(Georgia Institute of Technology, 2021-08-30)
Aguirre Quintana, Luis Manuel
This thesis focuses on the use of weak-field ligands as a synthetic tool to access molecular tetravalent lanthanide compounds that can be studied spectroscopically and electrochemically to address broader questions pertinent to better understanding the electronic phenomena observed in bulk f-element materials. First, two different iterations of a tris(diakylamido)imidophosphorane ligand were used to create saddled tetranuclear Cu(I) and Ag(I) clusters. One of the Ag(I) clusters was shown to react with a neutral homoleptic Ce(III) compound and cerium metal shavings to produce the monometallic Ce(IV) imidophosphorane product. The latter example marks the first instance of an oxidative transmetallation reaction between a bulk lanthanide metal with a reagent that exclusively produces a single well-defined molecular tetravalent lanthanide oxidation product. Next, a new ligand type of guanidinate ligand, supported by a tris(diakylamido)imidophosphorane moeitywas used to produce a neutral tris-homoleptic Ce(III) complex that was oxidized to produce a cationic tris-homoleptic Ce(IV) complex. Both compounds were studied electrochemically and spectroscopically. The Ce(IV) compound displayed a Epc of -1.98 V (vs. Fc0/+) in THF, which is more than 1 V more negative than that of other homoleptic cerium guanidinate complexes with a dialkylamido backbone. The pseudo-Voigt fit of the Ce L3-edge XANES spectrum of the tetravalent cerium compound resulted in a nf value of 0.50(2), which is lower than that of many compounds supported by other ligands in the literature. Finally, the tris(piperidinyl)imidophosphorane ligand, [NP(pip)3]1- , was used to build low-coordinate bimetallic Fe(II) and Co(II) molecular clusters with facially exposed metal-metal bonds. Both compounds were exposed to N2O, S8, and Se0, however, the Co(II) bimetallic complex did not react with any of these small molecules. The Fe(II) bimetallic complex reacted with N2O under mild conditions to produce a O2--bridged product and reacted with S8 and Se0 to produce isostructural S22- and Se22- products. The oxidation product, [Fe2(mu2-O)(mu2-NP(pip)3)2(NP(pip)3)2], is structurally unique as it possesses an uncommonly short Fe(III)-Fe(III) distance.