Rare-earth cyclobutadienyl and cyclopentadienyl complexes : synthesis, structure and magnetism

Cyclic π-conjugated organic ligands are widely used in rare-earth organometallic chemistry, and our group in particular has shown that cyclopentadienyl ligands are extremely effective in the synthesis of high-performance single-molecule magnets (SMMs). These remarkable magnetic properties are due to the strong axial ligand field that the monoanionic cyclopentadienyl ligands provide, with recent results including the record-breaking SMM [Dy(η⁵-C₅^iPr₅)(η⁵-C₅Me₅)]⁺. This thesis focuses on the coordination chemistry of a dianionic cyclobutadienyl ligand in rare-earth chemistry, i.e. [C₄(SiMe₃)₄]²⁻. My work on the fundamental coordination chemistry of the cyclobutadienyl ligand towards rare-earth elements and the reactivity of the new complexes is presented herein, in addition to the SMM properties of exemplar systems. The work presented in this thesis shows that cyclobutadienyl ligands can effectively replace cyclopentadienyl ligands in structurally similar rare-earth complexes, resulting in improved SMM properties. This thesis extends our understanding of magneto-structural correlations currently used in the design of high-performance organometallic rare-earth SMMs, and demonstrates that cyclobutadienyl-ligated SMMs should have the potential to surpass the current records set by bis-cyclopentadienyl dysprosium SMMs.