Experimental Studies and Mechanism Analysis of High-Sensitivity Luminescent Sensing of Pollutional Small Molecules and Ions in Ln4O4 Cluster Based Microporous Metal–Organic Frameworks

Two new isostructural 3D lanthanide metal–organic frameworks (Ln-MOFs) {[Ln4(μ3-OH)4(BPDC)3(BPDCA)0.5(H2O)6]­ClO4·5H2O}n (Ln = Tb (1) and Gd (2), BPDC2– = 3,3′-dicarboxylate-2,2′-dipyridine anion and BPDCA2– = biphenyl-4,4′-dicarboxylate anion) based on cubane-shaped [Ln4(μ3-OH)4]8+ clusters were successfully synthesized and fully characterized. There are two kinds of micropores with dimensions of 3.0 × 7.0 Å2 along the b-axis and 4.5 × 5.5 Å2 along the c-axis in the cationic framework. Ln-MOF 1 exhibits an intensive green luminescence triggered by the efficient antenna effect of ligands under UV light. Luminescent studies illustrate that Ln-MOF 1 could be an efficient multifunctional luminescent material for high-sensitivity sensing of small organic molecules, metal cations, and anions, especially for benzene and acetone, Cu2+, and CrO42–. The mechanism of the sensing properties was studied in detail as well. Additionally, this cationic framework also displays fast capture of pollutant CrO42– by anion exchange.