Valikoitujen harvinaisten maametalli- ja vismuttikompleksien magneettisen resonanssin kokeellisia ja laskennallisia tutkimuksia

The rare-earth elements (REEs) and bismuth, being classified as the ‘most critical raw materials’ (European Raw Materials Initiatives, 2017), have a high economic importance to the EU combined with a high relative supply risk. REEs are highly important for the evolving technologies such as clean-energy applications, high-technology components, rechargeable batteries, permanent magnets, electric and hybrid vehicles, and phosphors monitors.

This scientific research work aims at building a fundamental knowledge base concerning the electronic/molecular structure and properties of rare-earth element (REE) and bismuth complexes with dithiocarbamate (DTC) and 1,10-phenanthroline (PHEN) by employing state-of-the-art experimental techniques such as nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction (XRD) techniques together with ab initio quantum mechanical computational methods. This combination of methods has played a vital role in analysing the direct and significant effect of the heavy metal ions on the structural and magnetic resonance properties of the complexes, thereby, providing a framework of structure elucidation. This is of special importance for REEs, which are known to exhibit similar chemical and physical properties. The objectives of the work involve i) a systematic investigation of series of REE(III) as well as bismuth(III) complexes to get a profound understanding of the structure-properties relationship and ii) to find an appropriate theoretical modelling and NMR calculation methods, especially, for heavy metal systems in molecular and/or solid-state.
This information can later be used in surface interaction studies of REE/bismuth minerals with DTC as well as in design and development of novel ligands for extraction/separation of metal ions.

The REE(III) and bismuth(III) complexes with DTC and PHEN ligands have all provided a unique NMR fingerprint of the metal centre both in liquid and solid phase. The solid-state 13C and 15N NMR spectra of the diamagnetic REE(III) and bismuth(III) complexes were in accord with their structural data obtained by single crystal XRD. The density functional theory (DFT) methods were used to get complementary and refined structural and NMR parameters information for all diamagnetic complexes in the solid-state. The relativistic contributions due to scalar and spin-orbit correlations for the calculated 1H/13C/15N chemical shifts of REE complexes were analysed using two-component zeroth-order regular approximation (ZORA)/DFT while the ‘crystal-lattice’ effects on the NMR parameters were calculated by combining DFT calculations on molecular and periodic solid-state models. The paramagnetic REE complexes display huge differences in their 1H and 13C NMR spectral patterns. The experimental paramagnetic NMR (pNMR) chemical shifts, as well as the sizable difference of the 1H and 13C NMR shifts for these isoelectronic complexes, are well reproduced by the advanced calculations using ab initio/DFT approach. The accuracy of this approach is very promising for further applications to demanding pNMR problems involving paramagnetic f-block elements.

The results presented in this thesis demonstrate that a multidisciplinary approach of combined experimental NMR and XRD techniques along with computational modelling and property calculations is highly efficient in studying molecular complexes and solids containing heavy metal systems, such as rare-earths and bismuth.

(This press release is exceptionally published in English.)