UC San Diego

The modular assembly of molecular building blocks for the construction of functional extended materials has led to the design of numerous structures with interesting physical and chemical properties. Polyoxometalates (POMs) are a class of transition metal oxide clusters that can be strategically assembled into versatile framework materials with potential applications. In Chapter 1, the assembly of POM-based materials is introduced alongside key factors influencing the assembly process. Chapter 2 presents the study of the role of non-bridging cations on the assembly of anionic polyoxometalate with transition metal bridging ions. The formation of Ag-bridged coordination networks using the Preyssler anion was studied to explore the effect of incorporating counterions on the resulting network structure. Five different Ag-bridged coordinated networks were prepared by controlling the amount of K+ counterions and the method of crystallization. The final assembly of the networks is directed by the number and types of ion-pairs between the anionic clusters and cations during the crystallization step. Chapter 3 presents the influence of coordinating solvents on the framework assembly and the structural stability of polyoxometalate-based extended networks. The coordinating ligands not only act as structure directing agents but also as supporting ligands to enhance the overall structural stability of the materials. Three distinct Ag-bridged POM networks were prepared by incorporating different coordinating ligands (CH3CN, DMSO, and DMF) in the network. The DMF and DMSO ligands act as supporting ligands to further stabilize the structure and add another tunability to prepare stable hybrid framework. Greater coordination strength of DMSO compared to DMF and CH3CN enables the formation of DMSO-directed phases. Chapter 4 presents the synthesis of stable hybrid materials using pyridine carboxylate ligands, which offers structural support through their coordination to transition metal bridging ions. Hybrid Ag-bridged Preyssler networks with different overall structures are prepared by using isomers of pyridine carboxylate ligands. Other synthetic parameters such as pH, precursor ratio, and counterions were explored.