Iridium(III)-Based Metal-Organic Frameworks as Multiresponsive Luminescent Sensors for Fe3+, Cr2O72-, and ATP2- in Aqueous Media

Three iridium(III)-based metal-organic frameworks (MOFs), namely [Cd-3{Ir(ppy-COO)(3)}(2)(DMF)(2)(H2O)(4)]center dot 6H(2)O center dot 2DMF (1), [Cd-3{Ir-(ppy-COO)(3)}(2)(DMA)(2)(H2O)(2)]center dot 0.5H(2)O center dot 2DMA (2), and [Cd-3{Ir(ppy-COO)(3)}(2)(DEF)(2)(H2O)(2)]center dot 8H(2)O center dot 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 {Cd-3(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 Cr2O72-. 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+, Cr2O72-, 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 Cr2O72- detection and thus provides great potential for future applications.