Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Chemistry

First Advisor's Name

Raphael G. Raptis

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Christopher Dares

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Konstantinos Kavallieratos

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Kevin O'Shea

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Daniela Radu

Fifth Advisor's Committee Title

Committee member

Keywords

inorganic chemistry, radiochemistry

Date of Defense

6-29-2023

Abstract

The main objective of this project is to gain a fundamental understanding of technetium (Tc) pyrazolate chemistry through the synthesis and characterization of corresponding rhenium (Re) surrogates. With exclusively radioactive iostopes, a surrogate is required for preliminary Tc studies to minimize exposure to radiation. In total, twenty-eight new complexes were synthesized: ten ReV, ten ReIV, six FeII, and two FeII/ReVII mixed-metal complexes. In addition, a crystallographic and spectroscopic study of pyrazole ligands was performed.

Syntheses starting from Re(V) species and four equivalents of pyrazole afforded dimeric complexes of form [{ReV(O)X(PPh3)}2(μ-O)(μ-4-X′-pz)2] (X = Cl, Br; X′ = Cl, Br; and pz = pyrazolate). The same reaction with base and a 25-fold excess of pyrazole yields all pyrazole/pyrazolate complexes of the form [{ReV(O)(pz*H)(pz*)}2(µ-O)(µ-pz*)2] (where pz*H = pzH, 4-Cl-pzH, 4-Br-pzH, and 3-Me-pzH; and pz* = the corresponding pyrazolates) along with [{ReV(O)(4-NO2-pz)2}2(µ-O)(µ-4-NO2-pz)2]2-. Similarly, a nearly 100-fold excess of pyrazole yielded a monomeric species, trans-[ReVO2(4-Cl-pzH)4]1+. The dimeric complexes all feature a similar bent O=Re-O-Re=O backbone with a Re-O-Re angle of ca. 125°. These complexes also have a Re=O terminal bond length of ca. 1.68 Å, which is in between a double and triple bond length, whereas the monomeric species has a true Re=O double bond of 1.76 Å. Syntheses starting from Re(IV) materials [ReX6]2- (where X = Br, I) yielded monomeric rhenium adducts of the form: [ReIVX5(4-R-pzH)]- (where X = Br, I; and R = H, Cl, Br, I, NO2). It is known that the [ReBr6]2- motif is somewhat inert to substitution; therefore, successful substitution of more than one ligand is rarely reported and, to the best of our knowledge, successful substitution of more than two ligands has been reported only for cyanideand thiocyanate. However, we have isolated the complex cis-[ReIVBr4(4-Cl-pzH)(4-Cl-pz)]- and have evidence of fac-[ReIVBr3(4-Cl-pzH)(4-Cl-pz)2]-. Mixed-metal complexes of the form [FeII(ReVIIO4)3(OPPh3)2(4-R-pzH)2] (where R = H, Cl) were afforded from ReV or ReVII starting materials. These complexes are preceded by only six reported structures to feature an Fe-OReO3 covalent bond; currently, there are no reports of a complex with an Fe-OTcO3 bond. These complexes may give insight into Tc remediation via iron oxide minerals.

Identifier

FIDC011157

ORCID

0000-0001-8940-2185

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