Construction of olefinic coordination polymer single crystal platforms: precise organic synthesis, in situ exploration of reaction mechanisms and beyond

Olefin [2+2] photocycloaddition reactions based on coordination-bond templates provide numerous advantages for the selective synthesis of cyclobutane compounds. This review outlines the recent advances in the design and construction of single crystal platforms of olefinic coordination polymers for precise organic synthesis, in situ exploration of reaction mechanisms, and possible developments as comprehensively as possible. Numerous examples are presented to illustrate how the arrangements of the olefin pairs influence the solid-state photoreactivity and examine the types of cyclobutane products. Furthermore, the photocycloaddition reaction mechanisms are investigated by combining advanced techniques such as single crystal X-ray diffraction, powder X-ray diffraction, nuclear magnetic resonance, infrared spectroscopy, fluorescence spectroscopy, laser scanning confocal microscopy and theoretical calculations. Finally, potential applications resulting from promising physicochemical properties before and after photoreactions are discussed, and existing challenges and possible solutions are also proposed.

Visual Hg(II) sensing in aqueous solution via a new 2,5-Bis(4-pyridyl)thiazolo[5,4-d]thiazole-based fluorescence coordination polymer

A new fluorescence coordination polymer [Zn(Py₂TTz)(5-OH-IPA)]_n (1) (Py₂TTz = 2,5-bis(4-pyridyl)thiazolo[5,4-d]thiazole, 5-OH-IPA = 5-hydroxyisophthalic acid dianion) was synthesized, which exhibited the characteristics of fluorescence quenching and bathochromic shift toward Hg(II) in aqueous solution at pH 7.00. Mechanism study showed that the interactions between Hg(II) ions and Py₂TTz ligands in 1 were responsible for the fluorescence emission change. Thanks to the specific interactions between 1 and Hg(II), excellent selectivity was achieved both in aqueous solution and in solid test paper. The detection limit of 1 for Hg(II) sensing was 125.76 nmol L^-1 and a linear rang was 1.00-10.00 μmol L^-1. More importantly, satisfactory recovery and accuracy of 1 for Hg(II) sensing were also obtained in buffer-free real water samples.

Four MOFs with isomeric ligands as fluorescent probes for highly selective, sensitive and stable detection of antibiotics in water

Four complexes showed excellent discriminative probes for cefixime (CEF) and tetracycline (TEC) based on their sensitive fluorescence quenching. The PET and IFE effects resulted in high sensitivity and selectivity for the detection of CEF and TEC.

Assembly of a Zn(II) coordination polymer of tetrapyridyl tetraene ligands for selective sensing of CrO42- and Fe3+ in water via luminescence quenching and enhancement

Four Zn(II)-based coordination polymers (CPs), [Zn(4-tkpvb)(FB)2] (CP1), [Zn(4-tkpvb)(CB)2] (CP2), [Zn(4-tkpvb)(BB)2] (CP3) and [Zn(4-tkpvb)(NTP)]n (CP4), were prepared from solvothermal reactions of Zn(NO3)2•6H2O with 1,2,4,5-tetrakis((E)-2-(pyridin-4-yl)vinyl)benzene (4-tkpvb) in the presence of 3-florobenzoic acid...

A novel fluorometric chemosensor based on imidazo[4,5-b]phenazine-2-thione for ultrasensitive detection and separation of Hg2+ in aqueous solution

We synthesized and developed 1,3-dihydro-2H-imidazo[4,5-b]phenazine-2-thione as a ratiometric chemosensor for Hg2+ recognition in a DMSO/H2O (v/v = 9:1) binary solution. We rationally introduced the phenazine imidazole group as the fluorophore and the thione moiety as the recognition site to bind Hg2+. Interestingly, the chemosensor showed an ultrasensitive response to Hg2+, and the lowest limit of detection was 0.167 nM. In addition, it can also separate Hg2+ from aqueous solutions with excellent ingestion capacity, with an adsorption ratio of up to 96%. Furthermore, ion test strips based on chemosensors were fabricated for convenient and efficient detection of Hg2+.

Progress in Metal-Organic Frameworks Facilitated Mercury Detection and Removal

Metal Organic Frameworks (MOFs) are noted as exceptional candidates towards the detection and removal of specific analytes. MOFs were reported in particular for the detection/removal of environmental contaminants, such as heavy metal ions, toxic anions, hazardous gases, explosives, etc. Among heavy metal ions, mercury has been noted as a global hazard because of its high toxicity in the elemental (Hg0), divalent cationic (Hg2+), and methyl mercury (CH3Hg+) forms. To secure the environment and living organisms, many countries have imposed stringent regulations to monitor mercury at all costs. Regarding the detection/removal requirements of mercury, researchers have proposed and reported all kinds of MOFs-based luminescent/non-luminescent probes towards mercury. This review provides valuable information about the MOFs which have been engaged in detection and removal of elemental mercury and Hg2+ ions. Moreover, the involved mechanisms or adsorption isotherms related to sensors or removal studies are clarified for the readers. Finally, advantages and limitations of MOFs in mercury detection/removal are described together with future scopes.

Five water-stable luminescent CdII-based metal–organic frameworks as sensors for highly sensitive and selective detection of acetylacetone, Fe3+ and Cr2O72− ions

Five Cd^II-based MOFs with different topologies were prepared, in which 2 and 3 are rare examples which display excellent sensitivity, selectivity, recyclability and structural stability for detection of acac/Fe³⁺ and acac/Cr₂O₇²⁻, respectively.

Zn(ii)/Cd(ii) based mixed ligand coordination polymers as fluorosensors for aqueous phase detection of hazardous pollutants

The recent developments and prospects of fluorosensors with a handful of recent examples based on mixed ligand Zn(ii)/Cd(ii) coordination polymers for aqueous phase detection of organic as well as inorganic pollutants have been discussed.

Syntheses, crystal structures, dye degradation and luminescence sensing properties of four coordination polymers

Four coordination polymers based on the pyridyl-carboxyl ligand have been solvothermally synthesized and characterized. The heterogeneous catalytic oxidation activities of 1–3 and luminescence titration experiments for 4 have been studied.

Structural diversity, magnetic properties and luminescence of NiII, CoII and ZnII coordination polymers derived from 3,3'-[(5-carboxy-1,3-phenylene)bis(oxy)]dibenzoic acid and 1,10-phenanthroline

Three novel coordination polymers (CPs), namely poly[[di-μ-aqua-bis{μ₄-3,3'-[(5-carboxylato-1,3-phenylene)bis(oxy)]dibenzoato-κ⁵O¹:O^1',O³:O⁵:O^5'}bis(1,10-phenanthroline-κ²N,N')trinickel(II)] dimethylformamide 1.5-solvate trihydrate], {[Ni₃(C₂₁H₁₁O₈)₂(C₁₂H₈N₂)₂(H₂O)₂]·1.5C₃H₇NO·3H₂O}_n, (I), poly[[di-μ-aqua-bis{μ₄-3,3'-[(5-carboxylato-1,3-phenylene)bis(oxy)]dibenzoato-κ⁵O¹:O^1',O³:O⁵:O^5'}bis(1,10-phenanthroline-κ²N,N')tricobalt(II)] diethylamine disolvate tetrahydrate], {[Co₃(C₂₁H₁₁O₈)₂(C₁₂H₈N₂)₂(H₂O)₂]·2C₂H₇N·4H₂O}_n, (II), and catena-poly[[aqua(1,10-phenanthroline-κ²N,N')zinc(II)]-μ-5-(3-carboxyphenoxy)-3,3'-oxydibenzoato-κ²O¹:O³], [Zn(C₂₁H₁₂O₈)(C₁₂H₈N₂)(H₂O)]_n, (III), have been synthesized by the reaction of different metal ions (Ni²⁺, Co²⁺ and Zn²⁺), 3,3'-[(5-carboxy-1,3-phenylbis(oxy)]dibenzoic acid (H₃cpboda) and 1,10-phenanthroline (phen) under solvothermal conditions. All the CPs were characterized by elemental analysis, single-crystal and powder X-ray diffraction, FT-IR spectroscopy and thermogravimetric analysis. Complexes (I) and (II) have isomorphous structures, featuring similar linear trinuclear structural units, in which the central Ni^II/Co^II atom is located on an inversion centre with a slightly distorted octahedral [NiO₆]/[CoO₆] geometry. This comprises four carboxylate O-atom donors from two cpboda^3- ligands and two O-atom donors from bridging water molecules. The terminal Ni^II/Co^II groups are each connected to the central Ni^II/Co^II cation through two μ_1,3-carboxylate groups from two cpboda^3- ligands and one water bridge, giving rise to linear trinuclear [M₃(μ₂-H₂O)₂(RCOO)₄] (M = Ni²⁺/Co²⁺) secondary building units (SBUs) and the SBUs develop two-dimensional-networks parallel to the (100) plane via cpboda^3- ligands with new (3²·4)₂(3²·8³·9)₂(3⁴·4².8²·9⁴·10³) topological structures. Zinc complex (III) displays one-dimensional coordination chains and the five-coordinated Zn atom forms a distorted square-pyramidal [ZnO₃N₂] geometry, which is completed by two carboxylate O-atom donors from two distinct Hcpboda^2- ligands, one O atom from H₂O and two N atoms from a chelating phen ligand. Magnetically, CP (I) shows weak ferromagnetic interactions involving the carboxylate groups, and bridging water molecules between the nickel(II) ions, and CP (II) shows antiferromagnetic interactions between the Co²⁺ ions. The solid-state luminescence properties of CP (III) were examined at ambient temperature and the luminescence sensing of Cr₂O₇^2-/CrO₄^2- anions in aqueous solution for (III) has also been investigated.

High sensitivity fiber sensor for measurement of Cd2+ concentration in aqueous solution based on reflective Mach-Zehnder interference with temperature calibration

We propose a novel fiber chemical sensing system based on reflective Mach-Zehnder interference with temperature calibration for the measurement of Cd²⁺ in aqueous solution. The sensing system has high measurement sensitivity of Cd²⁺ with an estimated minimum detection limit of 4×10^-7 mol/L at a spectral resolution of 0.02 nm and with long-term stability. The fiber sensing head is prepared by coating a sensing membrane on a fused tapering single-mode fiber. The thiourea group of the sensing membrane has an effective combination effect on Cd²⁺. Disturbance from ambient temperature fluctuation on the measurement of Cd²⁺ concentration can be eliminated with the fiber Bragg grating.

A Bifunctional Luminescent Metal-Organic Framework for the Sensing of Paraquat and Fe3+ Ions in Water

The hydrothermal reaction of Zn²⁺ ions with a mixture of two ligands, Hcptpy and H₃ btc (Hcptpy=4-(4-carboxyphenyl)-2,2':4',4''-terpyridine; H₃ btc=1,3,5-benzenetricarboxylic acid), led to the formation of a 3D metal-organic framework (MOF) with 1D channels, [Zn₂ (cptpy)(btc)(H₂ O)]_n (1), which was structurally characterized by using single-crystal X-ray diffraction (SXRD). In MOF 1, two independent Zn²⁺ ions were interconnected by btc^3- ligands to form a 1D chain, whilst adjacent Zn²⁺ ions were alternately bridged by cptpy^- ligands to generate a 2D sheet, which was further linked by 1D chains to form a 3D framework with a new (3,3,4,4)-connected topology. Furthermore, compound 1 also exhibited excellent stability towards air and water and, more importantly, luminescence experiments indicated that it could serve as a probe for the sensitive detection of paraquat (PAQ) and Fe³⁺ ions in aqueous solution.

Two zinc(ii) coordination polymers based on flexible co-ligands featuring assembly imparted sensing abilities for Cr2O7 2- and o-NP

Two new Zn(ii) coordination complexes, formulated as [Zn(opda)(pbib)] (1) and [Zn(ppda)(pbib)(H2O)] (2), (H2opda = 1,2-phenylenediacetic acid, H2ppda = 1,4-phenylene-diacetic acid, pbib = 1,4-bis(1-imidazoly)benzene), have been synthesized. The opda ligands extend a 1D chain containing (Zn-pbib) polymer chains into a 2D layer in 1. In 2, the ppda ligands link Zn(ii) atoms to form a 2D network, then the rigid bis(imidazole) ligands give rise to the 3D structure. The fluorescence property application and mechanisms of two complexes for detecting Cr2O7 2- and o-NP have been researched. For two complexes, the high quenching percentage in low concentration aqueous solution are 95.75% (Cr2O7 2-, 1), 95.28% (Cr2O7 2-, 2) and 97.56% (o-NP, 1), 96.59% (o-NP, 2). Compared with 2, complex 1 has higher quenching percentage, this could be because 1 is a 3D supramolecular with a large hole. The detection limits have been measured to be 2.992 × 10-7 M (Cr2O7 2-, 1), and 4.372 × 10-7 M (Cr2O7 2-, 2), 2.103 × 10-7 M (o-NP, 1), 1.862 × 10-7 M (o-NP, 2), respectively. The emissions of two complexes could be effectively and selectively quenched by o-NP and Cr2O7 2-, showing their potential as multi-responsive luminescent sensors.

Synthesis, Molecular and Supramolecular Structures of New Cd(II) Pincer-Type Complexes with s-TriazineCore Ligand

The manuscript described the synthesis and characterization of the new [Cd(BDMPT)2](ClO4)2; 1 and [Cd2(MBPT)2(H2O)2Cl](ClO4)3.4H2O ; 2s-triazine pincer-type complexes, where BDMPT and MBPT are 2,4-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-methoxy-1,3,5-triazine and 2-methoxy-4,6-bis(2-(pyridin-2-ylmsethylene)hydrazinyl)-1,3,5-triazinerespectively.The synthesized complexes were characterized using Fourier-transform infrared spectroscopy (FTIR), 1H and 13C NMR spectroscopy, and the single-crystal X-ray diffraction technique.The homoleptic mononuclear complex (1)contains a hexa-coordinated Cd(II) center with two tridentate N-pincer ligand (BDMPT) with a highly distorted octahedral coordination environment located as an intermediate case between the octahedron and trigonal prism. The heteroleptic dinuclear complex (2) contains two hepta-coordinated Cd(II) coordination spheres where each Cd(II) is coordinated with one pentadentate pincer N-chelate (MBPT), one water, and one bridged chloride ligand connecting the two metal ions. The different intermolecular interactions in the studied complexes were quantified using Hirshfeld analysis. Their thermal stabilities and FTIR spectra were compared with the corresponding free ligands. The strength and nature of Cd–N, Cd–O, and Cd–Cl coordination interactions were discussed in light of atoms in molecules calculations (AIM). The M(II)–BDMPT and M(II)–MBPT interaction energies revealed that such sterically hindered ligands have higher affinity toward large-size metal ions (M =Cd) compared to smaller ones (M= Ni or Mn).

Zinc-based CPs for effective detection of Fe3+ and Cr2O72− ions

Four new zinc-based CPs for the sensitive and selective detection of Fe³⁺ and Cr₂O₇²⁻ ions.

A pillar-layer strategy to construct 2D polycatenated coordination polymers for luminescence detection of Cr2O72− and CrO42− in aqueous solution

Six polycatenated coordination polymers 1–6 based on the pillar-layer strategy have been designed and synthesized. Compound 6 exhibited strong fluorescence that was selectively quenched by Cr^VI ions in aqueous solution at low concentrations.

[2 + 2] cycloaddition reaction and luminescent sensing of Fe3+ and Cr2O72− ions by a cadmium-based coordination polymer

A cadmium-based coordination polymer can produce the corresponding photoproduct via [2 + 2] cycloaddition reaction, and can detect both Fe³⁺ and Cr₂O₇²⁻ ions.

A stable anionic metal–organic framework with open coordinated sites: selective separation toward cationic dyes and sensing properties

A multifunctional anionic metal–organic framework was successfully synthesized using a new pyridyl–tricarboxylate ligand. It could be applied as a luminescent sensor for Fe³⁺ ions and TNP and it showed selective adsorption of cationic dyes.

Fast and Selective Detection of Cr(III) in Environmental Water Samples Using Phosphovanadate Y(V0.2P0.8O4):Eu3+ Fluorescence Nanorods

Phosphovanadate Y(V_0.2P_0.8O₄):Eu³⁺ nanorods have been created via a simple hydrothermal method and used for the highly sensitive and selective fluorescence detection of Cr³⁺ over other common heavy metal ions within a 10 min period. It was found that the fluorescence intensity of Y(V_0.2P_0.8O₄):Eu³⁺ linearly decreases with Cr³⁺ concentrations ranging from 1 × 10^-9 to 1.2 × 10^-6 M. The sensing mechanism for Cr³⁺ is ascribed to the aggregation of Y(V_0.2P_0.8O₄):Eu³⁺ nanorods triggered by Cr³⁺ ions owing to the high affinity of phosphate groups to metal ions. The excellent chemical stability, photostability over a wide pH range of 3-12, and high salt-tolerance performance with ionic strength from 1× 10^-3 to 12 M of Y(V_0.2P_0.8O₄):Eu³⁺ allow these nanorods to successfully overcome the photobleaching and pH-dependent fluorescence property of traditional organic fluorescence probes. These characteristics ensure their applicability to environmental monitoring of Cr³⁺. The sensitive determination of Cr³⁺ in different environmental water samples demonstrated the potential application of Y(V_0.2P_0.8O₄):Eu³⁺ as a practical environmental probe. With the help of a UV lamp (254 nm), the visual Cr³⁺ values for dynamic monitoring in industrial wastewater further verified that this method can even exhibit on-site visible features in daytime and night easily. This allows for the direct monitoring of environmental Cr³⁺.

Luminescent Zn(ii) coordination polymers as efficient fluorescent sensors for highly sensitive detection of explosive nitroaromatics

Zn CPs 1–3 exhibit strong blue/cyan fluorescence emissions in toluene suspension for highly selective and sensitive detection of explosive nitroaromatics through remarkable fluorescence quenching responses. In addition, the framework Zn²⁺ ions in 3 were partially substituted by Cu²⁺ ions via a single-crystal to single-crystal (SCSC) transformation.

Highly selective and sensitive detection of Hg2+, Cr2O72−, and nitrobenzene/2,4-dinitrophenol in water via two fluorescent Cd-CPs

Taking advantage of fluorescent Cd-CPs with 3,3′-thiodipropionic acid and imidazole ligands, herein, we demonstrate the synthesis of functional CPs, and develop two Cd-CP fluorescence sensing materials with highly selective and sensitive detection of Hg²⁺, Cr₂O₇²⁻, NB,/2,4-DNP in water.

A series of Ln4III clusters: Dy4 single molecule magnet and Tb4 multi-responsive luminescent sensor for Fe3+, CrO42−/Cr2O72− and 4-nitroaniline

Five tetranuclear lanthanide clusters were synthesized. Dy₄ complex exhibits single molecule magnet (SMM) behavior and Tb₄ compound shows sensing properties towards Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and 4-nitroaniline (4-NA).