Linear {NiII-LnIII-NiII} Complexes Containing Twisted Planar Ni(μ-phenolate)2Ln Fragments: Synthesis, Structure, and Magnetothermal Properties

Sequential reaction of a multisite LH4 ligand {2-[2-hydroxy-3-(hydroxymethyl)-5-methylbenzylideneamino]-2-methylpropane-1,3-diol} with appropriate lanthanide salts followed by the addition of Ni(NO3)(2)center dot 6H(2)O in a 4:1:2 stoichiometric ratio in the presence of triethylamine afforded four heterobimetallic trinuclear complexes [Ni2Gd(LH3)(4)]center dot 3NO(3)center dot 3MeOH center dot H2O center dot CH3CN (1), [Ni2Tb(LH3)(4)]center dot 3NO(3)center dot 3MeOH center dot CH3CN (2), [Ni2Dy(LH3)(4)]center dot 3NO(3)center dot 3MeOH center dot H2O center dot CH3CN (3), and [Ni2Ho(LH3)(4)]center dot 3NO(3)center dot 3MeOH center dot H2O center dot CH3CN (4). Complexes 1-4 possess linear trimetallic cores with a central lanthanide ion. Magnetic studies revealed a predominant ferromagnetic interaction between the Ni and Ln centers. Alternating current susceptibility measurements of complex 3 showed a small frequency dependence of the out-of-phase signal, chi ''(M), under zero direct current field, but without achieving a net maximum above 2 K. Magnetic studies on 1 revealed that it has a significant magnetocaloric effect.