A new family of Fe4Ln4 (Ln = DyIII, GdIII, YIII) wheel type complexes with ferromagnetic interaction, magnetocaloric effect and zero-field SMM behavior†
Abstract
In this work, we report three isostructural Fe4Ln4 wheel type complexes with molecular formula [{Fe4(dea)4Dy4(deaH)8(μ2-OMe)4}(NO3)4]·4(H2O) (1), [{Fe4(dea)4Gd4(deaH)8(μ2-OMe)4}·(NO3)4]·4(H2O)·4(MeOH) (2) and [{Fe4(dea)4Y4(deaH)8(μ2-OMe)4}(NO3)4]·4(H2O)·6(MeOH) (3), (where dea = diethanolamine). Detailed structural analysis discloses that the 4LnIII and 4FeIII 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 LnIII and FeIII centers in complexes 1 and 2, whereas a weak antiferromagnetic interaction is observed between FeIII centers in complex 3. In addition, complex 1 shows slow magnetic relaxation behavior (Ueff = 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 (gx = 0.0024, gy = 0.0062, and gz = 19.82) in the ground state of each DyIII ion for complex 1. It was also found that the local anisotropy axis on each DyIII 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.