Defect-Dicubane Ni₂Ln₂ (Ln = Dy, Tb) Single Molecule Magnets

Two pairs of Ni₂Dy₂ and Ni₂Tb₂ complexes, [Ni₂Ln₂(L)₄(NO₃)₂(DMF)₂] {Ln = Dy (1), Tb (2)} and [Ni₂Ln₂(L)₄(NO₃)₂(MeOH)₂]·3MeOH {Ln = Dy (3), Tb (4)} (H₂L is the Schiff base resulting from the condensation of o-vanillin and 2-aminophenol) possessing a defect-dicubane core topology were synthesized and characterized. All four complexes are ferromagnetically coupled, and the two Dy-analogues are found to be Single Molecule Magnets (SMMs) with energy barriers in the range 18–28 K. Compound 1 displays step-like hysteresis loops, confirming the SMM behavior. Although 1 and 3 show very similar structural topologies, the dynamic properties of 1 and 3 are different with blocking temperatures (3.2 and 4.2 K at a frequency of 1500 Hz) differing by 1 K. This appears to result from a change in orientation of the nitrate ligands on the Dy^III ions, induced by changes in ligands on Ni^II.