of coordination chemistry and they were (i) increasing steric bulk to minimize metal–environment interactions; (ii) reducing Lewis basicity of the donor atoms to favor coordination to Eu⊃II⊃, which is electron rich with respect to Eu⊃III⊃; (iii) changing cavity size to favor coordination of the larger Eu⊃II⊃ ion over the Eu⊃III⊃ ion; and (iv) modifying hard–soft acid–base properties to favor coordination of the softer Eu⊃II⊃ ion with respect to the harder Eu⊃III⊃ ion. Cryptands 1–6 were reacted with Eu(NO⊂3⊂)⊂3⊂ to obtain aqueous Eu⊃II⊃ cryptate complexes in situ after bulk electrolysis. The oxidation potentials of these aqueous Eu⊃II⊃ cryptate complexes were determined using cyclic voltammetry. All cryptands produced using the four strategies were able to oxidatively stabilize the aqueous Eu⊃II⊃ ion, but the modification of hard–soft acid–base properties was the most effective strategy. The most oxidatively stable aqueous Eu⊃II⊃ complex in the study, 5,6-(Benzo)-4,7-dioxa-13,16,21,24-tetrathia-1,10-diazabicyclo[8.8.8]hexacos-5-ene europium(II) complex (6–Eu⊃II⊃), is the most stable aqueous Eu⊃II⊃ complex reported to date. It is more oxidatively stable than Fe⊃II⊃ in human hemoglobin under the same conditions, indicating the potential for future in vivo applications