Two Co-Based Metal-Organic Framework Isomers with Similar Metal-Carboxylate Sheets: Turn-On Ratiometric Luminescence Sensing Activities toward Biomarker N-Acetylneuraminic Acid and Discrimination of Ga 3+ and In 3 .

Two supramolecular Co-MOF isomers, namely, {[Co(L) 0.5 ( m -bimb)]·3H 2 O} n ( LCU-115 ) and {[Co(L) 0.5 ( p -bimb)]·3H 2 O} n ( LCU-116 ), were synthesized from an amide-containing carboxylic acid N , N ″-(3,5-dicarboxylphenyl)benzene-1,4-dicarboxamide (H 4 L) and two flexible positional isostructural N-containing ligands m -bimb and p -bimb ( m -bimb = 1,3-bis((1H-imidazol-1-yl)methyl)benzene; p -bimb = 1,4-bis((1H-imidazol-1-yl)methyl)benzene). The carboxylate ligands connect Co(II) centers to form 2D metal-carboxylate sheets, which are extended further by m -bimb and p -bimb to form a 2D bilayer with parallel stacking ( LCU-115 ) and a 3D framework ( LCU-116 ), respectively. Luminescence measurements indicated that these two complexes exhibited interesting multiresponsive sensing activities toward pH, biomarker N-acetylneuraminic acid, and trivalent cations Ga 3+ /In 3+ . They show highly sensitive turn-on fluorescence responses in the acidic range and can also be regarded as on-off-on vapoluminescent sensors to typical acidic and basic gases HCl and Et 3 N. It is worth noting that these complexes have excellent turn-on ratiometric fluorescence sensing ability for N-acetylneuraminic acid (NANA) with detection limits as low as 7.39 and 8.06 μ M, respectively. Furthermore, they were successfully applied for the detection of NANA in simulated urine and serum samples with satisfactory results. For ion detection, LCU-116 could detect both Ga 3+ and In 3+ , while LCU-115 could distinguish Ga 3+ from In 3+ with the latter showing luminescence quenching. The sensing mechanism was investigated in detail by XRD, UV-vis, EDS, XPS, SEM, and TEM. The results of interday and intraday precision studies gave low RSD values in the range of 1.19-3.53%, ascertaining the reproducibility of these sensors. The recoveries for the sensing analytes in simulated urine/serum or real water are satisfactory from 96.7 to 103.3% (toward NANA) and 96.6 to 115.0% (toward Ga 3+ and In 3+ ), indicating that these two complexes also possess acceptable reliability for monitoring in real samples. The results indicated that the supramolecular isomers LCU-115 and LCU-116 are promising material candidates for application in biological and environmental monitoring.