Pathological analysis of lesions in the exocrine pancreas of rats induced by Zinc Maltol

The pancreas plays an important role in the homeostasis of zinc (Zn), a nutritionally essential metal. In several previous studies, Zn ions induced inflammatory changes in the exocrine pancreas; however, little is known about Zn complexes. In this study, we microscopically, immunohistochemically, and ultrastructurally examined pancreatic lesions in Sprague-Dawley (SD) rats induced by a 4-week repeated oral dose toxicity study of Zinc Maltol (ZM), a zinc (II) complex. ZM induces acinar atrophy and increases the number of duct-like structures. Immunohistochemistry revealed a decrease in the number of trypsin-positive cells, and an increase in the number of SOX9-positive cells. Interstitial fibrosis and macrophage infiltration also correlated with the degree of acinar atrophy. Electron microscopic evaluation revealed that the acinar cells that lost granules were surrounded by fibroblasts and collagen fibers. In conclusion, we provided a detailed description of ZM-induced pancreatic lesions in SD rats.

Design, Synthesis and Evaluation of a Series of Zinc(II) Complexes of Anthracene-Affixed Multifunctional Organic Assembly as Potential Antibacterial and Antibiofilm Agents against Methicillin-Resistant Staphylococcus aureus

A novel class of zinc(II)-based metal complexes, i.e., [Zn₂(acdp)(μ-Cl)]·2H₂O (1), [Zn₂(acdp)(μ-NO₃)]·2H₂O (2), and [Zn₂(acdp)(μ-O₂CCF₃)]·2H₂O (3) (Cl^- = chloride; NO₃^- = nitrate; CF₃CO₂^- = trifluoroacetate) of anthracene-affixed multifunctional organic assembly, H₃acdp (H₃acdp = N,N'-bis[anthracene-2-ylmethyl]-N,N'-bis[carboxymethyl]-1,3-diaminopropan-2-ol), have emerged as promising antibacterial and antibiofilm agents in the domain of medicinal chemistry. Accordingly, complexes 1-3 were synthesized by utilizing H₃acdp in combination with ZnCl₂, Zn(NO₃)₂·6H₂O, and Zn(CF₃CO₂)₂·H₂O respectively, in the presence of NaOH at ambient temperature. The complexation between H₃acdp and Zn²⁺ was delineated by a combined approach of spectrophotometric and spectrofluorometric titration studies. The stoichiometry of acdp^3-/Zn²⁺ in all three complexes is observed to be 1:2, as confirmed by spectrophotometric/spectrofluorometric titration data. Elemental analysis (C, H, N, Zn), molar conductance, FTIR, UV-vis, and thermoanalytical (TGA/DTA) data were effectively used to characterize these complexes. Besides, the structures of 1-3 were established by density functional theory (DFT) calculation using B3LYP/6-311G, specifying a self-assembled compact geometry with average Zn···Zn separation of 3.4629 Å. All three zinc complexes exhibited significantly high antibacterial and antibiofilm activity against methicillin-resistant Staphylococcus aureus (MRSA BAA1717). However, complex 1 showed a more recognizable activity than 2 and 3, with minimum inhibitory concentration (MIC) values of 200, 350, and 450 μg/mL, respectively. The antimicrobial activity was tested by employing the minimum inhibitory concentration (MIC) and time-kill assay. The crystal violet (CV) assay and microscopic study were performed to examine the antibiofilm activity. As observed, complexes 1-3 had an effect on the production of extracellular polymeric substance (EPS), biofilm cell-viability, and other virulence factors such as staphyloxanthin and hemolysin production, autoaggregation ability, and microbial cell-surface hydrophobicity. Reactive oxygen species (ROS) generated due to inhibition of staphyloxanthin production in response to 1-3 were also analyzed. Moreover, complexes 1-3 showed an ability to damage the bacterial cell membrane due to accumulation of ROS resulting in DNA leakage. In addition, complexes 1-3 displayed a synergistic/additive activity with a commercially available antibiotic drug, vancomycin, with enhanced antibacterial activity. On the whole, our investigation disclosed that complex 1 could be a promising drug lead and attract much attention to medicinal chemists compared to 2 and 3 from therapeutic aspects.

Mono-, Bis-, and Tris-Chelate Zn(II) Complexes with Imidazo[1,5-a]pyridine: Luminescence and Structural Dependence

New mono-, bis-, and tris-chelate Zn(II) complexes have been synthesized starting from different Zn(II) salts and employing a fluorescent 1,3-substituted-imidazo[1,5-a]pyridine as a chelating ligand. The products have been characterized by single-crystal X-ray diffraction; mass spectrometry; and vibrational spectroscopy. The optical properties have been investigated to compare the performances of mono-, bis-, and tris-chelate forms. The collected data (in the solid state and in solution) elucidate an important modification of the ligand conformation upon metal coordination; which is responsible for a notable increase in the optical performance. An intense modification of the emission quantum yield along the series in the solid state is observed comparing mono-, bis-, and tris-chelate adducts; independently from the anionic ligand introduced by ionic exchange.

Syntheses, Characterization, Crystal Structures and Antimicrobial Activity of Copper(II), Nickel(II) and Zinc(II) Complexes Derived from 5-Bromo-2-((cychlopentylimino)methyl)phenol

Four new complexes of copper(II), nickel(II) and zinc(II), [CuL2] (1), [Ni3L2(4-BrSal)2(CH3COO)2(CH3OH)2]·2CH3OH (2), [ZnBr2(HL)2] (3) and [ZnL(dca)]n (4), where L is 5-bromo-2-((cychlopentylimino)methyl)phenolate, HL is the zwitterionic form of 5-bromo-2-((cychlopentylimino)methyl)phenol, 4-BrSal is the monoanionic form of 4-bromosalicylaldehyde, dca is dicyanamide anion, were synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy. The structures of the complexes were further confirmed by single crystal X-ray structure determination. Complex 1 is a mononuclear copper(II) compound, with a crystallographic two-fold rotation axis symmetry. The Cu atom is in distorted square planar coordination. Complex 2 is a trinuclear nickel(II) compound, with an inversion center symmetry. The Ni atoms are in octahedral coordination. Complex 3 is a mononuclear zinc(II) compound, while complex 4 is a dca bridged polymeric zinc(II) compound. The Zn atoms are in tetrahedral coordination. The compounds were assayed for their antimicrobial activities.

A DR/NIR Hybrid Polymeric Tool for Functional Bio-Coatings: Theoretical Study, Cytotoxicity, and Antimicrobial Activity

Among modern biomaterials, hybrid tools containing an organic component and a metal cation are recognized as added value, and, for many advanced biomedical applications, synthetic polymers are used as thin protective/functional coatings for medical or prosthetic devices and implants. These materials require specific non-degradability, biocompatibility, antimicrobial, and antiproliferative properties to address safety aspects concerning their use in medicine. Moreover, bioimaging monitoring of the biomedical device and/or implant through biological tissues is a desirable ability. This article reports a novel hybrid metallopolymer obtained by grafting zinc-coordinated fragments to an organic polymeric matrix. This hybrid polymer, owing to its relevant emission in the deep red to near-infrared (DR/NIR) region, is monitorable; therefore, it represents a potential material for biomedical coating. Furthermore, it shows good biocompatibility and adhesion properties and excellent stability in slightly acidic/basic water solutions. Finally, in contact with the superficial layers of human skin, it shows antimicrobial properties against Staphylococcus aureus bacterial strains.

Prophylactic and Therapeutic Potential Zinc Metallodrugs Drug Discovery: Identification of SARS-CoV-2 Replication and Spike/ACE2 Inhibitors

BACKGROUND

The emergence of severe acute respiratory syndrome coronavirus 2 (SARSCoV- 2) variants with novel spike protein mutations has been shown to be influencing the epidemiological and clinical aspects of the COVID-19 pandemic.

OBJECTIVE

Due to studies showing various dietary benefits of zinc as a viral replication inhibitor as well as an immunity enhancer, organometallic complexes incorporating zinc ions can be ideal antiviral candidates due to their structural variation and diverse stereochemistry.

METHODS

In silico studies were conducted for the virtual screening of zinc complexes with SARSCoV- 2 and host proteins to explore their effect on viral entry and replication activity. Molegro Virtual Docker along with AutoDock was used for the identification of potential SARS-CoV-2 inhibitor complexes from the Cambridge Structural Database (CSD). Molecular dynamics (MD), density functional theory (DFT), chemical absorption, distribution, metabolism, excretion, and toxicity properties (ADMET) were used to support the findings from virtual screening.

RESULTS

In correlation with SARS-CoV-2 RNA-dependent RNA polymerase and spike receptorbinding domain bound with ACE2 docking results, the compound (bis(3,5-dimethyl-1H-pyrazole)- bis(2-furoato)-zinc(ii)) (CSD code ECOZAA) occurs to be a potential metal complex SARS-CoV-2 receptor inhibitor. The compound ECOZAA was observed (in silico binding affinity = - 179.29kcal/mol) to behave better than the clinically approved drug Remdesivir (in silico binding affinity = -62.69kcal/mol) against SARS-CoV-2 RNA-dependent RNA polymerase. The large HOMO- LUMO gap for the ECOZAA compound is an indication of the low chemical reactivity as well as the great kinetic stability of the compound.

CONCLUSION

Thus, this study highlights the potential use of zinc metal complexes as SARS-CoV-2 viral entry and replication inhibitors.

Catalytic Enantioselective Cyclopropylalkynylation of Aldimines Generated In Situ from α-Amido Sulfones

A convenient procedure of synthesis of N-carbamoyl-protected propargylic amines substituted with a cyclopropyl group from α-amido sulfones and cyclopropylacetylene is described. The reaction is catalyzed by a chiral BINOL-type zinc complex and provides the corresponding products in good yields and enantioselectivities.

Synthesis, structural and electrochemical properties of a new family of amino-acid-based coordination complexes

Metalloproteins involved in oxidation-reduction processes in metabolism are fundamental for the wellbeing of every organism. The use of amino-acid-based compounds as ligands for the construction of biomimetic coordination systems represents a promising alternative for the development of new catalysts. Herein is presented a new family of copper, zinc and nickel coordination compounds, which show four-, five- and six- coordination geometries, synthesized using Schiff base ligands obtained from the amino acids L-alanine and L-phenylalanine. Structural analysis and property studies were performed using single-crystal X-ray diffraction data, spectroscopic and electrochemical experiments and DFT calculations. The analysis of the molecular and supramolecular architectures showed that the non-covalent interactions developed in the systems, together with the identity of the metal and the amino acid backbone, are determinants for the formation of the complexes and the stabilization of the resultant geometries. The Cu^II complexes were tested as candidates for the electrochemical conversion reduction of nitrite to NO, finding that the five-coordinate L-phenylalanine complex is the most suitable. Finally, some insights into the rational design of ligands for the construction of biomimetic complexes are suggested.

Thermo-Induced Fluorochromism in Two AIE Zinc Complexes: A Deep Insight into the Structure-Property Relationship

Solid-state emitters exhibiting mechano-fluorochromic or thermo-fluorochromic responses represent the foundation of smart tools for novel technological applications. Among fluorochromic (FC) materials, solid-state emissive coordination complexes offer a variety of fluorescence responses related to the dynamic of noncovalent metal-ligand coordination bonds. Relevant FC behaviour can result from the targeted choice of metal cation and ligands. Herein, we report the synthesis and characterization of two different colour emitters consisting of zinc complexes obtained from N,O bidentate ligands with different electron-withdrawing substituents. The two complexes are blue and orange solid-state fluorophores, respectively, highly responsive to thermal and mechanical stress. These emitters show a very different photoluminescent (PL) pattern as recorded before and after the annealing treatment. Through X-ray structural analysis combined with thermal analysis, infrared (IR) spectroscopy, PL, and DFT simulation we provide a comprehensive analysis of the structural feature involved in the fluorochromic response. Notably, we were able to correlate the on-off thermo-fluorochromism of the complexes with the structural rearrangement at the zinc coordination core.

Zinc Complexes Derived from 5-Bromo-2-(((2-isopropylamino)ethyl)imino)methyl)phenol: Microwave-Assisted Synthesis, Characterization, Crystal Structures and Antibacterial Activities

Three new zinc complexes [Zn3L2(μ2-η1:η1-CH3COO)2(μ2-η2:η0-CH3COO)2] (1), [ZnCl2(HL)] (2) and [ZnBr2(HL)] (3), where L = 5-bromo-2-(((2-isopropylamino)ethyl)imino)methyl)phenolate, HL = 5-bromo-2-(((2-isopropylammonio)ethyl)imino)methyl)phenolate, have been synthesized under microwave irradiation. The complexes were characterized by elemental analyses, IR, UV-Vis spectra, molar conductivity, and single crystal X-ray diffraction. X-ray analysis revealed that the Zn atoms in complex 1 are in square pyramidal and octahedral coordination, and those in complexes 2 and 3 are in tetrahedral coordination. The molecules of the complexes are linked through hydrogen bonds and π···π interactions. In order to evaluate the biological activity of the complexes, in vitro antibacterial against Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa was assayed.

Zinc (II) and AIEgens: The "Clip Approach" for a Novel Fluorophore Family. A Review

Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of "AIEgens" was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic-inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d10 zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016-2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II)-based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.

Induction of Λ-helicity in a zinc complex with an alanine-appended aminopyridine ligand

The crystal structure of tris[dimethyl 5-({1-[(pyridin-2-yl-κN)carbamoyl-κO]ethyl}carbamoyl)benzene-1,3-dicarboxylate]zinc(II) dinitrate acetonitrile trisolvate, [Zn(C₁₉H₁₉N₃O₆)₃](NO₃)₂·3CH₃CN or [Zn(L)₃](NO₃)₂·3CH₃CN, (1), has been determined by single-crystal X-ray diffraction. The neutral ligand L coordinates to the Zn²⁺ cation in a bidentate fashion via the pyridine N atom and an amide O atom, forming a six-membered chelate ring. The Λ-helical chirality of the Zn²⁺ coordination sphere is induced by pendant L-alanine residues through stacking interactions between the arene groups of two coordinated ligands, assisted by a hydrogen bond between amide groups bonded to the stacked arene rings. The third ligand is coordinated to the Zn²⁺ cation by the same six-membered chelate ring, but in the opposite direction with respect to the analogous chelate rings of the first two coordinated ligands. Besides ionic interactions between [ZnL₃]²⁺ complexes and NO₃^- anions, several types of hydrogen bonds and intermolecular stacking interactions contribute to the stability of the solid-state phase.

Ditopic Aza-Scorpiand Ligands Interact Selectively with ds-RNA and Modulate the Interaction upon Formation of Zn2+ Complexes

Nucleic acids are essential biomolecules in living systems and represent one of the main targets of chemists, biophysics, biologists, and nanotechnologists. New small molecules are continuously developed to target the duplex (ds) structure of DNA and, most recently, RNA to be used as therapeutics and/or biological tools. Stimuli-triggered systems can promote and hamper the interaction to biomolecules through external stimuli such as light and metal coordination. In this work, we report on the interaction with ds-DNA and ds-RNA of two aza-macrocycles able to coordinate Zn²⁺ metal ions and form binuclear complexes. The interaction of the aza-macrocycles and the Zn²⁺ metal complexes with duplex DNA and RNA was studied using UV thermal and fluorescence indicator displacement assays in combination with theoretical studies. Both ligands show a high affinity for ds-DNA/RNA and selectivity for ds-RNA. The ability to interact with these duplexes is blocked upon Zn²⁺ coordination, which was confirmed by the low variation in the melting temperature and poor displacement of the fluorescent dye from the ds-DNA/RNA. Cell viability assays show a decrease in the cytotoxicity of the metal complexes in comparison with the free ligands, which can be associated with the observed binding to the nucleic acids.

Synthesis and Binding Properties of a Tren-Capped Hexahomotrioxacalix[3]arene

The straightforward synthesis of a new hexahomotrioxacalix[3]arene-based ligand capped by a tren subunit was developed and the binding properties of the corresponding zinc complex were explored by NMR spectroscopy. Similarly to the closely related calix[6]tren-based systems, the homooxacalixarene core ensures the mononuclearity of the zinc complex and the metal center displays a labile coordination site for exogenous guests. However, very different host-guest properties were observed: i) in CDCl₃ , the zinc complex strongly binds a water molecule and is reluctant to recognize other neutral guests, ii) in CD₃ CN, the exo-coordination of anions prevails. Thus, in strong contrast to the calix[6]tren-based systems, the coordination of neutral guests that thread through the small rim and fill the polyaromatic cavity was not observed. This unique behaviour is likely due to the fact that the 18-membered ethereal macrocycle is too small to let a molecule threading through it. This work illustrates the key role played by the second coordination sphere in the binding properties of metal complexes.

Synthesis, structure and selective luminescence sensing for iron(III) ions of a three-dimensional zinc(II) (4,6)-connected coordination network

Coordination polymers constructed from conjugated organic ligands and metal ions with a d¹⁰ electronic configuration exhibit intriguing properties for chemical sensing and photochemistry. A Zn^II-based coordination polymer, namely poly[aqua(μ₆-biphenyl-3,3',5,5'-tetracarboxylato)(μ₂-4,4'-bipyridine)dizinc(II)], [Zn₂(C₁₆H₆O₈)(C₁₀H₈N₂)(H₂O)₂]_n or [Zn₂(m,m-bpta)(4,4'-bipy)(H₂O)₂]_n, was synthesized from a mixture of biphenyl-3,3',5,5'-tetracarboxylic acid [H₄(m,m-bpta)], 4,4'-bipyridine (4,4'-bipy) and Zn(NO₃)₂·6H₂O under solvothermal conditions. The title complex has been structurally characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction analysis, and features a μ₆-coordination mode. The Zn^II ions adopt square-pyramidal geometries and are bridged by two syn-syn carboxylate groups to form [Zn₂(COO)₂] secondary buildding units (SBUs). The SBUs are crosslinked by (m,m-bpta)^4- ligands to produce a two-dimensional grid-like layer that exhibits a stair-like structure along the a axis. Adjacent layers are linked by 4,4'-bipy ligands to form a three-dimensional network with a {4⁴.6¹⁰.8}{4⁴.6²} topology. In the solid state, the complex displays a strong photoluminescence and an excellent solvent stability. In addition, the luminescence sensing results indicate a highly selective and sensitive sensing for Fe³⁺ ions.

A two-dimensional Zn coordination polymer with a three-dimensional supra-molecular architecture

The characteristic structural feature of a new two-dimensional Zn coordination polymer is an infinite polymeric layer parallel to the crystallographic (132) plane.

The title compound, poly[bis­{μ₂-4,4′-bis­[(1,2,4-triazol-1-yl)meth­yl]biphenyl-κ²N⁴:N^4′}bis­(nitrato-κO)zinc(II)], [Zn(NO₃)₂(C₁₈H₁₆N₆)₂]_n, is a two-dimensional zinc coordination polymer constructed from 4,4′-bis­[(1H-1,2,4-triazol-1-yl)meth­yl]-1,1′-biphenyl units. It was synthesized and characterized by elemental analysis and single-crystal X-ray diffraction. The Zn^II cation is located on an inversion centre and is coordinated by two O atoms from two symmetry-related nitrate groups and four N atoms from four symmetry-related 4,4′-bis­[(1H-1,2,4-triazol-1-yl)meth­yl]-1,1′-biphenyl ligands, forming a distorted octa­hedral {ZnN₄O₂} coordination geometry. The linear 4,4′-bis­[(1H-1,2,4-triazol-1-yl)meth­yl]-1,1′-biphenyl ligand links two Zn^II cations, generating two-dimensional layers parallel to the crystallographic (132) plane. The parallel layers are connected by C—H⋯O, C—H⋯N, C—H⋯π and π–π stacking inter­actions, resulting in a three-dimensional supra­molecular architecture.

Crystal structure of bis-{1-phenyl-3-methyl-4-[(quinolin-3-yl)imino-methyl-κN]-1H-pyrazol-5-olato-κO}zinc methanol 2.5-solvate from synchrotron X-ray diffraction

A synthetic approach to the new zinc complex based on amino­methyl­ene derivative of 1-phenyl-3-methyl-4-[(quinolyl-3-yl)imino­meth­yl]-1H-pyrazol-5(4H)-one and its structural characterization by synchrotron single-crystal X-ray diffraction are reported.

The title compound, [Zn(C₂₀H₁₅N₄O)₂]·2.5CH₃OH, I, was synthesized via the reaction of zinc acetate with the respective ligand and isolated as a methanol solvate, i.e., as I·2.5CH₃OH. The crystal structure is triclinic (space group P-1), with two complex mol­ecules (A and B) and five methanol solvent mol­ecules in the asymmetric unit. One of the five methanol solvent mol­ecules is disordered over two sets of sites, with an occupancy ratio of 0.75:0.25. Mol­ecules A and B are conformers and distinguished by the conformations of the bidentate 1-phenyl-3-methyl-4-[(quinolin-3-yl)imino­meth­yl]-1H-pyrazol-5-olate ligands. In both mol­ecules, the zinc cations have distorted tetra­hedral coordination spheres, binding the monoanionic ligands through the pyrazolo­late O and imine N atoms. The two ligands adopt slightly different conformations in terms of the orientation of the terminal phenyl and quinoline substituents with respect to the central pyrazolo­late moiety. The mol­ecular geometries of A and B are supported by intra­molecular C—H⋯O and C—H⋯N hydrogen bonds. In the crystal of I, mol­ecules form dimers both by secondary inter­molecular Zn⋯O [3.140 (2)–3.553 (3) Å] and π–π stacking inter­actions. The dimers are linked by inter­molecular hydrogen bonds through the solvent methanol mol­ecules into a three-dimensional network.

A three-dimensional ZnII coordination polymer constructed from 1,1'-biphenyl-2,2',4,4'-tetracarboxylate and 1,4-bis(1H-imidazol-1-yl)benzene ligands exhibiting photoluminescence

Ligands based on polycarboxylic acids are excellent building blocks for the construction of coordination polymers; they may bind to a variety of metal ions and form clusters, as well as extended chain or network structures. Among these building blocks, biphenyltetracarboxylic acids (H₄bpta) with C₂ symmetry have recently attracted attention because of their variable bridging and multidentate chelating modes. The new luminescent three-dimensional coordination polymer poly[(μ₅-1,1'-biphenyl-2,2',4,4'-tetracarboxylato)bis[μ₂-1,4-bis(1H-imidazol-1-yl)benzene]dizinc(II)], [Zn₂(C₁₆H₆O₈)(C₁₂H₁₀N₄)]_n, was synthesized solvothermally and characterized by single-crystal X-ray diffraction, elemental analysis and IR spectroscopy. The crystal structure contains two crystallographically independent Zn^II cations. Both metal cations are located on twofold axes and display distorted tetrahedral coordination geometries. Neighbouring Zn^II centres are bridged by carboxylate groups in the syn-anti mode to form one-dimensional chains. Adjacent chains are linked through 1,1'-biphenyl-2,2',4,4'-tetracarboxylate and 1,4-bis(1H-imidazol-1-yl)benzene ligands to form a three-dimensional network. In the solid state, the compound exhibits blue photoluminescence and represents a promising candidate for a thermally stable and solvent-resistant blue fluorescent material.

Crystal structure of trans-di-aqua-bis-(4-cyano-benzoato-κO)bis-(N,N-di-ethyl-nicotinamide-κN)zinc(II)

In the crystal, the title centrosymmetric Zn^II complex mol­ecules are linked by O—H⋯O hydrogen bonds into supra­molecular chains propagating along the [110] direction.

In the title complex, [Zn(C₈H₄NO₂)₂(C₁₀H₁₄N₂O)₂(H₂O)₂], the Zn^II cation, located on an inversion centre, is coordinated by two water mol­ecules, two 4-cyano­benzoate (CB) anions and two di­ethyl­nicotinamide (DENA) ligands in a distorted N₂O₄ octa­hedral geometry. In the mol­ecule, the dihedral angle between the planar carboxyl­ate group and the adjacent benzene ring is 9.50 (14)°, while the benzene and pyridine rings are oriented at a dihedral angle of 56.99 (5)°. The water mol­ecules exhibit both an intra­molecular hydrogen bond [to the non-coordinating carboxyl­ate O atom, enclosing an S(6) hydrogen-bonding motif, where O⋯O = 2.6419 (19) Å] and an inter­molecular hydrogen bond [to the amide carbonyl O atom, enclosing an R₂²(16) ring motif, where O⋯O = 2.827 (2) Å]; the latter lead to the formation of supra­molecular chains propagating along the [110] direction.

Crystal structure of di-aqua-bis-(7-di-ethyl-amino-3-formyl-2-oxo-2H-chromen-4-olato-κ(2) O (3),O (4))zinc(II) dimethyl sulfoxide disolvate

A near-perfect octa­hedral zinc(II) complex coordinated to two coumarin fluoro­phores.

The structure of the title coordination complex, [Zn(C₁₄H₁₄NO₄)₂(H₂O)₂]·2C₂H₆OS, shows that the Zn^II cation adopts an octa­hedral geometry and lies on an inversion center. Two organic ligands occupy the equatorial positions of the coordination sphere, forming a chelate ring motif via the O atom on the formyl group and another O atom of the carbonyl group (a pseudo-β-diketone motif). Two water mol­ecules occupy the remaining coordination sites of the Zn^II cation in the axial positions. The water mol­ecules are each hydrogen bonded to a single dimethyl sulfoxide mol­ecule that has been entrapped in the crystal lattice.

Supramolecular hydrogen-bonding patterns in the organic-inorganic hybrid compound bis(4-amino-5-chloro-2,6-dimethylpyrimidinium) tetrathiocyanatozinc(II)-4-amino-5-chloro-2,6-dimethylpyrimidine-water (1/2/2)

Zinc thiocyanate complexes have been found to be biologically active compounds. Zinc is also an essential element for the normal function of most organisms and is the main constituent in a number of metalloenzyme proteins. Pyrimidine and aminopyrimidine derivatives are biologically very important as they are components of nucleic acids. Thiocyanate ions can bridge metal ions by employing both their N and S atoms for coordination. They can play an important role in assembling different coordination structures and yield an interesting variety of one-, two- and three-dimensional polymeric metal-thiocyanate supramolecular frameworks. The structure of a new zinc thiocyanate-aminopyrimidine organic-inorganic compound, (C6H9ClN3)2[Zn(NCS)4]·2C6H8ClN3·2H2O, is reported. The asymmetric unit consist of half a tetrathiocyanatozinc(II) dianion, an uncoordinated 4-amino-5-chloro-2,6-dimethylpyrimidinium cation, a 4-amino-5-chloro-2,6-dimethylpyrimidine molecule and a water molecule. The Zn(II) atom adopts a distorted tetrahedral coordination geometry and is coordinated by four N atoms from the thiocyanate anions. The Zn(II) atom is located on a special position (twofold axis of symmetry). The pyrimidinium cation and the pyrimidine molecule are not coordinated to the Zn(II) atom, but are hydrogen bonded to the uncoordinated water molecules and the metal-coordinated thiocyanate ligands. The pyrimidine molecules and pyrimidinium cations also form base-pair-like structures with an R2(2)(8) ring motif via N-H...N hydrogen bonds. The crystal structure is further stabilized by intermolecular N-H...O, O-H...S, N-H...S and O-H...N hydrogen bonds, by intramolecular N-H...Cl and C-H...Cl hydrogen bonds, and also by π-π stacking interactions.

Crystal structure of bis-(1,3-di-amino-propane-κ(2) N,N')bis-[2-(4-nitro-phen-yl)acetato-κO]zinc(II)

In the structure of the title compound, [Zn(C₈H₆NO₄)₂(C₃H₁₀N₂)₂], the Zn^II atom is located on a center of symmetry with one independent Zn—O distance of 2.199 (2) Å, and two Zn—N distances of 2.157 (2) and 2.144 (2) Å. The overall coordination geometry around the Zn^II atom is octa­hedral. Several types of hydrogen-bonding inter­actions are evident. Both intra­molecular [2.959 (3) Å] and inter­molecular [3.118 (3) and 3.124 (3) Å inter­actions occur between the O atoms of the acetate group and the amino N atoms, and weak inter­molecular C—H—O inter­actions involving the nitro groups, leading to an extended chain of the molecules aligned along the ac plane.

Crystal structure of catena-poly[[[tetra-aqua-zinc(II)]-μ-1,4-bis-[4-(1H-imidazol-1-yl)benzo-yl]piperazine] dinitrate monohydrate]

In the title polymeric complex, {[Zn(C₂₄H₂₂N₆O₂)(H₂O)₄](NO₃)₂·2H₂O}_n, the Zn^II cation, located about a twofold rotation axis, is coordinated by two imidazole groups and four water mol­ecules in a distorted N₂O₄ octa­hedral geometry; among the four coordinate water mol­ecules, two are located on the same twofold rotation axis. The 1,4-bis­[4-(1H-imidazol-1-yl)benzo­yl]piperazine] ligand is centro-symmetric, with the centroid of the piperazine ring located on an inversion center, and bridges the Zn^II cations, forming polymeric chains propagating along [201]. In the crystal, O—H⋯O and weak C—H⋯O hydrogen bonds link the polymeric chains, nitrate anions and solvent water mol­ecules into a three-dimensional supra­molecular architecture. A short O⋯O contact of 2.823 (13) Å is observed between neighboring nitrate anions.

Crystal structure of aqua-bis-[2-(1H-benzimidazol-2-yl-κN (3))aniline-κN]zinc dinitrate

The cation of the complex title salt, [Zn(C13H11N3)2(H2O)](NO3)2, lies about a twofold rotation axis, which passes through the Zn(II) atom and the O atom of the aqua ligand. The Zn(II) atom adopts a distorted trigonal-bipyramidal geometry defined by two N atoms in axial positions [angle = 166.24 (7)°], and two N and one O atom in the equatorial plane [range of angles: 115.17 (7)-122.42 (3)°]. The dihedral angle between the imidazole and aniline rings is 23.86 (5)°. In the crystal, N-H⋯O and O-H⋯O hydrogen bonds link the components into a three-dimensional network.

Crystal structure of hexa-kis-(μ2-4-tert-but-oxy-4-oxobut-2-en-2-olato)trizinc

The structure of a centrosymmetric trinuclear zinc(II) complex with the formula [Zn{ZnL₃}₂], where L is 4-tert-but­oxy-4-oxobut-2-en-2-olate, is presented.

The title complex, systematic name hexa­kis­(μ₂-4-tert-but­oxy-4-oxobut-2-en-2-olato)-1:2κ⁹O²,O⁴:O²;2:3κ⁹O²,O⁴:O²-trizinc, [Zn₃(C₈H₁₃O₃)₆], syn­the­sized from tert-butyl aceto­acetate and di­ethyl­zinc, consists of trinuclear centrosymmetric mol­ecules of an approximate C_3i symmetry. The three metal cations are arranged in a linear fashion, with the central Zn^II atom located on a centre of symmetry. All three metal cations exhibit a distorted octa­hedral coordination geometry. The terminal Zn^II cations are chelated by three tert-butyl aceto­acetate ligands and these units are connected to the central Zn^II atom by the bridging enolate O atoms.

Crystal structure of di-chlorido-(2,2':6',2''-terpyridine-κ(3) N,N',N'')zinc: a redeter-min-ation

The crystal structure of the title compound, [ZnCl₂(C₁₅H₁₁N₃)], was redetermined based on modern CCD data. In comparison with the previous determination from photographic film data [Corbridge & Cox (1956 ▶). J. Chem. Soc.159, 594–603; Einstein & Penfold (1966 ▶). Acta Cryst.20, 924–926], all non-H atoms were refined with anisotropic displacement parameters, leading to a much higher precision in terms of bond lengths and angles [e.g. Zn—Cl = 2.2684 (8) and 2.2883 (11) compared to 2.25 (1) and 2.27 (1) Å]. In the title mol­ecule, the Zn^II atom is five-coordinated in a distorted square-pyramidal mode by two Cl atoms and by the three N atoms from the 2,2′:6′,2′′-terpyridine ligand. The latter is not planar and shows dihedral angles between the least-squares planes of the central pyridine ring and the terminal rings of 3.18 (8) and 6.36 (9)°. The mol­ecules in the crystal structure pack with π–π inter­actions [centroid–centroid distance = 3.655 (2) Å] between pyridine rings of neighbouring terpyridine moieties. These, together with inter­molecular C—H⋯Cl inter­actions, stablize the three-dimensional structure.

Crystal structure of [2-({4-[2,6-bis(pyri-din-2-yl)pyri-din-4-yl]phenyl}(methyl)amino)-ethanol-κ(3) N,N',N'']bis-(thio-cyan-ato-κN)zinc N,N-di-methyl-formamide monosolvate

In the title compound, [Zn(NCS)₂(C₂₄H₂₂N₄O)]·C₃H₇NO, the Zn^II cation is N,N′,N′′-chelated by one 2-({4-[2,6-bis­(pyridin-2-yl)pyridin-4-yl]phen­yl}(meth­yl)amino)­ethanol ligand and coordinated by two thio­cyanate anions in a distorted N₅ trigonal–bipyramidal geometry. In the mol­ecule, the three pyridine rings are approximately coplanar [maximum deviation = 0.026 (5) Å], and the mean plane of the three pyridine rings is twisted to the benzene ring with a small dihedral angle of 5.9 (2)°. In the crystal, complex mol­ecules are linked by weak C—H⋯O hydrogen bonds into supra­molecular chains propagated along [110]; π–π stacking is observed between adjacent chains [centroid–centroid distance = 3.678 (4) Å]. The di­methyl­formamide solvent mol­ecules are linked with the complex chains via weak C—H⋯O hydrogen bonds.

Synthesis, crystal structures and characterizations of two homochiral coordination polymers based on a chiral reduced Schiff base ligand

Two homochiral coordination polymers based on a chiral reduced Schiff base ligand, namely poly[(μ5-4-{[(NR,1S)-(1-carboxylato-2-phenylethyl)amino]methyl}benzoato)zinc(II)], [Zn(C17H15NO4)]n, (1), and poly[(μ5-4-{[(NR,1S)-(1-carboxylato-2-phenylethyl)amino]methyl}benzoato)cobalt(II)], [Co(C17H15NO4)]n, (2), have been obtained by hydrothermal methods and studied by single-crystal X-ray diffraction, elemental analyses, powder X-ray diffraction, thermogravimetric analysis, IR spectroscopy and fluorescence spectroscopy. Compounds (1) and (2) are isostructural and crystallize in the P2(1)2(1)2(1) space group. Both display a three-dimensional network structure with a one-dimensional channel, with the benzyl group of the ligand directed towards the channel. An investigation of photoluminescence properties shows that compound (1) displays a strong emission in the purple region.

(Hexafluorosilicato-κ(2)F,F')bis(1,10-phenanthroline-κ(2)N,N')zinc(II) methanol monosolvate

The title compound, [Zn(SiF6)(C12H8N2)2]·CH3OH, contains a neutral heteroleptic tris-chelate Zn(II) complex, viz. [Zn(SiF6)(phen)2] (phen is 1,10-phenanthroline), exhibiting approximate molecular C2 point-group symmetry. The Zn(II) cation adopts a severely distorted octahedral coordination. As far as can be ascertained, the title complex represents the first structurally characterized example of a Zn(II) complex bearing a bidentate-bound hexafluorosilicate ligand. A density functional theory study of the isolated [Zn(SiF6)(phen)2] complex was undertaken to reveal the influence of crystal packing on the molecular structure of the complex. In the crystal structure, the methanol solvent molecule forms a hydrogen bond to one F atom of the hexafluorosilicate ligand. The hydrogen-bonded assemblies so formed are tightly packed in the crystal, as indicated by a high packing coefficient (74.1%).