New high nuclearity manganese carboxylate clusters as single-molecule magnets

Single-molecule magnets (SMMs) represent a molecular approach to nanoscale magnetic materials. They are individual molecules that, below a certain temperature, can function as magnetizable magnets. They exhibit slow rates of magnetization reorientation, which results in magnetization hysteresis loops, the classical property of a magnet. The first and still best understood SMMs is the [Mn 12O12(O2CR)16(H2O) 4] family. The aim of this work is the synthesis of new examples of SMMs to increase the available database of knowledge of this new magnetic phenomenon and to expand our understanding of the various factors that influence the observed magnetic properties.; In this thesis work, a variety of new synthetic methods have been developed to a number of new SMMs. Selective carboxylate (RCO2- ) exchange reactions have been employed to synthesize new mixed-carboxylate Mn12 complexes of formula [Mn12O12(O 2CR)8(O2CR')8(H 2O)4]. Electrochemical studies followed by chemical reduction with iodide have allowed the preparation and study of salts of the two-electron reduced derivatives, [Mn12]2-, the third oxidation level of the Mn12 family to have been prepared. Detailed comparisons of these species with the neutral Mn12 and one-electron reduced [Mn12]- compounds have been carried out. Also studied have been some Mn12 complexes displaying atypical magnetic properties, and magneto structural correlations have been achieved of their magnetic properties with the corresponding crystal structures, showing that small structural changes and small variations in the environment of a SMM have significant effects on the magnetic properties. Finally, a giant new SMM with size dimensions approaching the mesoscale has been discovered with the formula [Mn30O24(OH)8(O2CCH 2But)32(H2O) 2(MeNO2)4]. It also still exhibits quantum tunneling of the magnetization, showing that the quantum properties of small SMMs are also still retained at these much larger dimensions. All synthesized compounds have been investigated by spectroscopic, electrochemical and magnetochemical techniques. The obtained results will be invaluable for the rational synthetic design of new examples with technologically improved properties.