Field-induced slow magnetic relaxation in chiral seven-coordinated mononuclear lanthanide complexes

Abstract

Four couples of enantiomerically pure chiral seven-coordinated mononuclear lanthanide complexes, [(L_OEt)Dy((R,R)-Salphen)]₂·3H₂O (1, L_OEt = [(Cp)Co(P(O)(OEt)₂)₃], Cp = cyclopentadiene, Salphen = N,N′-1,2-diphenylethylenebis(salicylideneiminato) dianion), [(L_OEt)Dy((S,S)-Salphen)]₂·3H₂O (2), [(L_OEt)Dy((R,R)-5-Cl-Salcy)]·CH₃OH·1/8H₂O (3, Salcy = N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion), [(L_OEt)Dy((S,S)-5-Cl-Salcy)]·CH₃OH·1/8H₂O (4), [(L_OEt)Tb((R,R)-5-Cl-Salcy)]·CH₃OH·1/8H₂O (5), [(L_OEt)Tb((S,S)-5-Cl-Salcy)]·CH₃OH·1/8H₂O (6), [(L_OEt)Ho((R,R)-5-Cl-Salcy)]·CH₃OH·1/8H₂O (7) and [(L_OEt)Ho((S,S)-5-Cl-Salcy)]·CH₃OH·1/8H₂O (8), have been successfully synthesized by using tetradentate chiral salen-type ligands and the Kläui's tripodal ligand of L_OEt. Structural analyses reveal that all compounds have a typical double-decker sandwich structure, and the Ln(III) ions exhibit a rare seven-coordinated mode, situating in a distorted monocapped triangular prism polyhedron. Circular dichroism (CD) spectra confirm the enantiomeric nature of the optically active complexes and demonstrate that the chirality is successfully transferred from the ligand to the coordination environment of the Ln(III) ions. Field-induced slow relaxation of the magnetization is observed for complexes 1–4, suggesting that they can be rare chiral single-ion magnets (SIMs) based on the seven-coordinated lanthanide ions.