Unravelling the structure of paramagnetic materials by solid-state NMR – MatPNMR

Many devices of interest to sustainable chemistry and climate change have functions that depend on the underlying materials, ranging from the average long-range structure, down to more local environments of specific atoms and ions, whether the structure is ordered/disordered, and whether it is dynamic. Of particular interest are paramagnetic materials, since these lend many unique properties due to the unpaired electrons of their paramagnetic metal ions. The characterization of the structural environments of these metal ions is key to understanding the functions and limitations of these materials. Whilst some structural information is provided by X-ray, and neutron diffraction, and electron microscopy techniques, these methods often fail to appreciate the complexity of the all-important local structure, how this local structure varies throughout the material, and thus how these important features affect performance of the corresponding devices. Solid-state paramagnetic nuclear magnetic resonance (pNMR) is a key method for understanding this atomic-level structure, but the unpaired electrons result in broad, low intensity signals that are very difficult to excite, resolve, and interpret using standard NMR methods. We will develop new pNMR and computational methods for paramagnetic materials, on three themes. Firstly, we will develop new NMR methods for the broadband excitation and resolution of NMR signals from quadrupolar nuclei close to paramagnetic metal ions. We will also test new density-functional theory (DFT) protocols to enable unambiguous assignment. Secondly, we will push the boundaries of dynamic nuclear polarization (DNP) to the intrinsic metal ions to enhance the pNMR sensitivity in the immediate vicinity of the metal ions, and in parallel reduce shift dispersion by perturbing the measured paramagnetic shifts. Thirdly, we will take pNMR from the atomic to the nano-scale and develop a protocol based on bulk magnetostatics to characterize the distributions of shapes/sizes of paramagnetic nano/micro particles, and lengthscales of the surface layers deposited on these particles. The methods developed around these three themes will then be put into action enabling us to fourthly, solve the complete local and global structure of three materials with important applications in sustainable energy, and to link these structures to the performances of the corresponding devices.