Rare earth elements: donor and acceptor properties of binary fluorides

The unique specific properties of lanthanoids are to large extent responsible for the progress in many areas of science and technology. Lanthanoid binary fluorides are among key substances of these metals, therefore are among the best characterized, and their chemistry offer different challanges. In the investigation of amphoteric properties of lanthanoid binary fluorides new synthesis approaches will be introduced. Emphasis will be given on reactions in superacid anhydrous hydrogen fluoride which acidity or basicity will be controlled by addition of Lewis acids or bases. During the first two years of the project some new types of lanthanoid (Ln = La-Lu, Y) compounds were synthesized, LnFx(AsF6)3-x (x = 0, 1 or 1.5), and LnFx(BF4)3-x (x = 1 or 2). These compositions are nicely in accordance with decreasing basicity of LnF3 along the series. Crystallization and stabilization of these compounds was achieved with some fluoro acids or bases as an additional ligands and following compounds were obtained, La(HF)2(AsF6)3, La(CH3CN)9(AsF6)3 and Ce(AsF3)3(AsF6)3. The structure of La(HF)2(AsF6)3 reveals a novel type of bonding interactions as HF molecules are connected directly to the metal center. The whole new family of oxonium compounds, (H3O)xLnyFz(AsF6)x+3y-z was synthesized. These compounds represent precursors for new coordination and organometallic chemistry of lanthanoids. It is expected that structures of some new lanthanoid in complex compounds will govern interesting physical properties.