Heptanuclear heterometallic Cu5Ln2(Ln = Gd, Tb) complexes: Synthesis, crystal structures, and magnetic properties studies

The reaction of Ln(NO3)(3)center dot 6H(2)O (Ln = Gd, Tb) and Cu(O2CMe)(2)center dot H2O with the polydentate Schiff base ligand OH C10H7 CH=NC(C2H5)(CH2OH)(2) (H3L) in Me2CO afforded the heptanuclear heterometallic complexes [CusLn(2)(O2CMe)(2)(NO3)(4)(L)(2)(HL)(2)] (Ln = Gd (1), Tb (2)) which were characterized by single-crystal X-ray crystallography (1) and powder XRD measurements (2). Both complexes are isomorphous and consist of a central core {Cu(5)(II)Ln(2)(III)(mu(3)-OR)(6)(mu(3)-O2CMe)(2))8(+) described as two distorted centrosymmetrically related cubane subunits, (Cu(3)(II)Ln(III)(mu(3)-OR)(3)(mu(3)-O2CMe)}(5+), with the common apex, Cu(1), residing on an inversion center. Peripheral ligation and bridging is provided by two triply and two doubly deprotonated Schiff base ligands, two 14-acetates and four chelate nitrates. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic interactions for both complexes. The magnetocaloric effect of 1 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was found equal to 15.7 J kg(-1) K-1 at 2 K for AH = 5 T. Ac susceptibility measurements of 2 revealed slow magnetic relaxation process suggesting the presence of single-molecule magnet behavior. (C) 2018 Elsevier Ltd. All rights reserved.