A new family of Fe4Ln4 (Ln = DyIII, GdIII, YIII) wheel type complexes with ferromagnetic interaction, magnetocaloric effect and zero-field SMM behavior

In this work, we report three isostructural Fe(4)Ln(4) wheel type complexes with molecular formula [{Fe-4(dea)(4)Dy-4(deaH)(8)(mu(2)-OMe)(4)}(NO3)(4)]center dot 4(H2O) (1), [{Fe-4(dea)(4)Gd-4(deaH)(8)(mu(2)-OMe)(4)}center dot(NO3)(4)]center dot 4(H2O)center dot 4(MeOH) (2) and [{Fe-4(dea)(4)Y-4(deaH)(8)(mu(2)-OMe)(4)}(NO3)(4)]center dot 4(H2O)center dot 6(MeOH) (3), (where dea = diethanolamine). Detailed structural analysis discloses that the 4Ln(III) and 4Fe(III) ions are connected alternatively in a cyclic arrangement through the oxo-bridging of methanol and diethanolamine molecules. The detailed magnetic measurements reveal the presence of ferromagnetic exchange interactions between the Ln(III) and Fe-III centers in complexes 1 and 2, whereas a weak antiferromagnetic interaction is observed between Fe-III centers in complex 3. In addition, complex 1 shows slow magnetic relaxation behavior (U-eff = 9.8 K) under zero field and a remarkable entropy change was observed for complex 2 at 7 T magnetic field (magnetocaloric effect = 31.15 J kg(-1) K-1). The ab initio calculations disclose the presence of strong axial anisotropy and a minimum transverse component (g(x) = 0.0024, g(y) = 0.0062, and g(z) = 19.82) in the ground state of each Dy-III ion for complex 1. It was also found that the local anisotropy axis on each Dy-III ion is arranged in a vortex-like structure as observed in single molecule toroics (SMTs). From BS-DFT calculations, it was found that the exchange interactions between Fe-Ln metal centers mainly follow the charge transfer process between 3d and 4f orbitals.

Automated summary

This work presents three isostructural Fe(4)Ln(4) wheel type complexes with different magnetic properties and structural characteristics, including ferromagnetic and antiferromagnetic interactions, slow magnetic relaxation, and remarkable magnetocaloric effects. The detailed analysis of magnetic measurements and ab initio calculations provide insights into the exchange interactions between Fe-Ln metal centers mainly through charge transfer process between 3d and 4f orbitals.