Single-molecule magnet behavior and magnetocaloric effect in ferromagnetically coupled LnIII-NiII-NiII-LnIII (LnIII = DyIII and GdIII) linear complexes

Abstract

New types of linear tetranuclear LnIII-NiII-NiII-LnIII (LnIII = Dy (1), Gd (2)) complexes have been prepared using the multidentate ligand N,N′-bis(3-methoxysalicylidene)-1,3-diaminobenzene, which has two sets of NO and OO′ coordination pockets that are able to selectively accommodate NiII and LnIII ions, respectively. The X-ray structure analysis reveals that the NiII ions are bridged by phenylenediimine groups forming a 12-membered metallacycle in the central body of the complex, whereas the LnIII ions are located at both sides of the metallacycle and linked to the NiII ions by diphenoxo bridging groups. Phenylenediimine and diphenoxo bridging groups transmit ferromagnetic exchange interactions between the two NiII ions and between the NiII and the LnIII ions, respectively. Complex 1 shows slow relaxation of the magnetization at zero field 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-1 at T = 3 K and ΔB = 5 T). © 2014 American Chemical Society.