The role of guest molecules in the self-assembly of metal-ligand clusters

The role guest molecules play in the self-assembly of supramolecular metal-ligand clusters is examined in the context of several predictive design strategies for forming these types of assemblies. Chapter One serves as an introduction and literature survey of this topic. These large assemblies often house guest molecules which play a previously uncharacterized role in the self-assembly processes. Chapter One seeks to categorize this role: Do the guest molecules act as templates in the synthesis? Are the guest molecules necessary for cluster formation? Does the guest drive cluster assembly by forming a stable host-guest complex with the cluster?; In Chapter Two a series of heterometallic-hybrid ligand clusters of stoichiometry M₂M′₃L₆ are presented. These result from a predictive design strategy in which two different metals, one hard and one soft, supply all the symmetry elements in these C_3h “mesocates.” The early examples of these clusters were synthesized in a stepwise manner; however, complete self-assembly of all eleven components can be achieved using appropriate guest molecules.; The self-assembly of a novel geometry for metal-ligand clusters, D₃ symmetry M₆L₆ “cylinders,” is presented in Chapter Three. This chapter presents the fortuitous synthesis of these cylinders and demonstrates the tendency for discrete clusters to form over oligomers when rigid ligands and labile metals are combined. The ligand presented was designed to assemble M₄L₄ tetrahedra with trivalent metal ions, however cylinders were formed in all cases examined. Guest molecules were not found to play a role in this self-assembly, but solvent molecules were found disordered within the solid state structures of these clusters.; Chapter Four describes a bis-bidentate catecholamide ligand with a structure between the design for M₂L₃ helicate formation and M ₄L₆ tetrahedron formation. The two design strategies are briefly discussed, and molecular modeling studies are presented which suggested that two helicates were roughly equal in energy to one tetrahedron. The helicate was formed in the absence of any guest molecules. In the presence of suitable tetraalkylammonium cations, the helicate is quantitatively converted to the tetrahedral host-guest complex.; A related dicatecholamide ligand is presented in Chapter Five. This ligand has a rigid pyrene linker between the chelating moieties and modeled as a perfect candidate to assemble M₄L₆ tetrahedra. The ligand indeed forms tetrahedral clusters when treated with trivalent metal ions, but only in the presence of suitable monocationic guest molecules. This guest molecule thermodynamically drives cluster synthesis through formation of a host-guest complex.