Magnetic refrigeration and slow magnetic relaxation in tetranuclear lanthanide cages (Ln = Gd, Dy) with in situ ligand transformation

Three new Ln3+ coordination compounds having formulae, [Gd4(μ3-OH)2(L)2L1L2(HOCH3)2]·11H2O (1), [Dy4(μ3-OH)2(L)2L1L2(H2O)2]·11H2O (2) and [Dy4(μ4-O)(OMe)(HOMe)2(CH3COO)3(L3)2]·2H2O (3), have been synthesized in a one pot synthesis from O-vanillin, diaminomaleonitrile (DAMN), LnCl3·6H2O (Ln = Gd3+, Dy3+) and sodium acetate for 3, {H2L = 2,3-bis((E)-(2-hydroxy-3-methoxy benzylidene) amino)maleonitrile, HL1 = (2-amino-3-((E)-(2-hydroxy-3-methoxy benzylidene)amino)maleonitrile), H3L2 = ((1E,3Z,8Z,10E)-1,6,11-tris(2-hydroxy-3-methoxyphenyl)-2,5,7,10-tetraazaundeca-1,3,8,10-tetraene-3,4,8,9-tetracarbonitrile) and H2L3 = 2-((cyano(2-hydroxy-3-methoxyphenyl)methyl)amino)-3-((E)-(2-hydroxy-3-methoxybenzylidene)amino)maleonitrile. Single-crystal X-ray diffraction studies reveal that compounds 1 and 2 are quasi-isostructural, exhibiting tetranuclear hemicubane-like cores. For 3 the metal centers are arranged in a tetrahedral arrangement. Complexes 1–3 were formed with the ligands (L1–L3), which resulted in situ during synthesis. Magnetic studies reveal that compound 1 shows significant magnetocaloric effect (ΔSm = −27.2 J kg−1 K−1) at 3 K and 7 T. The magnetic properties of 2 and 3 are considerably different. Indeed, no out-of-phase alternating current (ac) signal is noticed for 2, whereas 3 shows a slow relaxation of magnetization. These differences are most likely due to the different Dy–O–Dy angles observed for the respective cores.