Hexanuclear Ni4IILn2III Complexes with SMM Behavior at Zero Field for Ln = Tb, Dy, Ho

A mononuclear Ni(II) complex, [NiL2]center dot 2H(2)O, was prepared by the reaction of a N2O2 donor monocondensed Schiff base ligand, 2-((3-aminopropylimino)methyl)-6-methoxyphenol (HL), with NiCl2 center dot 6H(2)O. The reaction of this complex with NiCl2 center dot 6H(2)O and LnCl(3)center dot 6H(2)O (Ln = Gd, Tb, Dy, Ho) in a 1:1:1 molar ratio leads to four hexanuclear Ni4Ln2 complexes formulated as [{(NiL)(2)Gd}(2)(mu(2)-Cl)(2)(mu(3)-OH)(4)(OH2)(4)]Cl-4 center dot CH3CN center dot H2O (1), [{(NiL)(2)Tb}(2)(mu(2)-Cl)(2)Cl-2(mu(3)-OH)(4)(OH2)(2)]Cl-2 center dot 12H(2)O (2), [{(NiL)(2)Dy}(2)(mu(2)-Cl)(2)Cl-2(mu(3)-OH)(4)(OH2)(2)]Cl-2 center dot 16H(2)O (3), and [{(NiL)(2)Ho}(2)(mu(2)-Cl)(2)(mu(3)-OH)(4)(OH2)(4)]Cl-4 center dot CH3CN center dot 1.8H(2)O (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.