Spacer Ligands Research Articles

A zinc-based coordination polymer as adsorbent for removal of trichlorophenol from aqueous solution: Synthesis, sorption and DFT studies

[Zn(hba)2(tmdp)]n (1), a Zn-coordination polymer (CP), prepared by the reaction of Zn(NO3)2•6H2O, 4-hydroxybenzoic acid (Hhba) and 4,4′- trimethylenedipyridine (tmdp) was reported. The compound was characterised, using CHN, single crystal and powder X-ray diffraction analysis, FT-IR, and TGA techniques. It exhibits a square pyramidal geometry, with the zinc (II) atom coordinated to two nitrogen atoms from two tmdp ligand molecules and to three oxygen atoms from two hba molecules. The zinc (II) carboxylate units are bridged through the N-donor spacer ligand, thereby giving rise to a one-dimensional CP. PXRD analysis confirmed the purity of the bulk of (1). Compound (1) presented an adsorption capacity of 207.8 mg/g for the removal of 2,4,6-trichlorophenol (TCP) from aqueous solution. The adsorption mechanism is governed by π-π stacking and electrostatic interactions, as obtained from DFT studies. The feasibility and exothermic nature of the adsorption process is indicated by the negative binding energy obtained.

A New One-Pot Way to Prepare Enzyme-Containing Coordination Polymers by Sonochemistry.

Enzyme-containing Coordination Polymers (CPs) were prepared by a one-pot sonochemical method, mixing Glucose Oxidase (GOx) enzyme, 4,4'-bipyridine as spacer ligand, and chloride zinc salt. The reaction took place in a very short time (a few minutes) with a minimum use of solvents compared to conventional methods. The obtained composite material, named GOx-[Zn(4,4'-bipy)Cl₂]∞, resulted from embedding the GOx molecules into uniformly sized [Zn(4,4'-bipy)Cl₂] nanocrystals. The structural and thermal characterization, confirmed that the adopted strategy allows the preparation of hybrid bio-nanomaterials in a very fast, facile and eco-friendly method, by simply synthesising the [Zn(4,4'-bipy)Cl₂] nanocrystals in the presence of the enzyme.

Energy/Charge Transfer Modulation with Spacer Ligands for Highly Emissive Quantum Dot-Polymer Blend.

A blend of perovskite quantum dots (QDs) and a hole transport layer (HTL) is a feasible candidate to solve the long-standing issues in light-emitting diodes (LEDs) such as charge injection, energy state matching, and defect passivation. However, QD:HTL blend structures for QD-based LEDs suffer from fast charge and energy transfers due to an inhomogeneous distribution of QDs and the HTL matrix. Here we report new cross-linkable spacer ligands between QDs and TFB that result in a highly emissive QD:TFB-blended LED device. We synthesize three representative spacer ligands to control the charge and energy transfers between QDs and the HTL. The first spacer ligand is used for controlling the molecular distance between QDs and TFB, and the second spacer ligand is designed to investigate how molecular interaction between QDs and the spacer ligand affects the optical property of the QD:TFB blend. Subsequently, the best spacer ligand, a 10-((2-benzoylbenzoyl)oxy)decanoic acid, is designed to anchor TFB (via a benzophenone group) and simultaneously bond to QDs (with a carboxylic acid functional group). The carboxylic acid group strongly interacts with QDs, dramatically improving the cross-linking rate between QDs and TFB. Due to the direct interaction between QDs and TFB, hole carriers can be effectively injected to perovskite QDs through the conductive backbone of TFB, resulting in the highest luminance values of 10917 cd/m2 at 7.4 V due to carrier injection balance. This is at least 10 times better LED performance compared with a pristine QD device.

Isostructural Hg(II) halide coordination polymers: A comparison of powder XRD, IR, emission and Hirshfeld Surface Analysis

Three isomorphous mercury(II) halide coordination polymers [Hg(dpndc)X2]n (X = Cl, 1; Br, 2; I, 3) have been synthesized by the reactions of HgX2 salts with the semi-rigid N,N’-di(pyridin-3-yl)naphthalene-1,4-dicarboxamide (dpndc), which form one-dimensional (1D) helical chains. Stuctural comparisons with the other similar CPs indicate that their structural diversity is governed by the co-crystallized solvent molecules and the identity of the spacer ligands, whereas the role of the halide anions is not significant. Hirshfeld Surface Analysis revels that chlorine atom contributes more non-covalent interactions compared to the bromine and iodine atoms. Complexes 1 - 3 provide a unique opportunity to demonstrate that the powder X-ray diffraction (PXRD) pattern is better than IR and emission spectra to differentiate isomorphous mercury(II) halide CPs.

Cobalt(ii) coordination polymers constructed from bis(N-pyrid-3-ylmethyl)adipoamide and polycarboxylic acids: reversible structural transformation upon proton delivery and removal

The reversible structural transformation upon proton delivery and removal in Co(ii) coordination polymers can be ascribed to the various bonding modes and the flexibility of the spacer ligands.

Unraveling the crucial role of spacer ligands in tuning the contact properties of metal–2D perovskite interfaces

The spacer ligand acts as a buffer layer and plays a crucial role in modulating the contact properties of metal–2D perovskite interfaces.

Synthesis and crystal structures of zinc(II) coordination polymers of trimethylenedipyridine (tmdp), 4-nitrobenzoic (Hnba) and 4-biphenylcarboxylic acid (Hbiphen) for adsorptive removal of methyl orange from aqueous solution

Two novel Zn(II) coordination polymers (CPs), [Zn(nba)2(tmdp)]n (1) and [Zn(biphen)2(tmdp)]n (2), were synthesised by reacting Zn(NO3)2·6H2O and 4,4′-trimethylenedipyridine (tmdp) with corresponding carboxylates: 4-nitrobenzoic (Hnba) and 4-biphenylcarboxylic acid (Hbiphen). Their structures were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. Compounds 1 and 2 are one-dimensional CPs with the zinc(II) carboxylate units bridged through the N-donor spacer ligand. The zinc (II) atom adopts a tetrahedral arrangement in 1 and 2 coordinated by two nitrogen atoms from two tmdp ligand molecules and two deprotonated oxygen atoms from two carboxylate ligand molecules. The adsorption capacities of MO in this study was found to be 546.31 mg/g and 22.67 mg/g for 1 and 2, respectively. DFT studies confirmed that adsorption is primarily due to π-π stacking and electrostatic interactions between MO and 1. It is noteworthy that binding energy (BE) values for 1 (-74.14 KJ/mol) and 2 (-61.11 KJ/mol) correlate reasonably well with the observed adsorption capacities of MO. The study demonstrated that 1 has higher adsorption efficiency in comparison to 2 and could be an effective and easily reusable adsorbent for the removal of MO from wastewater.

Efficient Slantwise Aligned Dion-Jacobson Phase Perovskite Solar Cells Based on Trans-1,4-Cyclohexanediamine.

The crystalline orientation and phase distribution are two important parameters for high-performance 2D perovskite solar cells. Therefore, it is essential to understand how the structure of spacer ligands influences the orientation and phase distribution of resulting 2D perovskite films. In this work, a new member of Dion-Jacobson (DJ) phase 2D perovskites based on trans-1,4-cyclohexanediamine (CHDA) is demonstrated and it is found that the crystalline orientation is self-aligned spontaneously, which is different from the well-known graded distribution in controlled sample with its isomer 1,6-diaminohexane (HDA) as spacer ligand. Grazing incident X-ray scattering suggests that the exact alignment is strongly slantwise to the substrate while it is still beneficial for charge transfer along the vertical structure of devices. The devices can achieve high efficiency up to 15.01% for (CHDA)MA3 Pb4 I13 (n= 4), one of the highest efficiencies reported by now. The encapsulated (CHDA)MA3 Pb4 I13 (n= 4) devices can retain 80.7% efficiency for 270 min under continuous maximum power point tracking. (CHDA)MA3 Pb4 I13 (n= 4) devices can retain 96.5% efficiency under 60°C and 74.4% efficiency under 70°C heating for 68 h. The results demonstrate the slantwise aligned DJ phase perovskite solar cells with excellent stability.

Tuning the structure of mercury (II) complexes as antibacterial agents by varying the halogen atoms (Cl and Br) and extending the spacer length of the imidazole-2-thione ligands

A series of mercury(II) complexes with empirical formula of Hg2LX4 (L = ligand and X = halogen) namely [Hg2(mbit)Cl4]n(1), {[Hg₂(mbit)Br₄]·CH3CN}n (2) [mbit = bis(1-methyl-imidazole-2-thione)methan], [Hg2(prbit)Br4]n (3), [Hg2(prbit)Cl4]n (4) [prbit = 1,3-bis(1-methyl-imidazole-2-thione) propane], [Hg2(pbit)Cl4]n (5) and [Hg2(pbit)Br4]n (6) [pbit = 1,5-bis (1-methyl-imidazole-2-thione) pentane] were designed and synthesized by a branched tube method. The complexes 2 to 5 have been fully characterized by single crystal X-ray diffraction, elemental chemical analysis (CHNS), infrared spectroscopy (IR), powder X-ray diffraction (PXRD), UV–Vis spectroscopy, thermogravimetric analysis (TGA) and photoluminescence spectroscopy (PL). On the base of PXRD patterns, the compounds 1 and 6 are not isostructural with the complexes 2 to 5. In the 2D structure of 2, the central atoms adopt distorted tetrahedral and octahedral geometries with HgBr4 and HgS2Br4 donor sets, respectively. Interestingly, by increasing the number of methylene groups in the ligand spacer from one in the mbit to three in the prbit, dimension of the polymer was increased from the 2D in 2 to the 3D in the structure of 3 with distorted HgBr4 trigonal pyramidal and HgS2Br2 seesaw environments. Further increasing the ligand flexibility and number of methylene moieties to five in the pbit, the structure of complex 5 was unexpectedly turned into a dinuclear species with distorted HgS2Cl2 seesaw and ideal HgCl4 trigonal pyramidal geometries. The polymers 3 and 4 with the same organic ligands and different halogen anions are isostructural. As a common feature, the complexes 2 and 5 were further stabilized by the intermolecular interactions to form a 3D non-covalent supramolecular structure. The in vitro bioefficacy of the complexes 2 to 5 were assessed against some Gram-positive and -negative bacteria and the results confirmed their substantial antimicrobial potential.

N,N′‐bridged binuclear NHC palladium complexes: A combined experimental catalytic and computational study for the Suzuki reaction

This work examines how N‐donor bridged spacer ligands affect N‐heterocyclic carbene (NHC) palladium complexes catalytic activities for Suzuki coupling reaction. Different degrees of structural flexibility binuclear NHC palladium complexes were synthesized. The more flexible nitrogen‐based alkyl chain ligand shows similar performance with cycloamine counterparts in the Suzuki coupling reaction. Suzuki coupling examples were used in air and ambient temperature to reach moderate to completion yields in short time. Density functional theory calculations showed that the chelate effect, associated with a single Pd complex mechanism, plays a fundamental role in the pre‐catalysis stage, supporting a reasonable of the kinetic activity observed experimentally.

Fabrication of Cu(ii) based halobenzoate appended ladder polymers with efficient charge transport properties

Two novel 1D Cu(ii) CPs based on halo-substituted benzoate ligands together with an N-donor bpe spacer ligand exhibit high electrical conductivity and reveal Schottky diode behaviour.

Two acetylenedicarboxylato-bridged 4-styrylpyridine appended 1D coordination polymers: synthesis, structural characterization and variable temperature magnetism

Two hitherto unknown one-dimensional coordination polymers (1D CPs) [M(adc)(4-spy)2(H2O)2]n, (M = Mn(II) (1) and Co(II) (2); H2adc = acetylenedicarboxylic acid and 4-spy = 4-styrylpyridine) have been characterized by infrared spectra, elemental analysis, thermogravimetric analyses (TGA), powder X-ray diffraction (PXRD) patterns and single-crystal X-ray diffraction techniques. Both these compounds 1 and 2, are isostructural and construct 3D supramolecular networks by the combination of hydrogen bonding and C–H···π interactions. Interestingly, these two materials exhibit variable temperature magnetic moment. Two new isostructural coordination polymers have been synthesized using linear spacer ligand acetylenedicarboxylate and monodented 4-styrylpyridine ligands. The X-ray crystallographic analysis exhibits that both the compounds form 1D chain structures which undergo hydrogen bonding and C–H···π interactions to furnish 3D supramolecular architectures. Effect of metal ion on variable temperature magnetic moment has been studied.

Polyoxoanion and secondary ligand spacer control of silver aggregates in Ag-imidazole-polyoxotungstate hybrids: From {Ag2} and {Ag4} clusters to infinite {Ag∞} chains

The integration of polyoxometalates (POMs) and silver aggregates into one compound could provide a promising route to approach novle strutures with improved properties. Herein, four new POM-based silver aggregate compounds, {[Ag2 (bim) (bimca)]2 [GeW12O40]}·2H2O (1), [Ag6(bim)6][BW12O40][OH]}·3H2O (2), {[Ag4(bim)4(P2W18O62)2][Ag2(bim)2]5[OH]2}·2H2O (3), and {[Ag6(bim)6(im)2][P2W18O62]}·4H2O (4) (bimca = 1H,3′H-[2,2']biimidazolyl-4,4′-dicarboxylic acid, bim = 2,2′-biimidazole, im = imidazole), have been synthesized via modulation of POM polyoxoanions and secondary ligand spacers. Compounds 1–4 show the distinct silver aggregate structures, namely from {Ag2} and {Ag4} to infinite {Ag∞} chains, which illustrates that the POMs and the secondary spacers are key factors to tune the silver aggregations and final dimensions of the POM-based inorganic-organic hybrids. Furthermore, the electrocatalytic and photocatalytic properties of 1–4 have been investigated in details.

Chemical Patterning in Single Crystals of Metal–Organic Frameworks by [2+2] Cycloaddition Reaction

AbstractConventional chemical patterning involves films of polymeric materials. Herein, we demonstrate that the presence or absence of guest solvents in the crystal voids modulates the patterning of the cyclobutane rings in highly strained metal–organic frameworks (MOFs) under UV light. The olefin pairs of the spacer ligands, which resemble a ladder‐like structure, in the MOF, undergo a [2+2] cycloaddition reaction in a single‐crystal‐to‐single‐crystal manner. For instance, a partial photoreaction in the MOFs in the absence of a guest solvent as well as with dimethylacetamide in the voids generated two different patterns of the cyclobutane rings. Surprisingly, the MOF with the lattice dimethylformamide undergoes 100 % photoreaction, but the photoproduct contains broken chains. Such chemical patterning at the molecular level represents a next step in crystal engineering.

Chemical Patterning in Single Crystals of Metal-Organic Frameworks by [2+2] Cycloaddition Reaction.

Conventional chemical patterning involves films of polymeric materials. Herein, we demonstrate that the presence or absence of guest solvents in the crystal voids modulates the patterning of the cyclobutane rings in highly strained metal-organic frameworks (MOFs) under UV light. The olefin pairs of the spacer ligands, which resemble a ladder-like structure, in the MOF, undergo a [2+2] cycloaddition reaction in a single-crystal-to-single-crystal manner. For instance, a partial photoreaction in the MOFs in the absence of a guest solvent as well as with dimethylacetamide in the voids generated two different patterns of the cyclobutane rings. Surprisingly, the MOF with the lattice dimethylformamide undergoes 100 % photoreaction, but the photoproduct contains broken chains. Such chemical patterning at the molecular level represents a next step in crystal engineering.

Cation-Controlled Formation and Interconversion of the fac/fac and mer/mer Stereoisomers of a Triple-Stranded Helicate.

Two biscatecholester ligands with oligoether spacers were used to prepare dinuclear titanium(IV) triscatecholate based helicates. In the case of Li4 [(1/2)3 Ti2 ], "classical" helicates with three internally bound Li+ ions and syn-oriented ligands in the complex units (fac/fac isomer) were obtained. In the case of the sodium salt Na4 [(2)3 Ti2 ], a different homochiral dinuclear triple-stranded helicate with two internally bound Na+ ions was formed. The complex units are anti-configured, and two of the ligand spacers are connecting internal with external positions of the helicate (mer/mer isomer). Removal of the sodium ions and addition of lithium ions leads to the switching from one topology to the other with an expanded helicate [(2)3 Ti2 ]4- as an intermediate. Switching back to the "non-classical" helicate cannot be observed because severe structural rearrangements would be required.

Photothermal enhanced enzymatic activity of lipase covalently immobilized on functionalized Ti3C2TX nanosheets

The rational design of new supports is critical for modern enzyme immobilization for advanced biocatalysis. Meanwhile, utilizing the photothermal effect of the support to achieve optical remote control of enzymatic activity remains a huge challenge. MXene, owing to its rich surface functional groups, biological compatibility and excellent photothermal effect, is a promising support material to satisfy the above requirements. Herein, a facile method to covalently bond lipase onto the surface of Ti3C2TX nanosheets through the coordination interaction with aminosilane ligand spacers is reported. The enzymatic activities of immobilized lipase are tuned based on the photothermal properties of Ti3C2TX nanosheets by exposure to near-infrared (NIR) light. The immobilized lipase shows an enhanced catalytic activity for the hydrolysis of p-nitrophenylpalmitate (pNPP) after NIR irradiation. In addition, immobilized lipase exhibits good pH, thermal stability and reusability, which are important in practical uses of enzymes.

Optimisation of Folate-Mediated Liposomal Encapsulated Arsenic Trioxide for Treating HPV-Positive Cervical Cancer Cells In Vitro.

High-risk human papilloma virus (HPV) infection is directly associated with cervical cancer development. Arsenic trioxide (ATO), despite inducing apoptosis in HPV-infected cervical cancer cells in vitro, has been compromised by toxicity and poor pharmacokinetics in clinical trials. Therefore, to improve ATO’s therapeutic profile for HPV-related cancers, this study aims to explore the effects of length of ligand spacers of folate-targeted liposomes on the efficiency of ATO delivery to HPV-infected cells. Fluorescent ATO encapsulated liposomes with folic acid (FA) conjugated to two different PEG lengths (2000 Da and 5000 Da) were synthesised, and their cellular uptake was examined for HPV-positive HeLa and KB and HPV-negative HT-3 cells using confocal microscopy, flow cytometry, and spectrophotometer readings. Cellular arsenic quantification and anti-tumour efficacy was evaluated through inductively coupled plasma-mass spectrometry (ICP-MS) and cytotoxicity studies, respectively. Results showed that liposomes with a longer folic acid-polyethylene glycol (FA-PEG) spacer (5000 Da) displayed a higher efficiency in targeting folate receptor (FR) + HPV-infected cells without increasing any inherent cytotoxicity. Targeted liposomally delivered ATO also displayed superior selectivity and efficiency in inducing higher cell apoptosis in HPV-positive cells per unit of arsenic taken up than free ATO, in contrast to HT-3. These findings may hold promise in improving the management of HPV-associated cancers.

Solvent-directed Anderson-type polyoxometalate-based metal–organic networks with flexible bis(1H-benzotriazoloxymethyl) ligands

Utilizing two uncommon organic ligands with different flexible linkers, 4,4′-bis(1H-benzotriazoloxymethyl)pentane (L1) and 4,4′-bis(1H-benzotriazoloxymethyl) hexane (L2), two novel Anderson polyoxometalate-based metal–organic networks with different structures, {Cu2(L1)2[CrMo6(OH)5O19]}·2H2O·2C2H5OH (1), {Cu3(L2)2[CrMo6(OH)6O18]2(H2O)4}·10H2O (2), have been constructed under solvothermal condition and characterized by IR spectra, single crystal X-ray diffraction and powder X-ray diffraction. The 2D network of complex 1 is constructed from inorganic {Cu-CrMo6} chains and L1 ligands. Complex 2 exhibits a 3D framework with {424, 64} topology, where the coordination between CrMo6 anions and CuII ions give a 2D inorganic layer, further extended into a 3D framework by L2 ligands. The influence of solvents on the synthesis of title complexes was investigated, and the effect of ligand spacer length on the structures of the title complexes was discussed. Two complexes display not only electrocatalytic activities toward the reduction of H2O2 and KNO2, but also good adsorption activities for organic dye crystal violet (CV) and methylene blue (MB).

Resonant Energy Transfer can Trigger Multiexciton Recombination in Dense Quantum Dot Ensembles.

Core/shell quantum dots/quantum rods are nanocrystals with typical application scenarios as ensembles. Resonance energy transfer is a possible process between adjacent nanocrystals. Highly excited nanocrystals can also relax energy by multiexciton recombination, competing against the energy transfer. The two processes have different dependencies and can be convolved, resulting in collective properties different from the superposition of the individual nanocrystals. A platform to study the interplay of energy transfer and multiexciton recombination is presented. CdSe/CdS quantum dot/quantum rods encapsulated in amphiphilic micelles with an interparticle distance control by spacer ligands are used for time-resolved photoluminescence and transient absorption experiments. At exciton populations around one, the ensemble starts to be in a state where energy transfer can trigger multiexciton Auger recombination, altering the collective dynamics.