First Examples of Metal–Organic Frameworks with the Novel 3,3′-(1,2,4,5-Tetrazine-3,6-diyl)dibenzoic Spacer. Luminescence and Adsorption Properties

Bioinspired Structure Regulation of Apyrase-Like Nanozyme with Intracellular-Generated H2O2 for Tumor Catalytic Therapy

Adenosine triphosphate (ATP) is the major resource of energy supply in tumor activity. Therefore, improving ATP consumption efficiencies is a promising approach for cancer therapy. Herein, inspired by the H₂O₂-involved structure regulation effect during the catalysis of natural protein enzymes, we developed an artificial H₂O₂-driven ATP catalysis-promoting system, the Ce-based metal-organic framework (Ce-MOF), for catalytic cancer therapy. In the presence of H₂O₂, the hydrolysis ATP activity of Ce-MOF(H₂O₂) was enhanced by around 1.6 times. Taking advantage of the endogenous H₂O₂ in cancerous cells, catalytic hydrolysis for intracellular ATP of the Ce-MOF achieves the inhibition of cancerous cell growth, which involves damaged mitochondrial function and autophagy-associated cell death. Furthermore, in vivo studies suggest that the Ce-MOF has a good tumor inhibition effect. The artificial H₂O₂-driven ATP catalysis-promoting system not only demonstrates high catalytic ATP consumption efficiencies for cancer therapy but also highlights a bioinspired strategy to expedite nanozyme research in both design and applied sciences.

Anti-diabetic and anti-parasitic properties of a family of luminescent zinc coordination compounds based on the 7-amino-5-methyl-1,2,4-triazolo[1,5-a]pyrimidine ligand

We report on the formation of a triazolopyrimidine derivative ligand, 7-amino-5-methyl-1,2,4-triazolo[1,5-a]pyrimidine (7-amtp), and a new family of coordination compounds based on this ligand and zinc as metal ion, synthesized by conventional routes. These materials possess different mononuclear structures, namely [ZnCl₂(7-amtp)₂] (1), [Zn(7-amtp)₂(H₂O)₄](NO₃)₂·2(7-amtp)·6H₂O (2) and [Zn(7-amtp)₂(H₂O)₄](SO₄)·1.5H₂O (3) derived from the use of different zinc (II) salts, in such a way that the counterions govern the crystallization to a large extent. These compounds present and show variable luminescent properties based on ligand-centred charge transfers which have been deeply studied by Time Dependent Density Functional Theory (TD-DFT) calculations. When these compounds are transferred to solution, preserving complex entities as corroborated by NMR studies, they present interesting anti-diabetic and anti-parasitic capabilities, with a comparatively higher selectivity index than other previously reported triazolopyrimidine-based materials. The results derived from in vivo experiments conducted in mice also confirm their promising activity as anti-diabetic drug being capable of dropping glucose levels after oral administration. Therefore, these new materials may be considered as excellent candidates to be further investigated in the field of luminescent coordination compounds with biomedical applications.

1,2,4,5-Tetrazine based ligands and complexes

One of the most intriguing nitrogen based aromatic heterocycles is 1,2,4,5-tetrazine or s-tetrazine (TTZ) thanks to its electron acceptor character and fluorescence properties and the possibilities of functionalization in the 3 and 6 positions allowing access to various ligands. In this review we focus on the two main families of TTZ based ligands, i.e. ditopic symmetric and monotopic non-symmetric, together with their metal complexes, with a special emphasis on their solid state structures and physical properties. After a description of the most representative complexes containing unsubstituted TTZ as a ligand, symmetric TTZ ligands and complexes derived thereof are discussed in the order: 3,6-bis(2-pyridyl)-tetrazine, 3,6-bis(3-pyridyl)-tetrazine, 3,6-bis(4-pyridyl)-tetrazine, 3,6-bis(2-pyrimidyl)-tetrazine, 3,6-bis(2-pyrazinyl)-tetrazine, 3,6-bis(monopicolylamine)-tetrazine, 3,6-bis(vanillin-hydrazinyl)-tetrazine and TTZ containing carboxylic acids. Remarkable results have been obtained in recent years for metal-organic frameworks and magnetic compounds in which magnetic coupling is enhanced when the tetrazine bridge is reduced to radical anions. Non-symmetric ligands, such as dipicolylamine-TTZ and monopicolylamine-TTZ, are comparatively more recent than the symmetric ones. They allow in principle the preparation of mononuclear complexes in a controlled manner, although binuclear complexes have been isolated as well. Moreover, in the monopicolylamine-TTZ-Cl ligand, deprotonation of the amine, thanks to the electron acceptor character of TTZ, afforded a negatively charged ligand equivalent of a guanidinate.

Versatile coordination behaviour of the chloro-tetrazine-picolylamine ligand: mixed-valence binuclear Cu(i)/Cu(ii) complexes

The 3-Cl-6-amino-(2'-picolyl)-1,2,4,5-tetrazine ligand HL¹ has been synthesized and structurally characterized. Its versatile coordination behavior has been evidenced through reactions with Cu(Hfac)₂ and Cu(triflate)₂ precursors, which provided mixed-valence bimetallic Cu^1.5Cu^1.5 complexes [Cu₂(μ-Cl)(L¹)₂] 2 and [Cu₂(μ-triflate)(L¹)₂] 5. Changing the Cu(ii) precursor and the solvent leads to the formation of mononuclear octahedral Cu(ii) complexes [CuCl₂(HL¹)₂]·2CH₃CN 3 and [Cu(Hfac)₂(HL¹)] 4, in which only the amino-pyridine unit is involved in the coordination of the metal center. In contrast, in complexes 2 and 5, the ligands are deprotonated and bridge the metal centers as pyridine-amido-tetrazine fragments, while a bridging chloride or triflate ligand completes the coordination sphere of the metal ions. The Cu-Cu distances of 2.4313(4) Å in 2 and 2.5198(10) Å in 5 lie among the shorter values within mixed-valence bimetallic Cu complexes. Mixed-valence character is strongly supported by DFT calculations, showing the equal repartition of the unpaired electron between the two metal centers.

Coordination polymers built up from an s-tetrazine derived ligand and rare-earth ions: from a sequential dimensional expansion to organic-inorganic energy transfer

Coordination polymers were prepared from a luminescent s-tetrazine ligand (OTz) and various rare-earth ions. Both the radii of the Ln ions and the synthetic conditions (especially pH) drive the formation of the product, and three crystalline phases were finally identified. Using a two-step process, it was possible to increase the dimensionality of one of these compounds from 1-D (MIL-165) to 2-D (MIL-166). The luminescence properties of these coordination polymers were studied. Whereas for Ln = La, Pr, Eu, Tb, the emission characteristic of the s-tetrazine core was observed, such emission was not detected for Ln = Nd, while the emission typical for the Nd ion was present, due to energy transfer from the tetrazine ligand to the Nd³⁺ ion.

Luminescence and Magnetic Properties of Two Three-Dimensional Terbium and Dysprosium MOFs Based on Azobenzene-4,4'-Dicarboxylic Linker

We report the in situ formation of two novel metal-organic frameworks based on terbium and dysprosium ions using azobenzene-4,4'-dicarboxylic acid (H₂abd) as ligand, synthesized by soft hydrothermal routes. Both materials show isostructural three-dimensional networks with channels along a axis and display intense photoluminescence properties in the solid state at room temperature. Textural properties of the metal-organic frameworks (MOFs) have been fully characterized although no appreciable porosity was obtained. Magnetic properties of these materials were studied, highlighting the dysprosium material displays slightly frequency-dependent out of phase signals when measured under zero external field and under an applied field of 1000 Oe.

Novel anti-diabetic and luminescent coordination compounds based on vanadium

Novel vanadium coordination compounds have been synthesized. Both compounds exhibit intense photoluminescence emission and showin vivoantidiabetic activity.

Four Pb(ii) metal–organic frameworks with increasing dimensions: structural diversities by varying the ligands

Four complexes with 1D, 2D and 3D frameworks were synthesized by three rigid, linear ligands. The ligands' effects and luminescence properties were studied.

Structural, photophysical and magnetic properties of transition metal complexes based on the dipicolylamino-chloro-1,2,4,5-tetrazine ligand

The ligand 3-chloro-6-dipicolylamino-1,2,4,5-tetrazine (Cl-TTZ-dipica) , prepared by the direct reaction between 3,6-dichloro-1,2,4,5-tetrazine and di(2-picolyl)-amine, afforded a series of four neutral transition metal complexes formulated as [Cl-TTZ-dipica-MCl2]2, with M = Zn(II), Cd(II), Mn(II) and Co(II), when reacted with the corresponding metal chlorides. The dinuclear structure of the isostructural complexes was disclosed by single crystal X-ray analysis, clearly indicating the formation of [M(II)-(μ-Cl)2M(II)] motifs and the involvement of the amino nitrogen atom in semi-coordination with the metal centers, thus leading to distorted octahedral coordination geometries. Moreover, the chlorine atoms, either coordinated to the metal or as a substituent on the tetrazine ring, engage respectively in specific anion-π intramolecular and intermolecular interactions with the electron-poor tetrazine units in the solid state, thus controlling the supramolecular architecture. Modulation of the emission properties is observed in the case of the Zn(II) and Cd(II) complexes when compared to the free ligand. A striking difference is observed in the magnetic properties of the Mn(II) and Co(II) complexes. An antiferromagnetic coupling takes place in the dimanganese(II) compound (J = -1.25 cm(-1)) while the Co(II) centers are ferromagnetically coupled in the corresponding complex (J = +0.55 cm(-1)), the spin Hamiltonian being defined as H = -JSA·SB.

4-(4-Carboxyphenoxy)phthalate-based coordination polymers and their application in sensing nitrobenzene

Structural characterization of 4-(4-carboxyphenoxy)phthalate-based Cd²⁺ and Mn²⁺ coordination polymers are reported, and Cd²⁺ coordination polymer can serve as probe to sense nitrobenzene.

Towards a potential 4,4′-(1,2,4,5-tetrazine-3,6-diyl) dibenzoic spacer to construct metal–organic frameworks

A new ligand has been designed and explored with the aim of using it as a linker to construct three-dimensional metal–organic frameworks (MOFs).

An efficient and mild oxidant for the synthesis of s-tetrazines

PhI(OAc)₂ serves as a mild and effective oxidant for the synthesis of s-tetrazine derivatives- molecules of emerging significance to the field of bioorthogonal chemistry. This reagent serves as a complementary oxidant to harsher nitrous reagents. Use of PhI(OAc)₂ improves the synthesis of 5-amino-di(pyridin-2-yl)-s-tetrazine, a molecule that has been broadly used for cellular imaging and nuclear medicine. The generality of PhI(OAc)₂ as the oxidant for tetrazine synthesis is demonstrated for nine tetrazines in 75-98% yield.