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Synthesis, Characterization, and Electronic Structure of Heteromultimetallic Complexes Incorporating a Redox-Active Metalloligand

  • Author(s): Wojnar, Michael Kenneth
  • Advisor(s): Heyduk, Alan F.
  • et al.

The theme of this dissertation centers around the synthesis and characterization of heteromultimetallic systems incorporating a redox-active metalloligand, a metal complex that acts as a ligand toward other metal centers. The redox-active metalloligand is comprised of two tridentate non-innocent ligands coordinated to a redox-active metal center.

Chapter 2 describes the synthesis and characterization of heterobimetallic Mo[SNS]2Ni(dppe) and heterotrimetallic Mo[SNS]2{Ni(dppe)}2 complexes that include Mo[SNS]2 as the metalloligand ([SNS] = bis(2-mercapto-p-tolyl)amine). These systems involve molybdenum-nickel metal-metal bonds, through a two-center two-electron bond in the bimetallic systems, and through a three-center four-electron bonding scheme in the trimetallic complex. Electrochemistry, supported by density functional theory (DFT) calculations, is in agreement with nickel-localized oxidations, making the heterotrimetallic Mo[SNS]2{Ni(dppe)}2 a viable molecular study of mixed valency in linear trinuclear systems.

Chapter 3 discusses the installation of a copper center on the the Mo[SNS]2 metalloligands. Considered as a one-electron-reduced form of Mo[SNS]2Ni(dppe), these bimetallic systems are best described as copper in its monovalent form coordinated to the monoanion of the metalloligand, Mo[SNS]2–1. Variation of the ligand on the copper centers leads to distinct changes in the metal-metal bond distance via X-ray crystallography, while spectroscopic techniques confirm almost identical electronic structures that are unperturbed by the ancillary ligand identity. Solid-state- and solution-based characterization methods lead to electronic structure assessment of these bimetallic molybdenum–copper systems as dynamic Mo(V)–Cu(I) ions in solution.

Chapter 4 revolves around a library of trimetallic systems incorporating the late transition metal centers cobalt, nickel, and copper, with the general formula, Mo[SNS]2{M(dppe)}2 (M= Co, Ni, Cu). As these trimetallic cluster compounds incorporate three-center bonding schemes, variation of the metal center from cobalt to nickel to copper leads to distinct variations in the coordination geometry of the metalloligand

bridge, as well as metal-metal bond length.

Chapter 5 focuses on a library of metalloligands of the general formula, Kx[M[SNS]2]. Electrochemical, spectroscopy, structural, and computational studies measure the HOMO-LUMO gaps of these compounds. Based on these methods, the covalency of these systems can be tuned through judicious choice of metal ion.

Chapter 6 describes the synthesis and characterization of a mixed-valent molecule, V[SNS]2{Ni(dppe)}2, which is the one-electron oxidized version of [K][V[SNS2{Ni(dppe)}2]. Oxidation of these trimetallic systems leads to metal-metal bond scission and localization of valence on the metalloligand. It is hypothesized that the energetic and spatial mismatch between the nickel and vanadium metal centers (as seen through the dative character of the metal-metal bonds) leads to valence trapping

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