Electrochemical approach to monitoring metal exchange reaction of acetylacetonate complexes with cadmium, copper and zinc ions

Metal exchange reactions of acetylacetonate complexes with Cd(II), Cu(II) and Zn(II) ions were investigated by using cadmium and copper ion selective electrodes. Changes in the electrode potential and pH of the solutions were monitored upon adding the pertinent metal Zn(II) of the acetylacetonate (AA) complexes. In the reverse system in which a stable Cu-AA complex exists in the solution prior to adding a secondary metal ion (Cd(II) or Zn(II)), no Cu(II) was replaced by either ion. In the systems containing Cd(II) and Zn(II) as a complexed form with AA or as free ions, the exchange reactions were not explained by considering the equilibrium stability constants of the Cd-AA and Zn-AA complexes.     

Characterization of dynamics and reactivities of solvated ions by ab initio simulations

Based on a systematic investigation of trajectories of ab initio quantum mechanical/molecular mechanical simulations of numerous cations in water a standardized procedure for the evaluation of mean ligand residence times is proposed. For the characterization of reactivity and structure-breaking/structure-forming properties of the ions a measure is derived from the mean residence times calculated with different time limits. It is shown that ab initio simulations can provide much insight into ultrafast dynamics that are presently not easily accessible by experiment.     

Synthesis,thermal and electrical studies on solvated oxovanadium(IV) complexes with schiff bases derived from aromatic diamines and 2-hydroxy-1-naphthaldehyde

Summary Solvated oxovanadium(IV) complexes of Schiff bases derived from aromatic diamines and 2-hydroxy-1-naphthaldehyde have been prepared from ethanolic medium. The elemental analyses reveal that the complexes have the ratio 1:1, 2:2 and 1:2 (ligand:metal) composition which are nonelectrolyte inDMF. The coordination number six (octahedral geometry) is proposed for the complexes prepared. This is based on the results of IR, electronic and EPR spectra. TGA as well as DTA studies and the electrical properties and (I–V) characteristics for the metal complexes were investigated.

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Synthese und thermische bzw. elektrochemische Untersuchungen an solvatisierten Oxovanadium(IV)-Komplexen mit Schiff-Basen aus aromatischen Diaminen und 2-Hydroxy-1-naphthaldehyd

Zusammenfassung Die im Titel genannten Komplexe wurden in ethanolischem Medium hergestellt. Sie sind inDMF Nichtelektrolyte und haben laut Elementaranalyse die Zusammensetzung Ligand:Metall=1:1, 2:2 und 1:2. Basierend auf IR-, UV- und EPR-Spektren wird die Koordinationszahl 6 (oktahedrale Geometrie) vorgeschlagen. Es wurden TGA- und DTA-Studien durchgeführt und das elektrochemische Verhalten der Metallkomplexe untersucht.

     

Trace analysis of heavy metal ions by ion chromatography

Summary An ion chromatographic separation technique for heavy metal ions is described. Using pressure-stable, silica-based, ion-exchange supports and standard HPLC equipment with post-column reaction detector high resolution is achieved as well as extremely high sensitivity in the parts per trillion (ppt)-range.     

Spin exchange between transition metal complexes and nitroxyl radicals in nonaqueous media

New complexes of diaza- and tetraaza-containing crown ethers, viz., 1,10-diaza-18-crown-6 (1), 1,4,8,12-tetraazacyclopentadecane (2), 1,4,8,11-tetraazacyclotetradecane (3), and 1,4,8,11-tetraazacyclotetradecane 1,4,8,11-tetrachloride tetraacetic acid tetrahydrate (4), with the divalent copper and nickel ions and the Cl^–, Br^–, ClO₄ ^–, NO₃ ^–, and AcO^– counterions were synthesized. The exchange interactions of these compounds and paramagnetic copper and nickel salts with the TEMPO radical in MeOH—CHCl₃ binary mixtures of different compositions were studied. The plots of the linewidths of the hyperfine coupling components of TEMPO vs. concentration of the ions and temperature show that the frequency of diffusion collisions is the rate-limiting step for spin exchange (strong exchange regime). A strong dependence of the exchange rate constant (k _ex) on the crown ether and counterion structure was found. The isotropic hyperfine coupling constants (a _Cu) and g factors (g _i ) were measured for the Cu^II complexes with the crown ethers. In the case of the crown ether complexes 1—3 with CuCl₂, the a _Cu constant decreases linearly with an increase in g _i = g _i – 2.0023 in the series 3 < 2 < 1, whereas k _ex increases linearly in the same series with a decrease in the contact HFC on the Cu^II nucleus (K) and a decrease in covalence of bonding. For the complexes of 2 with Cu^II and different axial ligands (counterions), k _ex increases in the series Cl^– < ClO₄ ^– AcO^– Br^–; < NO₃ ^–. In the case of the complexes of 2 with NiCl₂, k _ex increases in the series 1 < 4 < 3 2. For the Cu^II and Ni^II salts with the Cl^–, ClO₄ ^–, and NO₃ ^– anions, the k _ex values are almost independent of the anion nature. The correlation of the k _ex values with the electron-spin parameters of the complexes is discussed.     

Crystal structure of three solvated Alpinumisoflavones

Single crystals of alpinumisoflavone, C₂₀H₁₆O₅, {systematic name: 5-hydroxy-7-(4 hydroxyphenyl)-2, 2-dimethyl-2H, 6H-benzo [1, 2-b: 5, 4-b′]-dipyran-6-one}, solvated with water, methanol, and ethanol, have been obtained. The incorporation of the solvent molecules into the crystal structure creates a new short inter-molecular O–H···O and C–H···O contacts between the alpinumisoflavone moiety and its solvate molecule. The temperatures at which the solvated molecules lose their solvent molecules are 53, 54, and 65 °C for water, methanol, and ethanol, respectively. The observed temperatures at which the solvates efflorescence are reflective of the progressive increase in mass of the solvates from water to ethanol in the series. The benzopyrone moiety shows the usual planar conformation with the pyran ring deformed into a half-chair conformer as seen previously in the other analogous compounds with puckering parameters [Å], 0.2656(8), 0.3703(8), and 0.3957(9), respectively, for the water, ethanol, and methanol solvates. These are higher than the non-solvated alpinumisoflavone compound previously studied. The size of a substituent group proximal to the keto group has a more pronounced effect on the degree of puckering than substitution on the terminal phenyl ring. The attached phenyl ring shows consistent out-of-plane twist from the mean plane of the benzopyrone system as observed previously for this class of compounds. The observed dihedral angles are 30.26(3), 37.75(3), and 34.00(3)°, respectively, for the water, methanol, and ethanol solvates.     

Equilibria effects in the dynamic ion-exchange separation of metal ions

Summary Equilibria occurring during the dynamic ion exchange separation of metal ions were examined, and their effect on the chromatography of the metal ions was evaluated. Bonded reversed-phase silica, pure organic reversed phase, and silica columns were used to differentiate between the role of silica and the reverse phase. The results show that system peaks had the most important influence on the applicability of dynamic exchangers to quantitative metal ion determinations. The response of system peaks to sample composition (pH, ionic strength, matrix effects) was complicated and could not be predicted easily. Equilibria effects that can cause analytical errors were identified and recommendations for elimination of such errors are given.Dedicated to Professor S. R. Lipsky on the occasion of his 60th birthday.     

Empirical correlations between solvent acidity and the optical characteristics of solvated electrons

Correlations between essential characteristics of the optical absorption spectrum of the solvated electron (excitation energy, band-width) and the acceptor numbers of organic solvents are established.

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Eine empirische Korrelation zwischen der Acidität von Lösungsmitteln und spektralen Charakteristika solvatisierter Elektronen

Zusammenfassung Es wird eine Korrelation zwischen den wesentlichen Charakteristika des optischen Absorptionsspektrums von solvatisierten Elektronen (Anregungsenergie und Bandenbreite) und den Acceptornummern organischer Lösungsmittel gefunden.

     

Coordination properties of axially unfixed chiral dipyridine ligands towards metal and ammonium ions

New chiral dipyridine ligands with an axially unfixed 1,1′-biphenyl bridge were prepared via homocoupling of bromophenyl pyridines. The conformeric ratios of the free ligands in solution and their coordination properties towards metal ions were studied by NMR spectroscopy. X-Ray crystallography of the silver(I) and copper(I) complexes showed 1:1 metal to ligand complexes and S planar chirality. Interestingly, the biphenyl ligands show a 1:2 stepwise binding towards most ammonium ions tested with strong fluorescence enhancement, but a selectively 1:1 binding towards l-ornithine methyl ester hydrochloride with no fluorescence enhancement.     

Dynamic dispersion stability of graphene oxide with metal ions

Graphene oxide(GO),an important chemical precursor of graphene,can stably disperse in aqueous surrounding and undergo aggregation as metal cations introduced.The usual instability of GO with ions is caused by the shielding effect of ions and crosslinking between GO and ions.However,the dynamic stability of GO under ions exchange still remains unclear.Here,we investigated the dynamic dispersion stability of GO with metal ions and observed a redispersion behavior in concentrated Fe~(3+) solution,other than permanent aggregation.The exchange with Fe~(3+) ions drives the reversion of zeta(ζ) potential and enables the redispersion to individual GO-Fe~(3+) complex sheets,following a dynamic electric double layer(EDL) mechanism.It is found that the specifically strong electrostatic shielding effect and coordination attraction between Fe~(3+) and functional oxygen groups allows the selective redispersion of GO in concentrated Fe~(3+) solution.The revealed dynamic dispersion stability complements our understanding on the dispersive stability of GO and can be utilized to fabricate graphene-metal hybrids for rich applications.     

Cyclic voltammetry of highly hydrophilic ions at a supported liquid membrane

Cyclic voltammetry has been used to study the coupling of ion transfer reactions at a liquid membrane. The liquids are either supported by a porous hydrophobic membrane (polyvinylidene difluoride, PVDF) when the organic solvent is non-volatile (o-nitrophenyloctylether) or are merely a free standing organic solvent layer such as 1,2-dichloroethane comprised between two hydrophilic dialysis membranes supporting the adjacent aqueous phases. The passage of current across the liquid membrane is associated with two ion transfer reactions across the two polarised liquid liquid interfaces in series. It is shown that it is possible to study the transfer of highly hydrophilic ions at one interface by limiting the mass transfer of the other ion transfer reaction at the other interface. Indeed, for systems comprising an ion M in one aqueous phase and a reference ion R partitioned between the membrane and the other aqueous phase, the observed and simulated cyclic voltammograms have a half-wave potential determined by the Gibbs energy of transfer of M transferring at one interface and by the limiting mass transfer of R at the other interface. This new methodology opens a way to measure the Gibbs energy of transfer of highly hydrophilic or hydrophobic ions, which usually limits the potential window at single liquid liquid interfaces (ITIES).     

S-Methylation of polythiolactam: chemical transformation of macrocyclic anion receptor into new macrocyclic ligand for metal ions

The S-methylation of a macrocyclic tetrathiolactam afforded a new macrocyclic thioimidate that exhibited good affinity toward metal ions. The molecular structures of the macrocyclic ligand and its metal complexes were determined by X-ray crystallography.     

Ion chromatography with the indirect ultraviolet detection of alkali metal ions and ammonium using imidazolium ionic liquid as ultraviolet absorption reagent and eluent

Indirect ultraviolet detection was conducted in ultraviolet‐absorption‐agent‐added mobile phase to complete the detection of the absence of ultraviolet absorption functional group in analytes. Compared with precolumn derivatization or postcolumn derivatization, this method can be widely used, has the advantages of simple operation and good linear relationship. Chromatographic separation of Li⁺, Na⁺, K⁺, and NH₄⁺ was performed on a carboxylic acid base cation exchange column using imidazolium ionic liquid/acid/organic solvent as the mobile phase, in which imidazolium ionic liquids acted as ultraviolet absorption reagent and eluting agent. The retention behaviors of four kinds of cations are discussed, and the mechanism of separation and detection are described. The main factors influencing the separation and detection were the background ultraviolet absorption reagent and the concentration of hydrogen ion in the ion chromatography‐indirect ultraviolet detection. The successful separation and detection of Li⁺, Na⁺, K⁺, and NH₄⁺ within 13 min was achieved using the selected chromatographic conditions, and the detection limits (S/N = 3) were 0.02, 0.11, 0.30, and 0.06 mg/L, respectively. A new separation and analysis method of alkali metal ions and ammonium by ion chromatography with indirect ultraviolet detection method was developed, and the application range of ionic liquid was expanded.     

Coordination complexes of the dimethyl-thio-phosphonium cation and ligand exchange

The quantitative exchange of a 4-(dimethylamino)pyridine ligand on the dimethyl-thio-phosphonium cation by Me3P demonstrates the coordinative nature of the N-P and P-P bond and diversifies a fundamentally important new direction in the coordination chemistry of phosphorus as an acceptor.     

From solvated electrons to metal anions: Electronic structure and dynamics

The techniques of magnetic susceptibility and magnetic resonance (NMR, ESR) have proved to be invaluable in the study of the electronic structure and dynamics of both paramagnetic and diamagnetic species in solutions of metals in non-aqueous solvents. This paper contains a brief review of recent experimental work in this area, concentrating on localized excess-electron states ranging from solvated electrons, electron-cation encounter species, through finally to gas-like metal anion species existing in these non-aqueous solutions. Throughout, the emphasis is on the information gleaned from magnetic measurements about the microstructure and environment of these matrix-bound states.Session lecture, Ninth International Conference on Non-Aqueous Solutions, Pittsburgh, PA, August 1984.     

Transition metal carbene chemistry: Nucleophilic substitution reactions of imidazolide and benzimidazolide ions with Fischer carbene complexes in MeOH

Rate constants for the nucleophilic substitution reactions of imidazolide (IZ⁻) and benzimidazolide (BIZ⁻) ions with 4-Cr-Z and 5 in MeOH at 25 °C are reported and Hammett ρ values are evaluated to be 1.50 ± 0.10 and 1.51 ± 0.08 for 4-Cr-Z-IZ⁻ and 4-Cr-Z-BIZ⁻ reactions, respectively. The comparable reactivity and also almost identical ρ values for these reactions indicate that there is no difference in sensitivity towards electronic effects due to slightly bigger size of BIZ⁻ over IZ⁻ and bond formation at the transition states are equally progressed. The higher ρ values for these reactions compared to those with a wide range of nucleophiles may arise mainly due to lower polarity of the solvent MeOH which enhances the requirement for stabilization of the negative charge in the transition state by the Z-substituents.     

A study of the mechanisms involved in the separation of metal ions with a mixed-bed stationary phase

Summary The optimization of chromatographic methods for the determination of metal species require an understanding of the mechanisms involved. In this work, the separation of Cd, Co, Cu, Fe(II/III), Mn, Pb and Zn using a mixed bed column (IonPac CS5A) and a cation-exchange column (IonPac CS2) is studied as a function of mobile phase composition. The type and concentration of complexing agent and of ionic strength modificators were evaluated. The charge of analytes were calculated using the classical ion exchange approach to highlight the effect of eluent composition on retention. The comparative study enabled us to identify an optimal eluent composition for the separation of the nine metal species.     

Direct fluorometric detection of paramagnetic and heavy metal ions at sub-amol level using an aromatic polyaminocarboxylate by CZE: Combination of pre- and on-capillary complexation technique

The low sensitivity of simple CZE for detecting metal ions is a long-standing problem even when an LIF detection system is employed. We have successfully achieved an ultrasensitive CE-LIF using a simple CZE mode (typical detection limit: 10(-11)-10(-10) mol/dm(3)). Both the design of a newly synthesized ligand and the combination of a precapillary derivatizing technique with an on-capillary ternary complexing technique have enabled us to achieve this extremely low LOD and high resolution of large metal complexes. The direct fluorescent detection of the paramagnetic metal ions was achieved for the first time despite their intrinsic fluorescent quenching nature. The fluorescent ligand (L) consists of a polyaminocarboxylate chelating moiety, a strongly emissive fluorescein moiety and a spacer connecting the two portions. The migration behavior of various metal-L complexes was investigated. The resolution among the complexes was improved by the introduction of a ternary complex equilibrium of the kinetically stable mother complexes with OH(-) ion. The analytical potential of our simple system was examined, and it was proved that the system was one of the most sensitive methods without the need for any preconcentration process.     

Strong complex formation of carbohydrates with metal ions at alkaline pH studied by ligand exchange chromatography

Summary At alkaline pH, carbohydrates are highly retained on a sulphonated polystyrene resin loaded with rare earth or uranyl metal ions. The complex formation is governed by the ionization of the carbohydrate moiety. pH and the type of metal ion were found to have a decisive influence on the complex formation. Binding of the metal ion to the cation exchanger and to different carbohydrates is described. The competitive complexation between solute and hydroxide to the metal ions is described as a ligand exchange reaction and a retention model is proposed. The ligand exchange column was used as precolumn in a coupled column separation system and the high selectivity is demonstrated by the separation of paracetamol glucuronide from a urine sample after filtration and direct injection.