Hexanuclear NiII4LnIII2 Complexes with SMM Behavior at Zero Field for Ln = Tb, Dy, Ho

Abstract

A mononuclear Ni(II) complex, [NiL2]·2H2O, was prepared by the reaction of a N2O2 donor monocondensed Schiff base ligand, 2-((3-aminopropylimino)methyl)-6-methoxyphenol (HL), with NiCl2·6H2O. The reaction of this complex with NiCl2·6H2O and LnCl3·6H2O (Ln = Gd, Tb, Dy, Ho) in a 1:1:1 molar ratio leads to four hexanuclear Ni4Ln2 complexes formulated as [{(NiL)2Gd}2(μ2-Cl)2(μ3-OH)4(OH2)4]Cl4·CH3CN·H2O (1), [{(NiL)2Tb}2(μ2-Cl)2Cl2(μ3-OH)4(OH2)2]Cl2·12H2O (2), [{(NiL)2Dy}2(μ2-Cl)2Cl2(μ3-OH)4(OH2)2]Cl2·16H2O (3), and [{(NiL)2Ho}2(μ2-Cl)2(μ3-OH)4(OH2)4]Cl4·CH3CN·1.8H2O (4). The Ln(III) centers are octacoordinated with a triangular-dodecahedral geometry, and the geometries around the Ni(II) centers are distorted octahedral in all four complexes. The temperature-dependent DC magnetic measurements reveal the existence of ferromagnetic interactions in all four complexes (1–4). The AC susceptibility measurements performed with and without an applied DC field show SMM behavior in complexes 2–4 with a single slow relaxation process in 2 (SR) but slow (SR) and fast (FR) relaxation processes in 3 and 4. The energy barriers of the relaxation times for the SR processes are ca. 13, 20, and 19 K in 2–4, respectively.