Synthesis, structures and magnetic properties of cyano- and amide-bridged FeIII-LnIII tetranuclear heterometallic clusters

Three FeIII2LnIII2 tetranuclear heterometallic clusters, [H4LGd(H2O)Tp*Fe(CN)3]2·8H2O·2MeOH (1) and [H4LLn(MeOH)Tp*Fe(CN)3]2·6MeOH·2MeCN (Ln = Tb and Dy for 2 and 3, respectively, H6L = N,N′-(2,6-pyridine-dicarboxyl)-disalicylhydrazide, Tp* = hydridotris(3,5dimethylpyrazol-1-yl)-borate), were synthesized by use of the [(Tp*)Fe(CN)3]− unit as a metalloligand toward LnCl3 and H6L species. Structural analyses reveal that FeIII and LnIII ions in all complexes are connected to each other by one cyanide to form a heterobinuclear unit of [Ln(H4L)][(Tp*)Fe(CN)3], which is dimerized through Ln–N–C = O–Ln interaction. Magnetic susceptibility measurements show weak antiferromagnetic interactions between cyano-bridged FeIII and GdIII ions and amide-bridged GdIII ions are operative. Complex 1 displays the magnetocaloric effect with −ΔSmmax = 12.70 J·kg−1·K−1 at 4.0 K for ΔH = 7 T. No single-molecule magnetic properties are observed for 2 or 3 down to 1.8 K.