Family of Lanthanide–Manganese Heterometallic Metallacrowns: Syntheses, Structures, Magnetic Exchange, and Magnetocaloric Effects

Abstract

The intermetallic magnetic interaction is a key role for exploring magneto-structure relationship. Herein, a series of Mn-based clusters featuring metallacrowns with the formulas [MnIIMn4 III(L1)4(HL2)2(DMF)6]·4MeOH·3H2O (1), [GdMn4 III(L1)4(OAc)4]·H4TEA·2MeOH·H2O (2), [Gd4Mn4 III­(L1)4(HL2)2­(H2L1)4(OAc)4­(μ3-OH)2(DMF)2­(H2O)2]·4DMF·H2O·16MeOH·H3TEA (3), and [Gd6Mn4 III­Mn2 IV(L1)10(HL1)2­(H2L1)4(DMF)4­(H2O)4(MeOH)4]·4DMF·2MeOH·6H2O (4) (H3L1 = salicylhydroxamic acid, H2L2 = salicylic acid, MeOH = methanol, DMF = N,N-dimethylformamide, and H3TEA = triethylamine) were prepared using salicylhydroxamic acid as organic ligands. The structures of compounds 1–2, 3, and 4 featured 12-metallacrown-4, 16-metallacrown-6, and 28-metallacrown-10, respectively. Magnetic calculations showed that the obvious antiferromagnetic couplings of compounds 1–2 were mainly derived from MnIII···MnIII. For compound 3, the weak ferromagnetic couplings of GdIII···MnIII and MnIII···MnIII bridged through [M–O–N–M] manner were smaller than the antiferromagnetic couplings of GdIII···GdIII and GdIII···MnIII bridged by O atoms, resulting in the overall antiferromagnetic behavior. In compound 4, the weak ferromagnetic couplings of GdIII···MnIII/MnIII···MnIII/GdIII···MnIV/MnIII···MnIV bridged by the way of [M–O–N–M] were dominant. The abovementioned results revealed that the arrangement of metal ions displaying [M–N–O–M] is more likely to produce weak ferromagnetic coupling between metal ions, which is beneficial to the magnetocaloric effect (MCE). Meanwhile, compounds 3–4 showed considerable MCEs with a magnetic entropy change (−ΔS m) of 13.86 J kg–1 K–1 at 3.5 K, 7 T and 16.05 J kg–1 K–1 at 3 K, 7 T, respectively.