Highly Stable Rare Earth Metal–Organic Frameworks for Fluorescence Recognition of Folic Acid, Proton Conduction, and Magnetic Refrigeration

Abstract

Four new isostructural rare earth metal–organic frameworks (RE-MOFs) were synthesized and full characterized, namely, {[(CH)2NH2]3[RE2(BTDBA)2(HCOO)]·5H2O·2DMF} n (H4BTDBA = (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 Al3+ with detection limits of 0.02 mM and 0.05 μM, respectively. The presence of free [(CH)2NH2]+ 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 −ΔS m of JXUST-35 reaches 16.13 J kg–1 K–1 at 2 K and ΔH = 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.

A novel 2D Eu-MOF as a dual-functional fluorescence sensor for detection of benzaldehyde and Fe3+

“…MOF materials have attracted great interest due to their applications in catalysis, 32,33 gas storage and separation, 34,35 luminescence, 36,37 and chemical sensing. 38–42 As a special member of the MOFs, Ln-MOF materials consist of lanthanide metal ions or clusters combined with organic ligands, and they exhibit unique luminescence properties including long lifetime, large Stokes shift, high colour purity, and sharp characteristic fluorescence originating from the 4f electronic configuration. 43,44 Ln-MOFs, particularly Eu-MOFs and Tb-MOFs, are highly significant for research due to their unique fluorescence properties.…”

Highly proton-conducting lanthanide metal–organic frameworks featuring highly oxygenated ligands with slow magnetic relaxation or magnetocaloric effect

“…Lanthanide metal–organic frameworks (Ln-MOFs) have garnered increasing attention due to their diverse applications leveraging their magnetic, electrical, optical, and thermal properties in luminescent sensing, catalysis, molecular magnetism, and electrical conductivity. 1–10 A current challenge in designing Ln-MOFs is the incorporation of multiple properties, particularly those demonstrating cooperativity. 11 Consequently, various dual-functional Ln-MOFs, such as magnetic-electric Dy-MOFs 8,12,13 and fluorescent-electric Eu-MOFs, 14,15 have been developed.…”

“…1–10 A current challenge in designing Ln-MOFs is the incorporation of multiple properties, particularly those demonstrating cooperativity. 11 Consequently, various dual-functional Ln-MOFs, such as magnetic-electric Dy-MOFs 8,12,13 and fluorescent-electric Eu-MOFs, 14,15 have been developed. Notably, the design and construction of a multifunctional magnetic material where magnetism coexists and/or is coupled with conductivity is of great interest.…”