Synthesis, structures, and magnetic properties of a series of new heterometallic hexanuclear Co2Ln4(Ln = Eu, Gd, Tb and Dy) clusters

Abstract

A series of new Co–Ln heterometallic clusters formulated as [Co2Ln4(μ3-OH)2(piv)4(hmmp)4(ae)2]·(NO3)2·2H2O (Ln = Eu (1), Gd (2), Tb (3), Dy (4), H2hmmp = 2-[(2-hydroxyethylimino)methyl]-6-methoxyphenol, Hae = 2-aminoethanol, Hpiv = pivalic acid) were synthesized and characterized. X-ray crystallography reveals that each of them contains a heterometallic {Ln4Co2} core, which is supported by two μ3-hydroxide, four piv−, four hmmp2− and two ae− ligands. The magnetic investigation indicates that 2 exhibits weak antiferromagnetic interactions between GdIII ions, and a large MCE value of 24.9 J kg−1 K−1, while 4 shows a fast relaxation of magnetization. The TGA and VT-PXRD measurements suggest that all the compounds show good thermal stability and can be stable up to about 220 °C. In addition, to address the influence of the Gd–O–Gd angles on the magnetic properties, compound 2 was compared with a series of compounds involving different bridges between GdIII ions. The comparison reveals that the tiny difference in the Gd–O–Gd angles favors different magnetic coupling.