Lanthanide-MOFs as multi-responsive photoluminescence sensor for sensitively detecting Fe3+, Cr2O72- and nitrofuran antibiotics

Fast and selective detection of contaminants plays a key role in meeting human health and environmental concerns. Herein, two groups of isostructural lanthanide MOFs, [Ln(Hpta)(oxalic acid)]·H2O (1-Eu, 2-Gd) and [Ln(pta)(oxalic acid)0.5(H2O)2]·2H2O (3-Eu, 4-Gd) (H2pta = 2-(4-pyridyl)-terephthalic acid, C2O4- = oxalic acid), were synthesized by solvothermal method. Single crystal X-ray diffraction reveals that 1 and 2 are 3D neutral frameworks, while 3 and 4 consist of 2D layers with parallelogram holes and stack into 3D networks through O-H⋯N and O-H⋯O hydrogen bonding interactions. All complexes remain crystalline and stable below 400 °C, suggesting preeminent thermostability. Noteworthily, only 3 shows excellent chemical stability in water and organic solvent. Therefore, the solid-state fluorescence spectrum was used to characterize 3 which exhibited intense red luminescence. The N active sites in the pore channels of 3 are conducive to displaying a distinct quenching effect for Fe3+ cations in aqueous solutions, Cr2O72- anions in DMF and DMA solutions, and nitrofuran antibiotics in the DMF solvent. Overall, 3 is a prospective luminescent sensor for detecting Fe3+, Cr2O72- and nitrofuran antibiotics.

Stimuli-Responsive Zinc (II) Coordination Polymers: A Novel Platform for Supramolecular Chromic Smart Tools

The unique role of the zinc (II) cation prompted us to cut a cross-section of the large and complex topic of the stimuli-responsive coordination polymers (CPs). Due to its flexible coordination environment and geometries, easiness of coordination-decoordination equilibria, "optically innocent" ability to "clip" the ligands in emissive architectures, non-toxicity and sustainability, the zinc (II) cation is a good candidate for building supramolecular smart tools. The review summarizes the recent achievements of zinc-based CPs as stimuli-responsive materials able to provide a chromic response. An overview of the past five years has been organised, encompassing 1, 2 and 3D responsive zinc-based CPs; specifically zinc-based metallorganic frameworks and zinc-based nanosized polymeric probes. The most relevant examples were collected following a consequential and progressive approach, referring to the structure-responsiveness relationship, the sensing mechanisms, the analytes and/or parameters detected. Finally, applications of highly bioengineered Zn-CPs for advanced imaging technique have been discussed.

Structures and photocatalytic properties of two new Zn(ii) coordination polymers based on semi-rigid V-shaped multicarboxylate ligands

Two new metal-organic coordination polymers (CPs), aqua-2,2'-bipyridine-5-(4'-carboxylphenoxy)isophthalatezinc(ii) polymer [Zn(HL)(2,2'-bipy)(H₂O)] _n (1) and tris-4,4'-bipyridine-bis-5-(4'-carboxylphenoxy)isophthalatetrizinc(ii) polymer [Zn₃(L)2(4,4'-bipy)₃] _n (2) (H₃L = 5-(4'-carboxylphenoxy)isophthalic acid, 4,4'-bipy = 4,4'-bipyridine and 2,2'-bipy = 2,2'-bipyridine), were obtained under hydrothermal conditions and characterized by microanalysis, FTIR spectroscopy and single crystal X-ray diffraction. The single crystal X-ray diffraction indicated that in both the CPs the coordination networks exhibited varied topologies and coordination modes around the Zn(ii) centers. CP 1 exhibits a one-dimensional (1D) chain structure, which further forms a 3D supramolecular architecture via intermolecular π⋯π and hydrogen bonding interactions, while 2 possesses a 3D framework generated from a 2D layered motif comprising zinc and tripodal carboxylate subunits pillared by 4,4'-bpy ligands. Apart from the structural investigation, the photocatalytic performances of both the coordination polymers to photodecompose an aqueous solution of methyl violet (MV) were examined. The results indicated that both the CPs displayed the potential to photodecompose aromatic dyes and in particular 2 showed good photocatalytic activity for dye degradation under light irradiation. The photocatalytic mechanism through which these CPs executed degradation of dyes has been explained with the assistance of band gap calculations using density of states (DOS) and its decomposed partial DOS calculations.

Stable Ln-MOFs as multi-responsive photoluminescence sensors for the sensitive sensing of Fe3+, Cr2O72−, and nitrofuran

Stable Ln(iii)-MOFs with a versatile 2-(4-pyridyl)-terephthalic acid ligand can be used as a multifunctional sensing platform for Fe³⁺, Cr₂O₇²⁻, and nitrofuran detection.

Metal-Organic Framework (MOF)-based Nanomaterials for Biomedical Applications

BACKGROUND

Metal-organic frameworks (MOFs), as a new class of porous organic-inorganic crystalline hybrid materials that governed by the self-assembled of metal atoms and organic struts have attracted tremendous attention because of their special properties. Recently, some more documents have reported different types of nanoscale metal-organic frameworks (NMOFs) as biodegradable and physiological pH-responsive systems for photothermal therapy and radiation therapy in the body.

DISCUSSION

In this review paper aims at describing the benefits of using MOF nanoparticles in the field of biomedicine, and putting into perspective their properties in the context of the ones of other NPs. The first section briefly reviews the biomaterial scaffolds of MOFs. The second section presents the main types of stimuli-responsive mechanisms and strategies from two categories: intrinsic (pH, redox state) and extrinsic (temperature, light irradiation and magnetic field) ones. The combinations of photothermal therapy and radiation therapy have been concluded in detail. Finally, clinical applications of MOFs, future challenges and perspectives are also mentioned.

CONCLUSION

This review outlines the most recent advances MOFs design and biomedical applications, from different synthesis to their use as smart drug delivery systems, bioimaging technology or a combination of both.

A new Co(II) coordination polymer with the 2-(4-pyridyl)-terephthalate ligand: synthesis, crystal structure and magnetic properties

A new Co(II) complex, [Co(pta)(H2O)2] n (1), with the 2-(4-pyridyl)-terephthalate ligand (pta2−) has been synthesized and structurally and magnetically characterized. Single crystal X-ray analysis indicates that the unique Co(II) ion in the asymmetric unit of 1 displays stretched octahedral geometry. Compound 1 presents a bimetallic layer structure which is further expanded to a 3D supramolecular network through hydrogen bonding interactions. Magnetic measurements have revealed the temperature-dependent existence of antiferromagnetic and ferromagnetic interactions in compound 1.

Luminescent metal–organic frameworks with a 2-(4-pyridyl)-terephthalic acid ligand for detection of acetone

Employing an unsymmetrical pyridyl-dicarboxylate ligand, three MOFs with diverse structures were obtained. The Cd-MOF shows excellent selective sensing towards acetone molecules.

Temperature tuned syntheses of two new d10-based Cd(ii) cluster metal–organic frameworks: luminescence sensing and photocatalytic properties

The solvothermal reactions of 5,5′-(1,4-phenylenebis(methyleneoxy))diisophthalic acid (H₄L) and the N-donor ancillary ligand 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (bpz) with cadmium(ii) salts at two different reaction temperatures yielded two new metal–organic frameworks (MOFs), viz., [Cd(H₂L)(bpz)]_n (1) and [Cd₂(H₄L)(L)(bpz)₂]_n (2), which have been characterized by FTIR and single crystal X-ray diffraction. The single crystal X-ray diffraction studies revealed that 1 displays a 3-periodic network with monometallic SBU, while 2 exhibits a 3-periodic network with a 2-fold interpenetration feature. The effects of variation in reaction temperature on the architecture of MOFs 1 and 2 have been discussed. The luminescence investigation indicates that both 1 and 2 displayed good turn-off luminescence sensing against nitroaromatic compounds (NACs), especially m-nitrophenol (MNP), via a decrease in their luminescence intensities with a K_sv value of 6.43 × 10³ for 1 and 2.03 × 10⁴ for 2 and LOD values of 1.09 and 0.81 ppm for 1 and 2, respectively. The plausible mechanism for the decline in luminescence intensity of the MOFs with NACs has been addressed using theoretical calculations. The photocatalytic properties for both the MOFs demonstrated that they display efficient photocatalytic performances to degrade methyl violet (MV) under UV irradiation. The plausible mechanism through which these MOFs exhibited photocatalytic properties has been suggested using band gap calculations.

Two new d¹⁰-based Cd(ii) MOFs were synthesized and their photoluminescence sensing to selectively detect m-nitrophenol (MNP) and ability to decompose the organic dye methyl violet (MV) were explored.

Enabling Homochirality and Hydrothermal Stability in Zn4O-Based Porous Crystals

The [Zn₄O]⁶⁺ cluster is well-known to form the archetypal MOF-5 topology with dicarboxylate ligands. Here we report two new materials (CPM-300 and -301) that show dramatic alteration of topological and chemical behaviors of [Zn₄O]⁶⁺ clusters. In CPM-300, [Zn₄O]⁶⁺ untypically forms the MIL-88/MOF-235 type framework with a small pentane-ring-based chiral dicarboxylate. In contrast, in CPM-301, when mediated by [Zn₉(btz)₁₂]⁶⁺ clusters (btz = benzotriazolate), the MOF-5 topology is regenerated with the same chiral ligand, albeit with alternating [Zn₄O]⁶⁺ and [Zn₉(btz)₁₂]⁶⁺ clusters. Importantly, both CPM-300 and CPM-301 are homochiral, hydrothermally stable in boiling water and alcohol, and thermally stable to 440 °C or higher. It is concluded that small methyl groups on the chiral ligand is sufficiently powerful to shield [Zn₄O]⁶⁺ clusters from degradation by water, even at high temperatures. These results reveal a promising platform for the development of a new class of cluster-based homochiral and hydrothermally stable porous materials.

A novel Ag(i)-calix[4]arene coordination polymer for the sensitive detection and efficient photodegradation of nitrobenzene in aqueous solution

Nitrobenzene (NB) is a widespread and highly toxic organic pollutant in water, and consequently its detection and removal have attracted considerable attention. In the present study, we designed and synthesized a novel coordination polymer, [AgL_0.5(NO₃)]_n (1), {L = 25,26,27,28-tetra[(3-pyridylmethyl)oxy]calix[4]arene}, from AgNO₃ and a tetra-pyridyl-functionalized calix[4]arene ligand, which possessed a 2D network based on [Ag₄L(NO₃)₄] units. The 1-modified glassy carbon electrode (1/GCE) exhibited good electrocatalytic activity toward the reduction of NB, offering the selective detection of NB in a wide linear range (1-2450 μM) and a low detection limit (0.62 μM). Furthermore, it displayed excellent photocatalytic activity for the degradation of NB in aqueous solution under UV light. The kinetics of the catalytic degradation reaction and the stability of the catalyst were also studied. These results indicated that compound 1 is a favorable material for the effective determination and degradation of NB, which makes it a promising candidate in both monitoring water quality and treating wastewater.

Three Cluster Organic Frameworks Constructed from Tetranuclear Cluster Units: Structure and Properties

By treating a semirigid 5-oxyacetate isophthalic acid (H₃ OAIP) ligand with MnSO₄ /CoSO₄ /CdSO₄ under solvothermal conditions, three isostructural cluster organic frameworks, [M₂ (OH)(OAIP)(DMA)]⋅H₂ O (M=Mn²⁺ (1), Co²⁺ (2), Cd²⁺ (3); DMA=N,N'-dimethylacetamide) were constructed. The three complexes contain novel eight-connected tetranuclear M₄ (OH)₂ (COO)₆ (OCH₂ COO)₂ clusters with the unique hexagonal bipyramidal configuration, which are extended by four-connected OAIP linkers to form an uncommon (4,8)-connected alb-4,8-Cmce topology based on (3,6)-connected kgd sublayers. Both 1 and 2 showed significant antiferromagnetic interactions between the intracluster metal ions, whereas 3 revealed strong blue photoluminescence.

Construction of Four Zn(II) Coordination Polymers Used as Catalysts for the Photodegradation of Organic Dyes in Water

Hydrothermal reactions of Zn(OAc)₂·2H₂O with flexible bipyridyl benzene ligand and three dicarboxylic derivatives gave rise to four new coordination polymers, [Zn₇(μ₄-O)₂(OAc)₁₀(bpmb)]_n (1), [Zn(5-OH-1,3-BDC)(bpmb)]_n (2), [Zn(1,2-BDC)(bpmb)]_n (3) and [Zn₂(ADB)₂(bpmb)]_n (4) (bpmb = 1,4-bis(pyridine-3-ylmethoxy)benzene, 5-OH-1,3-H₂BDC = 5-hydroxy-1,3-benzenedicarboxylic acid, 1,2-H₂BDC = 1,2-benzenedicarboxylic acid, H₂ADB = 2,2’-azodibenzoic acid). Their structures were characterized by single-crystal X-ray diffraction, elemental analyses, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Compound 1 features a one-dimensional (1D) chain structure based on the rare heptanuclear [Zn₇(μ₄-O)(μ₃-OAc)₂(μ₂-OAc)₈] units. Compound 2 exhibits a novel 2D bilayer structure built from the two parallel 2D (4,4) layers. Compound 3 holds a 2D structure in which the 1,2-BDC ligands work as lockers interlocking 1D [Zn(bpmb)]_n chain. Compound 4 comprises a 3D framework constructed by 2D wrinkled [Zn₂(ADB)₄]_n networks and bpmb linkers with a six-connected pcu net. These results suggest that the motifs of the dicarboxylic ligands have significant effect on the final structures. These compounds exhibited relatively good photocatalytic activity towards the degradation of methylene blue (MB) in aqueous solution under a Xe lamp irradiation.

Structural diversity, luminescence and photocatalytic properties of six coordination polymers based on designed bifunctional 2-(imidazol-1-yl)terephthalic acid

Six CPs, based on 2-(imidazol-1-yl)terephthalic acid, have been prepared and characterized.

Construction of five Zn(ii)/Cd(ii) coordination polymers derived from a new linear carboxylate/pyridyl ligand: design, synthesis, and photocatalytic properties

Reactions of Cd(OAc)₂/Zn(OAc)₂ with a new linear carboxylate/pyridyl ligand under different templates via an in situ ligand transformation reaction produced five new CPs. Complexes 1–5 exhibited relatively good photocatalytic activity towards the degradation of methylene blue.

Structural diversity and photocatalytic properties of Cd(ii) coordination polymers constructed by a flexible V-shaped bipyridyl benzene ligand and dicarboxylate derivatives

Reactions of Cd(OAc)₂ with V-shaped bipyridyl benzene and five benzenedicarboxylic acid derivatives gave rise to five new CPs. Complexes 1–5 exhibited relatively good photocatalytic activity towards the degradation of methylene blue.

Hydrothermal syntheses, structural characterizations, and magnetic properties of five MOFs assembled from C2-symmetric ligand of 1,3-di(2′,4′-dicarboxylphenyl)benzene with various coordination modes

Five new complexes with appealing structural features from 0D paddle wheel {Cu₂(COO)₄} SBUs to 3D frameworks were reported to better understand the synthon selectivity in multifunctional crystal structures.

Assembly of a series of d10 coordination polymers based on W-shaped 1,3-di(2′,4′-dicarboxyphenyl)benzene: from syntheses, structural diversity, luminescence, to photocatalytic properties

Six d¹⁰ coordination polymers with different architectures based on W-shaped 1,3-di(2′,4′-dicarboxyphenyl)benzene (H₄DDB) have been prepared. Their photoluminescence and photocatalytic properties were also investigated.

Structural diversities and related properties of four coordination polymers synthesized from original ligand of 3,3′,5,5′-azobenzenetetracarboxylic acid

Four CPs, derived from the original 3,3′,5,5′-azobenzenetetracarboxylic acid ligand were obtained under solvothermal conditions.

Coligand syntheses, crystal structures, luminescence and photocatalytic properties of five coordination polymers based on rigid tetracarboxylic acids and imidazole linkers

Coligand syntheses, crystal structures, luminescence and photocatalytic properties of five coordination polymers based on rigid tetracarboxylic acids and imidazole linkers.

Positional isomeric effect on the structural variation of Cd(ii) coordination polymers based on flexible linear/V-shaped bipyridyl benzene ligands

Solvothermal reactions of Cd(OAc)₂·2H₂O with 2,2′-azodibenzoic acid and five positional isomeric N-donor bipyridyl benzene ligands in MeOH/H₂O at 170 °C gave rise to five coordination polymers. Complexes 1–5 were characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, and single-crystal X-ray diffraction.

Syntheses, structures, topologies, and luminescence properties of four coordination polymers based on bifunctional 6-(4-pyridyl)-terephthalic acid and bis(imidazole) bridging linkers

Four CPs, with the structure ranged from 2D sheet to 3D 3-fold penetrated net, have been designed with the mixed-ligand strategy of bifunctional 6-(4-pyridyl)-terephthalic acid and bis(imidazole) bridging linkers.

Structural diversity of five coordination polymers based on 2,6-bis(3,5-dicarboxyphenyl)pyridine ligand: solvothermal syntheses, structural characterizations, and magnetic properties

Five CPs, featuring diverse structures, have been assembled from the mixed ligands of H₄BDP and bib under different reaction conditions.

The three-dimensional coordination polymer poly[[aqua[μ4-2,2'-(diazene-1,2-diyl)dibenzoato]lead(II)] 1,2-bis(pyridin-4-yl)ethylene hemisolvate]

A novel three-dimensional coordination polymer, {[Pb(C14H8N2O4)(H2O)]·0.5C12H10N2}n, has been synthesized by hydrothermal reaction of Pb(OAc)2·3H2O (OAc is acetate), 2,2'-(diazene-1,2-diyl)dibenzoic acid (H2L) and 1,2-bis(pyridin-4-yl)ethylene (bpe). The asymmetric unit contains a crystallographically independent Pb(II) cation, one L(2-) ligand, an aqua ligand and half a bpe molecule. Each Pb(II) centre is seven-coordinated by six O atoms of bridging-chelating carboxylate groups from L(2-) ligands and by one O atom from a coordinated water molecule. The Pb(II) cations are bridged by L(2-) ligands, forming [PbO2]n chains along the a axis. These chains are further connected by L(2-) ligands along the b and c axes to give a three-dimensional framework with a 4(12)6(3) topology. The channel voids are occupied by bpe molecules.

A three-dimensional Pb(II) coordination framework: poly[[μ4-(E)-2,2'-(diazene-1,2-diyl)dibenzoato]dimethanollead(II)]

In the title coordination polymer, [Pb(C14H8N2O4)(CH3OH)2]n, the asymmetric unit contains half of a Pb(II) cation, half of a 2,2'-(diazene-1,2-diyl)dibenzoate dianionic ligand (denoted L(2-)) and one methanol ligand. Each Pb(II) centre is eight-coordinated by six O atoms of chelating/bridging carboxylate groups from four L(2-) ligands and two O atoms from two terminal methanol ligands, forming a distorted dodecahedron. The [PbL2(MeOH)2] subunits are interlinked via the sharing of two carboxylate O atoms to form a one-dimensional [PbL2(MeOH)2]n chain. Adjacent chains are further connected by L(2-) ligands, giving rise to a two-dimensional layer, and these layers are bridged by L(2-) linkers to afford a three-dimensional framework with a 4(12)6(3) topology.

A three-dimensional Zn(II) coordination framework: poly[[μ2-(E)-1,2-bis(pyridin-4-yl)ethene][μ4-(E)-2,2'-(diazene-1,2-diyl)dibenzoato][μ2-(E)-2,2'-(diazene-1,2-diyl)dibenzoato]dizinc(II)]

In the title coordination polymer, [Zn2(C14H8N2O4)2(C12H10N2)]n, the asymmetric unit contains one Zn(II) cation, two halves of 2,2'-(diazene-1,2-diyl)dibenzoate anions (denoted L(2-)) and half of a 1,2-bis(pyridin-4-yl)ethene ligand (denoted bpe). The three ligands lie across crystallographic inversion centres. Each Zn(II) centre is four-coordinated by three O atoms of bridging carboxylate groups from three L(2-) ligands and by one N atom from a bpe ligand, forming a tetrahedral coordination geometry. Two Zn(II) atoms are bridged by two carboxylate groups of L(2-) ligands, generating a [Zn2(CO2)2] ring. Each loop serves as a fourfold node, which links its four equivalent nodes via the sharing of four L(2-) ligands to form a two-dimensional [Zn2L4]n net. These nets are separated by bpe ligands acting as spacers, producing a three-dimensional framework with a 4(6)6(4) topology. Powder X-ray diffraction and solid-state photoluminescence were also measured.

Structural diversity and magnetic properties of six metal–organic polymers based on semirigid tricarboxylate ligand of 3,5-bi(4-carboxyphenoxy)benzoic acid

Six new metal–organic complexes with structural diversities constructed from 3,5-bi(4-carboxyphenoxy)benzoic acid and metal ions were synthesized and characterized.