This PhD is about novel functionalised ionic liquids with the ability to coordinate metals. These functionalised ionic liquids have the following functional groups; diphenylphosphine oxide (Ph2P=O) and phosphonate ((OEthP=O). The functional groups were grafted to different cations. The coordinating groups have been chosen for the coordination with rare earth elements and actinides. A detailed study of the coordinating abilities and the influence of the ionic species in the coordination chemistries has been performed and demonstrated . Phosphine oxide functionalised ionic liquids are an ionic version of well-known phosphine oxide ligands, commonly used to bind hard metals such as lanthanides or actinides. The phosphine oxide functionalised ionic liquids have been synthesised with two different anions, bis(trifluoromethylsulfonyl)imide and hexafluorophosphate. Different spacer units between the coordinating group and the cation have been synthesised and the influence of this spacer on the coordinating abilities of the ionic liquids was investigated. The crystal structures of some of the higher-melting ionic liquids with a phosphine oxide functionality were obtained and studied in detail in this thesis. The crystal structures of metal complexes with lanthanides were also obtained. Comprehensive simulation studies were also carried out to examine the charge distribution in these functionalised ionic liquids. In this work, structural data from the FILs and the metal complexes, such as crystal structures, UV-Vis absorption spectra and NMR complexation studies in the liquid state have been used to understand the coordination and the speciation of lanthanides and actinides in solution. Besides metal complexation studies with the functionalised ionic liquids, metal separation studies have been carried out . Hydrophobic FILs were used and coated on chromatographic silica in order to perform liquidsolid metal separations . The preliminary results of these experiments are shown and discussed in this thesis. Moreover, lanthanide salts have been mixed with phosphonium chloride salts in stoichiometric amounts resulting in novel compounds, lanthanide-containing chlorometallate ionic liquids. The physical properties, the structure and the luminescence properties of these liquid lanthanide complexes have been investigated.