The interaction of lanthanides and lanthanide-carbene complexes with crown ethers

Abstract

The syntheses of novel organometallic compounds, using cyclic and semi-cyclic compounds, were investigated. These included the synthesis of an air-sensitive lanthanide complex, by using a carbene as the ligands. This was achieved by using lanthanum as the metal centre, and a bis(iminophosphorano )methanide as the ligand. The intermediates of this reaction were successfully observed, but the final product was not obtained successfully. The syntheses of several air-stable lanthanide complexes, with the use of different oxygen-based crown ethers, were also carried out. The lanthanides used included lanthanum, europium, gadolinium, and ytterbium. The crown ethers which were used included 18-crown-6, 21-crown-7, and 24-crown-8. The synthesis of lanthanide-crown ether complexes, as high-quality single crystals, was carried out by using standard crystallisation techniques, such as grinding and vapour diffusion, using water-ethanol and water-propanone as solvent pairs. Crystals of a sufficient quality were analysed by means of microscopy, infra-red spectroscopy, hot-stage microscopy, and single crystal X-ray diffraction. A total of 32 unique samples were prepared, and eight of these samples produced adequate crystals for analysis. Single crystal X-ray diffraction was used to collect diffraction data for eight samples, all of which have now been analysed. These samples are not new complexes, but are instead identical to certain lanthanide-crown ether complexes which were previously produced. However, one sample (GG2112) showed intrinsic modulation of the crystal structure at low temperatures, which is not visible at room temperature.