Cation-Exchange Porosity Tuning in a Dynamic 4d-4f-3d Framework for Ni(II) Ion-Selective Luminescent Probe

Metal-Organic Frameworks: Synthetic Methods and Potential Applications

Metal-organic frameworks represent a porous class of materials that are build up from metal ions or oligonuclear metallic complexes and organic ligands. They can be considered as sub-class of coordination polymers and can be extended into one-dimension, two-dimensions, and three-dimensions. Depending on the size of the pores, MOFs are divided into nanoporous, mesoporous, and macroporous items. The latter two are usually amorphous. MOFs display high porosity, a large specific surface area, and high thermal stability due to the presence of coordination bonds. The pores can incorporate neutral molecules, such as solvent molecules, anions, and cations, depending on the overall charge of the MOF, gas molecules, and biomolecules. The structural diversity of the framework and the multifunctionality of the pores render this class of materials as candidates for a plethora of environmental and biomedical applications and also as catalysts, sensors, piezo/ferroelectric, thermoelectric, and magnetic materials. In the present review, the synthetic methods reported in the literature for preparing MOFs and their derived materials, and their potential applications in environment, energy, and biomedicine are discussed.

Modulating Magnetic and Photoluminescence Properties in 2-Aminonicotinate-Based Bifunctional Coordination Polymers by Merging 3d Metal Ions

Herein, the synthesis and study of bifunctional coordination polymers (CPs) with both magnetic and photoluminescence properties, derived from a heterometallic environment, are reported. As a starting point, three isostructural monometallic CPs with the formula [M(μ-2ani)₂ ]_n (M^II =Mn (1_Mn ), Co (3_Co ) and Ni (4_Ni ); 2ani=2-aminonicotinate), crystallise as chiral 2D-layered structures stacked by means of supramolecular interactions. These compounds show high thermal stability in the solid state (above 350 °C), despite which, in aqueous solution, compound 1_Mn is shown to partially transform into a novel 1D chain CP with the formula [Mn(2ani)₂ (μ-H₂ O)₂ ]_n (2_Mn ). A study of the direct current (dc) magnetic properties of 1_Mn , 3_Co and 4_Ni reveals a spin-canted structure derived from antisymmetric antiferromagnetic weak exchanges along the chiral network (as confirmed by DFT calculations) and magnetic anisotropy of the ions, in such a way that long-range ordering is observed with variable magnitude for the spin carriers. Moreover, compounds 3_Co and 4_Ni show no frequency-dependent alternating current (ac) susceptibility curves under zero dc field; this is characteristic behaviour of a glassy state that may be partially supressed for 3_Co by applying an external dc field. To overcome long-range magnetic ordering, Co^II ions are diluted in a diamagnetic Zn^II -based matrix, which enables single-molecule magnet behaviour. Interestingly, this strategy allows a bifunctional Co_x Zn_1-x 2ani material, which is imbued with a strong photoluminescent emitting capacity, as characterised by an intense blue light followed by a green afterglow, to be obtained.

Ln(iii)–Ni(ii) heteropolynuclear metal organic frameworks of oxydiacetate with promising proton-conductive properties

Heteropolynuclear metal organic frameworks (MOFs) of the general formula [Ln₂Ni₃(oda)₆(H₂O)₆]·xH₂O (oda = oxydiacetate, Ln = +3 rare earth ion) were synthesized and characterized.

Dual-Emitting Eu(III)-Cu(II) Heterometallic-Organic Framework: Simultaneous, Selective, and Sensitive Detection of Hydrogen Sulfide and Ascorbic Acid in a Wide Range

As important biomolecules, the deficiency or maladjustment of hydrogen sulfide (H₂S) or ascorbic acid (AA) is associated with the symptoms of the same disease (e.g., cardiovascular disease or cancer). There is an urgent need to develop a fluorescent probe capable of distinguishing between H₂S and AA simultaneously. Here, we report the syntheses, structure, and property of the first dual-detection fluorescent probe which can differentiate H₂S or/and AA in aqueous media. Accordingly, a novel [EuCu(pydc)₂(ox)_0.5(H₂O)₃·1.5H₂O]_{2 n} (1, H₂pydc = 2,3-pyridinedicarboxylic acid and ox = oxalic acid) for selective and sensitive detection of H₂S and AA in a wide range has been constructed (H₂S: [130 nM, +∞); AA: [55 nM, +∞)), exhibiting excellent catalytic activity comparable to horseradish peroxidase. In addition, the highly efficient detection in human serum sample also proves the potential application in medical diagnosis. Meanwhile, a combinatorial logic gate (AND(INH)-OR) based on activated 1 has also been constructed. Furthermore, this approach for simultaneous H₂S and AA detection suggests that the current work will expand the potential application of metal-organic frameworks for dual or multiple detections in biomedical fields.

Multifunctional Metal-Organic Frameworks Based on Redox-Active Rhenium Octahedral Clusters

The redox-active rhenium octahedral cluster unit [Re₆Se₈(CN)₆]^4- was combined with Gd³⁺ ions and dicarboxylate linkers in novel types of metal-organic frameworks (MOFs) that display a set of functional properties. The hydrolytically stable complexes [{Gd(H₂O)₃}₂(L)Re₆Se₈(CN)₆]·nH₂O (1, L = furan-2,5-dicarboxylate, fdc; 2, L = thiophene-2,5-dicarboxylate, tdc) exhibit a 3D framework of trigonal symmetry where 1D chains of [{Gd(H₂O)₃}₂(L)]⁴⁺ are connected by [Re₆Se₈(CN)₆]^4- clusters. Frameworks contain spacious channels filled with H₂O. Solvent molecules can be easily removed under vacuum to produce permanently porous solids with high volumetric CO₂ uptake and remarkable CO₂/N₂ selectivity at room temperature. The frameworks demonstrate an ability for reversible redox transformations of the cluster fragment. The orange powders of compounds 1 and 2 react with Br₂, yielding dark-green powders of [{Gd(H₂O)₃}₂(L)Re₆Se₈(CN)₆]Br·nH₂O (3, L = fdc; 4, L = tdc). Compounds 3 and 4 are isostructural with 1 and 2 and also have permanently porous frameworks but display different optical, magnetic, and sorption properties. In particular, oxidation of the cluster fragment "switches off" its luminescence in the red region, and the incorporation of Br^- leads to a decrease of the solvent-accessible volume in the channels of 3 and 4. Finally, the green powders of 3 and 4 can be reduced back to the orange powders of 1 and 2 by reaction with hydrazine, thus displaying a rare ability for fully reversible chemical redox transitions. Compounds 1-4 are mentioned as a new class of redox-active cluster-based MOFs with potential usage as multifunctional materials for gas separation and chemical contamination sensors.

Polymorphism and luminescence properties of heteropolynuclear metal–organic frameworks containing oxydiacetate as linker

A structural study concerning polymorphism control and the luminescence properties of lanthanide based MOFs.

Novel double layer lanthanide metal–organic networks for sensing applications

Two isostructural lanthanide-based 2D coordination polymers were synthesized under hydrothermal conditions and fully characterized. The obtained compounds display notable sensing ability for p-phenylenediamine, benzidine, and acetone analytes.

Elucidation of 1H NMR Paramagnetic Features of Heterotrimetallic Lanthanide(III)/Manganese(III) 12-MC-4 Complexes

The paramagnetic one-dimensional ¹H NMR spectra of twelve Ln^IIINa^I(OAc)₄[12-MC_Mn^III(N)shi-4] complexes, where Ln^III is Pr^III-Yb^III (except Pm^III) and Y^III, are reported. Their solid-state isostructural nature is confirmed in methanol-d₄ solution, as a similar pattern in the ¹H NMR spectra is observed along the series. Notably, a relatively well-resolved spectrum is reported for the Gd^III complex. The chemical shift data are analyzed using the "all lanthanides" method, and the Fermi contact and pseudo-contact contributions are calculated for the lanthanide-induced shift (LIS). For the Tb^III-Yb^III complexes, the pseudo-contact contributions are typically 1 order of magnitude higher than the Fermi contact contributions; however, for the Gd^III complex, the Fermi contact is the main contribution to the paramagnetic chemical shift. For the methyl protons of the axial acetate (^-OAc) ligands, the LIS is opposite in sign, with respect to that of the aromatic salicylhydroximate (shi^3-) protons, because of structural rearrangements that occur upon dissociation of the Na^I cation in solution. The calculated crystal field parameters (B_Ln) for the Tb^III (360 cm^-1), Dy^III (250 cm^-1), Ho^III (380 cm^-1), Er^III (410 cm^-1), Tm^III (620 cm^-1), and Yb^III (380 cm^-1) complexes are not constant, likely as a consequence of the inaccuracy of the Bleaney's constants and, to a smaller extent, the small structural changes that occur in solution. Overall, the metallacrown scaffold retains structural integrity and similarity in solution for the entire series; however, small structural features, which do not affect the overall similarity, do likely occur.

A series of Mg–Zn heterometallic coordination polymers: synthesis, characterization, and fluorescence sensing for Fe3+, CS2, and nitroaromatic compounds

Herein, three luminescent Mg–Zn coordination polymers were constructed, which demonstrated high fluorescence sensing of Fe³⁺, CS₂, and nitro explosive compounds.

Crystal structure of poly-[triaqua-(μ3-3,4,5,6-tetrafluoro-1,2-phthalato-κ4 O:O′:O′′,O′′′) (2,3,4,5-tetrafluoro-benzoato-κ2 O,O′) praseodymium(III)], C15H7F8O9Pr

C15H7F8O9Pr, monoclinic, P21/n (no. 14), a = 6.2167(3) Å, b = 9.7769(5) Å, c = 29.6562(15) Å, β = 93.2916(8)°, V = 1799.53 Å3, Z = 4, R gt(F) = 0.0317, wR ref(F 2) = 0.0729, T = 293(2) K.

Temperature-induced 1D lanthanide polymeric frameworks based on Lnn (n = 2, 2, 4, 6) cores: synthesis, crystal structures and luminescence properties

1D lanthanide polymeric frameworks were synthesized. White-light emission by two-/three-component complexes was realized. A Eu(iii)-complex could detect nitrobenzene and Ni²⁺ ion via a fluorescence quenching mechanism.

I2-induced SC–SC transformation within two-dimensional Zn(ii)-triazole framework: an ideal detector of cyano-containing molecules

A SC–SC transformation process driven by I₂ has been shown to generate a 2D + 1D → 2D interpenetrated architecture from a 2D + 2D → 2D network. For the first time we demonstrate a selective sensor toward cyano-containing molecules.

A Zn(ii) coordination polymer and its photocycloaddition product: syntheses, structures, selective luminescence sensing of iron(iii) ions and selective absorption of dyes

Nanospheres of a Zn(ii) complex are used to selectively sense iron(iii) ions while its photocycloaddition product can selectively absorb dyes.