DMF-Driven Modulation of Coordination Geometry and SMM Performance in Dinuclear Dysprosium(III) Complexes

Given the favorable nature of pentagonal-bipyramidal coordination geometry in achieving high-performance dysprosium(III)-based single-molecule magnets (SMMs), an equatorial pentadentate chelator of pyridyl-2,6-diacetylbis(salicylhydrazone) (H4Pdas) was employed in this study. The attempted replacement of Cl– in [Et3NH][Dy(H2Pdas)Cl2] by Ph3SiO– in various solvents with different bases gave two Dy(III) complexes, namely, [Dy2(H2Pdas)2(OSiPh3)2]·CH2Cl2 (Dy2) and [Dy2(H2Pdas)2(DMF)2(OSiPh3)2] (Dy2-DMF). Both Dy2 and Dy2-DMF have similar dinuclear skeletons with their two Dy(III) ions linked by a pair of H2Pdas2– linkers in a μ2-η1:η5 bridging mode. The major difference between Dy2-DMF and Dy2 is that there is one more DMF molecule for each Dy(III) ion in Dy2-DMF than in Dy2, which leads to pentagonal bipyramidal and triangular dodecahedral Dy(III) coordination geometries for Dy2 and Dy2-DMF, respectively. These structural differences between Dy2 and Dy2-DMF resulted in their different SMM performances with energy barriers of 51(1) and 31.8(3) K for Dy2 and Dy2-DMF, respectively. It demonstrated that the additional coordination of DMF in the dinuclear complex significantly tunes the structural parameters such as coordination geometry and bond angles, consequently influencing the magnetic anisotropy and SMM performance, which was further rationalized by CASSCF-SO theoretical calculations.