Hydrothermal synthesis and characterization of a series of luminescent Ag(i) coordination polymers with two new multidentate bis-(1,2,3-triazole) ligands: structural diversity, polymorphism and photoluminescent sensing

Abstract

In this work, two new multidentate bis-(1,2,3-triazole) ligands 1-(4-(2H-1,2,3-triazol-2-yl)butyl)-1H-1,2,3-triazole (L₁) and 1,6-bis(2H-1,2,3-triazol-2-yl)hexane (L₂) have been designed and synthesized. Under hydrothermal conditions, a series of luminescent Ag(I) coordination polymers, namely, {[Ag(L₁)₂]·(PF₆)}_n (1), {[Ag₂(L₁)₂(bbtr)]·(BF₄)₂}_n (2), {[Ag₂(L₁)₂(bbtr)]·(BF₄)₂}_n (3), {[Ag₂(L₁)₂(bbtr)]·(PF₆)₂}_n (4) and [Ag₂(L₂)(NO₃)₂]_n (5) (bbtr = 1,4-di(1,2,3-triazol-1-yl)butane) can be isolated. For 1, bidentate L₁ ligands bridge neighboring Ag(I) ions, forming a 1D tubular framework. Further, when L₁ and bbtr are used to react with AgBF₄, two scarcely reported mixed-ligand polymorphic cluster-based Ag^I frameworks, 2 (1D) and 3 (2D), can be isolated under different reaction temperatures. Further, free BF₄⁻ anions within the crystalline framework of 2 can be exchanged with PF₆⁻ anions to generate the anion exchanged crystalline product {[Ag₂(L₁)₂(bbtr)]·(PF₆)₂}_n (4) in a single-crystal-to-single-crystal (SC–SC) manner. For 5, tetradentate L₂ ligands bridge neighboring Ag^I centers, leading to a 3D coordination polymer. The solid state luminescence properties of 1–5 have been investigated, indicating strong fluorescent emissions. Additionally, luminescence measurements illustrate that complex 5 exhibits highly selective and sensitive luminescence sensing of Cr₂O₇²⁻ ions in aqueous solutions with high quenching efficiency (K_sv = 1.53 × 10⁴ L mol⁻¹) and low detection limit (0.23 μM (S/N = 3)), which make it a promising candidate for sensing Cr₂O₇²⁻ anion pollutants in the actual measurement process. 5 is the first coordination polymer based on a bis-(1,2,3-triazole) derivative as luminescent probes of Cr₂O₇²⁻ ions in aqueous solutions.