Cations on Board, Ready for Takeoff: Using Vanadyl and Its Terminal Oxo to Probe Ligand Donor Strength in Heterobimetallic Complexes

Abstract

The coordination chemistry of heterobimetallic complexes has become a highly studied research topic in the broader field of inorganic chemistry. This can be attributed in part to the appealing opportunities that are afforded by assembly of well-defined complexes containing two (or more) different metals. In particular, it has been shown that the properties of a core metal center can be systematically varied by incorporation of secondary metal cations in close proximity. In this thesis, a possible origin of these tuning effects has been explored though use of the vanadyl moiety as a spectroscopic and structural probe. Vanadyl, or oxovanadium(IV), is a dicationic, paramagnetic species bearing a terminal oxo ligand that is quite chemically robust, making it ideal for use as a probe moiety. The studies presented in this thesis represent an extended examination of the origin of such tuning effects, with a particular attention paid to adapting synthesis and characterization methods to complexities that arise due to inclusion of vanadyl. Chapter 1 describes structural, spectroscopic, and electrochemical studies conducted with heterobimetallic vanadyl complexes containing a series of mono-valent cations (i.e., potassium) and a di-valent cation (calcium). This chapter mentions the synthesis of a heterobimetallic complex incorporating the lithium cation, but this compound and its speciation profile are described in detail in Chapter 2. The complex containing lithium appears to behave differently than the other heterobimetallic complexes reported here and thus it is described separately. Chapter 3 describes spectroscopic experimentation on heterobimetallic complexes based on the same ligand framework as those in Chapters 1 and 2 but presents expansion of our previous series of complexes to analogues containing trivalent cations. Taken together, the results assembled in this thesis paint a comprehensive picture of the tuning effects that Lewis acidic metal cations can exert on the vanadyl ion.