Multiple Detection Characteristics of Two Zinc Phosphonates: Syntheses, Crystal Structures, and Luminescent Properties

A pair of metal phosphonates, {[(CH₃)₂NH₂]­[Zn₂(HEDP)­(BPDC)_0.5(H₂O)₂]·H₂O} (1) and {[CH₃NH₃]­[Zn₂(HEDP)­(BPDC)_0.5(H₂O)₂]·3.5H₂O} (2) (HEDP = 1-hydroxyethylidene diphosphonate, H₂BPDC = biphenyl-4,4′-dicarboxylic acid), have been successfully synthesized by virtue of a dual-ligand strategy. The Zn­(II) centers in both 1 and 2 are bridged by the −PO₃ units of HEDP to form 2D inorganic–organic hybrid layers. Adjacent Zn–HEDP layers are further pillared and connected by linear O-containing linkers to furnish 3D pillared-layer architectures showing a (3,4)-connected network. Solid-state photoluminescence studies of compounds 1 and 2 have been performed, displaying intense emissions at 335 and 340 nm under UV light irradiation, respectively. Moreover, luminescence sensing experiments suggest that compound 1 exhibits a great selectivity and sensitivity for detection of Cu²⁺/Fe³⁺, IO₄^–/Cr₂O₇^2– and nitrobenzene, which could be considered as a promising multiple sensor in an aqueous system.