Stable Lanthanide Metal–Organic Frameworks with Ratiometric Fluorescence Sensing for Amino Acids and Tunable Proton Conduction and Magnetic Properties

Abstract

Four new isostructural lanthanide metal−organic frameworks (MOFs), namely {[Ln(DMTP-DC) 1.5 (H 2 O) 3 ]•DMF} n [H 2 DMTP-DC = 2′,5′dimethoxytriphenyl-4,4″-dicarboxylic acid; Ln III = Eu III (1), Gd III (2), Tb III (3), and Dy III (4)], have been synthesized and characterized. Single-crystal structure analysis reveals that 1−4 are three-dimensional Ln-MOFs with rich H-bonding of coordinated H 2 O molecules in the network channels. The X-ray diffraction patterns indicate that Ln-MOF 1 displays good stabilities in organic solvents and aqueous solutions with distinct pH values. Both 1 and 3 show characteristic emission of Ln III ions. Ln-MOF 1 can be used as a ratiometric fluorescence sensor for arginine and lysine in aqueous solution, and the detection limits are 24.38 μM for arginine and 9.31 μM for lysine. All 1−4 show proton conductivity related to relative humidity (RH) and temperature, and the maximum conductivity values of 1−4 at 55 °C and 100% RH are 9.94 × 10 −5 , 1.62 × 10 −4 , 1.71 × 10 −4 , and 2.67 × 10 −4 S•cm −1 , respectively. The value of σ increases with the decrease in ionic radius, indicating that the radius of the Ln III ions can regulate the proton conductivity of these MOFs. Additionally, 2 exhibits a significant magnetocaloric effect (MCE) with a magnetic entropy change (−ΔS m ) of 18.86 J kg −1 K −1 for ΔH = 7 T at 2 K, and 4 shows weak field-induced slow relaxation of magnetization. The coexistence of good fluorescence sensing capability, attractive proton conductivity, and relatively large MCE in Ln-MOFs is rare, and thus, 1−4 are potentially multifunctional MOF materials.

Supramolecular encapsulation of hexaaquacobalt(ii) cations in a hydrogen-bonded framework for slow magnetic relaxation and high proton conduction

“…Recently, several lanthanide based molecular nanomagnets have been reported for proton conduction as emerging bifunctional magnetic materials. 32–35 Herein, the supramolecular architecture showing both magnetic and electrical functions is distinct from these reported systems based on structural and synthetic viewpoints.…”

Controllable Synthesis of TbIII Metal–Organic Frameworks with Reversible Luminescence Sensing for Benzaldehyde Vapor

“…Rare-earth-based optical materials with a large Stokes shift, high color purity, and strong luminescence properties have been widely used in optical devices, communication, sensing, and bioimaging. − Among them, lanthanide metal–organic frameworks (Ln-MOFs) have attracted great interest in the field of chemical sensing due to the tailorable luminescence properties and diverse energy-transfer processes derived from their editable components (organic ligands and metal ions/clusters). − Fluorescent signal changes in the sensing process gave high sensitivity and visualization to Ln-MOFs. − Up to now, Ln-MOFs have been used to detect heavy-metal ions or anions, nitroaromatic explosives, volatile organic compounds (VOCs), biomarkers, etc. − Shi’s group synthesized the novel {[Eu 2 (L) 3 (DMF) 2 ]·DMF·MeOH} n (Ln-MOF 1 ; H 2 L = 5-(4 H -1,2,4-triazol-4-yl)­benzene-1,3-dicarboxylic acid, DMF = N , N -dimethylformamide, and MeOH = methanol), which shows the red luminescence characteristic of Eu III . There is a competitive absorption between polychlorinated benzenes and Ln-MOF 1 , which prevents the “antenna effect”.…”

A Proton Conducting Cobalt(II) Spin Crossover Complex

“…[20][21][22][23][24][25] Interestingly, some single-molecule magnets (SMMs) are emerging as new bifunctional magnetic materials with proton conduction. [26][27][28][29] Yet proton conductive SCO material has not yet been reported.…”

“…Proton‐conductive magnetic compounds have been studied for years and led to a lot of fascinating multifunctional materials, including proton‐conductive magnetic ordering materials [20–25] . Interestingly, some single‐molecule magnets (SMMs) are emerging as new bifunctional magnetic materials with proton conduction [26–29] . Yet proton conductive SCO material has not yet been reported.…”