Turn-On Luminescent Sensor toward Fe3+, Cr3+, and Al3+ Based on a Co(II) Metal-Organic Framework with Open Functional Sites.

A novel Co-based metal-organic framework (MOF) with the formula of {[Co3(BIBT)3(BTC)2(H2O)2]·solvents}n (JXUST-2, where JXUST denotes Jiangxi University of Science and Technology, BIBT = 4,7-bi(1H-imidazol-1-yl)benzo-[2,1,3]thiadiazole, and H3BTC = 1,3,5-benzenetricarboxylic acid) has been solvothermally prepared, which takes 3D structure with a rare 3,4,6-c topology and contains intramolecular hydrogen bonds. Interestingly, the sensing investigations suggest that JXUST-2 could be considered as a multifunctional fluorescence sensor toward Fe3+, Cr3+, and Al3+ via a turn-on effect with good reusability and detection limits of 0.13, 0.10, and 0.10 µM, respectively. The turn-on effect of JXUST-2 could be ascribed to an absorbance caused enhancement (ACE) mechanism. Notably, JXUST-2 is the first turn-on MOF fluorescent sensor for Fe3+, Cr3+, and Al3+ simultaneously.

A ZnII-Based Metal-Organic Framework with a Rare tcj Topology as a Turn-On Fluorescent Sensor for Acetylacetone.

A ZnII-based metal-organic framework (MOF) with a rare tcj topology has been solvothermally synthesized and displays relatively good thermal and chemical stabilities. Interestingly, the MOF can sensitively and selectively sense acetylacetone (acac) via a fluorescence enhancement effect with a detection limit of 0.10 ppm and good reusability, which demonstrates the first example of a MOF-based turn-on fluorescent sensor for acac.

Dual-response fluorescence sensing of H2PO4- and CO32- using AJP filter paper based on a pH-stable CdII-based luminescent metal-organic framework.

A new CdII-based luminescent metal-organic framework (LMOF) with the formula {[Cd(BIBT)(NDC)]·solvents}n (JXUST-32, BIBT = 4,7-bi(1H-imidazol-1-yl)benzo-[2,1,3]thiadiazole and H2NDC = 2,6-naphthalenedicarboxylic acid) was successfully synthesized by a solvothermal method. JXUST-32 shows a two-dimensional (4,4)-connected network and exhibits significant fluorescence red shift and slight enhancement for H2PO4- and CO32- sensing with detection limits of 0.11 and 0.12 µM, respectively. In addition, JXUST-32 has good thermal stability, chemical stability and recyclability. Significantly, JXUST-32 represents a fluorescence red-shift dual response MOF sensor for H2PO4- and CO32- detection and the analytes can be identified by the naked eye, aerosol jet printing filter paper, light-emitting diode beads and luminescent films.

Turn-on and blue-shift fluorescence sensor toward L-histidine based on stable CdII metal-organic framework with tetranuclear cluster units.

A novel CdII-based two-fold interpenetrated metal-organic framework (MOF), namely {[Cd2(BTDB)2(4,4-bpy)]·DMF}n (JXUST-14), (H2BTDB = 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic acid and 4,4-bpy = 4,4-bipyridine), has been prepared and characterized. Single-crystal structure determination reveals that JXUST-14 has a tetranuclear cluster based 6-connected pcu topological network with Schlafli symbol {412·63}. When soaked in common organic solvents and aqueous solutions with diverse pH values of 2-12 for 48 h, JXUST-14 remains stable. JXUST-14 is a highly selective and sensitive luminescent sensor for L-histidine (His) with a detection limit of 11.1 ppm. JXUST-14 is the first CdII-based MOF for the detection of His via turn-on and fluorescence blue-shift effects. Experimental study and theoretical calculation suggest that the sensing process can be mainly attributed to a charge transfer and energy transfer mechanism. More interestingly, LED lamps of JXUST-14 and JXUST-14@His were successfully developed, which endowed efficient sensitivity for His detection and thus provide great potential for future applications.

Fluorescent sensors for aldehydes based on luminescent metal-organic frameworks.

Volatile aldehydes cause great harm to human health and the living environment, and the detection of aldehydes has attracted much attention from chemists and material scientists. In recent years, as one of the most promising classes of functional materials, luminescent metal-organic frameworks (LMOFs) have bloomed as fluorescent sensors for the detection of aldehydes. Herein, the sensing properties of LMOF sensors toward formaldehyde, benzaldehyde, acetaldehyde and other aldehydes have been reviewed, and the sensing mechanism and applications are also illustrated. Additionally, the current status and its potential development prospects in this field are outlined.

CdII -Organic Frameworks Fabricated with a N-Rich Ligand and Flexible Dicarboxylates: Structural Diversity and Multi-Responsive Luminescent Sensing for Toxic Anions and Ethylenediamine.

Three metal-organic frameworks {[Cd(L)(glu)]⋅3 H2 O}∞ (1), {[Cd2 (L)2 (adi)2 ]⋅5 H2 O}∞ (2) and {[Cd(L)(sub)]⋅3 H2 O⋅DMA }∞ (3) (L=pyridine-3,5-bis(5-azabenzimidazole), H2 glu=glutaric acid, H2 adi=adipic acid and H2 sub=suberic acid) were obtained under solvothermal conditions. Complex 1 shows a 2D (4,4) network constructing of Cd2 -glu and Cd-L chains. Complex 2 presents a 2-fold interpenetrating 3D framework with pcu topology. Complex 3 is a 3D framework with cds topology. Three complexes with versatile structures were obtained by changing aliphatic dicarboxylate ligands with different lengths based on a N-rich ligand. Moreover, the fluorescence measurements indicate that complex 1 is a good multifunctional chemosensor for the detection of Cr2 O7 2- and MnO4 - anions by fluorescence quenching effect, and ethylenediamine by fluorescence enhancement effect, with detection limits of 1.196 ppm, 0.551 ppm and 64.572 ppm, respectively. Both complexes 2 and 3 can selectively sense Cr2 O7 2- anion with detection limits of 1.126 ppm for 2 and 0.831 ppm for 3 by a fluorescence quenching effect.

A CdII -Based Metal-Organic Framework with pcu Topology as Turn-On Fluorescent Sensor for Al3.

A new metal-organic framework (MOF) {[Cd2 (bbib)2 (ndc)2 ]⋅2DMF}n (JXUST-1) (bbib=1,3-bis(benzimidazolyl)benzene, H2 ndc=1,4-naphthalenedicarboxylic acid, DMF=N,N-dimethylformamide) has been solvothermally synthesized and characterized by single-crystal X-ray diffraction, PXRD, TGA, IR and elemental analysis. JXUST-1 exhibits a three-dimensional 6-connected pcu topology with a Schläfli symbol {412 .63 } constructed by [Cd2 (CO2 )3 ] secondary building units. Fluorescence studies show that this MOF can sensitively and selectively recognize Al3+ via a fluorescence enhancement effect, and the detection limit is 0.048 ppm. Furthermore, JXUST-1 displays relatively good thermal and chemical stabilities as well as reusability. All these results suggest JXUST-1 to be a highly selective and recyclable luminescent sensing material for the detection of Al3+ .

Temperature- and vapor-induced reversible single-crystal-to-single-crystal transformations of three 2D/3D GdIII-organic frameworks exhibiting significant magnetocaloric effects.

By using Gd2O3, propanedioic acid (H2pda) and oxalic acid (H2ox), a new Gd-based metal-organic framework (MOF) [Gd(pda)(ox)0.5(H2O)2]n (1) has been successfully constructed and structurally characterized. Interestingly, temperature- and vapor-induced reversible single-crystal-to-single-crystal transformations occurred and two new MOFs, namely [Gd(pda)(ox)0.5(H2O)]n (1a) and [Gd(pda)(ox)0.5]n (1b), have been obtained. Complex 1 displays a two-dimensional (2D) layer structure composed of zigzag [Gd(pda)]n chains and it could also be made up of numerous Gd6 macrocycles. Thermal dehydration leads to more complicated three-dimensional (3D) 'pillar-layer' structures (1a and 1b) with the same coordination mode of pda2- anions. Magnetic studies suggest the presence of ferromagnetic couplings between the intrachain or intralayer GdIII ions and large magnetocaloric effects (MCEs) with -ΔS = 45.0 J kg-1 K-1 (1), 46.1 J kg-1 K-1 (1a) and 46.8 J kg-1 K-1 (1b) under a 7 T applied field. Therefore, the interest of 'robust magnetocaloric MOFs' is now extended to compounds showing weak ferromagnetic couplings and hence having better magnetocaloric performances for small field changes.