Chiral Pseudo-D6h Dy(III) Single-Molecule Magnet Based on a Hexaaza Macrocycle

A mononuclear complex [Dy(phenN₆)(HL')₂]PF₆·CH₂Cl₂ (H₂L' = <i>R</i>/<i>S</i>-1,1'-binaphthyl-2,2'-diphenol) with local <i>D</i>_6h symmetry was synthesized. Structural determination shows that Dy³⁺ was encapsulated within the coordination cavity of the neutral hexaaza macrocyclic ligand phenN₆, forming a non-planar coordination environment. The axial positions are occupied by two phenoxy groups of binaphthol in the <i>trans</i> form. The local geometry of Dy³⁺ closely resembles a regular hexagonal bipyramid <i>D</i>_6h configuration. The axial Dy-O_phenoxy distances are 2.189(5) and 2.145(5) Å, respectively, while the Dy-N bond lengths in the equatorial plane are in the range of 2.524(7)-2.717(5) Å. The axial O_phthalmoxy-Dy-O_phthalmoxy bond angle is 162.91(17)°, which deviates from the ideal linearity. Under the excitation at 320 nm, the complex exhibits a characteristic emission peak at 360 nm, corresponding to the naphthalene ring. The AC susceptibility measurements under an applied DC field of 1800 Oe show distinct temperature-dependent and frequency-dependent AC magnetic susceptibility, typical of single-molecule magnetic behavior. The Cole-Cole plot in the temperature range of 6.0-28.0 K was fitted using a model incorporating Orbach and Raman relaxation mechanisms, giving an effective energy barrier of <i>U</i>_eff = 300.2 K. Theoretical calculations on complex <b>1</b> reveal that the magnetization relaxation proceeds through the first excited Kramers doublets with a calculated magnetization blocking barrier of 404.1 cm^-1 (581.4 K).