Isolation of soft donor complexes of d- and f-block metals using ionic liquids
Ionic liquids (ILs) are alternatives to conventional molecular liquids or high-melting salts which can be used to gain new insight into long-standing scientific questions. The ability to access a compositionally variable, purely ionic liquid environment in an IL is particularly significant in coordination chemistry, which often involves the manipulation of an ionic metal-ligand bond. This study aims to demonstrate the potential utility of ILs in coordination chemistry by using them to access unusual metal complexes with soft Lewis bases, especially those of f-elements. Such complexes are particularly important use in studying the nature of f-element chemical bonding and the interactions involved in their isolation, propagation through the environment, or distribution in living organisms. A number of strategies using ILs and systems derived from ILs are explored. In reactions of dicyanamide-containing ILs with uranyl salts, the use of an IL as a source of nitrogen-containing soft donor ligands led to the isolation of uranyl dicyanamide complexes through substitution of oxygen-donor ligands by IL anions. By reacting actinide nitrate hydrates with a nitrate-containing IL, anhydrous complexes were obtained which could be used as precursors for the formation of nitrogen-donor adducts. The permanent elimination of oxygen-containing anions from a metal salt was explored through reactions of an acidic azole with metal acetate salts, although this approach was found to be limited by side reactions. The use of a partially anionic sulfur ligand derived from an IL led to the formation of uranyl and neodymium sulfur-donor complexes. The scope of nitrogen-containing ligands which could be incorporated into an IL was expanded by demonstrating the use of combinations of acidic and basic azoles as liquids for nitrogen donor coordination chemistry. These platforms have considerable room for expansion beyond the metal complexes already isolated. Future studies will expand the range of soft donors incorporated in the IL beyond nitrogen. Combinations of these strategies will also be explored with the aim of producing entirely soft-donor ligated complexes from readily available starting materials.