A Combined Synthetic, Magnetic, and Theoretical Study on Enhancing Ligand-Field Axiality for Dy(III) Single-Molecule Magnets Supported by Ferrocene Diamide Ligands

摘要

Molecular design is crucial for improving the performanceof single-moleculemagnets (SMMs). For dysprosium(III) SMMs, enhancing ligand-field axialityis a well-suited strategy to achieve high-performance SMMs. We synthesizeda series of dysprosium(III) complexes, (NNTIPS)DyBr(THF)(2) (1, NNTIPS = fc((NSiPr3)-Pr- i )(2); fc = 1,1 '-ferrocenediyl,THF = tetrahydrofuran), [(NNTIPS)Dy(THF)(3)][BPh4] (2), (NNTIPS)DyI(THF)(2) (3), and [(NNTBS)Dy(THF)(3)][BPh4] (4, NNTBS = fc((NSiBuMe2)-Bu- t )(2)), supported by ferrocene diamideligands. X-ray crystallography shows that the rigid ferrocene backboneenforces a nearly axial ligand field with weakly coordinating equatorialligands. Dysprosium(III) complexes 1-4 all exhibit slow magnetic relaxation under zero fields and possesshigh effective barriers (U (eff)) around1000 K, comparable to previously reported (NNTBS)DyI(THF)(2) (5). We probed the influences of structuralvariations on SMM behaviors by theoretical calculations and foundthat the distribution of negative charges defined by r (q), i.e., the ratio of the charges on the axial ligandsto the charges on the equatorial ligands, plays a decisive role. Moreover,theoretical calculations on a series of model complexes 1 '-5 ' without equatorial ligands unveilthat the axial crystal-field parameters B (2) (0) are directly proportional to the N-Dy-Nangles and support the hypothesis that enhancing the ligand-fieldaxiality could improve SMM performance. @@@ Aseries of dysprosium(III) and yttrium(III) complexes composedof strongly coordinating axial ferrocene diamide ligands and weaklycoordinating equatorial ligands were synthesized and characterized.All dysprosium(III) complexes show slow magnetic relaxation underzero fields and possess similar U (eff) around1000 K. Magnetic analysis and theoretical calculations unveil magneto-structuralcorrelations in this series, especially for the role of the substituentson nitrogen and the equatorial ligands.

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