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

A series of new Co-Ln heterometallic clusters formulated as [Co(2)Ln(4)(mu(3)-OH)(2)(piv)(4)(hmmp)(4)(ae)(2)]center dot (NO3)(2)center dot 2H(2)O (Ln = Eu (1), Gd (2), Tb (3), Dy (4), H(2)hmmp = 2-[(2-hydroxyethylimino)methyl]-6-methoxy-phenol, Hae = 2-aminoethanol, Hpiv = pivalic acid) were synthesized and characterized. X-ray crystallography reveals that each of them contains a heterometallic {Ln(4)Co(2)} core, which is supported by two mu(3)-hydroxide, four piv(-), four hmmp(2-) and two ae(-) ligands. The magnetic investigation indicates that 2 exhibits weak antiferromagnetic interactions between Gd-III 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 degrees 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.