Enhancing magnetic relaxation through subcomponent self-assembly from a Dy₂ to Dy₄ grid

The subcomponent self-assembly of 4,6-dihydrazinopyrimidine and o-vanillin/salicylaldehyde with different Dy^III salts leads to the formation of Dy₂ (1-3) and grid-like Dy₄ (4) compounds with formulas of [Dy₂L(DMF)₄(NO₃)₄]·2DMF (1), [Dy₂L₂(CH₃COO)₄(CH₃OH)₂]·10H₂O (2), [Dy₂L'₂(CH₃COO)₄(CH₃OH)₂]·2H₂O·2CH₃OH (3) and [Dy₄Na₂L₂(μ₂-OH)₂(PhCOO)₈(CH₃OH)(H₂O)]·CH₃CN·2CH₃OH·7H₂O (4). In all cases, the Dy^III ions are nine coordinate but the different features of coordinated solvent molecules and anions result in diverse coordination geometries in their respective structures. Notably, by introducing various axial coordinating anions with different electronegativities (NO₃^-, CH₃COO^- and C₆H₅COO^-), the effective energy barriers were progressively enhanced (52-207 K) in this system. Detailed magnetic studies for these complexes revealed obvious magnetic interactions in complex 1 and clear single molecule magnet (SMM) behavior with anisotropy barriers of 52, 56 and 58.4 K for 1-3, respectively. Moreover, we find that the incorporation of benzoates into the axial position of the Dy^III ions in complex 4 leads to the occurrence of two clear distinct relaxation processes, with energy barriers of 94.9 and 207.2 K, respectively. This result presents an example of the effects of axial coordinating anions on the SMM behavior, providing a valid route towards enhancing the slow magnetic relaxation of 4f based SMMs via incorporating diverse coordination anions into the subcomponent self-assembly system.