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

A mononuclear complex [Dy(phenN6)(HL')2]PF6.CH2Cl2 (H2L' = R/S-1,1'-binaphthyl-2,2'-diphenol) with local D6h symmetry was synthesized. Structural determination shows that Dy3+ was wrapped in the coordination cavity of the neutral hexaaza macrocyclic ligand phenN6, and the whole coordination plane was not planar. The axial positions are coordinated by two phenoxy groups of binaphthol in the trans form. The local configuration of Dy3+ is close to the regular hexagonal bipyramid D6h configuration. The axial Dy-Ophenoxy distances are 2.189(5) and 2.144 (5) Å, respectively, and the bond lengths of Dy-N on the equatorial plane are in the range of 2.525 (7)–2.719 (5) Å. The axial Ophthalmoxy-Dy-Ophthalmoxy bond angle is 162.89(18), which deviates from the ideal linearity. Under the excitation of 320 nm, the characteristic emission peak of naphthalene ring appeared at 360 nm in the complex. The results of AC magnetic susceptibility test show obvious temperature dependence and frequency dependence in the AC magnetic susceptibility signals, typical of single-molecule magnetic behavior. The Cole-Cole curve in the temperature range of 6.0-28.0 K is fitted by the formula including Orbach and Raman relaxation mechanisms, giving the effective energy barrier Ueff = 300.2 K and the relaxation time τ0 = 6.7×10-7 s.