“…The choice of Ln III compounds for this study was caused by the unique properties of such ions, i.e., their ability to exhibit slow magnetic relaxation (the so-called Single-Molecule Magnetism, SMM, or Single Ion Magnetism, SIM) [ 21 ] along with luminescence [ 22 ]. A lot of coordination polymers, containing only Ln III ions as paramagnetic centers, exhibit SMM properties (in particular, slow relaxation of magnetization) [ 23 , 24 , 25 ], however, in many cases, the role of the exchange coupling between Ln III ions (if any) in the occurrence of SMM properties was not clear. In some cases, it was shown that exchange interactions between paramagnetic ions can facilitate magnetic relaxation via the mechanism of quantum tunneling of magnetization (QTM) [ 26 ], but the opposite effect was also found: QTM was quenched due to the Cr III ···Dy III coupling compared to the analog containing diamagnetic Co III [ 27 ].…”