Lanthanide Beta-Diketonate Compounds: Synthesis, Characterization, and Reactivity
Abstract
This dissertation is mainly focused on the synthesis of Lanthanide (Ln) betadiketonate hydrates which serve as the starting materials for a variety of lanthanide coordination complexes. Due to their distinct optical and magnetic properties, these diverse complexes have a wide range of applications. The main goal of this study was to synthesize a variety of lanthanide beta-diketonate starting materials using mechanochemistry that can be used for synthesizing supramolecular or complex lanthanide structures. In addition to conventional solution synthesis, the focus of this study was to investigate environmentally sustainable mechanochemical methods using mortar and pestle and ball milling to minimize solvent usage and loss of soluble starting materials and products. In a mortar and pestle reactions, the main issue was the sensitive dependance of reaction products on reaction conditons. We observed different reaction products depending on the reaction conditions. We discovered differences in product distributions between using unpurified or crystallized sodium beta-diketonates for the reaction. Our initial studies included the volatile hexafluoroacetylacetone ligand (Hhfac). When the crude sodium salt of hfac (Nahfac), was used, we obtained pentakis-hfac (La-Nd except Pm), and tetrakis-hfac (Sm) complexes consistently. When purified Nahfac was used the products were the expected Ln(hfac)3(H2O)x (Ln=La-Sm) alongside an expected impurity containing a dinuclear cluster bridged with a trifluoroacetate ligand. Using other salts of hfac containing other alkali metal cations: Khfac, Cshfac and Lihfac, resulted in a mixture of pentakis-hfac and tetrakis-hfac complexes. As was seen previously, the use of crystallized Khfac, Cshfac and Lihfac resulted in the expected hydrates both in mechanochemical and solution synthesis as seen in case of Nahfac. Along with hydrates, anhydrous Ln beta-diketonate DME (dimethoxy ethane) complexes were synthesized using mortar and pestle reactions and veratrole starting materials were synthesized using solution synthesis and characterized. The displacement reactions of the early Ln starting materials with the bipyridine (Bpy) ligand were performed to determine the reactivity. The purity of these products was determined using Differential Scanning Calorimetry and melting points. 2-Thenoyl trifluroacetylacetone (TTA) was another beta-diketonate ligand of interest due to its luminescent properties. The TTA ligand acts as the antenna for enhancing the luminescent properties of the Ln, which have weak absorption coefficients. We report the synthesis of Ln(tta)3(H2O)x (x = 2 or 3) (Ln= La-Sm except Pm) using both mechanochemistry and conventional solution synthesis. An attempt to synthesize the Ln(tta)3 hydrates resulted in the isolation of a Ce(tta)4 neutral complex with two different morphologies from solution and mechanochemical reactions. The products synthesized were characterized using Fourier Transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), X-ray diffraction (XRD- for single crystals and bulk powder), differential scanning calorimetry (DSC) elemental analysis (EA) and melting points (MP). Overall, we report the synthesis and characterization of a variety of Ln beta-diketonate starting materials and coordination complexes.