Zn Metal Center Research Articles

Role of the Environment Polarity on the Photophysical Properties of Mesogenic Hetero-Polymetallic Complexes.

New hetero-polynuclear coordination complexes based on a pentacoordinated Zn(II) metal center with tridentate terpyridine-based ligands and monoanionic gallates functionalized with long alkyl chains containing ferrocene units were designed, synthesized and characterized using spectroscopic and analytical methods. The complexes are mesomorphic, exhibiting columnar hexagonal mesophases. The photophysical properties in a solution and in an ordered condensed state were accurately investigated and the influence of the polarity of the solvent was evidenced.

Optimization of the Electrochemical Nature of Ni/Co MOF Assisted by Zn Metal Centres for Better Electrode Performance in Hybrid Devices

Owing to the exceptional porous coordination chemistry and expanded redox culture of mixed metal organic framework (MMOF) materials are now presenting a hot matter for their potential usage in battery-supercapacitor electrodes. Here, we synthesized Ni/Co-MOF and its based Zn x -(Ni/Co)y-MOF nanoparticles containing different transition metals ratio; x: y = 0.25:0.75, 0.50:0.50, and 0.75:0.25 by hydrothermal process and named as ZMOF1, ZMOF2 and ZMOF3. Their electrochemical profile was carried out by CV, GCD and EIS characterization in three electrode setup. Among the MOFs nanoparticles, partially Zn enriched ZMOF1 shows prominent specific capacity of 177.23 and 181.12 C g−1 in 1.0 and 3.0 M KOH electrolyte solution at current density of 0.3 A g−1 along with good rate capability performance. Meanwhile, it retains brilliant specific capacity ∼ 86% of its original value compared to other displayed by ZMOF2 and ZMOF3 (80% and 69%) after charging-discharging for 3000 cycles at j = 4.0 A g−1. Moreover, modified power law was utilized to estimate the battery-type charge storage worth of ZMOF1 from CV cycle (at 5 mV s−1) in 1.0 and 3.0 M electrolytes medium thereby found the contribution 91.58% and 94.32%, respectively. These features of ZMOF1 attributed to particle diverse morphology, enriched redox sites and admiring electrical conductivity.

Cd(ii) and Zn(ii) coordination polymer-assisted CO2/cyclohexene oxide copolymerization with a double metal cyanide catalyst

Three new coordination polymers with Zn(ii) and Cd(ii) metal centers were synthesized and applied to cocatalyze CO2/CHO polymerization with DMC.

Effects of Defects and Presence of Open-Metal Sites on the Structure and Dynamics of Water in Hydrophobic Zeolitic Imidazolate Frameworks.

Most of the chemistry in nanoporous materials with small pore sizes and windows takes place on the outer surface, which is in direct contact with the substrate/solvent, rather than within the pores and channels. Here, we report the results of our comprehensive atomistic molecular dynamics (MD) simulations to decipher the interaction of water with a realistic finite ∼5.1 nm nanoparticle (NP) model of ZIF-8, with edges containing undercoordinated Zn metal sites, vs a conventionally employed pristine crystalline bulk (CB) model. The hydrophobic interior surface of the CB model imparts significant dynamical behavior on water molecules with (i) increasing diffusivity from the surface toward the center of the pores and (ii) confined water, at low concentration, showing similar diffusivity to that of the bulk water. On the other hand, water molecules adsorbed on the surface of the NP model exhibit a range of characteristics, including "coordinated", "confined", and "bulk-like" behavior. Some of the water molecules form coordinative bonds with the undercoordinated Zn metal centers and act as nucleation sites for the water droplets to form, facilitating diffusion into the pores. However, diffusion of water molecules is limited to the areas near the surface and not all the way to the core of the NP model. Our atomistic MD simulations provide insights into the stability of ZIFs in aqueous solutions despite hydrolysis of their outer surface. Such insights are helpful in designing more robust nanoporous materials for applications in humid environments.

Syntheses, characterization of Ni(II)/Zn(II) complexes derived from flexible tricarboxylate ligand and 2,2′-bipyridine and their methyl violet dye photodegradation applications

Three new complexes comprising Ni(II) and Zn(II) metal centers having compositions [Zn2(HL)2(bpy)2(H2O)2] (1), [Ni(H2L)(bpy)(H2O)2(OH)] (2) and [Ni(H2L)2(bpy)2] (3) have been synthesized by adopting mixed ligand strategy using 4′-(3,4- dicarboxylphenyloxy) -4-biphenylcarboxylic acid (H3L) as main ligand and 2,2′-bipyridine (bpy) as co-ligand. These complexes have been characterized by microanalyses, FTIR and single crystal X-ray diffraction technique. The single crystal X-ray analyses reveal that all the three complexes have 2D supramolecular network constructed by hydrogen bonding interactions. These complexes have been employed as photocatalysts for the photodegradation of methyl violet (MV) dye. The photocatalytic experiments reveal that amongst all three complexes, the complex 2 exhibits best photocatalytic performance and degrades 92.8% of MV in time span of 100 min. The plausible photocatalytic degradation mechanism have been proposed with the help of trapping experiments and density of states calculations.

A Luminescent Zinc(II) Coordination Polymer for Selective Detection of Fe3+ and Cr2O72− in Water and Catalytic CO2 Fixation

AbstractFluorescence‐based detection technique using coordination polymer has been considered an attractive alternative over conventional approaches. Herein, a new luminescent zinc(II) coordination polymer, [Zn(4‐ABPT)(NIPA)(H2O)], SSICG‐5, is synthesized by using a Lewis acidic Zn(II) ion, aromatic nitro group containing ligand 5‐nitroisophthalic acid (H2NIPA), and basic −NH2 rich ligand 3,5‐di(pyridine‐4‐yl)‐4H‐1,2,4‐triazol‐4‐amine (4‐ABPT). SSICG‐5 can detect Fe3+ and Cr2O72− selectively with a LOD of 0.16 μM and 1.94 μM, respectively. Additionally, carbon dioxide (CO2) fixation via one‐pot CO2 cycloaddition reaction has significant importance for reduced waste formation, minimizing reaction time and lowering chemical usage. Zn metal centre of SSICG‐5 possesses a replaceable coordinated water molecule. The active metal sites combined with the Lewis acidic and basic sites of the ligands make SSICG‐5 an ideal bifunctional heterogeneous catalyst for efficient CO2 cycloaddition reaction under room temperature (RT), solvent‐free conditions. Notably, SSICG‐5 exhibits near quantitative conversion (turnover number (TON) of 198) of propylene oxide to its carbonate compound under mild reaction conditions.

Lewis Acidic Zinc(II) Complexes of Tetradentate Ligands as Building Blocks for Responsive Assembled Supramolecular Structures

This review presents representative examples illustrating how the Lewis acidic character of the Zn(II) metal center in Zn(salen)-type complexes, as well as in complexes of other tetradentate ligands, and the nature of the medium govern their supramolecular aggregation, leading to the formation of a variety of supramolecular structures, either in solution or in the solid state. Stabilization of these Lewis acidic complexes is almost always reached through an axial coordination of a Lewis base, leading to a penta-coordinated square-pyramidal geometry around the metal center. The coverage is not exhaustive, mainly focused on their crystallographic structures, but also on their aggregation and sensing properties in solution, and on their self-assembled and responsive nanostructures, summarizing their salient aspects. The axial ligands can easily be displaced, either in solution or in the solid state, with suitable Lewis bases, thus being responsive supramolecular structures useful for sensing. This contribution represents the first attempt to relate some common features of the chemistry of different families of Zn(II) complexes of tetradentate ligands to their intrinsic Lewis acidic character.

The importance of spodium bonds, H-bonds and π-stacking interactions in the solid state structures of four zinc complexes with tetradentate secondary diamine ligands

The study is devoted to the analysis of the Zn⋯O contacts established between the square-pyramidal Zn metal centers and the co-crystallized DMF and DMSO molecules.

Design and structural analysis of centrosymmetric and non-centrosymmetric Zn(II) complexes by the host-guest complexation method

Crystalline molecular complexes of 2-salicylichydrazono-1,3-dithiolane-based Zn(II) coordination complexes analogues [Zn(H2L)2(Cl)2].(MeOH); (complex 1), [Zn(H2L)2(H2O)2].(ClO4); (complex 2) and [Zn(HL)2]n (complex 3) have been synthesized and characterized by spectroscopic methods and single-crystal XRD analysis. The XRD-structure of the desired complexes were unravelled in that the complexes (1) and (2) possess centrosymmetric form in which Zn(II) metal centre had octahedral coordination environment, while the non-centrosymmetric complex 3 is a coordination polymer with a square pyramidal geometry around the metal centre. The coordination-driven supramolecular self-assembly through distinct intermolecular interactions is observed in the three Zn(II) complexes which are achieved by the host-guest complexation. In the solid state, the coordination geometry and molecular packing by various non-covalent interactions are discussed qualitatively using crystal structure analysis. Graphical tools based on 3-D Hirshfeld surface (dnorm and shape index), 2-D fingerprint plots, RDG-based NCI isosurface embedded with QTAIM and molecular electrostatic potential map are shown to be valuable for visualizing and analyzing intermolecular interactions in different crystal forms of Zn(II) complexes and allows easier and rapid comparison. In addition, the geometrical optimization of the Zn(II) complexes was realized by the electronic structure method using density functional theory (DFT) to identify the active sites and the chemically reactive parameters of the three Zn(II) complexes.

Limitation of room temperature phosphorescence efficiency in metal organic frameworks due to triplet-triplet annihilation.

The effect of triplet-triplet annihilation (TTA) on the room-temperature phosphorescence (RTP) in metal-organic frameworks (MOFs) is studied in benchmark RTP MOFs based on Zn metal centers and isophthalic or terephthalic acid linkers (ZnIPA and ZnTPA). The ratio of RTP to singlet fluorescence is observed to decrease with increasing excitation power density. Explicitly, in ZnIPA the ratio of the RTP to fluorescence is 0.58at 1.04mWcm-2, but only 0.42at (the still modest) 52.6mWcm-2. The decrease in ratio is due to the reduction of RTP efficiency at higher excitation due to TTA. The density of triplet states increases at higher excitation power densities, allowing triplets to diffuse far enough during their long lifetime to meet another triplet and annihilate. On the other hand, the shorter-lived singlet species can never meet an annihilate. Therefore, the singlet fluorescence scales linearly with excitation power density whereas the RTP scales sub-linearly. Equivalently, the efficiency of fluorescence is unaffected by excitation power density but the efficiency of RTP is significantly reduced at higher excitation power density due to TTA. Interestingly, in time-resolved measurements, the fraction of fast decay increases but the lifetime of long tail of the RTP remains unaffected by excitation power density. This may be due to the confinement of triplets to individual grains, leading decay to be faster until there is only one triplet per grain left. Subsequently, the remaining "lone triplets" decay with the unchanging rate expressed by the long tail. These results increase the understanding of RTP in MOFs by explicitly showing the importance of TTA in determining the (excitation power density dependent) efficiency of RTP. Also, for applications in optical sensing, these results suggest that a method based on long tail lifetime of the RTP is preferable to a ratiometric approach as the former will not be affected by variation in excitation power density whereas the latter will be.

Electronic properties of heterometallic zeolitic imidazolate framework and its encapsulation with Ni, Pd and Pt

The electronic properties of heterometallic zeolitic imidazolate frameworks (ZIF-8) containing Cd and Zn metal centres have been examined using density functional theory to reveal the nature of metal to ligand interaction, band gap, density of states and charge distribution. The band gap energy of mixed-metal ZIF-8(Zn/Cd) has been calculated for each ratio of Cd and Zn in the mixed-metals showing a small window of possible alternating the electronic states of this material. The band gap energy shifts from 4.84 eV in pristine ZIF-8(Zn) to 4.33 eV when all the Zn2+ metal centres were replaced by Cd2+ ions. Increasing the ratio of Cd to Zn decreases the band gap energy due to the shifting of the electronic states of Cd at the edge of the conductance band. Modification of the electronic structure was also examined when several metals of Ni, Pd, and Pt were dopped in the mixed-metal ZIF-8(Zn/Cd) to give band gap energies of 2.19, 3.35, and 3.41 eV, respectively. The presence of mixed-metal seems to fine tune the band gap energy than doping the metals in ZIF-8(Zn) only. Density of states have been evaluated to reveal the coordination nature in the mixed-metal ZIF-8(Zn/Cd) as well as after doping with the metals. Additional electronic parameter of the net atomic charge distribution based on the repeating electrostatic potential extracted atomic method was also determined in a range of van der Waals (vdW) radius to see the effect of mixed metals in ZIF-8(Zn/Cd). The net atomic charge of each metal centre is observed to be convergence when the vdW radius scale was set to 0.8, 0.9 and 1.0.

Pillar Modularity in fsc Topology Hybrid Ultramicroporous Materials Based upon Tetra(4-pyridyl)benzene.

Hybrid ultramicroporous materials (HUMs) are porous coordination networks composed of combinations of organic and inorganic linker ligands with a pore diameter of <7 Å. Despite their benchmark gas sorption selectivity for several industrially relevant gas separations and their inherent modularity, the structural and compositional diversity of HUMs remains underexplored. In this contribution, we report a family of six HUMs (SIFSIX-22-Zn, TIFSIX-6-Zn, SNFSIX-2-Zn, GEFSIX-4-Zn, ZRFSIX-3-Zn, and TAFSEVEN-1-Zn) based on Zn metal centers and the tetratopic N-donor organic ligand tetra(4-pyridyl)benzene (tepb). The incorporation of fluorinated inorganic pillars (SiF62–, TiF62–, SnF62–, GeF62–, ZrF62–, and TaF72–, respectively) resulted in (4,6)-connected fsc topology as verified using single-crystal X-ray diffraction. Pure-component gas sorption studies with N2, CO2, C2H2, C2H4, and C2H6 revealed that the large voids and narrow pore windows common to all six HUMs can be leveraged to afford high C2H2 uptakes while retaining high ideal adsorbed solution theory (IAST) selectivities for industrially relevant gas mixtures: >10 for 1:99 C2H2/C2H4 and >5 for 1:1 C2H2/CO2. The approach taken, systematic variation of pillars with retention of structure, enables differences in selectivity to be attributed directly to the choice of the inorganic pillar. This study introduces fsc topology HUMs as a modular platform that is amenable to fine-tuning of structure and properties.

Pentacoordinated Liquid Crystalline Zn(II) Complex Organized in Smectic Mesophase: Synthesis, Structural and Electrochemical Properties

The synthesis and structural characterization of a new liquid crystalline coordination complex based on pentacoordinated Zn(II) metal centre with the coordination fulfilled by the tridentate chelating N^N^N 2,2′;6′,2″-terpyridine ligand and two monoanionic gallates decorated with several long alkyl chains is described. The mesomorphic properties were accurately investigated by small- and wide-angle X-ray scattering studies. Despite the bulky coordination around the metal centre, the complex self-organizes into a smectic phase and, based on the structural and geometrical parameters, a model for the supramolecular organization in the liquid crystalline phase is proposed. Electrochemical investigations showed the importance of the molecular structure of the coordination complex in enhancing its aqueous sensing capacities: the bulky organic ligands form an organic shell separating the metal centres and favouring the redox system through their reduction followed by stripping.

Remotely controllable supramolecular rotor mounted inside a porphyrinic cage

Remotely controllable supramolecular rotor mounted inside a porphyrinic cage

Very intense polarized emission in self-assembled room temperature metallomesogens based on Zn(ii) coordination complexes: an experimental and computational study

Polarized emission in highly luminescent room temperature columnar metallomesogens based on Zn(ii) metal centre.

Zinc-Based Metal-Organic Frameworks in Drug Delivery, Cell Imaging, and Sensing.

The design and structural frameworks for targeted drug delivery of medicinal compounds and improved cell imaging have been developed with several advantages. However, metal-organic frameworks (MOFs) are supplemented tremendously for medical uses with efficient efficacy. These MOFs are considered as an absolutely new class of porous materials, extensively used in drug delivery systems, cell imaging, and detecting the analytes, especially for cancer biomarkers, due to their excellent biocompatibility, easy functionalization, high storage capacity, and excellent biodegradability. While Zn-metal centers in MOFs have been found by enhanced efficient detection and improved drug delivery, these Zn-based MOFs have appeared to be safe as elucidated by different cytotoxicity assays for targeted drug delivery. On the other hand, the MOF-based heterogeneous catalyst is durable and can regenerate multiple times without losing activity. Therefore, as functional carriers for drug delivery, cell imaging, and chemosensory, MOFs’ chemical composition and flexible porous structure allowed engineering to improve their medical formulation and functionality. This review summarizes the methodology for fabricating ultrasensitive and selective Zn-MOF-based sensors, as well as their application in early cancer diagnosis and therapy. This review also offers a systematic approach to understanding the development of MOFs as efficient drug carriers and provides new insights on their applications and limitations in utility with possible solutions.

Recent Advances in Crystalline Oxidopolyborate Complexes of d-Block or p-Block Metals: Structural Aspects, Syntheses, and Physical Properties.

Crystalline materials containing hybrid inorganic–organic metal borates (complexes with oxidoborate ligands) display a variety of novel framework building blocks. The structural aspects of these hybrid metallaoxidoborates containing Cd(II), Co(II), Cu(II), Ga(III), In(III), Mn(II), Ni(II) or Zn(II) metal centers are discussed in this review. The review describes synthetic approaches to these hybrid materials, their physical properties, their spectroscopic properties and their potential applications.

Ferrocene-Functionalized Dithiocarbamate Zinc(II) Complexes as Efficient Bifunctional Catalysts for the One-Pot Synthesis of Chromene and Imidazopyrimidine Derivatives via Knoevenagel Condensation Reaction.

Four new mononuclear/coordination polymeric (CP) zinc(II) complexes (1-4) of ferrocenyl/pyridyl-functionalized dithiocarbamate ligands, N-ferrocenylmethyl-N-butyl dithiocarbamate (L1), N-ferrocenylmethyl-N-ethylmorpholine dithiocarbamate (L2), N-ferrocenylmethyl-N-2-(diethylamino)ethylamine dithiocarbamate (L3), and N-4-methoxybenzyl-N-3-methylpyridyl dithiocarbamate (L4), have been synthesized and characterized by elemental analyses, IR, UV-vis, and 1H and 13C{1H} NMR spectroscopic techniques. The solid-state structures of complexes 1, 3, and 4 have been determined by single-crystal X-ray crystallography as well as powder X-ray diffraction. Single-crystal X-ray crystallography revealed a monomeric structure for complex 1 but 1D polymeric structures for complexes 3 and 4. In all complexes, dithiocarbamate ligands are bonded to the Zn(II) metal ion in a S^S chelating mode, and in the CPs, N atoms on the 2-(diethylamino)ethylamine and 3-pyridyl functionalities in the ligands on the neighboring molecules are also bonded to metal centers, leading to the formation of either a discrete tetrahedral molecule in 1 or 1D CP structures in 3 and 4. The Zn(II) metal centers in the polymeric structures exhibited either square-pyramidal or octahedral geometries. The supramolecular structures in these complexes are sustained via C-H···π (ZnCS2, chelate; 3 and 4), C-H···π, and H···H interactions. The catalytic performances of complexes have also been assessed in the Knoevenagel condensation and one-pot multicomponent reactions. Catalysis results showed that the CP 3 acts as a heterogeneous bifunctional catalyst with excellent transformation efficiency at low catalyst loading.

Degradation of a Main Plastic Pollutant Polyethylene Terephthalate by Two Distinct Proteases (Neprilysin and Cutinase-like Enzyme).

In this DFT study, hydrolysis of polyethylene terephthalate (PET), a major cause of plastic pollution, by two distinct enzymes, neprilysin (NEP, a mononuclear metalloprotease) and cutinase-like enzyme (CLE, a serine protease), has been investigated. These enzymes utilize different mechanisms for the degradation of PET. NEP uses either the metal-bound hydroxide attack (MH) mechanism or reverse protonation (RP) mechanism, while CLE utilizes a general acid/base mechanism that includes acylation and deacylation processes. Additionally, the RP mechanism of NEP can proceed through three pathways, RP0, RP1, and RP2. The DFT calculations predict that, among all these mechanisms, the MH mechanism is the energetically most favorable one for the NEP enzyme. In comparison, CLE catalyzes this reaction with a significantly higher barrier. These results suggest that the Lewis acid and nucleophile activations provided by the Zn metal center of NEP are more effective than the hydrogen bonding interactions afforded by the catalytic Ser85-His180-Asp165 triad of CLE. They have provided intrinsic details regarding PET degradation and will pave the way for the design of efficient metal-based catalysts for this critical reaction.

Steric crowding of a series of pyridine based ligands influencing the photophysical properties of Zn(II) complexes

The combination of α-acetamidocinnamic acid (HACA) and differentN,N,NandN,N,Npyridines (dPy) leads to crowded Zn(ii) metal centers. The increasing bulkiness competes with the chelation enhanced effect (CHEF) in the resulting quantum yields.