Desolvation‐Induced Highly Symmetrical Terbium(III) Single‐Molecule Magnet Exhibiting Luminescent Self‐Monitoring of Temperature

Abstract A conjunction of Single‐Molecule Magnet (SMM) behavior and luminescence thermometry is an emerging research line aiming at contactless read‐out of temperature in future SMM‐based devices. The shared working range between slow magnetic relaxation and the thermometric response is typically narrow or absent. We report Tb III ‐based emissive SMMs formed in a cyanido‐bridged framework whose properties are governed by the reversible structural transformation from Tb III (H 2 O) 2 Co III (CN) 6 ⋅ 2.7H 2 O ( 1 ) to its dehydrated phase, Tb III Co III (CN) 6 ( 2 ). The 8‐coordinated complexes in 1 show the moderate SMM effect but it is enhanced for trigonal‐prismatic Tb III complexes in 2 , showing the SMM features up to 42 K. They are governed by the combination of QTM, Raman, and Orbach relaxation with the energy barrier of 594(18) cm −1 (854(26) K), one of the highest among the Tb III ‐based molecular nanomagnets. Both systems exhibit emission related to the f–f electronic transitions, with the temperature variations resulting in the optical thermometry below 100 K. The dehydration leads to a wide temperature overlap between the SMM behavior and thermometry, from 6 K to 42 K. These functionalities are further enriched after the magnetic dilution. The role of post‐synthetic formation of high‐symmetry Tb III complexes in achieving the SMM effect and hot‐bands‐based optical thermometry is discussed.