Unprecedented homochiral 3D lanthanide coordination polymers with triple-stranded helical architecture constructed from a rigid achiral aryldicarboxylate ligand

Abstract

Eight homochiral lanthanide coordination polymers, namely [Ln₂L₃(H₂O)₂]_n·4nH₂O [Ln = Sm (1); Eu (2); Gd (3); Tb (4); Dy (5); Ho (6); Er (7); Yb (8)], based on an achiral rigid ligand, 5-[(pyridin-4-ylmethyl)amino]-isophthalic acid (H₂L), have been hydrothermally prepared and characterized by single X-ray diffraction, elemental analysis, infrared spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and circular dichroism spectroscopy. Compounds 1–8 featured three-dimensional frameworks with triple-stranded helical chains, exhibiting a topological structure with the Schläfli symbol {4⁵·6·10⁴}{4⁵·6}. Solid-state circular dichroism (CD) spectroscopy revealed the occurrence of spontaneous chiral symmetry breaking during crystallization and that the origin of chirality might be the helicity. Furthermore, luminescence and second harmonic generation (SHG) activity have been studied. Compound 5 showed SHG activity. Compounds 1, 2 and 4 displayed characteristic luminescence stemming from the trivalent lanthanides.