Novel Co-based metal-organic frameworks and their magnetic properties using asymmetrically binding 4-(4'-carboxyphenyl)-1,2,4-triazole

Modulation of Hierarchical Pores in Metal-Organic Frameworks for Improved Dye Adsorption and Electrocatalytic Performance

The hierarchical porous metal-organic framework (HP-MOF) has emerged as a hot topic in porous materials in consideration of their advantages in storage capacity and catalysis performance. Herein, we report the construction and property investigation of a series of HP-MOFs. A series of isoreticular microporous MOFs featuring the pacs topology network based on 2,4,6-tris(4-pyridyl)-1,3,5-triazine and different carboxylic acid ligands are found to be potential precursors to construct HP-MOFs. Through the decarboxylation of carboxylate ligands at high temperatures, a hierarchical porous structure could be obtained with the reservation of a crystalline framework. The formation of hierarchical pores is highly dependent on the structural and component nature (carboxylate ligands and metal centers) of the pristine MOF and the pyrolysis conditions (temperature and treatment time), indicating the highly tunable hierarchical pore characteristic of the HP-MOFs. By taking advantage of the increased pore volume and more exposed activation sites, the HP-MOFs reveal enhanced anionic dye adsorption capacity (800 mg·g^-1 for Congo red and 140 mg·g^-1 for methyl blue) and catalytic activity toward electrocatalytic oxygen reduction reaction (overpotential of 0.302 V at a current density of 10 mA·cm^-2, 51 mV lower than that of the pristine MOF).

1,2,4-Triazolyl-4-acetate: a ditopic ligand combining soft and hard donor sites in homometallic (AgI) and heterometallic (AgI/UVI) coordination polymers

A 1,2,4-triazol-4-yl-acetic acid (trGly-H) was used for the synthesis of AgI and AgI/UVI coordination polymers. The composition space diagram was built for the AgNO3/trGly-H/UO2(NO3)2·6H2O system shows the crystallization fields of two AgI/UVI-compounds were found.

Design Strategy for the Controlled Generation of Cationic Frameworks and Ensuing Anion-Exchange Capabilities

Cationic frameworks are an emerging class of exceptional solid adsorbents capable of encapsulating highly toxic and persistent anionic pollutants. The controlled generation of cationic frameworks, however, lags behind the abundant design strategies devised to control the structures and topologies of neutral frameworks. In this regard, we report a rational approach that allows the conversion of the synthetic approach toward constructing a neutral framework into one allowing for the synthesis of a cationic one without incurring any changes to the overall topology or the selected metal ion. We demonstrate that the replacement of a functional group on an organic linker that promotes a similar coordination mode, but bearing one less negative charge, can yield the systematic generation of cationic frameworks. Moreover, we confirm the cationic nature of the metal-organic frameworks through preliminary anion-exchange experiments and propose a method to retain permanent porosity in cationic frameworks through the use of strongly binding anions. Altogether, these results show great promise for the construction of tunable nanoporous frameworks capable of carrying out anion-exchange processes.

Redox-Active Cobalt(II/III) Metal-Organic Framework for Selective Oxidation of Cyclohexene

We report herein a new cobalt(II/III) mixed-valence metal-organic framework formulated as [Co^IICo₂^III(μ₃-O)(bdc)₃(tpt)]·guest 1, where bdc = benzene-1,4-dicarboxylate and tpt = 2,4,6-tri(4-pyridinyl)-1,3,5-triazine, which can be used as a redox-active heterogeneous catalyst for selective oxidation of cyclohexene on the allylic position without destroying the adjacent double bond. Two oxidants were chosen to demonstrate this result. For using tert-butyl hydroperoxide, the conversion rate is 63% and only allylic oxidation products ( tert-butyl-2-cyclohexenyl-1-peroxide, 86%; 2-cyclohexen-1-one, 14%) are found, whereas if using O₂ as oxidant, a total conversion of 38% is achieved and also only the allylic oxidation products (cyclohexenyl hydroperoxide, 72%; 2-cyclohexen-1-one, 20%; and cyclohex-2-en-1-ol, 8%) are found. The absence of any adduct on the double bond may be due to the unique radical chain mechanism triggered by the mixed-valent [Co^IICo₂^III(μ₃-O)] centers.

Chemotherapeutic Drug Based Metal-Organic Particles for Microvesicle-Mediated Deep Penetration and Programmable pH/NIR/Hypoxia Activated Cancer Photochemotherapy

A novel metal-organic particle (MOP) based nanodrug formed by mild self-assembly of chemotherapeutic drugs, including banoxantrone and doxorubicin, through Cu(II)-mediated coordination effects, is reported. In this nanodrug, Cu(II) acts as a bridge to join AQ4N and DOX, and then, self-assembly of [-AQ4N-Cu(II)-(DOX)2-Cu(II)-] n complexes forms nanosized MOPs (referred to as ADMOPs) through multiple interactions including host-metal-guest coordination, hydrophobic interactions, π-stacking, and van der Waals force. The ADMOPs reported here have several important features over conventional drugs, including tumor microenvironment pH-sensitive drug release that can be tracked by "turning on" the fluorescence of AQ4N or DOX through proton competition with Cu(II) to break the coordination bonds and much deeper penetration into solid tumors via microvesicle-mediated intercellular transfer. Most strikingly, the ADMOPs can serve as stimuli-responsive nanocarriers to efficiently load the photosensitizer phthalocyanine due to their inherent highly porous characteristics. Thus, the ADMOPs significantly enhance the chemotherapeutic efficacy by "on-demand" photodynamic therapy, which further induces a hypoxic environment that enhances the reduction of AQ4N to systematically increase the therapeutic efficiency. Taken together, the designed ADMOPs composed of chemotherapeutic drugs may serve as a potential programmable controlled synergistic agent for cancer therapy.

Structural Diversity of Three Pyrazoyl-Carboxyl Bifunctional Ligand-Based Metal-Organic Frameworks: Luminescence and Magnetic Properties

Three metal-organic frameworks (MOFs), [Cd(Hpzbpdc)(H₂ O)]⋅H₂ O (1), [Mn₂ (Hpzbpdc)₂ (dmf)₂ ] (2), and [H₂ N(CH₃ )₂ ]_0.5 [Eu(Hpzbpdc)_1.5 (HCOO)_0.5 (dmf)_0.5 ]⋅DMF⋅0.5 H₂ O (3) (H₃ pzbpdc=4'-(2 H-pyrazol-3-yl)biphenyl-3,5-dicarboxylic acid), have been solvothermally synthesized from one pyrazoyl-carboxyl bifunctional ligand and characterized by single-crystal structures. The H₃ pzbpdc ligand in 1-3 displays various coordination modes through the pyrazoyl and carboxyl groups. Both 1 and 3 contain dinuclear cluster building units and reveal a four-connected gismondine (gis) zeolite 3D framework and a 2D grid layer structure, respectively. Compound 1 shows blue luminescence, compound 3 reveals red luminescence that arises from efficient energy transfer from the organic ligand to the europium(III) ion, and compound 2 reveals an uncommon (3,8)-connected tfz-d; UO₃ net with a rare Mn₄ (COO)₆ cluster and shows antiferromagnetic interactions between the manganese(II) ions.

Different magnetic responses observed in Co, Co and Co-based MOFs

Four magnetic MOFs with anisotropic Co(II) ions, {[Co5(H2O)2(μ3-OH)2(atz)2(stp)2]·1.5H2O}n (1), {[Co5(H2O)2(μ3-OH)2(trz)2(stp)2]·1.3H2O}n (2), {[Co5(H2O)6(μ3-OH)2(trz)2(stp)2]·2.5CH3OH}n (3) and {[Co3(H2O)4(Hdatrz)2(stp)2]·3H2O}n (4) (stp(3-) = 2-sulfoterephthalate, trz(-) = 1,2,4-triazolate, atz(-) = 3-amino-1,2,4-triazolate and Hdatrz = 3,5-diamino-1,2,4-triazole) were solvothermally isolated by varying the substituent groups appended on the N-heterocyclic triazole and structurally and magnetically characterized. Structural analyses indicate that the former two complexes are crystallographically isostructural, exhibiting pillared-layer frameworks with mixed triazolyl and carboxylate extended Co + Co layers supported by rigid stp(3-) connectors. Complex 3 is built from butterfly-shaped Co cluster-based layers, which are interconnected with single cobalt(ii) octahedra by ditopic stp(3-) bridges. By contrast, complex 4 consists of linear {Co3(μ-N1,N4-Hdatrz)2} subunits, which are extended by 3-connected stp(3-) linkers into a stable 3D framework. Magnetically, 1 exhibits ferromagnetic ordering below 2.7 K due to the well-organized alignment of the non-compensated resultant moment from octahedra and tetrahedral cobalt(ii) carriers, while 3 is in a non-zero paramagnetic state above 2.0 K resulting from the coexistence of intermetallic ferromagnetic and antiferromagnetic interactions. The magnetic competition between weak inter-subunit antiferromagnetic interactions and the external magnetic field makes 4 behave as a field-induced metamagnet with a critical field of 27.5 kOe. These interesting magnetostructural results suggest that the anisotropy of the moment carrier and the interlayer/intersubunit separations significantly dominate the magnetic responses in extended MOFs, providing an informative platform for the further development of interesting magnetic materials, both of academic and industrial interest.

An air-stable Dy(iii) single-ion magnet with high anisotropy barrier and blocking temperature

A mononuclear Dy(iii) complex assembled just from five water molecules and two phosphonic diamide ligands combines the advantages of high anisotropy barrier, high blocking temperature and significant coercivity, apart from its remarkable air- and moisture-stability.

Herein we report air-stable Dy(iii) and Er(iii) single-ion magnets (SIMs) with pseudo-D_5h symmetry, synthesized from a sterically encumbered phosphonamide, ^tBuPO(NHⁱPr)₂, where the Dy(iii)-SIM exhibits a magnetization blocking (T_B) up to 12 K, defined from the maxima of the zero-field cooled magnetization curve, with an anisotropy barrier (U_eff) as high as 735.4 K. The Dy(iii)-SIM exhibits a magnetic hysteresis up to 12 K (30 K) with a large coercivity of ∼0.9 T (∼1.5 T) at a sweep rate of ∼0.0018 T s^–1 (0.02 T s^–1). These high values combined with persistent stability under ambient conditions, render this system as one of the best-characterized SIMs. Ab initio calculations have been used to establish the connection between the higher-order symmetry of the molecule and the quenching of quantum tunnelling of magnetization (QTM) effects. The relaxation of magnetization is observed via the second excited Kramers doublet owing to pseudo-high-order symmetry, which quenches the QTM. This study highlights fine-tuning of symmetry around the lanthanide ion to obtain new-generation SIMs and offers further scope for pushing the limits of U_eff and T_B using this approach.

A series of Zn(ii) and Cd(ii) coordination compounds based on 4-(4H-1,2,4-triazol-4-yl)benzoic acid: synthesis, structure and photoluminescence properties

Seven d¹⁰ coordination compounds based on a triazolate–carboxylate bifunctional ligand have been synthesized and structurally characterized. Their thermal stability and photoluminescence properties were also investigated.

Structural stabilization of a metal–organic framework for gas sorption investigation

In this contribution, by inserting a ligand intoCo-MOF1, the reformed aggregation of triangle grids (Co-MOF1-tpt) shows enhanced stability. In addition, owing to the maintenance of porosity,Co-MOF1-tptalso reveals a certain CO₂storage ability and CO₂/CH₄adsorption selectivity as expected.

Turn-on luminescence based discrimination of protic acids using a flexible layered metal–organic coordination polymer

A flexible layered metal–organic coordination polymer used as probe for turn-on luminescence based discrimination of protic acids and amino acids.

Visible detection of explosive nitroaromatics facilitated by a large stokes shift of luminescence using europium and terbium doped yttrium based MOFs

Two lanthanide doped highly luminescent MOFs have been synthesized and characterized. The MOFs are highly efficient for the detection of trace amount of explosive nitroaromatics by visible colour change.

A hydrothermally stable Zn(ii)-based metal–organic framework: structural modulation and gas adsorption

A hydrothermally stable MOF, [Zn₂(tcpt)OH]·solvents (1·solvents), was synthesized, in which an unusual paddlewheel SBU, Zn₂(COO)₃, was found. Furthermore, 1 can adsorb considerable amounts of H₂ and displays high selective adsorption of CO₂ over N₂.

Structural diversity of five new bitriazole-based complexes: luminescence, sorption, and magnetic properties

Employing a new bitriazole ligand, five complexes were assembled that display diverse structures, selective CO₂/CH₄ adsorption, luminescent sensing, and antiferromagnetic properties.