Extending The Family Of Heptanuclear Heterometallic Cu(5)Ln(2) (Ln = Gd, Tb, Dy) Complexes: Synthesis, Crystal Structures, Magnetic And Magnetocaloric Studies

The reaction of Ln(NO3)(3)center dot 6H(2)O (Ln = Gd, Tb, Dy) and Cu(O2CMe)(2)center dot H2O with the polydentate Schiff base ligands OH-C10H6-CH=NC(R)(CH2OH)(2) (R = CH3, H(3)L1; R = C2H5, H(3)L2) in Me2CO afforded the heptanuclear heterometallic complexes [Cu(5)Ln(2)(O2CMe)(2)(NO3)(4)(L1)(2)(HL1)(2)(Me2CO)(2)] (Ln = Gd (1), Tb (2), Dy (3)) and [Cu(5)Ln(2)(O2CMe)(2)(NO3)(4)(L2)(2)(HL2)(2)] = Gd (4), Tb (5), Dy (6)). Crystallographic studies revealed that complexes 1-3 and 4-6 consist of a central core {Cu(5)(II)Ln(2)(III)(mu(3)-OR)(6)(mu(3)-O2CMe)(2)}(8+) described as two distorted cubane subunits, {Cu(3)(II)Ln(2)(III)(mu(3)-OR)(6)(mu(3)-O2CMe)}(5+), with a Cu-II ion in the common apex. Peripheral and bridging ligation is provided by two triply and two doubly deprotonated Schiff base ligands, two mu(3)-acetates and four chelating nitrates. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic interactions in all complexes. The magnetocaloric effect of 1 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was 16.3 J kg(-1) K-1 at 2 K for Delta H = 5 T. Ac susceptibility measurements of 2, 3 and 6 revealed slow magnetic relaxation processes suggesting the presence of single-molecule magnet behavior. (C) 2019 Elsevier Ltd. All rights reserved.