Assembly of chiral 3d-4f wheel-like cluster complexes with achiral ligands: single-molecule magnetic behavior and magnetocaloric effect

Under solvothermal conditions, five chiral 3d-4f wheel-like heterometallic hexanuclear clusters with the Schiff base ligand [H2L =N,N '-bis(3-methoxysalicylidene)-1,3-diaminopropane] were synthesized by thein situligand reaction of the 1,3-bis(2-pyridyl)-1,3-propanedione and generated the pyridine-2-carboxylate (PyCO2-) that acted as a bridging ligand; a peroxide anion formed by the spontaneous reduction of dioxygen plays a key role in the assembly of these complexes. The five isomeric 3d-4f heterometallic complexes, with molecular formula [M(3)Ln(3)(O-2)L-3(PyCO2)(3)](OH)(2)(ClO4)(2)center dot 8H(2)O (M = Zn, Cu; Ln = Dy, Tb, Gd) represent the first anion-orientated chiral heterometallic cluster complexes composed of achiral components. Except for complex1, we randomly measured the crystal structure of one of the two chiral enantiomers of complexes2-5. Magnetic measurements show that the Zn(3)Gd(3)complex exhibits a moderate magnetocaloric effect. The Cu(3)Tb(3)complex is a single-molecule magnet (SMM) with an energy barrier (U-eff/k) value of 31.7(0.3) K under zero dc field, which is a larger value for Cu-Tb SMMs; the other three compounds Zn3Dy3, Zn3Tb3, and Cu(3)Dy(3)exhibit field-induced magnetic relaxation. TheU(eff)/kvalue of Zn3Dy3[>100 K,H-dc= 1000 Oe] is obviously larger than those of equilateral triangular Dy(3)complexes (<= 62 K).