Iridium(III)-Based Metal–Organic Frameworks as Multiresponsive Luminescent Sensors for Fe³⁺, Cr₂O₇^2–, and ATP^2– in Aqueous Media

Abstract

Three iridium(III)-based metal-organic frameworks (MOFs), namely [Cd₃{Ir(ppy-COO)₃}₂(DMF)₂(H₂O)₄]·6H₂O·2DMF (1), [Cd₃{Ir(ppy-COO)₃}₂(DMA)₂(H₂O)₂]·0.5H₂O·2DMA (2), and [Cd₃{Ir(ppy-COO)₃}₂(DEF)₂(H₂O)₂]·8H₂O·2DEF (3) (ppy-COOH = methyl-3-(pyridin-2-yl)benzoic acid, DMF = N,N-dimethylformamide, DMA = N,N-dimethylacetamide, DEF = N,N-diethylformamide), have been synthesized and characterized. Single-crystal structural determinations reveal that compounds 1-3 are isostructural, showing a three-dimensional framework structure with (3,6) connected rtl topologyin whose trimers of {Cd₃(COO)₆} are cross-linked by Ir(ppy-COO)₃^3-. The structures are completely different from those of other Ir(III)-based MOFs. Compound 1 was selected for a detailed study on sensing properties. The excellent luminescence as well as good water stability of 1 makes it a highly selective and sensitive multiresponsive luminescent sensor for Fe³⁺ and Cr₂O₇^2-. The detection limits are 67.8 and 145.1 ppb, respectively. Compound 1 can also be used as an optical sensor for selective sensing of adenosine triphosphate (ATP^2-) over adenosine diphosphate (ADP^2-) and adenosine monophosphate (AMP^2-) in aqueous solution. This is the first example of iridium(III)-based MOFs for the optical detection of Fe³⁺, Cr₂O₇^2-, and ATP^2-. More interestingly, the luminescent composite film doped with 1% (w/w) of compound 1, 1@PMMA (PMMA = poly(methyl methacrylate)), can be successfully prepared, which endows efficient sensitivity for Fe³⁺ and Cr₂O₇^2- detection and thus provides great potential for future applications.