Mixed-ligand lanthanide complexes constructed by flexible 1,3-propanediaminetetraacetate and rigid terephthalate

Abstract

Coordination polymers (CPs) of mixed-ligand lanthanide complexes [Ln2(1,3-pdta)(TPA)(H2O)2]n·nH2O [Ln = La, 1; Ce, 2; Pr, 3; Nd, 4] (1,3-H4pdta = 1,3-propanediaminetetraacetic acid; H2TPA = terephthalic acid) were hydrothermally synthesized with flexible 1,3-pdta and rigid TPA ligands. Moreover, lanthanide propanediaminetetraacetates [Ln(1,3-Hpdta)(H2O)]2n·nH2TPA·xH2O [Ln = Sm, 5; Gd, 6] with multi-layered structures were also obtained. In 1–4, both 1,3-pdta and TPA coordinate with lanthanide ions through carboxyl oxygen and nitrogen atoms. In 5 and 6, only 1,3-Hpdta coordinates with the central lanthanide ion, where one nitrogen atom in 1,3-Hpdta is protonated, and TPAs are crystallized as H2TPA with the central multi-layered structures of [Ln(1,3-Hpdta)(H2O)]2n through very strong hydrogen bonds [2.504(4) Å]. Solid-state 13C NMR analysis of 1 revealed the coordination of carboxyl groups. However, the methylene groups of 1,3-pdta showed an obvious upfield shift, which can be attributed to the effects of the phenyl ring in TPA ligand. The successful synthesis of these mixed-ligand lanthanides provides a rational design of such lanthanide CPs with flexible and rigid ligands.