Construction of terpyridine–Ln(iii) coordination polymers: structural diversity, visible and NIR luminescence properties and response to nerve-agent mimics

Abstract

Reactions of Ln(III) salts with 4′-(2,4-disulfophenyl)-2,2′:6′2′′-terpyridine (H₂DSPT) result in five types of coordination polymers, namely, {[Gd(DSPT)(OH)(H₂O)₂]·4H₂O}_n (type I, 1), {[Ln(DSPT)(ox)_0.5]·H₂O}_n (type II, Ln = Nd (2), Eu (3), Tb (4), Er (5), Yb (6), Lu (7), ox = oxalate), {[Ln(DSPT)(ox)_0.5(H₂O)]·4H₂O}_n (type III, Ln = Yb (8), Lu (9)), {[Ln(DSPT)(pBDC)_0.5·(H₂O)₂]·5H₂O}_n (type IV, Ln = Yb (10), Lu (11), H₂pBDC = 1,4-benzenedicarboxylic acid), and {[Ln(DSPT)(pBDC)_0.5·(H₂O)₂]·5H₂O}_n (type V, Ln = Dy (12), Er (13)). Type I is a 1D chain built from binuclear Ln₂(DSPT)₂ building blocks and OH⁻ linkers. Type II is a 2D layer with (4,5)-connected topology constructed by binuclear Ln₂(DSPT)₂ building blocks and ox⁻ anions. Type III is also a 2D network based on Ln(III), DSPT²⁻, and ox⁻, but with (3,4)-connected topology. The ox⁻ anion is generated in situ from carboxylic acid precursor in type II and type III structures. The formation of Lu(III) complexes of type II or type III can be tuned by the addition of different carboxylic precursors. Type IV posseses a 2D layered structure based on the [Ln(DSPT)]_n chain connected by pBDC²⁻. Type V exhibits a 3D framework formed by binuclear [Ln₂(SO₃)₂(COO)₂] secondary building blocks and DSPT²⁻ and pBDC²⁻ linkers, resulting in a uninodal 8-connected sqc4 topology. The Nd- and Yb-centered complexes show strong NIR luminescence, whereas the Tb- and Eu-centered complexes exhibit strong luminescence in the visible region at room temperature in both solid state and water emulsions. Their luminescence intensity can be strongly quenched by the addition of diethylchlorophosphonate (DCP), but significantly less influenced by dimethylmethylphosphonate (DMMP), diethylcyanophosphonate (DCNP) and other selected organophosphate, which make this material have a potential application in nerve-agent detection.