Minor Synthetic Modifications Induce Major Changes: From {MnII6LnIII6} to {MnIII2LnIII2} Metallomacrocycles

Abstract

A new family of dodecanuclear metallomacrocycles, with a {MnII6LnIII6} core, has been synthesized by the reaction of MnII and LnIII salts with the Schiff base (H4L1) derived from the condensation of carbohydrazide and o-vanillin, resulting in a series of complexes 1MnTb, 2MnDy, 3MnHo, 4MnEr, 5MnYb, and the YIII analogue 6MnY. Interestingly, the same reaction with the closely related ligands obtained by employing 3-ethoxysalicylaldehyde (H4L2) as a precursor instead of o-vanillin afforded tetranuclear metallorings with a {MnIII2LnIII2} core (7MnGd, 8MnTb, 9MnDy, 10MnHo, and the YIII analogue 11MnY), which show a different nuclearity and oxidation state for the manganese cation. To evaluate the effect of the substituents on the aromatic ring, the ligands obtained by employing salicylaldehyde (H4L3) or 5-bromomethoxysalicylaldehyde (H4L4) instead of o-vanillin were tested with the GdIII cation, resulting in two new tetranuclear rings 12MnGd and 13 MnGd. Analysis of their magnetic properties has been performed, and out-of-phase susceptibility measurements revealed field-induced slow relaxation of the magnetization for the 2MnDy complex. Furthermore, the magnetocaloric effect (MCE) has been studied for the complexes with the highest values of magnetization (1MnTb, 2MnDy, and 3MnHo).