Multi-Responsive Luminescent Sensors Based on Two-Dimensional Lanthanide–Metal Organic Frameworks for Highly Selective and Sensitive Detection of Cr(III) and Cr(VI) Ions and Benzaldehyde

Four new isostructural two-dimensional lanthanide(III)–metal organic frameworks (MOFs), namely, [Ln(L)(HCOO)(H 2 O)] n (Ln = Eu 1, Gd 2, Ho 3, and Tb 4, H 2 L = 5-((2′-cyano-[1,1′-biphenyl]-4-yl)methoxy)isophthalic acid), with a uninodal {4 4 .6 2 }- sql topology have been successfully isolated. Compounds 1 and 4 exhibit excellent applications as luminescent sensors for sensing benzaldehyde in methanol and Cr 3+, CrO 4 2–, and Cr 2 O 7 2– in water with high sensitivity and selectivity based on luminescence quenching effects. Interestingly, 1 and 4 display excellent recyclable behaviors and can be recycled at least five times for sensing benzaldehyde, Cr(III) and Cr(VI) ions. These two compounds are the first multifunctional Ln–MOFs sensors for detecting benzaldehyde, Cr(III) and Cr(VI) ions, simultaneously. Therefore, these two materials may be excellent multifunctional recyclable luminescent sensors.