A series of Salen-type homodinuclear lanthanide complexes and their slow magnetic relaxation in Dy2 and Ho2

A series of homodinuclear lanthanide complexes, namely, Ln₂(L)₂(MeOH)₂(NO₃)₂] Ln = Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), and Ho ( 4 )], were synthesized by the reaction of Salen-type ligand, namely N, N′-bis(5-bromosalicylidene)ethane-1,2-diamine (H₂L), with lanthanide salts in methanol and acetonitrile solution. The two Ln^III ions in 1 – 4 are linked by two O_phenoxo atoms of two L^2? ligands to build a dinuclear skeleton. The eight-coordinate Ln^III center adopts a triangular dodecahedron geometry of D_2d symmetry. Theoretical calculations revealed that antiferromagnetic interactions exist in those complexes. Dynamic magnetic properties studies indicate that the Dy₂ complex behaves as a single-molecule magnet with an anisotropy barrier of U_eff ≈ 47.68 K and a pre-exponential factor τ₀ = 3.17 × 10^?6 s under a zero applied field, whereas the Ho₂ complex exhibits a fast tunneling relaxation process that is rationalized through ab initio calculations.