Syntheses, structures and photoluminescent properties of three new coordination polymers based on semirigid zwitterionic ligand

Three new coordination polymers, namely, [Zn(L)2]n (1), [Cd(L)2(H2O)2]n (2) and [Pb(L)(NO3)]n (3), have been synthesized by reactions of the corresponding metal salts with semirigid zwitterionic ligand 1-carboxymethylpyridinium-3-carboxylate (L). The results of X-ray crystallographic analysis indicate that complex 1 shows a 1D double-stranded chain structure composed of cyclic linkage, which are further connected by C–H⋯O hydrogen bonds to generate a 3D structure. In contrast to complex 1, 2 displays a 2D rhombic grid with (4, 4) topology, which is made up of single-stranded double helices. Complex 3 is an infinite 1D tube containing cyclic M2L2 subunits. Moreover, the ligand L acts as a 2-connected linker in 1 and 2, as well as 4-connected linker in 3, but all of them present the same ‘L’ conformation. The results indicate that the geometry of metal centers, together with coordination mode and conformations of ligand L, have a great effect on the formations of various structures. In addition, the photoluminescent properties of complexes 1–3 were also studied in the solid state at room temperature.