In Situ Reaction and Coordination Site Regulation to Form Binuclear Dysprosium Complexes with Different Connections and Magnetic Properties

How to construct and control multinuclear dysprosium clusters with excellent single-molecule magnet (SMM) properties have been a great concern and challenge. Herein, we obtained two pyridine monoacylhydrazone ligands that are isomers of each other by a solvothermal in situ reaction, and the position of the N coordination site on the pyridine ring was controlled to achieve two binuclear dysprosium-based complexes with different SMM performance and cluster core connections. Specifically, 2-pyridinecarboxylhydrazide and 1-methyl-1H-imidazole-2-carbaldehyde undergo an in situ Schiff base reaction at 80 degrees C solvothermal conditions and coordinate with Dy(NO3)(3)middot6H(2)O to obtain a binuclear dysprosium complex [Dy-2(L-1)(2)(NO3)(4)(H2O)](HL1)middot(H2O)(2)(CH3CN)(2) (1) with a Dy2O2 cluster nucleus. In addition, the mononuclear dysprosium complex [Dy(L-2)(NO3)(2)(H2O)(2)]middotCH(3)CN (2) and binuclear dysprosium complex [Dy(L-2)(2)(NO3)](2)middot4CH(3)CN (3) were obtained by changing 2-pyridinecarboxylhydrazide to 3-pyridinecarboxylhydrazide and adjusting the solvent ratio of the reaction system. In the structure of binuclear dysprosium complex 3, DymiddotmiddotmiddotDy is not bridged by O atoms and has a long distance. Magnetic studies show that complexes 1-3 all exhibit field-induced SMM behaviors. Under the external field, the inversion energy barriers and relaxation times of complexes 1-3 are U-eff = 22.40(6) K and tau(0) = 7.33(1) x 10(-5) s (1), U-eff = 16.38(1) K and tau(0) = 1.25(6) x 10(-4) s (2), and U-eff = 59.25(9) K and tau(0) = 6.30(1) x 10(-5) s (3), respectively. This work demonstrates that the design of the coordination sites for organic ligands is an effective strategy to tune the SMM properties of the polynuclear dysprosium complexes. It also provides a vivid example for the directional construction of multinuclear dysprosium complexes with SMM behaviors by in situ reactions in a black-box system.