Modulating the Magnetic Dynamics of Five‐Coordinate DyIII Single‐Molecule Magnets by the Substitution Effect on the Axial Ligand

Two five‐coordinate mononuclear Dy III single‐molecule magnets [(Trapen TMS )Dy(L)] (Trapen=tris(2‐aminobenzyl) amine; TMS=SiMe 3 ; L=OPMe 3 1 , OPEt 3 2 ) have been synthesized by the reaction of [(Trapen TMS )Dy(THF)] and OPMe 3 , OPEt 3 , respectively. The molecular structures of 1 and 2 were fully established by single crystal X‐ray diffraction. The centre Dy III ions of both complexes exhibit distorted triangular bipyramid geometries, varying with different neutral ligands L on the apex. The Trapen TMS ligand forms the pyramid base of the trigonal bipyramid. Subtle structural modifications of the axial O‐ligand terminal substituent result in different dynamic magnetic behaviors. Magnetic data analysis reveals that 1 and 2 exhibit the characteristic behavior of SMM without a dc field, accompanying an unambiguous quantum tunneling of the magnetization. Field‐induced slow magnetic relaxation was observed for 1 and 2 under an applied bias dc field of 1000 Oe, the relaxation energy barriers are 107 K and 88 K for 1 and 2 , respectively. We have investigated the differences in magnetism and magnetic anisotropy between the two complexes by ab initio calculations.