A series of triple-stranded lanthanide(III) helicates: Syntheses, structures and single molecular magnets

Abstract

Bis-β-diketones have been proven to be effective for the construction of multiple-stranded helicates, where there commonly are two distinct Ln3+ centers with subtle geometric difference. In this study, a series of triple-stranded helicates [Ln2(BTB)3(DME)2]·C6H14 have been prepared with the ligand H2BTB and trivalent metallic ions, respectively [Ln=La (1), Ce (2), Pr (3), Eu (4), Dy (5), Ho (6) and Yb (7), H2BTB=4,4′-bis(4,4,4-trifluoro-1,3-dioxobutyl)biphenyl and DME=dimethoxyethane]. All products have been fully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction analyses. Structural analysis reveals that 1–7 are isostructurally crystallized in the orthorhombic space group of Pna21 and each Ln3+ ion is ligated to six O atoms of three BTB ligands and two O atoms of one DME molecule. Interestingly, DME molecule as a chelator to the Ln3+ centers has played a unique role in the crystallization of the triple-stranded helicate 1–7. Magnetic measurement shows that 5 displays significant single-molecule magnetic property, exhibiting magnetic slow relaxation. And the large separation between Dy3+ ions in the same helicates leads to two distinct magnetic relaxation processes.