Assembly of Hydrazine-Bridged Cyclic FeIII4LnIII4 Octanuclear Complexes

The elaborate design and synthesis of three isomorphous cyclic octanuclear clusters [Fe(4)Ln(4)(L)(8)(H2O)(4)-(NO3)(4)](NO3)(4) (Ln = Dy (1 & BULL;5CH(3)CN & BULL;14H(2)O), Gd (2 & BULL; 5CH(3)CN & BULL;19H(2)O), Y (3 & BULL;6CH(3)CN & BULL;16H(2)O)) with the Schiff base ligand H2L (2-(hydroxyimino)propionic acid (dipyridin-2ylmethylene)hydrazide) have been achieved. The compartmental ligand H2L has N-3-inner and N2O-outer coordination sites, which chelate low-spin Fe(III) and Ln(III), respectively. The remaining coordination sites around the rare-earth ions are occupied by nitrate ions and water molecules. This is the first report on the use of a hydrazine group within a ligand to connect Fe-III and Ln(III) ions, which can not only stabilize the skeleton of the molecular ring but also transmit a weak antiferromagnetic interaction between Fe-III and Ln(III) (Ln = Dy, Gd) ions. ac magnetic susceptibility measurements under an external applied dc field of 1600 Oe reveal the SMM behavior of complex 1 with U-eff = 25.8 K. The magnitude of the magnetic exchange between Fe(III) and Gd(III) in complex 2 is evaluated to be 2J(FeGd) = -0.324 cm(-1); meanwhile, complex 2 shows a moderate magnetocaloric effect (MCE) with -& UDelta;S-m = 17.06 J kg(-1) K-1 under 5 T at 2 K.

Automated summary

The successful design and synthesis of three isomorphous cyclic octanuclear clusters with unique ligands resulted in clusters with strong magnetic properties.