Understanding the stability, electronic and molecular structure of some copper(III) complexes containing alkyl and non alkyl ligands: Insights from DFT calculations

DFT calculations have been performed for some Cu(III)-alkyl complexes. Complexes 1-19 were optimized to the square planar (sq) geometry and observed no imaginary frequencies. Although formally copper adopts d⁸ configuration (Cu(III)) in all the complexes, the Natural Population Analysis (NPA) revealed that the copper actually in d¹⁰ (Cu(I)) configuration, Bond order calculation suggested that the Cu(III)-Et_trans bond gets more bond order in the presence of poor π-acidic co-ligand (probe ligand). Relatively smaller bond order was calculated for Cu(III)-Me_cis bond than Cu(III)-Et_trans bond and therefore Cu(III)-Et_trans bond is the strongest bond in all the complexes. Calculated less Chemical hardness (η) of complexes 1-19 suggested that all these complexes are less stable in nature. Energy Decomposition Analysis (EDA) revealed that the Cu(III)-Et_trans bond is relatively more stable than the Cu(III)-Me_cis and Cu(III)-L (L = co-ligand/probe ligand) bonds. And also the Cu(III)-alkyl (Cu(III)-Me_cis and Cu(III)-Et_trans) bond in complexes 1-17 is more of ionic in nature. However, Cu(III)-Et_trans bond is relatively more ionic than Cu(III)-Me_cis bond.     

Current-sampled polarographic techniques for the measurement of species reduced at more negative potentials than the major component

With conventional d.c. polarography. a particular depolarizer cannot be determined accurately in the presence of a considerable concentration of another species which is reduced at more positive potentials. Current-sampled read-out has been suggested previously to improve the situation; this idea has now been tested experimentally. The read-out of Tast (current-sampled), derivative Tast and pulse polarographic techniques permits determinations of this type to be achieved accurately and conveniently over quite a wide concentration range, provided that a three-electrode potentiostat is used to minimize ohmic iR drop effects. The maximal concentration and the limiting concentration ratio of the two depolarizers were generally fixed more by instrumental than chemical limitations, although at very high concentrations of the major species some evidence of electrochemical interference was found.     

Solution Characteristics for Adsorption of Copper Ion with Iron(III) Hydroxide from Aqueous Ammonia Solution

The distribution of copper ion species in aqueous ammonia solution is evaluated as a function of pH by a numerical approach. Adsorption of copper on colloidal iron(III) hydroxide in solutions of total ammonia (0.14-1.2 M) are performed at various values of pH. The maximum efficiency of adsorption occurs when the sum of the fractions of the species Cu(NH₃)²⁺, Cu(NH₃)₂²⁺ and Cu(NH₃)₃²⁺ in the solution reaches its maximum. With varied solution pH, the distribution of copper species is the determining factor for maximum adsorption, whereas the surface properties of the adsorbing particles show smaller effects under the test conditions.     

A Comparative Study of Stabilities and Coordination Modes of β-Alaninephosphonic Acid in Copper(II) Heteroligand Complexes with Ethylenediamine, Diethylenetriamine or N,N,N′,N′,N″-Pentamethyldiethylene Triamine in Aqueous Solution

Solution equilibrium studies on Cu²⁺?CL₁?CL₂ ternary systems have been performed by pH-potentiometry, UV?CVis spectrophotometry and EPR methods {where L₁ corresponds to a polyamine such as ethylenediamine (en), diethylenetriamine (dien), N,N,N??,N??,N??-pentamethyldiethylenetriamine (Me₅dien)} and L₂ denotes 2-aminoethylphosphonic acid (??-alaninephosphonic acid)}. The results suggest the formation of heteroligand complexes with [Cu(L₁)(??-Ala(P))] stoichiometry in all of the studied systems. Additionally, in the system with en, [Cu(en)(??-Ala(P))H_?1]^? is formed in basic solutions. Our spectroscopic results indicate tetragonal geometry for the [Cu(en)(??-Ala(P))] species, a geometry slightly deviated from square pyramidal for the [Cu(dien)(??-Ala(P))] complex, and somewhat stronger geometry distortion was present for the [Cu(Me₅dien)(??-Ala(P))] complex. The coordination modes in these heteroligand complexes are discussed.     

Amperometric determination of sulfide ion by glassy carbon electrode modified with multiwall carbon nanotubes and copper (II) phenanthroline complex

Electrocatalytic oxidation of sulfide ion on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNTs) and a copper (II) complex was investigated. The Cu(II) complex was used due to the reversibility of the Cu(II)/Cu(III) redox couple. The MWCNTs are evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on Cu(II) complex adsorbed on MWCNTs immobilized on the surface of GCE. The modified GCE was applied to the selective amperometric detection of sulfide at a potential of 0.47 V (vs. Ag/AgCl) at pH 8.0. The calibration graph was linear in the concentration range of 5 µM–400 µM; while the limit of detection was 1.2 µM, the sensitivity was 34 nA µM^?1. The interference effects of SO₃ ^2?, SO₄ ^2?, S₂O₃ ^2?, S₄O₆ ^2?, Cysteine, and Cystein were negligible at the concentration ratios more than 40 times. The modified electrode is more stable with time and more easily restorable than unmodified electrode surface. Also, modified electrode permits detection of sulfide ion by its oxidation at lower anodic potentials.      

Construction and Activity of a New Catalytic System in the Hydrolysis of Bis(4‐nitrophenyl) Phosphate Ester

A new catalytic system containing an unsaturated heterocyclic nitrogen ligand and lanthanum(III) was constructed and used as a catalyst in the hydrolysis of bis(4‐nitrophenyl) phosphate ester (BNPP) in this work. The results indicated that this catalytic system showed greater catalytic activity in the hydrolysis of BNPP and better reproducibility and stability than other similar lanthanum(III) systems. The catalytic rate of the BNPP hydrolysis was about 10⁷‐fold faster than that of its spontaneous hydrolysis at the same conditions. Compared with the previous Cu(II) or Ni(II) complex containing the same ligand in the water, the activity of the macrocyclic La(III) complex increases ca. 10³‐fold for BNPP catalytic hydrolysis. The experimental data showed that the monohydroxy complex made of the heterocyclic nitrogen ligand and lanthanum(III) is the real active species as a catalyst in BNPP catalytic hydrolysis.     

Towards asymmetric Au-catalyzed hydroxy- and alkoxycyclization of 1,6-enynes

The efficiency of a Au(III)/chiral ligand system has been studied. The association of several chiral mono- and bidentate phosphanes with gold has been tested in the formal addition of an oxygen nucleophile to an alkene followed by a cyclization process, namely the hydroxycyclization reaction of 1,6-enynes. The use of (R)-4-MeO-3,5-(t-Bu)₂-MeOBIPHEP ligand led to clean cycloisomerizations and afforded the highest enantiomeric excesses. The enantiomeric excesses were highly dependant on the substrate/nucleophile combination. A ³¹P NMR study of the catalytic species tends to prove that Au(III) catalyst may be reduced to Au(I) intermediate in the presence of phosphanes.     

Investigation of the use of diphenyl-2-pyridylmethane in benzene as an extractant for palladium from aqueous thiocyanate-nitrate solutions

The extraction of palladium/II/ with diphenyl-2-pyridylmethane /DPPM/ in benzene has been investigated from thiocyanate-nitrate media and optimized. Thiosulphate ions showed strong interference and reduced the extraction below 1%. Separation factors determined for most of the elements were better than 10³. This extraction method affords palladium preconcentration and its separation from Sc/III/, Co/II/, Cu/II/, Zn/II/, Se/IV/, Sr/II/, Ru/III/, Cd/II/, Cs/I/ and Eu/III/. Few possible applications of such separations have been cited.     

Stabilities and coordination modes of histidine in copper(II) mixed-ligand complexes with ethylenediamine,diethylenetriamine or N,N,N′,N″,N″-pentamethyldiethylenetriamine in aqueous solution

Solution equilibrium studies on the Cu(II)–polyamine–histidine ternary systems (polyamine: ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N″,N″-pentamethyldiethylenetriamine (Me₅dien)) have been performed by pH-potentiometry, UV–Vis spectrophotometry and EPR methods. The obtained results suggest the formation of the mixed-ligand complexes with [Cu(A)(His)]⁺ stoichiometry in all studied systems. Additionally, in the systems with dien and Me₅dien protonated [Cu(A)(H–His)]²⁺ species also exists in acid solution. Our spectroscopic results indicate the tetragonal geometry for the [Cu(en)(His)]⁺, the geometry slightly deviated from square pyramidal for the [Cu(dien)(His)]⁺ and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me₅dien)(His)]⁺ species. The coordination modes in these mixed-ligand complexes are discussed.     

Evaluation of bathocuproine for the spectro-photometric determination of copper(I) in copper redox studies with applications in studies of natural waters

Copper(I) is determined at submicromolar levels in the presence of copper(II) in aqueous media by spectrophotometric measurement of the copper(I) complex of bathocuproine (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline). Copper(II) interference produced by reduction to copper(I) is described. Ethylenediamine can serve as a masking ligand to inhibit Cu(II) interference. The limit of detection is 1 × 10^?8 mol l^?1. Although this is not sensitive enough for use at natural copper concentrations, the procedure can be used in laboratory studies of copper redox processes at elevated levels in natural waters such as sea water. The dependence of results on pH and ionic strength was studied to evaluate the usefulness of the method in other aqueous systems.     

Reduction of chemical interference and speciation studies in the hydride generation—atomic absorption method for selenium

A simple procedure is described for reducing the chemical interference of heavy metal ions with the hydride—atomic absorption spectroscopic method for the determination of selenium. This is achieved through the formation of stable chlorocomplexes of these ions in 7.5 M HCl. Up to 30 μg Cu(II) ml^-1, 500 μg Ni(II) ml^-1, and 500 μg Fe(III) ml^-1 do not interfere. Recoveries of selenium from standard reference samples, fortified with known interfering concentrations of heavy metals, range between 92 and 101%. The reducing property of hydrochloric acid is used to differentiate between Se(IV) and Se(VI) species.     

Determination of copper(II) in a complex matrix after prereduction to copper(I) in a flow-injection system with an amperometric detector

A flow-injection system with a carbon paste detector is proposed for the determination of copper in complex media at +0.050 V vs. Ag/AgCl. Both the reduction current peak of Cu(II) and the oxidation peak of Cu(I) (obtained in the presence of hydroxylamine in the reagent stream) were proportional to the Cu(II) concentration in the original sample. The stabilization of Cu(I) in the hydroxylamine system provides a novel approach; the inherent repeatability of operation of flow-injection systems (timing, etc.) proved ideal for this utilization. Acidified Cu(II) samples containing additional metal ions [Fe(lI), Zn(II), Pb(II)] and relatively high concentrations of serum albumin were analysed. A chelating column retained heavy metal ions while allowing albumin to run to waste. The retained metals were subsequently eluted with nitric acid into a stream of sodium acetate or sodium acetate-hydroxyl- amine. Before reaching the detector, the pH of the sample plug was adjusted. With the hydroxylamine system, Fe(III) interference was minimized and the sensitivity and reproducibility were improved. The sample throughput was 25 h^?1. National Bureau of Standards Standard Reference Material 909 Human Serum was used to test the method.     

Preparation and thermal properties of palmitic acid/polyaniline/copper nanowires form-stable phase change materials

Form-stable phase change materials (PCMs) with high thermal conductivity are essential for thermal energy storage systems, which in turn are indispensible in solar thermal energy applications and efficient use of energy. In this paper, a new palmitic acid (PA)/polyaniline (PANI) form-stable PCMs were prepared by surface polymerization. The highest loading of PA in the form-stable PCMs was 80 mass% with the phase change enthalpy (ΔH _melting) of 175 J g^?1. Copper nanowires (Cu NWs) were introduced to the form-stable PCM by mixing the Cu NWs with PA and ethanol prior to the emulsifying of PA in surfactant solution. The Cu NWs would remain intact in case the ethanol was eliminated before the PA/Cu NWs mixture was mixed with surfactant solution. Otherwise, the Cu NWs would be partially oxidized under the attack of ethanol and ammonium persulfate. The ΔH _melting of the form-stable PCMs containing Cu NWs decreased linearly with the increasing of Cu NWs loading. The ΔH _melting of the form-stable PCMs doped with 11.2 mass% Cu NWs was 149 J g^?1. The thermal conductivity of the form-stable PCMs could be effectively improved by Cu NWs. By adding 11.2 mass% Cu NWs, the thermal conductivity of the form-stable PCM could attain 0.455 W m^?1 K^?1.     

Simultaneous determination of Mn(II), Cu(II) and Fe(III) as 2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol complexes by adsorptive cathodic stripping voltammetry at a carbon paste electrode

A simple and precise square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV) method has been described for simultaneous determination of Mn(II), Cu(II) and Fe(III) in water samples using a carbon paste electrode. In 0.1 mol L⁻¹ acetate buffer (pH 5) containing 50 μmol L⁻¹ of 2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol (5-Br-PADAP), Mn(II), Cu(II) and Fe(III) were simultaneously determined as metal-complexes with 5-Br-PADAP following preconcentration onto the carbon paste electrode by adsorptive accumulation at +1.0 V (vs. Ag/AgCl/3 M KCl). Insignificant interference from various cations (K⁺, Na⁺, Mg²⁺, Ca²⁺, Al³⁺, Bi³⁺, Sb³⁺, Se⁴⁺, Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Pb²⁺, V⁵⁺, Ti⁴⁺ and NH₄⁺), anions (HCO₃⁻, Cl⁻, NO³⁻, SO₄²⁻ and PO₄³⁻) and ascorbic acid was noticed. Limits of detection of 0.066, 0.108 and 0.093 μg L⁻¹ and limits of quantitation of 0.22, 0.36 and 0.31 μg L⁻¹ Mn(II), Cu(II) and Fe(III), respectively, were achieved by the described method. The described stripping voltammetry method was successfully applied for simultaneous determination of Mn(II), Cu(II) and Fe(III) in ground, tap and bottled natural water samples.     

Electrochemical deposition of praseodymium (III) and copper (II) and extraction of praseodymium on copper electrode in LiCl-KCl melts

Cyclic voltammogram and square wave voltammograms indicated that Cu (II) ion being reduced to Cu(0) was a two-electron process: Cu(II)?+?e^??→?Cu(I) and Cu(I)?+?e^??→?Cu(0). The diffusion activation energy for Cu (I) ions was calculated as 42.85 kJ mol^?1. The equilibrium potential and apparent standard potential for Cu (I)/Cu(0) redox couple was measured by open circuit chronopotentiometry at a temperature of 773–923 K. Three reduction peaks, corresponding to the formation of Pr_xCu_y intermetallic compounds, were detected from cyclic voltammogram and square wave voltammogram obtained by co-reduction of Pr (III) and Cu (II) or electrodeposition of Pr (III) on Cu electrode. Furthermore, potentiostatic electrolysis was performed to extract the element Pr on Cu electrode, and the electrolytic products were analyzed by scanning electron microscopy equipped with energy dispersive spectrometry. Meanwhile, the highest extraction efficiency of Pr (III) ions could reach about 99.81% at ??2.20 V for 22 h at 823 K.     

Fast recovery of Au (III) and Ag(I) via amine-modified zeolitic imidazolate framework-8

In this paper, zeolitic imidazolate framework-8 modified by the ethanediamine (NH₂-ZIF-8) was employed for adsorbing Au (III) and Ag(I) from aqueous solutions. The adsorption capacities of NH₂-ZIF-8 towards Au (III) and Ag(I) were found to be significantly affected by the pH values of the solution. The adsorption kinetics studies show that NH₂-ZIF-8 presents a fast adsorption property towards metals, attaining 93% of adsorption equilibrium uptake for Au (III) within the first 30 min. This phenomenon can be ascribed to the coordination interaction between the amino group and Au (III). The thermodynamic data suggest that the adsorption of NH₂-ZIF-8 towards Au (III) is endothermic process, while that for Ag(I) is exothermic. The maximum adsorption capacities of NH₂-ZIF-8 toward Au (III) and Ag(I) can be achieved to 357 mg·g⁻¹ and 222.25 mg·g⁻¹, respectively. The metal ions interference results show that Cu (II) and Ni (II) hardly have no interference on Au (III) adsorption in e-waste containing 1500 mg·l⁻¹ Cu (II),100 mg·l⁻¹ Ni (II) and 10 mg·l⁻¹ Au (III); while for Ag(I), Cd (II) and Zn (II) have little interference on Ag(I) adsorption in the hybrid solutions containing Ag(I), Ni (II), Cd (II) and Zn (II) with equal concentration (50 mg·l⁻¹), but Ni (II) interference most. The XPS study shows that partial Au (III) was reduced to Au(I), and that Ag(I) was completely reduced to Ag(0) during the adsorption process. The abundant of active sites of NH₂-ZIF-8 containing C=N, N-H, and Zn-OH groups play a key role in the adsorption of Au (III) and Ag(I). In addition, electrostatic interaction can be responsible for the adsorption of Au (III) by NH₂-ZIF-8. The regeneration experiments results show that the adsorption capacities of NH₂-ZIF-8 towards Au (III) and Ag(I) can maintain after three cycles. This work provides a reliable method to improve the adsorption kinetics for metal ions.     

Determination of Cu(III) in semiconductor ceramics using cationic violet reagent

A method is presented for the determination of Cu(III) ion in semiconductor ceramic materials. It is based on (a) the reaction of copper(III) with Fe(II) ions, (b) the quantitative formation of Fe(III) ions, (c) liquid-liquid extraction of Fe(III) in the form of an ion associate between the FeCl ₄ ^- anion with a Cationic Violet dye, and (d) spectrophotometric quantitation of the ion associate. All processes are executed in a single sequence of steps. The absorbance of the colored extracts obeys Beer's law in the range from 0.16 to 1.92 mg L^?1 of Cu(III). The molar absorptivities range from 38,000 to 82,000 L mol^?1 cm^?1 depending on the kind of extractant used. The effects of other ions on the recovery of Cu(III) were studied, and those that generally occur with copper in semiconductor samples do not interfere.     

Iron(III) as releasing agent for copper interference in the determination of selenium by hydride-generation atomic absorption spectrometry

Iron(III0 has a very effective releasing effect on the depressive interference from copper(II) on the determination of selenium by hydride-generation atomic absorption spectrometry. In solutionwith 100 mg 1^?1 Cu(II), 10 μg 1^?1 Se(IV) and 2.0 mol l^?1 HCl, the absorbance obtained was much higher when 8 g 1^?1 Fe(III) was added than for any earlier releasing agent.     

New insights into the metal ion–peptide hydroxamate interactions: Metal complexes of primary hydroxamic acid derivatives of common dipeptides in aqueous solution

Complex formation of primary dipeptide hydroxamic acids, L-Ala-L-AlaNHOH and L-Ala-L-SerNHOH, as well as the corresponding Z-protected ones, Z-L-Ala-L-AlaNHOH and Z-L-Ala-L-SerNHOH (Z = benzyloxycarbonyl), with iron(III), aluminium(III), nickel(II), copper(II) and zinc(II) was studied in aqueous solution by pH-potentiometric and spectroscopic (UV–Vis, EPR, CD, ¹H NMR) methods. The exclusive formation of [O,O] chelated hydroxamate complexes was found with iron(III) and aluminium(III) with all the ligands. Formation of linkage isomers with the involvement of either [O,O] hydroxamate or [NH₂,CO] chelates was detected both in the zinc(II)-L-Ala-L-AlaNHOH and -L-Ala-L-SerNHOH systems. Upon increasing the pH, none of these chelating sets are capable of preventing the hydrolysis of the metal ion. The formation of stable complexes was found in the nickel(II) and copper(II) systems above pH ∼ 6 with a [NH₂, N_amide, N_hydrox.] binding mode after deprotonation and coordination of the peptide amide and the hydroxamate group. With an excess of copper(II), the formation of trinuclear [Cu₃H_xL₂]^x+4 type (x = −4 to −6) complexes as the major species was also detected. Blocking the terminal amino group in the Z-protected ligands results in a dramatic decrease of the nickel(II) and zinc(II) binding strengths, and insoluble complexes with copper(II). No indication was found for the role of the hydroxyl group of the serine moiety in metal ion binding.     

Interaction of Molybdenum(VI) Oxyanions with +2 Metal Cations

The association of molybdenum(VI) oxyanions with metal cations was investigated in solutions of low ionic strength, such as those prevailing in most natural waters. Potentiometric titrations were carried out for the systems containing molybdenum(VI) anions and divalent metal cations (M = Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb). This selection includes the major cations and some other cations of high environmental relevance. The interaction of iron(III) with Mo(VI) anions was also studied. At neutral and basic pH values and for those systems where the solubility of the molybdate salt is high enough, ionic species pairs such as [M(MoO₄)] predominate. At acidic pH values, [M(HMoO₄)]⁺ and [M(Mo₇O₂₄)]^4– are formed, the latter species are only relevant for total molybdenum concentrations higher than 1 mmol·L^?1. These results provide the basis for molybdenum speciation in natural aquatic systems, on which the environmental fate, bioavailability and toxicity of the element depend.