Supramolecular Aggregate of Cadmium(II)-Based One-Dimensional Coordination Polymer for Device Fabrication and Sensor Application

Exploitation of a 1D coordination polymer as a portable kit for an eye-catching fluorometric response towards sensing of trivalent cations

The development and utilization of coordination polymers (CPs) have drawn interest for potential applications in different fields. Detection of metal ions in efficient and selective manners is an important field of research. It paves the way to protect human health by balancing toxic metal ions and biologically active metal ions in the atmosphere. In this regard, a new one-dimensional (1D) 4-(1-naphthylvinyl)pyridine (4-nvp) based CP [Cd(NCS)2(4-nvp)2]n (1) was synthesized and characterized structurally by single-crystal X-ray diffraction. Interestingly, this 1D CP underwent supramolecular aggregation via π⋯π stacking interactions, which specifically generated an environment for a potent "turn on" response in the presence of trivalent cations (Fe3+, Al3+, and Cr3+) in the nanomolar range but remained silent in the presence of other metal ions. Density functional theory (DFT) computations and X-ray photoelectron spectroscopy (XPS) were performed to establish the sensing phenomena. Fascinatingly, utilizing the sensitivity of 1 in an aqueous medium, a hands-on portable cotton swab kit was developed for instant identification of these three important trivalent metal cations.

Facile construction of an anthracene-decorated highly luminescent coordination polymer for the selective detection of explosive nitroaromatics and the mutagenic pollutant TNP

Explosive nitroaromatic compounds (epNACs) are a group of chemicals that have caused significant human casualties through terrorist attacks and they also pose health risks. For the benefit of homeland security and environmental health, there is room for advancing research on the precise detection of epNACs. Coordination polymers (CPs) successfully serve this purpose because of their binding abilities and quenching capabilities. In this regard, a one-dimensional (1D) CP [Zn(bdc)(avp)2(H2O)]n (1; H2bdc = 1,4-benzenedicarboxylic acid and avp = 4-[2-(9-anthryl)vinyl]pyridine) was synthesized, which remarkably demonstrated extremely efficient ratiometric and selective sensing capacity toward epNACs and the mutagenic pollutant 2,4,6-trinitrophenol (TNP) with a quick response. Density functional theory (DFT) calculations provided a thorough analysis of the mechanistic routes behind the quenching reaction. Herein, geometrically accessible interaction sites were strategically decorated using anthracene moieties, allowing the quick and precise detection of explosive nitro derivatives and the carcinogenic pollutant TNP with increased sensitivity.

Correlation in Structural Architecture toward Fabrication of Schottky Device with a Series of Pyrazine Appended Coordination Polymers

Energy is the center of importance for the survivability of civilization. Use of fossil fuel is going to be suspended, and renewable energy is technologically costlier. In the quest for new energy sources and to minimize fuel expenditure, the design of energy efficient devices is one of the solutions. Toward this objective, highly delocalized π-acidic N-hetreocycle pyrazine bridged Cd(II)-based coordination polymers (CPs), [Cd(tppz)(adc)(MeOH)] (1), [Cd(tppz)(trep)] (2), and [Cd(tppz)(2,6-ndc)] (3; tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) are synthesized in combination with π-accessible dicarboxylato linkers (acetylene dicarboxylic acid (H2adc), terephthalic acid (H2trep), and 2,6-naphthalene dicarboxylic acid (2,6 H2ndc)). The structures of the compounds, 1-3, have been confirmed by single-crystal X-ray diffraction measurements. Analysis of electrical property demonstrates that light irradiation enhances the conductivity and follows the order 3 > 2 > 1; compound 3 possesses the highest conductivity (1.93 × 10-3 (light), 1.12 × 10-4 S m-1 dark)), than 2 (1.80 × 10-4 (light), 1.10 × 10-4 S m-1 (dark)) and 1 (5.06 × 10-5 (light), 4.72 × 10-5 S m-1 (dark)). This light-induced electrical conductivity can pave the way toward fabrication of an active electronic device by using the discussed materials.

Coordination polymers: a promising candidate for photo-responsive electronic device application

The design and synthesis of electrically conductive coordination polymers (CPs) are of special interest due to their applications in the fabrication of many environmentally benign emerging technologies, such as molecular wires, photovoltaic cells, light emitting diodes (LEDs), field effect transistors (FETs) and Schottky barrier diodes (SBDs). Owing to their structural flexibility, easy functionality and adjustable energy levels, CPs are promising candidates for providing a better pathway for superior charge transport. Again, the utilization of visible light as an external stimulus to control and manoeuvre the electrical properties of the CPs is exceptionally motivating for the development of many optoelectronic devices, such as photodetectors, photo-switches, photodiodes and chemiresistive sensors. The applications of such materials in devices will solve questions regarding the energy crisis and environmental concerns. This study provides an overview of the recent advances in the development of photo-responsive CPs and the possibility of their application in developing optoelectronic devices. In this regard, a thorough literature survey was performed and the studies related to the fabrication of photosensitive conducting CPs for applications in optoelectronic devices are listed.

In Situ Oxidation of Pyridyl-Dihydrobenzoimidazoquinazoline and the Synthesis of a Highly Luminescent Cd(II) Coordination Polymer: A Promising Candidate for Mutagenic Nitroaromatic Detection and Device Fabrication

Pyridyl-substituted imidazoquinoline, a potent fluorescent framework, is advantageous to architect multifunctional coordination networks for sensing and fabricating emergent electrical conductors. In this work, a Cd(II)-based one-dimensional (1D) coordination polymer (1D CP), [Cd(glu)2(pbiq)2(H2O)]n (1), [H2glu = glutaric acid and pbiq = 4-(6-(pyridin-4-yl)benzo[4,5]imidazo[1,2-c]quinazoline)], has been structurally confirmed by single-crystal X-ray crystallography. The H-bonding and π···π interactions built a three-dimensional (3D) supramolecular structure that strongly emits at 416 nm in acetonitrile suspension. Potentially intrusive nitroaromatics (NAs) and trinitrophenol (TNP) selectively quench the strong emission of 1, and the highest quenching is noted in the case of TNP. A detection limit (limit of detection (LOD)) of 1.51 × 10-7 M for TNP is determined. The band gap (3.31 eV) of 1 recognizes semiconducting behavior, and an electronic device is fabricated. The correlation of current vs voltage (I-V plot) reveals a substantial non-ohmic electrical conductivity of 1 (Λ: 1.10 × 10-5 S m-1) along with a low energy barrier (ΦB: 0.69), and the series resistance (Rs) becomes 6.21 kΩ.

Aminoisophthalate Bridged Cd(II)-2D Coordination Polymer: Structure Description, Selective Detection of Pd2+ in Aqueous Medium, and Fabrication of Schottky Diode

Photoluminescence activity of coordination polymers (CPs) has evoked intricate applications in the field of materials science, especially sensing of ions/molecules. In the present study, 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 5-aminoisophthalate (HAIPA^-) coordinated to Cd(II) to architect a coordination polymer, {[Cd(HAIPA)(tppz)(OH)]·3H₂O}_n (CP1) which unveils blue emission in an aqueous acetonitrile (98% aqueous) suspension. The emission is selectively quenched by Pd²⁺ only without interference in the presence of as many as 16 other cations. The structure of CP1 shows the presence of a free -COOH group, and the interlayer (-CO)O(2)···O(7) (OC-) distance, 4.242 Å, along with the π···π interactions (3.990, 3.927 Å), may make a cavity which suitably accommodates only Pd²⁺ (van der Waal's radius, 1.7 Å) through the Pd(II)-carboxylato (-COO-Pd) coordination. The stability of the composite, [CP1 + Pd²⁺] may be assessed from the fluorescence quenching experiment, and the Stern-Volmer constant (K_SV) is 7.2 × 10⁴ M^-1. Therefore, the compound, CP1, is a promising sensor for Pd(II) in a selective manner with limit of detection (LOD), 0.08 μM. The XPS spectra of CP1 and [CP1 + Pd²⁺] have proven the presence of Pd²⁺ in the host and the existence of a coordinated -COO-Pd bond. Interestingly, inclusion of Pd²⁺ in CP1 decreases the band gap from 3.61 eV (CP1) to 3.05 eV ([CP1 + Pd²⁺]) which lies in the semiconducting region and has exhibited improved electrical conductivity from 7.42 × 10^-5 (CP1) to 1.20 × 10^-4 S m^-1 ([CP1 + Pd²⁺]). Upon light irradiation, the electrical conductivities are enhanced to 1.45 × 10^-4 S m^-1 (CP1) and 3.81 × 10^-4 S m^-1 ([CP1 + Pd²⁺]); which validates the highly desired photoresponsive device applications. Therefore, such type of materials may serve as SDG-army (sustainable development goal) to battle against the environmental issues and energy crisis.

Crystallographic Aspects, Photophysical Properties, and Theoretical Survey of Tetrachlorometallates of Group 12 Metals [Zn(II), Cd(II), and Hg(II)] with a Triply Protonated 2,4,6-Tris(2-pyridyl)-1,3,5-triazine Ligand

Zn(II) (complex 1), Cd(II) (complex 2), and Hg(II) (complex 3) complexes have been synthesized using a triply protonated tptz (H₃tptz³⁺) ligand and characterized mainly by single-crystal X-ray analysis. The general formula of all of the complexes is (H₃tptz)³⁺·Cl^-·[MCl₄]^2-·nH₂O (where n = 1, 1.5, and 1.5 for complexes 1, 2, and 3, respectively). The crystallographic analysis reveals that the anion···π, anion···π⁺, and several hydrogen bonding interactions play a fundamental role in the stabilization of the self-assembled architectures that in turn help to enhance the dimensionality of all of the complexes. In addition, Hirshfeld surfaces and fingerprint plots have been deployed here to visualize the similarities and differences in hydrogen bonding interactions in 1-3, which are very important in forming supramolecular architectures. A density functional theory (DFT) study has been used to analyze and rationalize the supramolecular interactions by using molecular electrostatic potential (MEP) surfaces and combined QTAIM/NCI plots. Then, the device parameters for the complexes (1-3) have been thoroughly investigated by fabricating a Schottky barrier diode (SBD) on an indium tin oxide (ITO) substrate. It has been observed that the device made from complex 2 is superior to those from complexes 1 and 3, which has been explained in terms of band gaps, differences in the electronegativities of the central metal atoms, and the better supramolecular interactions involved. Finally, theoretical calculations have also been performed to analyze the experimental differences in band gaps as well as electrical conductivities observed for all of the complexes. Henceforth, the present work combined supramolecular, photophysical, and theoretical studies regarding group 12 metals in a single frame.

Synthesis, Molecular, and Supramolecular Structures of Two Azide-Bridged Cd(II) and Cu(II) Coordination Polymers

Two 1D coordination polymers were synthesized by reaction of two ligands, 2-amino-4-picoline (2A4Pic) and quinoline-6-carboxylic acid (Qu-6-COOH) with two metal (II) nitrate (M = Cd and Cu) in the presence of azide as a linker. The synthesized metal complexes [Cd(2A4Pic)2(N3)2]n; (1) and [Cu(Qu-6-COO)(N3)(H2O)]n; (2) were isolated in single crystals and their X-ray structures revealed a 1D polymeric structure. Due to symmetry considerations, the asymmetric formula is half a [Cd(2A4Pic)2(N3)2] unit for 1 and one [Cu(Qu-6-COO)(N3)(H2O)] unit for 2. In complex 1, the Cd(II) is hexa-coordinated with two 2A4Pic molecules and four μ(1,1) azide units. Hence, the CdN6 coordination environment has a slightly distorted octahedral geometry. In 2, the Cu(II) is hexa-coordinated with three different ligands (Qu-6-COO¯, H2O and μ(1,1) N3¯) where all are connectors between the crystallographically related Cu(II) sites. Additionally, complex 2 distorted CuN2O4 octahedral geometry. In both complexes, the polymer arrays are connected by N…H hydrogen bonds and π–π stacking interactions. Based on Hirshfeld analysis, the percentages of N…H contacts are 43.1 and 27.4% for 1 and 2, respectively, while %C...C are 5.6 and 9.3%, respectively. Analysis of Cu-N, Cu-O, and Cd-N bonds using DFT calculations showed predominantly closed-shell coordination interactions with little covalent characters. Additionally, the negatively charged ligand groups were found to compensate the positive charge of the central metal ion to a larger extent than the electrically neutral ligands.

Explosive and pollutant nitroaromatic sensing through a Cd(II) based ladder shaped 1D coordination polymer

In the existing leanings of environmental and national security issues, establishment of appropriate sensors for explosive as well as pollutant nitroaromatic compounds may be considered as one of the most prodigious job for material researchers. In the current study a new Cd(II) based 1D ladder coordination polymer (CP), [Cd(4-bpd)(3-cbn)₂]_n, has been synthesized and well characterized through single crystal X-ray diffraction analysis. Interestingly, the supramolecular assembly of this compound has efficiently identified 2,4,6-trinitrophenol through fluorescence quenching method. The Stern-Volmer coefficient (K_sv) has been calculated as 6.047 × 10³ M^-1, which can be attributed to the quenching of the emission intensity. The limit of detection (LOD) has been determined as 0.260 μM following the 3σ method along with almost 95% fluorescence intensity reduction. FESEM study revealed that the crystalline nature of the compound has been altered upon interaction with the above mentioned nitroaromatic analyte. Theoretical studies were performed to get the insight idea of fluorescence quenching mechanism which also substantiated the experimental observation. The present study can pave the way for the fabrication of future generation technology in sensor field.

Fluorescence-Responsive Detection of Ag(I), Al(III), and Cr(III) Ions Using Cd(II) Based Pillared-Layer Frameworks

Two Cd(II) based coordination polymers, {Cd₃(btc)₂(BTD-bpy)₂]∙1.5MeOH∙4H₂O}_n (1) and [Cd₂(1,4-ndc)₂(BTD-bpy)₂]_n (2), where BTD-bpy = bis(pyridin-4-yl)benzothiadiazole, btc = benzene-1,3,5-tricarboxylate, and 1,4-ndc = naphthalene-1,4-dicarboxylate, were hydro(solvo)thermally synthesized. Compound 1 has a three-dimensional non-interpenetrating pillared-bilayer open framework with sufficient free voids of 25.1%, which is simplified to show a topological (4,6,8)-connected net with the point symbol of (3²4²56)(3⁴4⁴5⁴6²8)(3⁴4²6¹⁹7²8). Compound 2 has a three-dimensional two-fold interpenetrating bipillared-layer condense framework regarded as a 6-connected primitive cubic (pcu) net topology. Compounds 1 and 2 both exhibited good water stability and high thermal stability approaching 350 °C. Upon excitation, compounds 1 and 2 both emitted blue light fluorescence at 471 and 479 nm, respectively, in solid state and at 457 and 446 nm, respectively, in the suspension phase of H₂O. Moreover, compounds 1 and 2 in the suspension phase of H₂O both exhibited a fluorescence quenching effect in sensing Ag⁺, attributed to framework collapse, and a fluorescence enhancement response in sensing Al³⁺ and Cr³⁺, ascribed to weak ion-framework interactions, with high selectivity and sensitivity and low detection limit.

Spectrophotometric Determination of Trace Amount of Total FeII/FeIII and Live Cell Imaging of a Carboxylato Zn(II) Coordination Polymer

The coordination polymer, (Zn(II)-CP, 1), {[Zn(2,6-NDC)(4-Cltpy)](H₂O)₄} (1) (2,6-H₂NDC = 2,6-naphthalene dicarboxylic acid and 4-Cltpy = 4'-chloro-[2,2';6',2″]terpyridine) is structurally characterized by single crystal X-ray diffraction measurement and other physicochemical studies (PXRD, FTIR, thermal analysis, microanalytical data). 4-Cltpy acts as end-capping ligand, and NDC^2- is a carboxylato bridging motif to constitute ZnN₃O₂ distorted trigonal bipyramid core that propagates to construct 1D chain. The coordination polymer, 1, detects total iron (Fe³⁺ and Fe²⁺) in aqueous solution by visual color change, colorless to pink. Absorption spectrophotometric technique in aqueous medium measures the limit of detection (LOD) 0.11 μM (Fe²⁺) and 0.15 μM (Fe³⁺), and binding constants (K_d) are 6.7 × 10⁴ M^-1 (Fe³⁺) and 3.33 × 10⁴ M^-1 (Fe²⁺). Biocompatibility of 1 is examined in live cells, and intracellular Fe²⁺ and Fe³⁺ are detected in MDA-MB 231 cells. Zn(II) substitution is assumed upon addition of Fe^III/Fe^II solution to the suspension of the coordination polymer, 1, in water-acetonitrile (41:1) (LZn^II + Fe^III/II → LFe^III + Zn^II, where L is defined as coordinated ligands), which is accompanied by changing from colorless to pink at room temperature. The color of the mixture may be assumed to the charge transfer transition from carboxylate-O to Cltpy via Fe(II/III) bridging center (carboxylate-O-Fe-CltPy). The product isolated from the reaction is finally characterized as Fe(III)@1-CP. It is presumed that product Fe(II)@1-CP may undergo fast aerial oxidation to transform Fe(III)@1-CP. The Fe^III exchanged framework (Fe(III)@1-CP) has been characterized by PXRD, IR, TGA and energy dispersive X-ray analysis (EDX)-SEM. The MTT assay calculates the cell viability (%), and the tolerance limit is 100 μM to total Fe²⁺ and Fe³⁺.

A Highly Selective MOF-Based Probe for Turn-On Luminescent Detection of Al3+, Cr3+, and Fe3+ in Solution and Test Paper Strips through Absorbance Caused Enhancement Mechanism

Trivalent metal ions (Cr³⁺, Al³⁺, and Fe³⁺) constitute a major section of the environmental pollutants, and their excess accumulation has a detrimental effect on health, so their detection in trace quantity has been a hot topic of research. A highly scalable 3D porous Zn-based luminescent metal-organic framework (MOF) has been synthesized by exploiting the mixed ligand synthesis concept. The strategic selection of an aromatic π-conjugated organic linker and N-rich spacer containing the azine functionality as metal ion binding sites immobilized across the pore spaces, have made this MOF an ideal turn-on sensor for Al³⁺, Cr³⁺, and Fe³⁺ ions with very high sensitivity, selectivity, and recyclability. An in-depth study revealed absorbance caused enhancement mechanism (ACE) responsible for such turn-on phenomena. In order to make the detection process straightforward, convenient, portable, and economically viable, we have fabricated MOF test paper strips (the MOF could be simply immobilized onto the paper strips) for naked eye visual detection under UV light, which, thus, manifests its potential as a real-time smart sensor for these trivalent ions.

Coordination-Guided Conformational Locking of 1D Metal-Organic Frameworks for a Tunable Stimuli-Responsive Luminescence Region

One-dimensional (1D) metal-organic frameworks (MOFs) have shown great potential for designing more sensitive and smart stimuli-responsive photoluminescence metal-organic frameworks (PL-MOFs). Herein, we propose a strategy for constructing the 1D MOFs with tunable stimuli-responsive luminescence regions based on coordination-guided conformational locking. Two flexible 1D MOF microcrystals with trans- and cis-coordination modes, respectively, were synthesized by controlling the spatial constraint of solvents. The two 1D frameworks possess different conformation lockings of gain ligands, which have a great influence on the rotating restrictions and corresponding excited-state behaviors, generating the remarkably distinct color-tunable ranges (cyan-blue to green and cyan-blue to yellow, respectively). On this basis, the two 1D MOF materials, benefiting from the varied stimuli-responsive ranges, have displayed great potential in fulfilling the anticounterfeiting and information encryption applications. These results provide valuable guidance for the development of smart MOF-based stimuli-responsive materials in information identification and data encryption.

A Zero-Dimensional Organic Lead Bromide of (TPA)2PbBr4 Single Crystal with Bright Blue Emission

Blue-luminescence materials are needed in urgency. Recently, zero-dimensional (0D) organic metal halides have attractive much attention due to unique structure and excellent optical properties. However, realizing blue emission with near-UV-visible light excitation in 0D organic metal halides is still a great challenge due to their generally large Stokes shifts. Here, we reported a new (0D) organic metal halides (TPA)2PbBr4 single crystal (TPA+ = tetrapropylammonium cation), in which the isolated [PbBr4]2− tetrahedral clusters are surrounded by organic ligand of TPA+, forming a 0D framework. Upon photoexcitation, (TPA)2PbBr4 exhibits a blue emission peaking at 437 nm with a full width at half-maximum (FWHM) of 50 nm and a relatively small Stokes shift of 53 nm. Combined with density functional theory (DFT) calculations and spectral analysis, it is found that the observed blue emission in (TPA)2PbBr4 comes from the combination of free excitons (FEs) and self-trapped exciton (STE), and a small Stokes shift of this compound are caused by the small structure distortion of [PbBr4]2− cluster in the excited state confined by TPA molecules, in which the multi-phonon effect take action. Our results not only clarify the important role of excited state structure distortion in regulating the STEs formation and emission, but also focus on 0D metal halides with bright blue emission under the near-UV-visible light excitation.

Synthesis, Structure, and Properties of Complexes Based on 2,4-Bis-(triazol-1-yl)benzoic Acid as a Ligand

Using 2,4-bis-(triazol-1-yl)-benzoic acid as the main ligand and terephthalic acid (TPA) as the auxiliary ligand, combined with Cd(NO₃)₂·4H₂O and Zn(NO₃)₂·6H₂O, self-assembly under solvothermal conditions gave three novel complexes: [Cd_0.5(L)(H₂O)] (1), [Cd(L)(TPA)_0.5(H₂O)]·H₂O (2), and [Zn(L)(TPA)_0.5]·H₂O (3) (TPA = terephthalic acid). The crystal structure test showed that complex 1 belongs to the triclinic crystal system and the P1̅ space group and complexes 2 and 3 belong to the monoclinic crystal system and the P2₁/c space group. Solid-state fluorescence experiments show that complexes 1, 2, and 3 all have excellent optical properties: among them, complexes 1 and 3 can selectively detect MnO₄ ^- with low detection limits (0.96 μM and 0.232 μM, respectively) and complex 2 can detect Cr₂O₇ ^2- [limit of detection (LOD) = 0.035 μM], and the most interesting thing is that all three complexes can be used as sensors for detecting Fe³⁺ (LOD = 0.76 μM, 0.657 μM, and 0.11 μM, respectively). In addition, the detection capabilities of these three complexes for different amino acids and antibiotics were also analyzed, and the results showed that all three complexes can effectively detect tetracycline hydrochloride through the quenching effect and 2 and 3 can selectively detect tryptophan via the fluorescence enhancement effect.

Post-synthetic modification mechanism for 1D spin crossover coordination polymers

Suitable solvent os crucial to achieve a quantitative PSM reaction. Then, this method is not restricted to porous materials.

Dicyanamide-intertwined assembly of two new Zn complexes based on N2O4-type pro-ligand: Synthesis, crystal networks, spectroscopic insights, and selective nitroaromatic turn-off fluorescence sensing

Two new dicyanamide bridged multinuclear Zn complexes, [Zn₂(L¹)(µ_1,5-dca)₂(µ₁-dca)]_n (1) and [Zn₂(L²)(µ_1,5-dca)₂(µ₁-dca)]_n (2) have been synthesized using N₂O₄-based pro-ligands (H₂L¹ = N,N'-bis(5-bromo-3-methoxysalicylidenimino)-1,3-diaminopropane, H₂L² = N,N'-bis(3-ethoxysalicylidene)-2,2-dimethyl-1,3-propanediamine) and characterized by microanalytical and spectroscopic techniques. Both complexes are stable in solution and solid-state. Thermogravimetric analysis (TGA) findings showed that complexes are stable at room temperature. Single-crystal X-ray diffraction (SCXRD) has proven that complexes are identical structures where two zinc metal ions are crystallographically independent. The directional properties of dicyanamide co-ligands via µ_1,5 bridging have resulted in different connectivity of zinc metal ions leading to 1D templates. SCXRD revealed some notable non-covalent interactions (π⋯π, C-H····π, and H-bonding) in their solid-state crystal structures. 1-2 have strong fluorescence behaviour over pro-ligands, which may be quenched in the presence of various electron-deficient explosive nitroaromatic compounds (epNACs). Complex 2 fluorescence intensity is sharper than 1; hence the former retained high sensitivity and selectivity for trinitrophenol (TNP). The enhancement of fluorescence mechanism, detection limit (LOD), and the quenching constant (K_SV) have been calculated using the Stern-Volmer equation (SV), where the K_SV value for TNP is found to be 1.542 × 10⁴ M^-1. The solution phase quenching mechanism has been rationalized by (a) electrostatic interactions through charge-transfer complex, (b) photo-induced electron transfer (PET) by the HOMO-LUMO energy gap via DFT, and (c) fluorescence resonance energy transfer (FRET). Finally, complex 2 is applied as a sensor by turn-off fluorescence response to detecting TNP nitroaromatics in the DMF medium.

Porphyrin-Based Metal-Organic Framework Probe: Highly Selective and Sensitive Fluorescent Turn-On Sensor for M3+ (Al3+, Cr3+, and Fe3+) Ions

The development of porphyrin-based metal-organic frameworks (MOFs) has attracted significant interest in the scientific community in recent years because of their versatile applications particularly in optical and electronic fields. In this study, a highly selective and sensitive fluorescent turn-on sensor using a porphyrinic MOF, Tb-TCPP, is presented, which displays a 10-fold fluorescence enhancement in the presence of Al³⁺, Cr³⁺, and Fe³⁺ ions. The detection limit is in the nM region. For the Al³⁺ ion, it could be visually detected at concentrations as low as 5 mM within 15 min. Tb-TCPP could also be used as an indicator for acidic or alkaline solutions at pH values of >9 and <3. The studies on the detection mechanism illustrate that cation exchange proceed between Tb-TCPP and these M³⁺ ions, and consequently, energy transfer from TCPP to Tb³⁺ is suppressed and π*-π energy transfer of the porphyrin ligand is significantly enhanced.

A highly stable Zn coordination polymer exhibiting pH-dependent fluorescence and as a visually ratiometric and on–off fluorescent sensor

A thermally and chemically stable Zn coordination polymer exhibiting pH-dependent fluorescence behaves as a multi-responsive fluorescent sensor for ratiometric and on–off detection of multiple analytes.

An experimental and theoretical exploration of supramolecular interactions and photoresponse properties of two Ni(ii) complexes

Two new nickel(ii) complexes, C₃₂H₂N₈NiClO₉ (1) and C₃₆H₂₈N₁₂NiOF₂₄P₄ (2) are reported. The noncovalent interactions witnessed in their crystal packing have been analysed using DFT calculations.

The influence of linker substitution on the fluorescence responsive sensing of isostructural coordination polymers: visual turn-on, ratiometric, and turn-off sensing in water

Linker substituents show great impacts on the luminescence properties and sensing performances of isostructural coordination polymers, causing turn-on or ratiometric sensing of Fe³⁺, Al³⁺, and Cr³⁺ and turn-off sensing of CrO₄²⁻ and Cr₂O₇²⁻.

Sunlight assisted SCSC dimerization of a 1D coordination polymer impacts the selectivity of Pd(II) sensing in water

A one-dimensional coordination polymer (1D CP) [Cd(4-nvp)2(5-ssa)]·(4-nvp) (1) [4-nvp = 4-(1-naphthylvinyl)pyridine and 5-ssa = 5-sulfosalicylic acid] undergoes topochemical [2+2] cycloaddition by sunlight irradiation to generate a two-dimensional (2D) CP [Cd(rctt-4-pncb)0.5(4-nvp)(5-ssa)]·(4-nvp) (1') [rctt-4-pncb = 1,3-bis(4'-pyridyl)-2,4-bis(naphthyl)cyclobutane] in a single-crystal to single-crystal manner. Interestingly, 1' can be reverted back to 1 by heating and both the CPs selectively recognize Pd2+ in aqueous medium; however, the limit of detection is improved after photodimerization.

Pair of chiral molecular ladders and successive hydration in single-crystal-to-single-crystal mode

Self-assembly of Zn(NO3)2 with a pair of new tridentate chiral Ls produced a pair of chiral ladder-type 1D coordination polymers, where crystals were transformed into different hydrated products of zigzag 1Ds depending on chirality in the SCSC mode.

Ultra-trace level detection of Cu2+ in an aqueous medium by novel Zn(ii)-dicarboxylato–pyridyl coordination polymers and cell imaging with HepG2 cells

Fluorescent 1D Zn(ii) coordination polymers are aggregated via noncovalent interactions. The emission of the CPs is exclusively quenched by Cu²⁺ and the LOD is at μM range. In aqueous medium internalization CPs within HepG2 cells is detected by microscopic cell image using Cu²⁺.

Electrically conductive 1D coordination polymers: design strategies and controlling factors

Due to the easy functionality and structural diversity of coordination polymers (CPs) coupled with superior thermal stability, many researchers have been prompted to explore the opportunity of introducing these hybrid materials as active components in various electronic devices, such as light emitting diodes (LED), solar cells, field effect transistors (FET), and Schottky barrier diodes (SBD). Therefore, the judicious selection of the structural components of CPs is directly related to their structure-property relationship and applications. One-dimensional (1D) CPs have recently emerged as excellent electrical conductors and are gaining enormous attention owing to their simple chain-like coordination arrays. In this article, we review the rational design strategies for synthesising 1D CPs and also point out the structural factors that affect the charge transport properties as well as the electrical conductivity of these materials.

Crystal Structures, Hirshfeld Surfaces, and Thermal Study of Isostructural Polymeric Ladders of La(III) and Sm(III) Coordination Compounds with 4,4'-Bipyridine and Dibromoacetates

Two novel mixed ligand complexes with general formula [M2(4,4'-bpy)1.5(CBr2HCOO)6(H2O)2]n (where 4,4'-bpy = 4,4'-bipyridine) were synthesized. Thermal analysis was used to describe a solid intermediate and final products of thermolysis. A coupled TG-MS system was used to monitor principal volatile fragments evolved during pyrolysis. Crystal structures of the complexes were determined. Cationic dinuclear M2 (M(III) = La, Sm) coordination cores were obtained. Both crystal structures are isostructural. Single crystal X-ray diffraction analysis revealed that investigated structures of 1D coordination polymers assembled in ladder-like systems. The central atom replacement resulted in unit cell identity parameter П = 0.0091. Additionally, the isostructurality of the reported La(III) and Sm(III) complexes was revealed using Hirshfeld Surface analysis supported by Enrichment Ratio calculations.

Reprogrammable fluorescence logic sensing for biomolecules via RNA-like coenzyme A-based coordination polymer

In this study, coenzyme A (CoA)-based coordination polymers (CPs) have been generated in situ by exploiting the reaction of thiols with metal ion (Au(III) or Ag(I)), which are dependent on both thiol-metal and aurophilic metal∙metal interaction. It is interesting to note that CPs-related biosensing capabilities toward some biomolecules including ascorbic acid (AA), cysteine (Cys) and glutathione (GSH) are also investigated via SYBR Green II (SGII)-derived fluorescence switchable mechanisms. The synthesized CPs display especial RNA-like structure and are capable of initiating the fluorescence of SGII. Conversely, AA, Cys or GSH can give rise to the structural destruction of RNA-like CPs, thus inhibiting the fluorescence signal, and quantitative detection of these biomolecules are achieved favorably with a detection limit of 7.2, 0.55 and 0.48 nM, respectively. Meanwhile, the fascinating fluorescence on-off property and simple synthetic process are employed to build a series of basic logic gates (YES, NOT, OR, AND, INHIBIT and NOR) and multiple configurable logic gates (OR-AND and OR-OR-INHIBIT) along with different logic inputs. In view of these, developing CoA-based CPs as a new material to execute logic operations provides a valuable platform to establish the next generation of advanced molecular devices for clinic diagnostic and biomedical research.

Biporous Cd(II) Coordination Polymer via in Situ Disulfide Bond Formation: Self-Healing and Application to Photosensitive Optoelectronic Device

A heteroporous metal-organic framework, [Cd₂(2,2'-DSB)₂(INH)₂(H₂O)₂]_n (1), is fabricated by the reaction of CdI₂, 2-mercaptobenzoic acid (2-MBAH), and isoniazid (INH). The X-ray structure of the compound 1 shows the bridging INH and 2,2'-disulfanediyldibenzoic acid (H₂2,2'-DSBA) around the Cd(II) ion center. 2-MBAH has been in situ dimerized to the formation of 2,2'-DSB^2- (S-S-bonded dianion), which has further extended to form the 2D network. However, supramolecular assembly via π···π and hydrogen bonds strengthens the structural motif within the 3D array. Optical stimulation generated the thiol radical under an argon environment followed by the electron paramagnetic resonance (EPR) study, but upon exposure to air, the EPR signal gradually disappeared by the formation of the S-S bond, which was commonly known as a self-healing property. Again, compound 1 exhibited as a semiconducting material with a band gap of 3.7 eV. The I-V characteristics of 1 show that the conductivity is intensified by an optical response. The Schottky diode property of 1 shows a lower barrier height, a lower resistance, and a higher conductivity upon illumination at 360 nm.

Zinc(ii)-based coordination polymer encapsulated Tb3+ as a multi-responsive luminescent sensor for Ru3+, Fe3+, CrO4 2-, Cr2O7 2- and MnO4. RSC Adv 2020;10:6022-6029. [PMID: 35497449 PMCID: PMC9049217 DOI: 10.1039/c9ra09541a]

A zinc(ii)-based coordination polymer (CP), namely [Zn(modbc)2] n (Zn-CP) (modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4'-bipyridine-5-carbonitrile), has been synthesized and characterized. Single-crystal structural determination reveals that Zn-CP is a two-dimensional framework structure with tetranuclear homometallic Zn4(modbc)4 units cross-linked by modbc. The excellent luminescence as well as good stability of Zn-CP do not enable it to have selective sensing capability for different ions. After encapsulation of Tb3+ in Zn-CP, the as-obtained fluorescent functionalized Tb3+@Zn-CP maintained excellent luminescence as well as stability, which made it a highly selective and sensitive multiresponsive luminescent sensor for Ru3+, Fe3+, CrO4 2-, Cr2O7 2-, and MnO4 - with high sensitivity, good anti-interference performance, and quick response time (∼10 s). The detection limits are 0.27 μM, 0.57 μM, 0.10 μM, 0.43 μM and 0.15 μM, respectively. A possible sensing mechanism was discussed in detail.

Studies on Magnetic and Dielectric Properties of Antiferromagnetically Coupled Dinuclear Cu(II) in a One-Dimensional Cu(II) Coordination Polymer

A one-dimensional Cu(II) coordination polymer with encapsulated antiferromagnetically coupled binuclear Cu(II) has been synthesized by using 5-nitroisophthalic acid (5-N-IPA) and 4-aminopyridine (4-APY) [Cu₂(5-N-IPA)₂(4-APY)₄] _n (1). Electrical properties are examined by complex impedance (Z*), dielectric permittivity (ε*), and ac conductivity studies at different frequencies (10 kHz-5 MHz) and temperatures (253-333 K). The contribution of grain and grain boundary has been explained by a different theoretical model. The variable temperature magnetic susceptibility data for compound 1 were recorded between 300 and 2 K. The shape of the curve (χ_M T vs T) indicates dominant antiferromagnetic coupling, which results from the interaction between the copper(II) atoms.

Supramolecular assembly of a 4-(1-naphthylvinyl)pyridine-appended Zn(ii) coordination compound for the turn-on fluorescence sensing of trivalent metal ions (Fe3+, Al3+, and Cr3+) and cell imaging application

The as-synthesized Zn(ii) coordination compound exhibited turn-on fluorescence sensing of analytical group-IIIA metal ions (Fe³⁺, Al³⁺, and Cr³⁺) and applications in cell imaging.

Novel alkaline earth metal–organic frameworks with thiophene groups for selective detection of Fe3+

This work demonstrates that the alkaline earth ion radii play an important role in coordination numbers and topologies for constructing MOFs, and these MOFs can be used as fast-response fluorescence sensors for the detection of Fe³⁺.