Pentanuclear Heterometallic {Ni2Ln3} (Ln = Gd, Dy, Tb, Ho) Assemblies. Single-Molecule Magnet Behavior and Multistep Relaxation in the Dysprosium Derivative

The reaction between Ln­(III) chloride and NiCl2·4H2O salts in presence of a multidentate sterically unencumbered ligand, (E)-2,2′-(2-hydroxy-3-((2-hydroxy­phenyl­imino)­methyl)-5-methyl­benzyl­azanediyl)­diethanol (LH4) leads to the synthesis of four isostructural pentanuclear hetereometallic complexes [Ni2Dy3(LH)4]Cl (1), [Ni2Gd3(LH)4]Cl (2), [Ni2Tb3(LH)3(LH2)]­Cl2 (3), [Ni2 Ho3 (LH)3 (LH2)]­Cl2 (4) with unprecedented topology. Here the two compounds 1 are 2 are monocationic and crystallize in chiral space group, P212121 whereas compounds 3 and 4 are dicationic and crystallize in achiral space group P21/n. The total metal framework, {Ni2Ln3} unit is held by four triply deprotonated ligands [LH]3– in 1 and 2 whereas in case of 3 and 4 three triply deprotonated [LH]3– and one doubly deprotonated [LH2]2– ligands are involved. In these complexes both the lanthanide ions and the nickel­(II) ions are doubly bridged and the bridging is composed of oxygen atoms derived from either phenolate or ethoxide groups. The analysis of SQUID measurements reveal a high magnetic ground state and a slow relaxation of the magnetization with two relaxation regimes for 1. For the thermally activated regime we found an effective energy barrier of Ueff = 85 K. Micro Hall probe loop measurements directly proof the single-molecule magnet (SMM) nature of 1 with a blocking temperature of TB = 3 K and an open hysteresis for sweep rates faster than 50 mT/s.