Chiral six-coordinate Dy(<scp>iii</scp>) and Tb(<scp>iii</scp>) complexes of an achiral ligand: structure, fluorescence, and magnetism

Abstract

Two new chiral six-coordinate lanthanide complexes (1 for Dy and 2 for Tb) have been synthesized using the achiral flexible ligand H₂L (2,2'-[1,2-ethanediylbis[(methylimino)methylene]]bis[4,5-dimethylphenol]). Both complexes crystallize in the chiral P1 group space, and the enantiomers [Zn(L)Cl]₃Dy·MeOH·0.5H₂O (Λ-1), [Zn(L)Cl]₃Dy·1.5H₂O (Δ-1), [Zn(L)Cl]₃Tb·1.5H₂O (Λ-2) and [Zn(L)Cl]₃Tb·H₂O (Δ-2) are isolated in the reaction. Three [Zn(L)Cl]^- anions coordinate to the central lanthanide ion using two phenoxo oxygen atoms of L^2-, and the lanthanide ion has the coordination geometry of D₃. Complex 1 exhibits a field-induced slow magnetization relaxation, which is typical of a single-ion magnet (SIM). Ab initio calculations on complex 1 and studies on magneto-structural correlationship of six-coordinate Dy(iii) SIMs indicate that the small energy barrier of complex 1 might be related to the absence of a unique anisotropic axis for the regular octahedral coordination configuration of Dy(iii) and the high quantum tunneling gap between the ground states (m_J = ±15/2). Complex 2 displays green photofluorescence and triboluminescence.