Nuclear magnetic resonance (NMR) spectroscopy is one of the most important analytical techniques used in chemistry for the characterisation and identification of compounds. An abundance of chemical, physical, electronic and biological information can be deduced making NMR a versatile technique which is used routinely across multiple scientific disciplines. The NMR spectra of closed shell (diamagnetic) systems can be easily interpreted experimentally and also via theoretical and computational means. However open shell (paramagnetic) systems pose problems for experimentalists and theoreticians alike. The presence of unpaired electrons can cause extreme paramagnetic shifts and line broadening making the interpretation of paramagnetic NMR (PNMR) spectra extremely complicated. The effects can be profound and unpredictable, creating spectra that are unrecognisable when compared against the analogous diamagnetic system. Many of the actinides and lanthanides in their most stable oxidation states are characterised as paramagnetic, meaning the assignment of NMR chemical shifts in f-element systems remains challenging. These difficulties have motivated the development of quantum chemical approaches capable of reliably predicting the chemical shifts of paramagnetic molecules. The accurate theoretical calculation of PNMR spectra containing light elements has been achieved, and extending the approach to the transition metals has been successful. However the actinides and lanthanides, being the heaviest elements with complex electronic structures, still present a significant challenge to quantum chemists. The reliable calculation of PNMR spectra of f-element compounds is yet to become routine and has only recently become feasible. In this work we present our computational approach and the protocol we have developed for the prediction of PNMR spectra of actinide and lanthanide complexes with useful accuracy. Our purpose is to aid the interpretation of experimental data, provide understanding of the factors that govern the observed spectra and, where necessary, develop improved computational approaches for handling the f-elements.

Computational prediction of paramagnetic NMR spectra of f-element complexes

253rd National Meeting (2017)

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