Effect of ammonia on the Zn(Hg)/Zn(II) electrode reactions in aqueous chloride solutions

The title subject has been studied using single pulse and chronopotentiometric polarization measurements on the Zn(Hg)/Zn(II) electrode and equilibrium measurements on the same and the Zn/Zn(II) electrode, mainly in 2 M NH₄Cl with 0–0.3 M NH₃. At low ammonia concentrations, the Zn(Hg)/Zn(II) reactions are found to occur in two consecutive charge-transfer steps with Zn(I) as intermediate, and with little or no participation of ammonia. At higher ammonia concentrations, however, nearly symmetric transfer by divalent zinc ion (α=0.5 and n=2) to and from diammine species appears to be the predominant charge-transfer step.     

Single-ion activities and Zn/Zn(II) reactions in alkali chloride solutions

The title subject has been studied through equilibrium potential measurements on the Zn/Zn(II) and the Ag/AgCl electrode vs. SCE and galvanostatic single-step and chronopotentiometric polarization measurements on the former electrode, all in acidified (to pH about 3) solutions of 0.005 M ZnCl₂+0.99 M MeCl (for Me=Li, Na, K, and Cs) at 25°C. It is found that the Zn(II) activity decreases together with the alkali-ion activity along the sequence LiCl>NaCl>KCl>CsCl, that the chloride-ion activity essentially is insensitive to mutual substitutions of alkali ions, and that the Zn/Zn(II) reactions exhibit no other than pure activity effects of such substitutions. The results support that the Zn/Zn(II) electrode reacts in two consecutive steps with Zn(I) as intermediate, and that some sluggishness appears in chemical reactions to and from electroactive Zn(II) species.     

Kinetics of Zn/Zn(II) reactions in acidified solutions of potassium chloride

The title subject has been studied using stationary, single-pulse, and chronopotentiometric polarization measurements on the Zn/Zn(II) electrode and equilibrium measurements on the same and the Ag/AgCl electrode in 0.5–4 M chloride solutions at 25°C. The Zn/Zn(II) electrode reactions are found to occur in two consecutive charge-transfer steps with Zn(I) as intermediate. The ion-transfer step Zn/Zn(I) is too fast to exhibit its kinetics. The electron-transfer step Zn(I)/Zn(II) mostly occurs by the couple ZnCl₂(H₂O)_y/ZnCl₂(H₂O)_y, but species with one or no chloride ligand take over as the main electroactive ones at chloride (or salt) concentrations below 1 M. The value of y is not clearly revealed by the data. Some sluggishness in complex equilibration and some, double-layer effects are observed. A convenient scale for single-ion activities is described, used, and recommended.     

The influence of ms-substitution on the properties of 3,3′-bis(dipyrrolylmethenes) and their coordination compounds

We have compared the coordination properties of decamethyl-substituted 3,3′-bis-(dipyrrolylmethenes) (H₂L) with different ms-spacers separating the dipyrrolylmethene domains: methylene -CH₂-, methoxyphenylmethylene -CH(p-C₆H₄OMe)-, and trifluoromethylmethylene -CH(CF₃)-. The stable binuclear homoligand complexes [M₂L₂] are formed in reactions of the ligands with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) acetates. In the cases of all H₂L ligands the thermodynamic constants of the complex formation reactions increase in the following series: Cu(II) < Cd(II) < Hg(II) < Ni(II) < Co(II) < Zn(II). The change in -CH₂- ms-spacer to -CH(p-C₆H₄OMe)- or -CH(CF₃)- results in a decrease in the constant of H₂L complex formation by 1–4 orders of magnitude, the cation being the same. The influence of ms-substitution on the stability and luminescence properties of [M₂L₂] has been discussed.     

Oligoether-strapped meso-pyrimidinylporphyrins

Bis(oligoether-strapped) zinc(II)-meso-pyrimidinylporphyrins were readily synthesized via nucleophilic aromatic substitution reactions of biscathechol-substituted tri- or tetraethylene glycol straps on the upper and lower faces of a Zn(II)-A₂B₂-meso-dichloropyrimidinylporphyrin precursor. The crown ether-like bridges surrounding the porphyrin core create peculiar cavities above and below the macrocyclic plane with appealing features for supramolecular host–guest chemistry.     

Complexation between decamethyl-3,3′-bis(dipyrrolylmethene) and zinc(II), copper(II), and cobalt(II) acetates

Decamethyl-3,3′-bis(dipyrrolylmethene) dihydrobromide H₂L · 2HBr (H₂L is bis(3,4,7,8,9-pentamethylpyrrol-3-yl)methane), which is the simplest representative of a novel class of oligo(dipyrrolylmethenes) belonging to chromophore chelating nonmacrocyclic ligands, were examined by ¹H NMR, IR, and electronic absorption spectroscopy. Complexation reactions of H₂L · 2HBr with M(AcO)₂ (M = Zn(II), Cu(II), and Co(II)) in DMF at 298.15 K were monitored by electronic absorption spectroscopy and studied by the molar ratio method. The thermodynamic constants K ⁰ of these reactions were estimated. The d metal ions coordinate H₂L to give the binuclear homoleptic complexes [M₂L₂]. The reactions proceed through the intermediate binuclear heteroleptic complex [M₂L(AcO)₂] detected by spectroscopic methods. The thermodynamic stabilities of [M₂L₂] and [M₂L(AcO)₂] increase when moving from Cu(II) to Zn(II) and Co(II). The probability of formation and stability of [M₂L₂] containing 3,3′-bis(dipyrrolylmethene) are substantially higher than those of analogous complexes with the 2,2′-isomer (decamethyl-2,2′-biladienea, c). The low K ⁰ values for the complexation between H₂L and Cu(AcO)₂ are due to slow oxidation of the biladiene ligand into a bilatriene with participation of Cu²⁺ ions.     

Facile, divergent route to bis-Zn(II)dipicolylamine type chemosensors for pyrophosphate

A new, two-step synthesis has been developed for a series of bis-DPA-type ligands whose dinuclear Zn(II) complexes function as fluorescent anion sensors. The Zn(II) complexes exhibit good selectivity for PP_i over other anions in aqueous medium (pH 7.5) and may be used to monitor the extent of enzyme-catalysed reactions, in which PP_i is produced or consumed.     

Four Zn(II)/Cd(II)-3-amino-1,2,4-triazolate frameworks constructed by in situ metal/ligand reactions: Structures and fluorescent properties

Four Cd(II) and Zn(II) complexes with the in situ-generated ligand of 3-amino-1,2,4-triazolate (AmTAZ⁻) were isolated from the solvothermal reactions of the corresponding Cd(II) or Zn(II) salts with 5-amino-1H-1,2,4-triazole-3-carboxylic acid (AmTAZAc). Their structures were determined by single-crystal X-ray diffraction analysis. [Zn(AmTAZ)(CH₃COO)] (1) presents a two-dimensional framework constructed from Zn(II) ions and μ₃-AmTAZ⁻ ligands. A remarkable feature of [Zn₄(AmTAZ)₄(SO₄)(OH)(C₂O₄)_0.5]·2H₂O (2) is the construction of the building units of octagonal cylinders which interact with each other by sharing one face or overlapping, resulting in the formation of a three-dimensional framework with three kinds of 1D channels. [Cd(AmTAZ)Br] (3) crystallizes in a chiral space group P2₁2₁2₁, giving a homochiral three-dimensional framework with two types of helical channels (left- and right-handed). Different from the others, the 3-amino-1,2,4-triazole molecules in [Cd(AmTAZH)SO₄] (4) behave as neutral μ₂-2,4-bridges to connect the two-dimensional CdSO₄ sheets into a three-dimensional framework. Of all, 2 and 3 display different fluorescent properties probably due to different metal ions, coordination environments and structural topologies.     

Synthesis,crystal structure,spectral and biological studies of Cu–M(M = Zn and Pb) heterodinuclear complexes of new phenol-based macrocyclic ligands

Eight new heterodinuclear Cu(II)–M(II) (M = Pb and Zn) complexes of four new phenol based compartmental macrocyclic ligands, possessing contiguous (N₂O₂) and (N_xO₂) (x = 2, 3) coordination sites, were prepared by the template reaction of [N,N′-bis(3-formyl-5-methylsalicylidene)ethane-1,2-diaminato]copper(II), with various di- and/or tri-amines in the presence of Pb(II) and Zn(II) ions. The crystal structure of [CuZnL³(H₂O)](ClO₄)₂, 6, was determined by X-ray diffraction and shows that the Zn(II) and Cu(II) ions reside in the N₂O₂ sites of the macrocyclic ligand. The fifth coordination site of the Zn centre is occupied by a water ligand. All the complexes have been characterized by elemental analysis, molar conductivity and spectroscopic methods (IR and UV). Also, all the synthesized complexes were screened for their antibacterial and antifungal activity against Escherichia coli, Staphyloccocus aureus and Candida albicans.     

Thermochemistry of adducts of some bivalent transition metal bromides with pyridine

The compounds [MBr₂(py)₂] (where M is Mn(II), Co(II), Ni(II), Cu(II) or Zn(II); py = pyridine) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyridine in 25% (v/v) 1.2 M aqueous HCl in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean bond dissociation enthalpies of the M(II)-nitrogen bonds have been estimated as well as the enthalpies of the adducts formation in the gaseous phase.     

Coupled zinc transport through a bis(2-ethylhexyl)phosphoric acid solid-supported liquid membrane from aqueous perchlorate media

The rate of Zn(II) transport from 1.0 M (Na,H)ClO₄ aqueous media through a liquid membrane consisting of bis(2-ethylhexyl)phosphoric acid (HDEHP, HR) dissolved in Isopar-H and a teflon-type solid support, has been investigated as a function of the chemical composition of the system and the hydrodynamic conditions at 25°C. The measured transfer rates have been explained in terms of aqueous diffusion, diffusion of ZnR₂(HR)₂ and ZnR₂(HR) species through the liquid membrane and the rate of chemical reactions of Zn(II) in this system. The results are in agreement with the kinetic and equilibrium models proposed for this sytem in previous studies.     

A New Trinuclear Zn(II) Complex {[Zn(μ-ONN)(μ<Subscript>2</Subscript>-O)(μ-OO)]<Subscript>2</Subscript>Zn}: Synthesis,Characterization, Thermal Decomposition and Antibacterial Activity

New centrosymmetric trinuclear zinc(II) complex {[Zn(μ-ONN)(μ₂-O)(μ-OO)]₂Zn} has been synthesized by the reaction of a potentially ONN tridentate Schiff base ligand, and N,N-dimethylethylendiamin, with Zn(OAc)₂·2H₂O in methanol, in the refluxed conditions and characterized by elemental analysis, FT-IR and UV–Vis spectroscopy. Single crystal X-ray structure analysis reveals a trinuclear complex {[Zn(μ-ONN)(μ₂-O)(μ-OO)]₂Zn} with zinc(II) ions connected by three different bridges, (μ-ONN) of the Schiff base ligand, μ₂-O and μ-OO of the acetate. The complex is centrosymmetric, with one of the Zn atoms located at the inversion center. While the central Zn(II) ion is six-coordinated, the coordination number of the other Zn(II) ions is five. Finally, the {[Zn(μ-ONN)(μ₂-O)(μ-OO)]₂Zn} complex was thermally decomposed in air at 700 °C resulted in ZnO nano crystalites with the average size of 42 nm. The antibacterial activity of ligand and its zinc(II) complex were tested against gram-positive and gram-negative bacteria. The ligand showed higher activity than its zinc(II) complex.     

Pyrene Carboxylate Ligand Based Coordination Polymers for Microwave-Assisted Solvent-Free Cyanosilylation of Aldehydes

The new coordination polymers (CPs) [Zn(μ-1κO¹:1κO²-L)(H₂O)₂]_n·n(H₂O) (1) and [Cd(μ₄-1κO¹O²:2κN:3,4κO³-L)(H₂O)]_n·n(H₂O) (2) are reported, being prepared by the solvothermal reactions of 5-{(pyren-4-ylmethyl)amino}isophthalic acid (H₂L) with Zn(NO₃)₂.6H₂O or Cd(NO₃)₂.4H₂O, respectively. They were synthesized in a basic ethanolic medium or a DMF:H₂O mixture, respectively. These compounds were characterized by single-crystal X-ray diffraction, FTIR spectroscopy, thermogravimetric and elemental analysis. The single-crystal X-ray diffraction analysis revealed that compound 1 is a one dimensional linear coordination polymer, whereas 2 presents a two dimensional network. In both compounds, the coordinating ligand (L²⁻) is twisted due to the rotation of the pyrene ring around the CH₂-NH bond. In compound 1, the Zn(II) metal ion has a tetrahedral geometry, whereas, in 2, the dinuclear [Cd₂(COO)₂] moiety acts as a secondary building unit and the Cd(II) ion possesses a distorted octahedral geometry. Recently, several CPs have been explored for the cyanosilylation reaction under conventional conditions, but microwave-assisted cyanosilylation of aldehydes catalyzed by CPs has not yet been well studied. Thus, we have tested the solvent-free microwave-assisted cyanosilylation reactions of different aldehydes, with trimethylsilyl cyanide, using our synthesized compounds, which behave as highly active heterogeneous catalysts. The coordination polymer 1 is more effective than 2, conceivably due to the higher Lewis acidity of the Zn(II) than the Cd(II) center and to a higher accessibility of the metal centers in the former framework. We have also checked the heterogeneity and recyclability of these coordination polymers, showing that they remain active at least after four recyclings.     

The thermodynamics of synergistic solvent extraction of Zn(II) with 1-phenyl-3- methyl-4-benzoyl-pyrazole-5-one

The synergistic extraction of Zn(II) has been studied in the PMBP—TBP system (where PMBP = 1-phenyl-3-methyl-4-benzoyl-pyrazole-5-one and TBP = tri-n- butyl phosphate) at various temperatures using a radiochemical technique. The thermodynamic parameters for the reactions involved support the mechanism for the synergistic extraction in which the 5-coordinate monohydrated Zn(PMBP) ₂ chelate exchanges a water molecule for TBP.     

Structural zinc(II) thiolate complexes relevant to the modeling of Ada repair protein: Application toward alkylation reactions

The TtZn(II)-bound perchlorate complex [TtZn–OClO₃] 1 (Ttxyly = hydrotris[N-xylyl-thioimidazolyl]borate) was used for the synthesis of zinc(II)-bound ethanthiothiol complex [TtZn–SCH₂CH₃] 2 and its hydrogen-bond containing analog Tt–ZnSCH₂CH₂–NH(CO)OC(CH₃)₃ 3. These thiolate complexes were examined as structural models for the active sites of Ada repair protein toward methylation reactions. The Zn[S₃O] coordination sphere in complex 1 includes three thione donors from the ligand Tti^xyl and one oxygen donor from the perchlorate coligand in ideally tetrahedral arrangement around the zinc center. The average Zn(1)–S(thione) bond length is 2.344 Å, and the Zn(1)–O(1) bond length is 1.917 Å.     

Synthesis,crystal structure,and density functional theory study of a zinc(II) complex containing terpyridine and pyridine-2,6-dicarboxylic acid ligands: Analysis of the interactions with amoxicillin

An octahedral zinc(II) complex of 2,2′:6′,2″-terpyridine (Tpy) and pyridine-2,6-dicarboxylate (Pydc), [Zn(II)(Tpy)(Pydc)·4H₂O] was synthesized and its structure was determined by a single-crystal X-ray diffraction. The ligand pyridine-2,6-dicarboxylate coordinated to the zinc(II) ion via two pairs of carboxylate oxygens and one nitrogen atom, whereas 2,2′:6′,2″-terpyridine also contributed three coordination bonds through its nitrogen atoms. [Zn(II)(Tpy)(Pydc)·4H₂O] showed luminescence properties between 412 and 435 nm in DMSO. The solid-state octahedral geometry of [Zn(II)(Tpy)(Pydc)·4H₂O] was also preserved in solution as confirmed by the observed UV λ_ex = 346. Experimental and theoretical studies indicated that [Zn(II)(Tpy)(Pydc)·4H₂O] interacted with amoxicillin. Density functional theory calculations at B3LYP/LanL2dz level of theory suggested that [Zn(II)(Tpy)(pydc)·4H₂O] dimer interacts with (2S,5R,6R)-6-{[(2R)-2-amino-2-(4-hydroxyphenyl)-acetyl]amino}-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-24-carboxylic acid (amoxicillin) via highest occupied molecular orbital and lowest unoccupied molecular orbital, π–π interaction, hydrogen bond interaction, and van der Waals forces, thus influencing [Zn(II)(Tpy)(Pydc)·4H₂O] properties.     

Photochemistry of covalently-linked multi-porphyrinic systems

Synthesis, structural characteristics, and optical and electrochemical properties of various covalently-linked porphyrin arrays are described. First, aromatic-spacer bridged diporphyrins were prepared in which the diporphyrin geometries were conformationally-restricted and thus suitable for detailed studies on the exciton coupling and the intramolecular energy and/or electron transfer reactions. Secondly, the Ag(I)-salt oxidation of 5,15-diaryl Zn(II) porphyrins provided meso–meso-linked Zn(II)-diporphyrins. This reaction is advantageous in light of its high regioselectivity and easy extension to longer porphyrin arrays. The doubling reaction was repeated up to the synthesis of a discrete 128-mer, which is, to the best of our knowledge, the longest man-made molecule. Finally, the oxidation of meso–meso-linked Zn(II) porphyrin arrays with a combination of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and Sc(III)(OTf)₃ produced fused porphyrin arrays with full π-conjugation, which displayed extremely small HOMO–LUMO gaps that reach into the infrared region.     

Syntheses, crystal structures, and magnetic and fluorescence properties of three metal complexes coordinated by mixed flexible (2-pyridylmethyl,3-pyridylmethyl)amine and rigid 5-sulfoisophthalate ligands

Three new complexes, {[Cu₃(2,3-pyma)₂(sip)₂(H₂O)₅]·5H₂O} _n , {[Zn(H-2,3-pyma)(sip)(H₂O)]·H₂O} _n , and {[Cd(H-2,3-pyma)(sip)(H₂O)]·H₂O} _n (2,3-pyma = (2-pyridylmethyl,3-pyridylmethyl)amine and H₃sip = 5-sulfoisophthalic acid) were synthesized and structurally characterized by single-crystal X-ray diffraction. The Cu(II) complex crystallizes in neutral two-dimensional layers in which the Cu(II) centers are bridged by both the flexible 2,3-pyma and the rigid sip ligands. The Zn(II) and Cd(II) complexes contain neutral one-dimensional chains linked by the rigid sip anions, whereas the flexible H-2,3-pyma ions only act as terminal ligands. The Cu(II) complex shows weak antiferromagnetic interactions, while the Zn(II) and Cd(II) complexes exhibit fluorescent emissions in the solid state.     

Adduct formation properties of mono- and bidentate phosphine oxide compounds in the liquid—liquid extraction of some divalent metals with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone

The bidentate phosphine oxide compounds bis(diphenylphosphinyl)methane (BDPPM) and bis(diphenylphosphinyl)ethane (BDPPE) were synthesized and the liquid—liquid extraction equilibria of some divalent metal ions such as Co(II), Ni(II), Zn(II) and Cd(II) with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP) and the neutral phosphine oxide compounds were investigated. BDPPM was found to be much more powerful than BDPPE and the monodentate neutral ligand trioctylphosphine oxide (TOPO). The composition of the extracted species were determined by a graphical method to be M(PMBP)₂(TOPO)_s (s = 2 for Co, Ni, Cd and s = 1 for Zn), M(PMBP)₂(BDPPM) and M(PMBP)₂(BDPPE). The adduct formation constants between the acylpyrazolone chelates and the neutral ligands were determined and are discussed in terms of the molecular structure.     

A modern technique for preparation of zinc(II) and nickel(II) nanometric oxides using Schiff base compounds: synthesis,characterization, and antibacterial properties

The purpose of the work reported in this paper was the preparation and characterization of Zn(II) and Ni(II) nanometric oxides by using a simple Schiff compound as precursor for complexation then thermal degradation at 600 °C. Metal complexes [Ni(L)₂(Cl)₂] and [Zn(L)₂](NO₃)₂, where L is the Schiff base formed by condensation of 2-thiophenecarboxaldehyde with phenylhydrazine, were prepared and characterized by elemental analysis and by magnetic and spectroscopic measurements (infrared, Raman, X-ray powder diffraction, and scanning electron microscopy). Elemental analysis of the chelates suggests the stoichiometry is 1:2 (metal–ligand). Infrared spectra of the complexes are indicative of coordination of the nitrogen of the phenylhydrazine (–Ph–NH–) group and the sulfur atom of the thiophene ring with the central metal atom. Magnetic susceptibility data and electronic and ESR spectra suggest a distorted octahedral structure for the Ni(II) complex and tetrahedral geometry for the Zn(II) complex. The Schiff base and its metal chelates were screened for in-vitro activity against four bacteria, two Gram-positive (Bacillus subtilis and Staphylococcus aureus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa), and two strains of fungus (Aspergillus flavus and Candida albicans). The metal chelates were shown to have greater antibacterial activity than the free Schiff-base chelate.