The role of terminal ligands in the slow relaxation of magnetisation and luminescence thermometry of dinuclear Nd^III complexes

Single-molecule magnets (SMMs) are promising candidates as components for the next generation of molecule-based electronics. As the state-of-the-art in this field is mainly focused on heavy lanthanide(III) (Ln(III)) ions, examples of light lanthanide-based systems, e.g., those based on Nd-III, have fallen far behind. Besides the slow relaxation of magnetisation, the luminescence of multifunctional Ln(III) complexes can be leveraged for in situ temperature monitoring via luminescence thermometry. To help understand how both magnetic and luminescence performance can be improved through structural modifications in Nd-III-based SMMs, two dinuclear Nd-III complexes, [Nd-2(III)(valdien)(2)(X)(2)] (X = acac(-){1-Nd-2} or NO3- {2-Nd-2}), are herein reported, and we discuss opto- and magneto-structural correlations depending on the terminal ligand. The Nd-III complexes display field-induced slow relaxation of magnetization, but for {2-Nd-2}, QTM has a lower contribution because the longer Nd-III-O-terminal distances induce a weaker equatorial crystal field component. The systems were further used to develop luminescent temperature probes featuring a maximum thermal sensitivity of 0.52% K-1 at 40 K for {2-Nd-2}, confirming its multifunctional slow relaxation of magnetisation and temperature readout features.