Synthesis, structures and photoluminescence of a series of 3D lanthanide–organic coordination polymers constructed from versatile 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide and oxalic acid

Abstract

A series of 3D coordination polymers {[Ln₂(bdcd)(ox)₂(H₂O)₃]·4H₂O}_n (Ln = Eu (1), Tb (2), Sm (3), Dy (4), and Gd (5)), which crystallize in the triclinic space group P with Z = 2, have been synthesized successfully based on the versatile ligands 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide (H₂bdcd) and oxalic acid (H₂ox). The compounds were characterized by means of IR spectroscopy, elemental analysis, TG, and powder X-Ray diffraction, whereby compounds 1 and 2 were structurally characterized. All of the compounds are isomorphous and have a 3D open framework in which ox²⁻ ligands bridge Ln³⁺ ions through their carboxylate groups resulting in the formation of a 1D Ln–ox infinite chain in the ac plane. The adjacent 1D Ln–ox infinite chains are then connected to each other through coordination interactions between Ln³⁺ ions and the carboxylate groups and N-oxide atoms of bdcd²⁻ ligands resulting in a 3D (7,8)-connected open framework with a (3⁸·4⁹·5⁴) (3⁷·4⁹·5¹¹·6) topology possessing 1D channels with lattice water molecules as residents. The photoluminescence properties of compounds 1, 2 and 4 were investigated in detail.