Zinc Center Research Articles

A π-extended β-diketiminate ligand via a templated Scholl approach.

We report a templated Scholl oxidation strategy for the preparation of the first β-diketiminate (BDI) ligands embedded within a 24-electron π-system backbone. The resulting benzo[f,g]tetracene BDI ligand was coordinated to a zinc centre and electrochemical studies showed the redox active nature of the ligand.

Cover Picture: Visible Light Responsive Dinuclear Zinc Complex Consisting of Proximally Arranged Two d10‐Zinc Centers (Angew. Chem. Int. Ed. 50/2023)

Cover Picture: Visible Light Responsive Dinuclear Zinc Complex Consisting of Proximally Arranged Two d¹⁰‐Zinc Centers (Angew. Chem. Int. Ed. 50/2023)

2,1,3-Benzoselenadiazole-containing zinc(II) halide complexes: Chalcogen bonding in the solid state and catalytic activity in the Schiff condensation

XRD study of crystals of zinc(II) halide complexes featuring 2,1,3-benzoselenadiazole (L) ligands [ZnL2X2] (X = Cl, Br, I) indicated availability of intramolecular chalcogen bonds between the Se atom and the halide ligands, which affect a rotation barrier around the Zn–N bonds and thus control a geometry of these species. In the solid state, the Se atom additionally forms intermolecular chalcogen bonds with the N atom of the 2,1,3-benzoselenadiazole ligands, which results in formation of infinite 1D chains. Theoretical calculations and experimental kinetic study indicated that although the Se atom serves as a Lewis acid, coordination of the organic ligand to the zinc(II) center does not provide enhanced catalytic activity of the latter in the model reaction of the Schiff condensation.

Synthesis of 2D bi-metallic Zn/Cu metal-organic framework integrated graphene nanocomposites for all-solid-state asymmetric supercapacitors

In this work, a novel two-dimensional (2D) bi-metallic metal-organic frameworks (MOFs) consisting of zinc and copper metal centers with 1,3,5-tricarboxylic acid as a chief and efficient organic linker (Zn/Cu-BTC) and its composite with exfoliated graphene nanosheets (EGNSs) have been investigated for supercapacitor applications. The composites were synthesized via facile in-situ solvothermal process. Different spectroscopic, microscopic, and surface analyses confirmed the successful formation of porous electroactive composites, where 2D MOF nanosheets were vertically grown on the EGNS surfaces. In the two-electrode symmetric system, the as-synthesized Zn/Cu-BTC MOF@EGNS electrode achieved an enhanced specific gravimetric capacitance and equivalent volumetric capacitance of 1284.9 F/g and 813.3 F/cm3 at 0.5 A/g. It exhibits high-rate performance and prolonged cycling stability with >90 % retention after 8000 cycles. All-solid-state asymmetric supercapacitor (ASC) device was constructed with Zn/Cu-BTC MOF@EGNS composite and EGNS electrodes, where PVA-KOH membrane served as a separator-cum-electrolyte. The ASC device delivered a satisfactory energy density of 60.55 Wh kg−1 and a maximum power density of 10 kW kg−1 with an admirable cycling stability of 92 % after 10,000 charge-discharge cycles. In the future, this work can encourage manufacturing innovation.

LUMINESCENT DYE MOLECULES FOR NEW PHOTONIC ANTENNAE

A zinc dipyrrin complex with a structural and functional design, that mimics the natural photonic antenna of a green plant, has been synthesized and incorporated into new designed model of mesoporous silica. The dye complex is composed of two dipyrromethene ligands which are connected to a central zinc(II) metal ion through the four nitrogen atoms. The dye complex has been characterized using various spectroscopic techniques,1HNMR, IR, and X-ray crystallography to elucidate their structure. UV-vis absorption and fluorescence spectroscopy were used to determine the optical properties of the dye before its encapsulation into the silica framework, and after being trapped in the silica pores. A comparison of the results obtained shows that the silica pores have a significant effect on the fluorescence quantum yield, the excited state lifetime, and the emission of the encapsulated dye molecules.

Visible Light Responsive Dinuclear Zinc Complex Consisting of Proximally Arranged Two d10 -Zinc Centers.

So far, Zn(II)-based d10 complexes have been known to be colorless unless they are accompanied by chromophoric groups, and therefore both fundamental and advanced photophysical performance of Zn centers of complexes, especially in visible-light regions has been unexplored. Here, we first demonstrate a dinuclear Zn(II) complex that shows visible light absorption using an orbital distributed over closely contacted two Zn centers experimentally determined by X-ray crystallography. A contrastive study demonstrated that intermetallic orbital interaction in dinuclear Zn(II) complex is responsible for capturing visible light to exhibit orangish yellow color, whereas an analogous one without such an interaction is colorless. This work demonstrates that introduction of Zn-Zn interactions to Zn(II) molecules contradicts the common notion that Zn is unresponsive to visible light and expands the photophysical field of zinc chemistry.

Visible Light Responsive Dinuclear Zinc Complex Consisting of Proximally Arranged Two d10‐Zinc Centers**

AbstractSo far, Zn(II)‐based d10 complexes have been known to be colorless unless they are accompanied by chromophoric groups, and therefore both fundamental and advanced photophysical performance of Zn centers of complexes, especially in visible‐light regions has been unexplored. Here, we first demonstrate a dinuclear Zn(II) complex that shows visible light absorption using an orbital distributed over closely contacted two Zn centers experimentally determined by X‐ray crystallography. A contrastive study demonstrated that intermetallic orbital interaction in dinuclear Zn(II) complex is responsible for capturing visible light to exhibit orangish yellow color, whereas an analogous one without such an interaction is colorless. This work demonstrates that introduction of Zn−Zn interactions to Zn(II) molecules contradicts the common notion that Zn is unresponsive to visible light and expands the photophysical field of zinc chemistry.

Mononuclear Zn(II) Complex Based on N2O Ligand Compartment: First Case to Detect Nitro Explosives.

This paper scrutinises the development of low-cost hypersensitive fluorescent probes manipulated chemically with Schiff base complexes and their prospective applicability for the detection of nitro explosives in light of the rapidly expanding demand for anti-trafficking measures. In this study, a new Zn(II) metal complex has beensynthesized in one pot using the Schiff base ligand L= 2-methoxy-5-methyl-N-(2-pyridin-2-ylmethylene) aniline. The complex was also thoroughly characterised using various spectroscopic tools and subjected to single crystal XRD analysis. In the asymmetric unit, square pyramidal zinc (II) centre exist in the inner N2O compartment of the ligand L. The intermolecular Cg···Cg interactions exist between two different asymmetric residual units lead to supramolecular assembly along b axis. By turning off the fluorescence response, the complex serves as a sensor for the detection of nitro aromatics in CH3CN solution. A significant quenching efficiency has been reported with a quenching constant (KSV) 1.8 × 104 M-1 for 4-nitrobenzoic acid during investigation of sensing phenomenon in solution phase. In addition, determining the binding stoichiometry of the chemosensor with NO2 and the binding constant, the mechanism of fluorescence quenching has also been postulated. The detection limit of NO2 is 7.6×10 -7 M, with the binding constant k = 1.1021× 108 M-1. Additionally, the DFT calculation makes it easier to comprehend the appropriate binding process in light of the findings of experiments. We also designed a paper sensor strip for the visual detection of Nitro Explosive Residues in light of the sensor's potential used in forensic investigations.

Crystal structure, vibrational analysis, electronic properties, static and dynamic NLO response and molecular docking study of oxadiazole/pyridine-based Zn(II) complex

In this study, a complex consisting of oxadiazole and pyridine groups coordinated with zinc(II) chloride was synthesized and characterized by using the experimental (FT-IR, Raman and UV spectroscopic techniques) and computational methods. The molecular coordination of the complex exhibited a different orientation due to the position of the Cl-Zn-Cl bond angle, resulting in a distorted octahedral molecular geometry around the central zinc(II) metal ion. The exact crystal molecular structure was uncovered with the experimental single crystal X-Ray diffraction (SCXRD) analysis. Theoretical modeling on the electronic structure properties was performed with the DFT/B3LYP method at the 6–311G(2d,2p)+LanL2DZ computational level. The computational molecular geometry analysis was used to support the experimental structural geometric parameters. Some significant characteristic vibrational bands such as intra-ligand, metal-ligand and metal-chloride groups were investigated by using the experimental FT-IR and Raman spectral techniques and computational method. The electronic transition features and the nature of metal-ligand/chloride coordination environment were determined via help of the UV–Vis., HOMO, LUMO and NBO analyses. The MEP analysis was investigated for the complex. The NLO profile was investigated by analyzing the polarizabilities and the first- and second-order hyperpolarizabilities (α, β and γ) at the static and dynamic (ω = 532 nm and 1064 nm) states with theoretical approach. Lastly, the molecular docking study was performed to determine the anxiolytic activity of the synthesized complex.

Screening and Experimental Validation for Selection of Open Metal Sites Metal-Organic Framework (M-CPO-27, M = Co, Mg, Ni and Zn) to Capture CO2

The release of CO2 into the atmosphere has become a primary issue nowadays. Recently, researchers found Metal-Organic Frameworks M-CPO-27 (M = Mg, Co, Ni, and Zn) to be revolutionary for CO2 adsorption due to the presence of open metal sites enhancing CO2 binding and leading to higher capacity. This study aims to select the best metal center for CPO-27 with the high performance of CO2 adsorption by screening metal centers using simulation as a preliminary selection method. Then, the different metal centers were synthesized using the solvothermal process for validation. The synthesis of MOFs is confirmed through PXRD and FTIR analysis. Subsequently, by using simulation and experimental methods, it is discovered that Ni-CPO-27 gives the best performance compared with magnesium, zinc, and cobalt metal centers. The CO2 adsorption capacity of synthesized Ni-CPO-27 is 5.6 mmol/g, which is almost 20% higher than other MOFs. In conclusion, the prospective outcome of changing the metal from Mg-CPO-27 to Ni-CPO-27 would be advantageous in this investigation owing to its excellent performance in capturing CO2.

Self-aggregation behavior of dimeric chlorophyll-a derivatives linked with ethynylene and m-phenylene moieties.

Chlorophyll(Chl)-a derivatives inserting an ethynylene-m-phenylene group between a zinc chlorin ring and a hydroxymethyl group, in which various substituents were introduced on the benzene spacer, were prepared as model compounds for the light-harvesting antennae (chlorosomes) of photosynthetic green bacteria. These compounds were synthesized from a C3-ethynylated Chl-a derivative via sequential Sonogashira cross-coupling reaction, and the effects of the substituents on the phenylene linker on their self-aggregation behaviors were investigated by electronic absorption, circular dichroism, and infrared absorption spectroscopic measurements. These studies exhibited that some compounds gave the disordered self-assemblies including several species; however, the zinc complex of the dimeric Chl-a derivative primarily allowed a single J-aggregate species in an aqueous Triton X-100 micellar solution. Additional control experiments revealed that its self-assembly was constructed through the hydrogen and coordination bonding involving the hydroxymethyl group on benzene ring, keto-carbonyl group at C13-position, and central zinc atom, and this is consistent with a conventional chlorosomal manner.

Osmium ester-hinged chlorin dimers

A bis(dihydroxychlorin) osmate ester is formed as a side product in the osmylation of meso-tetraphenylporphyrin. The product can also be formed in good yield along well-known reaction pathways of osmate esters by treatment of the monomeric chlorin diol osmate ester bispyridine complex with acid. The dimer was spectroscopically characterized. The free base dimer can be metalated with zinc(II). The bis([dihydroxychlorinato]zinc) osmate ester dimer was spectroscopically and structurally characterized, showing its clamshell architecture with a 42[Formula: see text] angle between the mean planes of the two metallochlorin chromophores and a 9.11 Å zinc-to-zinc separation. Upon reaction with dimethylaminopyridine (DMAP), the clamshell structure pivots around the osmium center and arranges the two chromophores, each zinc center coordinated to DMAP, in maximum separation from each other, as shown by structural analysis. Preliminary 1H NMR titration data are presented that show the bis-zinc clamshell structure to form a 1:1 supramolecular complex with diethylenetriamine (DETA), expressing a three-point recognition motive: the terminal amine functionalities coordinate to the zinc ions in each half-shell, thus bridging both chromophores, and the central amine functionality was deduced to be H-bonded to the osmium oxo group pointing toward the inside of the host. The UV-vis spectroscopic response upon DETA binding shows greater complexity in the interaction at higher ligand:host ratios, suggesting multiple binding modes. A similarly complex binding situation is also observed for the interactions of the chlorin osmate ester monomer with DETA.

Mesomorphism and luminescence in coordination compounds and ionic salts based on pyridine-functionalized β-diketones. Influence of the pyridine nitrogen position

Pyridine-functionalized β-diketones with the pyridine nitrogen atom at 3 or 4 position (L3N and L4N, respectively) have been used as building blocks to obtain two new families of compounds with mesomorphic and luminescent behaviors. The N-pyridine coordination of the β-diketones to zinc(II), palladium(II) and platinum(II) metal centers has allowed to synthesize neutral coordination compounds of the type [MCl2(LZN)2] (M = Zn(II), Pd(II), Pt(II); Z = 3, 4). Particularly, coordination of L4N towards Pt(II) gives rise to the cationic species [Pt(NH3)2(L4N)2]2+. Otherwise, protonation of the pyridine moiety was strategically used to obtain a novel series of pyridinium ionic salts of the type (HLZN)nA (n = 1, A = Cl; n = 2, A = MCl4, M = Zn(II), Pd(II), Pt(II); Z = 3, 4). The neutral or ionic nature of the complexes, as well as the β-diketone ligands and the metal center in both the neutral and anionic complexes, has a great influence on the mesomorphic behavior. Thus, columnar or smectic mesophases can be selectively formed. Single-crystal and temperature-dependent powder X-ray diffraction studies have been performed to analyze the molecular packing in the crystal and the supramolecular ordering in the mesophase. All the aforementioned factors also play a key role on the luminescence properties, the Zn(II) coordination compounds and ionic salts being the best candidates as bifunctional materials.

A new 2d coordination polymer based on zinc(ii), 1,2,3-benzenetricarboxylic acid and 4,4ʹ-bis(imidazol-1-ylmethyl)biphenyl: synthesis and crystal structure

The solvothermal reaction of zinc(II) nitrate with 1,2,3-benzenetricarboxylic acid (1,2,3-H3BTC) and 4,4ʹ-bis(imidazol-1-ylmethyl)biphenyl (BIBPh) produced a crystalline solid {[Zn3(BIBPh)3(BTC)2]∙H2O}n. The product has been structurally characterised and investigated by X-ray diffraction, IR and thermogravimetric methods. The polymer has a bidimentional structure and crystallizes in the P21/c space group of the monoclinic system with the following unit cell parameters: a= 14.8687(16), b= 36.915(4), c= 13.8378(16) (Å), β= 105.584(6)°. The asymmetric unit of the crystal structure contains three zinc(II) ions, three BIBPh ligands and two BTC3- monodentate ligands with all three deprotonated carboxylate groups that balance the overall charge. All zinc centers have similar coordination environment: each metal ion is four coordinated exhibiting a slightly distorted tetrahedral coordination, where two positions are occupied by oxygen atoms of the carboxylic acid and the other two by nitrogen atoms of imidazole subunits

2.2]Paracyclophane Derivatives as Building Blocks for Coordination Polymers.

Several new di- and tetracarboxylic [2.2]paracyclophane derivatives were obtained via Suzuki coupling between the appropriately brominated [2.2]paracyclophanes and 4-(methoxycarbonyl)phenylboronic acid. The reaction of one of these products, namely pp-bis(4-carboxyphenyl)[2.2]paracylophane (12), with zinc nitrate afforded a 2D coordination polymer comprising zinc-carboxylate paddlewheel clusters linked together by cyclophane cores. The zinc center is five-coordinated in a square-pyramidal geometry, with a DMF oxygen atom at the apex and four carboxylate oxygen atoms in the base.

Linker-length dependent intra/intermolecular coordination of synthetic zinc chlorophyll-a derivatives bearing a pyridine terminal in the C132-substituent

An ω-(m-pyridyl)alkyl group was introduced at the C132-methoxycarbonyl group of methyl pheophorbide-a as a chlorophyll-a derivative by exchange of the esterifying moiety. To avoid allomerization and epimerization of the C132-chiral center in the β-keto-ester moiety, a propyl group was substituted at the C132-position. The free bases were zinc-metalated to give zinc methyl 132-propyl-pheophorbides-a bearing an oligomethylene chain with a pyridyl terminal at the C132-position. Depending on the length of the alkyl chain between the terminal pyridine and C132-carboxylate moieties, the coordination of the m-pyridyl group with the central zinc atom in the stereochemically pure and fixed zinc chlorin–pyridine conjugates occurred in intra- or intermolecular fashions.

Synthesis, crystal structure and antibacterial activity of zinc(II) complexes with Schiff bases derived from 5-fluorosalicylaldehyde

By a condensation of aliphatic amine containing adamantyl groups (amantadine, memantine, or 3-amino-1-adamantanol) and 5-fluorosalicylaldehyde, three new Schiff base ligands, HL1 – 3 , were synthesized. One Schiff base, zinc(II) chloride, and NaOH were stirred in anhydrous methanol generating three new zinc(II) complexes, C34H38F2N2O2Zn (1), C38H46F2N2O2Zn (2), and C34H38F2N2O4Zn (3), respectively. These complexes were characterized by melting point, elemental analysis, infrared spectrum, ultraviolet–visible spectrum, 1H NMR analysis, thermal analysis, and single-crystal X-ray diffraction analysis. Single-crystal X-ray diffraction analysis shows that 1 and 3 crystallize in the monoclinic system with space group P2 1 /c, but 2 crystallizes in the orthorhombic system with space group Pbca. Each asymmetric unit in 1 is composed of one zinc(II) and two deprotonated ligands; each asymmetric unit in 2 is constituted of one zinc(II), two deprotonated ligands as well as one dichloromethane. Each asymmetric unit in 3 is made up of one zinc(II), two deprotonated ligands, one methanol, and one lattice water. The central zinc(II) in 1–3 is four-coordinate via two nitrogen atoms and two oxygen atoms from the corresponding Schiff base ligands, forming a distorted tetrahedral geometry. The antibacterial activities of the three Schiff base ligands and the corresponding complexes against two gram positive bacteria, Staphylococcus aureus and Bacillus subtilis, and a gram negative bacteria, Escherichia coli, were tested.

Preparation of Coupling Catalyst HamZIF-90@Pd@CALB with Tunable Hollow Structure for Efficient Dynamic Kinetic Resolution of 1-Phenylethylamine.

Chiral amines are essential components for many pharmaceuticals and agrochemicals. However, the difficulty in obtaining enantiomerically pure amines limits their application. In this study, hollow amorphous ZIF-90 (HamZIF-90) materials were prepared by template engraving, and chemical-enzyme coupling catalysts (HamZIF-90@Pd@CALB) were constructed for the chiral resolution of 1-phenylethylamine. Different from conventional materials, HamZIF-90 had tunable hollow structures by altering its central node zinc ion concentrations, and the embedded hydrogel template gave it more pore structures, which facilitated the loading of enzyme molecules and Pd nanoparticles (NPs). The establishment of the coupling catalysts shortened the mass transfer distance of the reactant molecules between the metal nanoparticles and the enzyme catalyst in the dynamic kinetic resolution (DKR) reaction, resulting in 98% conversion of 1-phenylethylamine and 93% selectivity of Sel.R-amide. The proposal of this idea provided a good idea for future tailor-made MOFs loaded with chemical and enzyme coupled catalyst.

Cooperative effects of Schiff base binuclear zinc complexes on the synthesis of aliphatic and semi-aromatic polyesters.

In this paper, we use mono- and bimetallic complexes based on Earth-abundant, cheap and benign zinc for the synthesis of sustainable aliphatic and semi-aromatic polyesters. Tridentate and hexadentate aldimine-thioetherphenolate ligands were used to obtain the desired zinc complexes by the reaction of proligands with opportune equivalents of zinc bis[bis(trimethylsilyl)amide]. The obtained bimetallic complexes 1 and 2 and the monometallic complex 3 were used as catalysts in the Ring-Opening Polymerization (ROP) of landmark cyclic esters, such as ε-caprolactone and lactide, and in the Ring-Opening COPolymerization (ROCOP) of cyclohexene oxide and phthalic anhydride under different reaction conditions. All catalysts were active in these two classes of reactions, showing good control of the polymerization processes. Interestingly, the bimetallic complexes have higher activity compared to their monometallic counterparts, highlighting the cooperation between the two zinc centers.

Synthesis, spectroscopic characterization and photophysical properties of transition metal complexes of 4-((3-fluoro-2-methylbenzylidene)amino)-5-methyl-4H-1,2,4-triazole-3-thiol

This study focused on the synthesis and spectral investigation of divalent transition metal complexes of novel ligand 4-((3-fluoro-2-methylbenzylidene)amino)-5-methyl-4H-1,2,4-triazole-3-thiol (FMMT). Extensive physical, spectroscopic and theoretical investigations are performed on the ligand and its complexes, and the results are compatible with their expected compositions. Based on IR and NMR spectral data, metal complexes with coordination number of 6 and 4 were proposed, with FMMT functioning as a bidentate ligand. The metal complexes display an octahedral geometry around bivalent cobalt, nickel and zinc centers, and for copper and palladium tetrahedral environment was suggested and also optimized by Avogadro program. The polarity of the solvent used promoted the complex solvatochromism. Furthermore, optical bandgap was calculated with the help of Tauc's plot. Thermogravimetric study was employed to estimate the thermal stability and coordinated H2O in the complexes. CV endorsed a reversible one electron transfer Cu(II)/Cu(I) redox reaction. In vitro antibacterial and antifungal studies of compounds exhibited modest to substantial activity against different microbial strains. The bio-efficacy data proved that the complexation of ligand with metal centers leads to enhanced bio–activity which could be elucidated by chelation and Overton’s theory.