The Sensitivity of Magnetic Anisotropy in the Solid State for Lanthanide Complexes with Small Crystal Field Splitting

Knowledge of the crystal structure of a monometallic inorganic molecule is often sufficient to calculate its electronic structure and interpret its magnetic properties. Here we show that for a series of nine-coordinate lanthanide complexes based on the 1,4,7-tris[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane ligand, the electronic structure is hypersensitive to geometric structure and to the presence of non-coordinated lattice solvent, which renders the magnetic and spectroscopic properties very difficult to interpret. We explore possible explanations for the peculiar electron paramagnetic resonance (EPR) spectra and conclude that a number of entangled factors are at play across the samples, and hence that great care should be taken in the interpretation of EPR spectra for systems with small magnetic anisotropy, even when the molecular structure is known.