Highly Stable Rare Earth Metal–Organic Frameworks for Fluorescence Recognition of Folic Acid, Proton Conduction, and Magnetic Refrigeration
Ke Wang, Zhi‐Yuan Li, Yan Peng, Teng‐Fei Zheng, Jing‐Lin Chen, Sui‐Jun Liu, He‐Rui Wen
Abstract
Four new isostructural rare earth metal–organic frameworks (RE-MOFs) were synthesized and full characterized, namely, {[(CH) 2 NH 2 ] 3 [RE 2 (BTDBA) 2 (HCOO)]·5H 2 O·2DMF} n (H 4 BTDBA = (4′,4′′′-(benzo[ c ][1,2,5]thiadiazole-4,7-diyl)bis([1,1′-biphenyl]-3,5-dicarboxylic acid); RE = Eu ( JXUST-34 ), Gd ( JXUST-35 ), Tb ( JXUST-36 ), and Dy ( JXUST-37 )). The single-crystal structures analysis shows that JXUST-34 – 37 are chain-based three-dimensional structures. Importantly, JXUST-34 exhibits excellent water, organic solvents, and acid–base stability, which can be used as a fluorescence sensor for folic acid and Al 3+ with detection limits of 0.02 mM and 0.05 μM, respectively. The presence of free [(CH) 2 NH 2 ] + cations in the channels can engage the proton carrier during proton conduction. JXUST-34 – 37 display good proton conductivity, and the conductivities vary with relative humidity and temperatures, among which JXUST-37 has the highest conductivity of 9.66 × 10 –3 S·cm –1 at 60 °C and 98% RH. The magnetic studies show that the −Δ S m of JXUST-35 reaches 16.13 J kg –1 K –1 at 2 K and Δ H = 7 T. JXUST-34 – 37 show multifunctional properties of fluorescence sensing, high proton conductivity, and magnetic refrigeration, which provides a new clue for the development of fluorescent-responsive, magnetic-refrigerant, and proton-conductive RE-MOF materials.