Single-Molecule Magnet Behavior and Magnetocaloric Effect in Ferromagnetically Coupled Ln-Ni-Ni-Ln (Ln = Dy and Gd) Linear Complexes†

A new type of linear tetranuclear Ln-Ni-Ni-Ln (Ln = Dy 1, Gd 2) complexes have been prepared using multidentate ligand N,N’-bis(3-methoxysalicylidene)-1,3diaminobenzene having two sets of NO and OO’ coordination pockets which can selectively accommodate Ni and Ln ions, respectively. The X-ray structure analysis reveals that the Ni ions are bridged by phenylenediimine groups forming a twelvemembered metallacycle in the central body of the complex, whereas the Ln ions are located at both sides of the metallacycle and linked to the Ni ions by diphenoxo bridging groups. Phenylenediimine and diphenoxo bridging groups transmit ferromagnetic exchange interactions between the two Ni ions but also between Ni and Ln ions, respectively. Complex 1 shows slow relaxation of the magnetization at zerofield and a thermal energy barrier Ueff =7.4 K with Hdc = 1000 Oe, whereas complex 2 exhibits an S = 9 ground state and significant magnetocaloric effect (-ΔSm = 18.5 J kg -1 K at T = 3 K and B = 5 T).