Scanning lanthanoid magnetic susceptibility tensors in solids using spy molecules via paramagnetic fast magic-angle spinning NMR spectroscopy.

Magnetic properties of lanthanoid ions at the atomic level are challenging to derive especially in the solid state despite the wealth of chemical and structural information encoded in them. We herein report proton-detected paramagnetic solid-state NMR experiments at magic-angle spinning frequencies of 100 kHz and more that allow the scanning of the magnetic susceptibility tensors of europium(III)-based π-containers in the solid state. An isolated water molecule and a guanidinium cation binding non-covalently to the aromatic cavity of such containers have been explored as highly sensitive reporters that make use of the chemical shift changes caused by the molecular orientation of the magnetic susceptibility tensors (pseudo-contact shifts). By not diluting the lanthanoid complex in a diamagnetic matrix, we study the importance of inter-complex interactions in the solid state on the measured pseudo-contact shift values of the spy molecules. Our study shows how the field of paramagnetic solid-state NMR is opening up to increasingly complex molecules allowing the electronic structures to be connected with the materials properties for solid lanthanoid-based compounds.