Two- and three-dimensional lanthanide-based coordination polymers assembled by the synergistic effect of various lanthanide radii and flexibility of a new binicotinate-containing ligand: in situ synthesis, structures, and properties

Abstract

Ten lanthanide coordination polymers have been obtained by the hydrothermal reactions between 3,3′-dimethoxy-2,2′-bipyridine-6,6′-dicarboxylic acid (H₂mbpdc) and rare earth ions, in which H₂mbpdc undergoes an in situ ligand transformation reaction, giving 3,3′-hydroxy-2,2′-bipyridine-6,6′-dicarboxylic acid (hbpdcH₄). The structures are governed by the synergistic effect of lanthanide contraction with diverse coordination modes and conformations of the ligand. They have three structural types from 3D to 2D polymers. Type I for large ions with the general formula [Ln(hbpdcH)(H₂O)]_n (Ln = La^III (1), Ce^III(2), Pr^III (3)), possesses a 6-connected pcu network with unprecedented 2D entangled layers of warp-and-woof threads interwoven by left- and right-handed helical chains; type II for intermediate ions (Ln = Eu^III (4), Gd^III (5)) and type III for small ions (Ln = Tb^III (6), Dy^III (7), Ho^III (8), Er^III (9), Lu^III (10)), with general formula [Ln(hbpdcH)(H₂O)₂]_n. The type II and III comprised 2D Ln-hbpdcH grids. A magnetic study of 6–8 indicated that the coupling interaction between Ln³⁺ ions is weak. In addition, the photophysical properties of Eu and Tb polymers at room temperature were investigated.