Solvent-dependent Ln(III) clusters assembled by immobilization of CO in air: zero-field single-molecule magnets and magnetic refrigerant materials.

The automatic fixation of CO in air played a key role in the construction of Dy(III) single-molecule magnets (SMMs) and Gd(III) magnetic refrigeration molecular materials when Ln(III)Cl (Ln = Dy and Gd) was reacted with a new hydrazone Schiff base ligand {HL = ()-'-(4-fluoro-2-hydroxybenzylidene)pyrimidine-4-carbohydrazide}, which is condensed from pyrimidine-4-carbohydrazide and 4-fluorosalicylaldehyde. Surprisingly, the small difference in methanol and ethanol solvents leads to dramatic changes in the structures of these Ln(III) cluster complexes. When methanol and ethanol participated in the reaction, a trapezoidal pyramid Dy(III) pentanuclear cluster [DyL(OH)(CO)(OCOMe)(MeOH)(HO)]·3MeOH·3.5HO (1) and a triangular prism Dy(III) hexanuclear cluster [DyL(CO)(EtOH)(HO)Cl]·6EtOH (2) were obtained, respectively, and a tub-like Gd(III) octanuclear cluster [GdL(CO)(MeOH)(HO)]·12MeOH·3CHCl·3.25HO (3) and a trapezoidal pyramid Gd(III) pentanuclear cluster [GdL(HL)(CO)O(OH)(EtOH)(HO)Cl]·EtOH·3HO (4) were yielded, respectively. Notably, 1 contains not only the carbonate anion, but also the monomethyl carbonate anion as the bridging ligand, which are formed by immobilizing CO in air, while 2, 3 and 4 contain the carbonate bridging ligand only. Magnetic properties' investigations revealed that both 1 and 2 are zero-field SMMs, with / values of 93.2 K and 133.5 K, respectively, while 3 and 4 show large magnetocaloric effects, with the largest -Δ values of 27.49 J kg K at 2.0 K for Δ = 7 T for 3 and 27.58 J kg K at 2.5 K for Δ = 7 T for 4.