Impact of anionic co-ligands on nuclearity and single-molecule magnetism in a {Co III2DyIII} trimeric and two {Co III2Dy III2} tetrameric complexes†

We report herein the use of a new Schiff base ligand, 3-((2-hydroxy-3-methoxy-5-methylbenzylidene)amino)propane-1,2-diol (H₃L), as a racemate, derived from the condensation reaction of methyl-substituted o-vanillin and (±)-3-amino-1,2-propanediol, to explore Co–Dy coordination chemistry. This investigation led to the isolation of a trinuclear complex, [Co^III₂Dy^III(HL)₄](NO₃)·CH₃CN·4CH₃OH·2H₂O (1), and two tetranuclear complexes, [Co^III₂Dy^III₂(HL)₂(μ₃-OH)₂(μ-OAc)₂(OAc)₄]·6CH₃CN (2) and [Co^III₂Dy^III₂(HL)₂(μ₃-OH)₂(μ-mnba)₂(mnba)₄]·0.5H₂O (3), where Hmnba is m-nitrobenzoic acid. AC magnetic susceptibility studies revealed that all three complexes exhibit zero-field slow magnetic relaxation behavior, which is further enhanced under an applied magnetic field, with U_eff values of 32 K, 200 K, and 28 K for 1–3, respectively. Notably, complex 1 is an important inclusion within the limited family of trinuclear Co^III₂Dy^III complexes that display zero-field SMM behavior. Meanwhile, complexes 2 and 3 are valuable additions to the expanding family of tetranuclear Co^III₂Dy^III₂ clusters with butterfly-like topologies, as only a single type-I butterfly example has been reported thus far, in which Dy^III ions occupy the wingtip positions. To interpret the experimental magnetic data, ab initio calculations were performed, providing deeper insights into the magnetic anisotropy and relaxation dynamics of these systems. Overall, this study not only reports that complex 2 displays the highest U_eff value among the Co^III₂Dy^III and Co^III₂Dy^III₂ families but also highlights the influence of anionic co-ligands on nuclearity and magnetic dynamics, further enriching the field of Co^III–Dy^III-based SMMs.