The role of terminal ligands in the slow relaxation of magnetisation and luminescence thermometry of dinuclear NdIII complexes

Abstract

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^III₂(valdien)₂(X)₂] (X = acac⁻{1-Nd₂} or NO₃⁻{2-Nd₂}), 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-Nd₂}, 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-Nd₂}, confirming its multifunctional slow relaxation of magnetisation and temperature readout features.