Heavy atom building units for magnetic clusters and molecular catalysts for generating hydrogen from water

Presented in two parts, this dissertation describes the synthesis of a series of novel building units for the directed assembly of magnetic clusters and investigations into water reduction catalysis based on molecular metal-oxo complexes.;Chapter One introduces single-molecule magnets with an emphasis on the parameters which need to be optimized to someday realize the goal of data storage in the Angstrom scale. The importance for sustainable and cost efficient methods for hydrogen production is also presented, along with current methods for hydrogen generation which do not, at present, meet the requirements as a viable replacement for fossil fuel. This motivates the search for new catalysts, specifically molecular complexes, where optimization of the catalysis through structural modification lies within the scope of synthetic chemistry.;Due to well established synthetic routes, first-row transition metals are predominantly used for the assembly of magnetic molecules. However, most of these clusters do not show single-molecule magnet behavior, partly due to the low anisotropy of the constituent metal centers. A method to increase the anisotropy of these metals by using heavy atoms as auxiliary ligands, demonstrated through the magnetic properties of the mixed cyanide-halide complexes [Cr(dmpe)2(CN)X]1+ (X = CI, Br, and I) and Cr(dmpe) 2(CN)X (X = Cl and I), is described in Chapter Two.;Chapter Three introduces the use of a mixed cyanide/carbonyl ligand set to stabilize two new pentagonal bipyramidal complexes: [W(CN) 5(CO)2]3- and [W(CN)5(CO) 2]2- and the oxidation induced ligand isomerization of the former is studied through electron spin resonance and vibrational spectroscopy as well as Density Functional Theory calculations.;Chapter Four describes the synthesis of a series of novel seven-coordinate trimethylsilylcyanide complexes of molybdenum and tungsten. Their versatility as precursor complexes for cluster synthesis is demonstrated through ligand exchange and metathesis reactions.;The synthesis and metallation of a new blocking ligand for magnetic building units is described in Chapter Five, and its potential to form an anionic complex in order to stabilize high oxidation state metals is discussed. Appendix A details the synthesis and rich electrochemistry of some new second- and third-row transition metal building units of the pentapyridine PY5Me2 ligand that may be of utility for the synthesis of clusters displaying strong magnetic super-exchange and double-exchange interactions.;This work changes focus at the end to introduce a molecular molybdenum-oxo complex in Chapter Six, which upon reduction, initiates a rapid catalytic cycle for the generation of hydrogen from neutral water, and even straight sea-water, with a turn-over frequency of ca. 8300 mol H 2/mol catalyst·h, and turn-over numbers in excess of 609,600 mol H2/mol catalyst. Appendix B describes some preliminary work on fine-tuning this system to optimize the catalysis. This metal-oxo complex serves as a paradigm for employing high-oxidation state complexes for reductive catalysis that has broad implications for producing molecular systems that are robust and functional in aqueous media.