Slow Magnetic Relaxation in a Co₂ Dy Trimer and a Co₂ Dy₂ Tetramer

The combination of Co(III) and Dy(III) with a compartmental Schiff base ligand (H₃ L=3-[(2-Hydroxy-3-methoxy-benzylidene)-amino]-propane-1,2-diol), presenting three different coordinating pockets, has allowed the synthesis of two novel Co(III)-Dy(III) complexes: [Co₂ Dy(HL)₄ ]NO₃  ⋅ 2CH₃ CN (1), a rare example of trinuclear linear Co^III ₂ Dy^III complex (and the first with slow relaxation of magnetization in absence of a DC field) and [Co₂ Dy₂ (μ₃ -OH)₂ (HL)₂ (OAc)₆ ] ⋅ 4.6H₂ O (2), the first tetranuclear Co^III ₂ Dy^III ₂ cluster with a rhomb-like structure where the Co(III) ions are connected along the short diagonal of the rhomb. 1 presents two different relaxation processes: a fast relaxation dominated by Quantum tunnelling (QT) and a slow relaxation with an energy barrier of 40 K. 2 shows two close relaxation processes without applied DC fields that follow QT and Orbach mechanisms whereas for H_DC =500 Oe, the QT is cancelled and a direct term appears. Here we present the synthesis, X-ray structure and magnetic characterization of these two Co(III)-Dy(III) single-ion/molecule magnets.